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Uranium Enrichment Methods and Implications on Middle East Countries

Scientific Essay 2018 22 Pages

Engineering - Nuclear Engineering

Excerpt

Contents

1. Introduction

2. Nuclear fuel Cycle
2.1 Fuel Cycle
2.2 Encapsulation
2.3 Fuel Rods

3. Chemistry and Physics of Uranium fuel cycle
3.1 Chemistry
3.2 Physics and Enrichment Units
3.2.1 Separative Work Unit (SWU)
3.2.2 Separative Power
3.2.3 Separative Process Materials
3.2.4 Separative Work
3.2.5 Separation Factor

4. Enrichment History- Process and Methods
4.1 History of enrichment
4.2 Methods of enrichment
4.2.1 Electromagnetic Enrichment
4.2.2 Gaseous Diffusion Enrichment
4.2.3 Aerodynamic Nozzle Separation
4.2.4 Laser Enrichment
4.2.5 Centrifuge Enrichment
4.2.6 Centrifuge Rotor Construction
4.2.7 Cascading
4.2.8 Advantages Disadvantages of Enrichment Methods
4.3 Reprocessed Uranium Enrichment
4.4 Reprocessing Expired Nuclear Weapons

5. Enrichment in Middle East countries Israel /Iran
5.1 History of Enrichment in Middle East countries
5.2 Israel’s Nuclear Program
5.2.1 History of Israel’s nuclear Program
5.2.2 Israel’s Nuclear Fuel and Dimona Plant
5.2.3 Israel’s Nuclear Capacities and Weapons
5.3 Nuclear Program and Uranium enrichment in Iran
5.3.1 History of Iran’s nuclear program
5.3.2 Iran’s centrifuge facilities and plants
5.3.3 Joint Comprehensive Plan of Action (JCPOA) agreement

6. Conclusions

7. References

8. Appendix.

Abstractthis paper is a Journal Scientific paper analyzing various methods of Uranium enrichment explaining how this leads to either Nuclear reactor fuel feed material or Nuclear Weapons.

Enrichment of Uranium is the basis for the production of fissile material 235U and since it is a well proven process it is preferred by the industry. The methods to be used for enrichment are Gaseous diffusion, Electromagnetic enrichment, aerodynamic nozzle separation, centrifuge enrichment and finally enrichment from lasers like AVLIS, SILEX and MLIS.

Out of the five methods the gas centrifuge is the most favorable one and can be done by centrifuges in line cascading. Centrifuging is made by a dense called gas centrifuge UF6 and is based on the physics of accelerating molecules in a gaseous diffusion. This is done by centrifugal forces which separate the lighter from heavier atoms.

Uranium enrichment and plutonium/uranium separation besides creation of nuclear fuel for nuclear plants can also be used in creating nuclear weapons and the paper will address this issue. It will also try to give some answers in the nuclear programs of some Middle East countries like Iran and Israel. It will not debate in political terms nuclear capabilities but will only mention technical facts received from the International Atomic Energy Agency (IAEA) and the United Nations.

The paper is written in standard IEEE form and is addressed to those with an elementary to medium knowledge of science who are interested in knowing what uranium enrichment is and how this can lead in the creation of either nuclear fuel or nuclear weapons.

1. INTRODUCTION

Enrichment of Uranium is the basis for the production of fissile material and since it is a well proven process it is preferred by many countries to mainly provide their required fuel to feed the nuclear reactors and produce the needed electric power in nuclear factories.

A nuclear factory, in its main cycle, does not differ much from a gas or coal factory. It is based on power generated by turbines run by steam (Fig. 3). The production of steam though is by either burning fuel like gas or coal or by heat generated by a nuclear reaction in a nuclear reactor. The feed of fuel in these reactors are pallets (rods) of enriched uranium 235U produced by various methods. The methods used for enrichment are enrichment by electromagnetic process, by gas diffusion, by, aerodynamic separation, by centrifuge and enrichment from lasers like AVLIS and MLIS.

Out of all the methods, the gas centrifuge by cascading is the most favorable one and can be done by centrifuges in line (cascading). Centrifuging is made by a dense gas called centrifuge Uranium Hexafluoride UF6 and is based on the physics of accelerating molecules in a gaseous diffusion. This is done by centrifugal forces which separate the lighter from heavier atoms [5].

The main feed, for the centrifugal rotors, gas UF6 is consisting of molecules of 235U and 238U. The output with increased content of 235U is fed in to other centrifugal rotors in cascade thus increasing constantly the content of 235U (enrichment) up to the desired level of 4-5% for creating nuclear fuel, or 90% for nuclear weapons [3].

The uranium, that can be found in the earth, mostly consists of two isotopes, Uranium 238 (238U) and Uranium 235 (235U) in addition to other elements in small quantities. In every 100 Kg of Uranium 99.289 Kg are 238U and only 0.711 Kg are 235U. Since there is a mass difference between the 238U isotope and the 235U isotope (three more neutrons), if you infuse them in a rotor the difference in mass will separate them. This procedure is common in medicine and biology [1].

Enrichment increases the percentage in 235U up to the desired level, usually 3-5% for nuclear fuel, 20% for research reactors and 85% and above for nuclear weapons. The 85% grade is connected with the critical mass required for detonation, which means if we increase the enrichment to 97% a very small weapon can be designed ready to equip the head of a small missile (higher grade -smaller weapon).

Enrichment can be done mainly by five enrichment processes. The older diffusion process, the electromagnetic process the aerodynamic nozzle separation, the centrifuge process and the laser process. Enrichment can also be done in reprocessed uranium or depleted UF6 tails or old nuclear heads.

Of the five processes the one in favor of small countries that want to create their own nuclear fuel or create an atomic weapon is centrifuge enrichment for many reasons which will be analyzed in the paper.

Middle East countries, for political reasons, in the end of the 20th century wanted somehow to find away either to survive in a hostile environment, like Israel, or to maintain their authoritarian regimes having nuclear weapons as a deterrent measure towards other countries. That is why they engaged in an arm race to produce those nuclear weapons. Nuclear weapons cannot be found in the open market so the countries had to create them from scratch and also to create a nuclear program from scratch. The fissile material to do this was either 235U Uranium or 239U plutonium. The 239U plutonium required the existence of an unregulated, from the IAEA, separation factory to produce it and the 235U Uranium required enrichment [2].

2. Nuclear fuel Cycle and encapsulation

2.1 Fuel Cycle

Uranium is an ore as common as tin. You can find it anywhere from soils to rocks, in sea water, rivers etc. To understand how common it is, the rock granite which is 60% of earth’s crust has four parts/million and in fertilizers this amount is 400 parts per million [4].

Most of the uranium is mined using the in-situ leach method in a mill close to the ore excavation. In the mills Uranium ore in its natural form cannot be used as nuclear fuel. It must be processed first as follows [19]:

a. The Uranium ore is excavated and sent in refining plants
b. In refining plants, the ore is transformed to Yellow Cake Triuranium Octoxide (U308).
c. Yellow cake is sent to Conversion plants and UF6 is created.
d. UF6 is enriched in 235U in the enrichments plants.
e. Enriched UF6 is transformed to Uranium Dioxide UO2 in reconversion plants.
f. UO2 then is packaged in cylinders in a fuel fabrication plant.
g. Fuel cylinder assemblies are sent to the Nuclear Power plant for consumption.
h. Spent fuel is sent either to Interim Storage facility or to a reprocessing plant.
i. From the reprocessing plant, the Uranium is sent back to the Conversion plant or the Plutonium is sent to the fuel fabrication plant.

The typical Nuclear Fuel cycle is as the following figure:

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Figure 1: Nuclear fuel Cycle [19]

In the mills, we have the production of Uranium oxide, also known as yellow cake, with uranium percentage over 80% compared with the concentration of 0.1% of the original ore. The separation of uranium from the waste rock is done by first crashing the rock and then by leaching it with sulfuric acid. The product is U3O8, which is stored in cylinders 200 liters in capacity. A large nuclear plant would require 200 tons of U3O8 to operate. The remaining products, also called tails, are isolated, since they are radioactive and toxic and contain heavy elements [16].

This product then goes to conversion plants where UF6 is created. The original UF6 is low in 235U, which is required for fission in a nuclear plant and needs to be enriched. This is dome in enrichment plants using various technics with the most common being the centrifuge enrichment.

The enriched UF6 then goes to the nuclear plant for fission. There are some heavy water reactors, like the Canadian and Indian reactors that do not require enriched uranium. This means that are harder to be regulated by the IAEA which inspects the encapsulated nuclear fuel and the plutonium 239U they produce [25].

2.2 Encapsulation

Nuclear fuel encapsulation and transportation process is done in various stages until the canister final product according to Figure 2. The feed cylinders are category 48Y, 48 inches diameter Y type cylinder, used for transportation of natural uranium, which withstand corrosion for over 40 years and withstand temperatures over 113o Celsius. The output cylinders are category 30B, 30 inches diameter B type, with the same characteristics filled with low enriched UF6 cooled in to a solid state.

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Figure 2: Nuclear fuel Encapsulation [28]

2.3 Fuel Rods

The reactor fuel are metal tubes, also known as fuel rods, which are pressed UO2 baked at temperatures over 1400o C and in ceramic pallets form.

A typical 1000 MWe reactor, in a nuclear factory, usually needs 27 tons of enriched fuel per year.

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Figure 3: Typical Nuclear Factory Outlay [29]

The heat produced by the fission of the 235U, in the fuel rods, is used to create steam from the steam generator which goes in to regular steam turbines and axially the electrical generator, transformer produces electricity. A nuclear factory of 1000MWe usually can produce 8 TW hours per year.

The fuel rods have to be replaced at regular intervals 16 to 24 months. Every year usually 1/3 of the rods are withdrawn to maintain a constant flow. The used rods contain 239U plutonium and heavy elements. The typical concentration in a used rod is 95% 238U, 3% heavy elements, and actinides, 1% 235U and 1% 239U. Some of the rods are reprocessed to extract whatever is still usable and the rest are send to storage.

Abbildung in dieser Leseprobe nicht enthalten

Figure 4: Fuel rods in breeder plutonium reactors [39]

In the reprocessing plant the 235U and 239U are separated from the mixture. Plutonium and uranium are transformed in to MOX (mixed oxide fuel) for special breeder plutonium reactors. The Russians are pursuing such reactors because they claim that they produce more fuel than they actually consume. The reactor uses 238U rods around the reactor’s core which can capture the escaping neutrons thus creating plutonium 239U which can be reprocessed to new fuel [39].

3. Chemistry and physics of Uranium Fuel circle

3.1 Chemistry

Uranium which is found in nature is called Uraninite and is a mixture of Thorium, Uranium Trioxide UO3, and Uranium Dioxide UO2, oxides of lead and elements or rare earth. This compound must be cleared from impurities so it is heated in high temperatures and then it is formed in to a mass (agglomerated) of Triuranium Octoxide U3O8 which is the most stable form of Uranium thermodynamically and kinetically. The final product has the name of “Yellow Cake” (although the color is brown/green) it this is how it is distributed in solid form by countries who export Uranium.

To clear the compound in the mills from impurities the Uraninite is put in reaction with hydrogen according to the following reactions inside a thermally insulated chamber:

Abbildung in dieser Leseprobe nicht enthalten

The produced Uranium dioxide UO2 is then put in reaction with hydrogen Fluoride HF again in a thermally insulated chamber to produce Uranium Tetrafluoride:

Abbildung in dieser Leseprobe nicht enthalten

This product is then fluidized in a bed reactor passing through a catalyst, fluorine and producing Uranium Hexafluoride UF6. This product is also cleared from impurities with steam at 7000 C and put in to reaction with Hydrogen and water:

Abbildung in dieser Leseprobe nicht enthalten

This final product is called Urania (Yellow Cake) contains 70% - 90% U3O8 by weight but also UO2 and UO3 and is cleared from impurities.

Yellow cake has excellent storage properties as a solid. It can also be switched in to liquid but mostly as a gas in the Uranium Hexafluoride UF6 form for uranium enrichment [19].

From the above reaction it is clearly understood how Yellow Cake can be transformed to Uranium Hexafluoride UF6 and vice versa.

Since UF6 consists of 6 fluorine atoms and one uranium atom its molecular weight is 238+ 6x19 =352 grams/mol which means that the actual uranium mass is 67.6 % of the UF6.

3.2 Physics and Enrichment Units

Nuclear reactors need fuel. This fuel is based in Uranium and the metal oxide of it. Metal oxides are used for the reason of the melting point which is higher than the actual metal and since they are in oxidized state they can neither burn [1]

The actual fuel is the UO2 (UOX) which is put in to rods, at high temperatures; and formed in to solid. This is the way they are transported and distributed by companies to the nuclear factories around the world. Other kinds of fuel also exist like Mixed Oxide fuel (MOX) or training research isotopes general atomic (TRIGA), molten plutonium, ceramic fuels etc. but the majority of uranium enrichment feeds are uranium dioxide UO2 (UOX) and Uranium Hexafluoride UF6 with quantities of 235U and 238U. Separating those two isotopes is very hard since they both have the same number of protons and electrons and they only different in three neutrons which makes the difference. This means that normal chemical separation is not possible and some other method of separation must be used.

Before, some values in the process must be identified.

3.2.1 Separative Work Unit (SWU): This unit actually is the work needed to separate atoms. Tt is based in thermodynamics theory and it is the actual cost of energy needed for separation. The required state is in entropy state lower than before so we must put work to it. SWU is based in the following function which is dimensionless, where x is the concentration of the material:

Abbildung in dieser Leseprobe nicht enthalten

The units of SWU are mass units or kilograms Separative Work Units [18].

3.2.2. Separative Power: This unit is the Separative work been done in a certain period and the usual expression is Kg, per SWU, per hour or year which is actually the rate the enrichment a facility can produce enriched uranium. As a rule of thumb, we must produce 120 kSWU per year for a nuclear plant that will produce 1300 MW of electricity with the energy cost of an SWU at 50-60 kWh [19].

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Figure 5: Enrichment Flow [16]

What must be noted is that the increase in concentration of 235U is directly related to the previous concentration of the substance. According to Figure 4 if we want to increase the 235U concentration by 10%, from 60% to 66%, less work is required than an increase of 10 % from 6 % to 6.6%. As we increase the concentration at 25% the SWU significantly decreases with the lowest point at 55%.

Worldwide it is noted that by the year 2010 France was producing 10800 kSWU per year while US was producing 11300 kSWU per year.

3.2.3 Separative Process Materials: These materials are the mass of the input material Mf, the mass of the product material Mp, and the mass of the remaining material (also called tails) Mt. If we denote by xf, xp, xt the equivalent concentrations then the amounts are defined by the formula:

Abbildung in dieser Leseprobe nicht enthalten

Figure 6: Enrichment Concentration and mass flow [18]

By solving this equation for Mf, we get the following feed mass that will tell us how much natural uranium we will need as a feed to produce the requested enriched product [18]:

Abbildung in dieser Leseprobe nicht enthalten

3.2.3 Separative Work: This is the work required for separation of the uranium and is given by the following formula:

Abbildung in dieser Leseprobe nicht enthalten

Where xp, xt, xf are the concentrations mentioned in the Separative Process Materials, P is the mass of the product, T is the mass of the tails and F is the mass of the feed.

Tails can also be enriched but with a cost and if we consider a cost of $ 160/SWU, a cost of yellow cake feed of $ 41 per pound and a mass of 50 t we can the following figure with the cost of the feed residual mass and the SWU price:

Abbildung in dieser Leseprobe nicht enthalten

Figure 7: Function of tails enrichment with the black line being the cost of feed needed and the blue line the SWU cost [19]

3.2.4 Separation Factor: This tells us how efficient the enrichment facility is in separating the isotopes 235U and 238U. This factor is given by the following equation where x are the same previous mentioned concentrations.

Abbildung in dieser Leseprobe nicht enthalten

The denominator is the ratio of the tails output and the nominator is the ratio of the products stream. For uranium grade reactor α=4.3 and

the separation factor must be over 4.32=18. For diffusion for one machine the separation factor is close to 1.003, for centrifuge enrichment is ≥ 1.5, for electromagnetic separation is 10 and higher depending on space charge. For laser enrichment it is ≥ 10 for a single stage.

4. Enrichment History, methods and processes

4.1 History of Enrichment

The idea of Enrichment was first introduced in 1919 but the process was not feasible until 1934 when researchers in the University of Virginia succeeded in separation of chlorine-35 from chlorine-37. The program seemed achievable and succeeded in gaining funds to proceed with uranium separation.

When World War II started and the Manhattan project was a necessity, to gain nuclear superiority from the Germans, several techniques were used for uranium isotope separation. Centrifugal separation was tested but was abandoned due to high energy requirements so scientists had to turn to gaseous diffusion.

In the same year with the Manhattan project electromagnetic enrichment was suggested, but the method required a lot of time for the isotope separation so it was abandoned because the army needed something immediately to create the bomb in favor of gaseous diffusion enrichment

In the beginning of 1950, in the ex-Soviet Union, two German prisoners of war suggested the creation of a new type of centrifuge for uranium enrichment which was immediately adopted since gaseous diffusion was sufficient in creating nuclear weapons but when used for electrical nuclear factories it required more energy than they actually produced. After their release from the prisoner’s camp, the scientists returned to the free world and from memory, (since they had not any blue prints) they designed the initial centrifugal rotors [9].

In the beginning of 1970, the Department of Defense in the US decided to switch from gas diffusion enrichment to centrifugal enrichment and build its first plant in Oak ridge. The plant was a success so a second plant in Portsmouth was build. This method today is the proffered method of enrichment around the world.

4.2 Methods of Enrichment

Enrichment can mainly be done by five enrichment processes. The basic idea in all methods is gas separation. These are the older electromagnetic and diffusion processes, the aerodynamic nozzle separation, the laser process, the electromagnetic process and the centrifuge process. Typical enrichment grades are 4-5% for a power reactor, 20% for a research reactor and 90% and above for nuclear weapons.

Enrichment can also be done in reprocessed uranium or depleted UF6 tails or expired nuclear weapons.

The electromagnetic process is the oldest one based in isotope separation by a magnetic field.

Gaseous diffusion method was more popular until the year 2000, but it is slowly abandoned in favor of centrifuge, which by the year 2020 will be 93% of the enrichment processes worldwide.

Aerodynamic nozzle separation is a method used mostly for scientific purposes and is not used in large commercial scale.

Laser process is the new scientific method of enrichment, it is under development in many countries due to its lower power consumption and it is the most promising method of enrichment in the future.

Finally, the centrifuge process is the most widely used in enrichment plants and is done by centrifuge rotors in long cascades. These cascades can be easily hidden allowing the country that has them to easily move to the next level of enrichment and be able to create an atomic weapon.

Inside the gas centrifuge in an evacuated casing the UF6, which is in gaseous form, spins rapidly and creates a thin layer next to the rotor wall with the same speed as the wall itself [18]. The casing is needed to hold a number of rotors and to keep a vacuum environment. The centrifugal forces created causes the 238U to move closer to the wall than the 235U since it is heavier[2].

The size of the rotor as well as the rotor speed are very important. The higher the speed the better centrifugal results can be achieved. The material of which the rotor is made is also a major factor since it is in an immediate touch with the UF6. Several corrosion resistant material have been suggested with the currently most in use being the maraging steel (superior iron alloys), which is the best strength to weight ratio and can produce wall speeds in the range of 500 m/sec [2].

Research for more endurable components in rotor manufacturing have been made with composites of aluminum and titanium reinforced by glass and fiber that can achieve wall speeds in the range of 600 m/sec.

4.2.1 Electromagnetic Enrichment

The Electromagnetic Isotope separation (EMIS) process is dated from the early Manhattan Project, still in use today, and reappeared in IRAQ’s nuclear program in 1992. It is based on the physics of the mass spectrometer where vapors of metallic Uranium are created and then transformed into positively charged ions [9]. These ions are accelerated and ejected in a magnetic field and subsequently deflected since 235U and 238U have arcs of different radii and are thus separated in a magnetic field. This kind of enrichment is also very energy consuming.

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Figure 8: Electromagnetic Enrichment [19]

In the process, uranium tetrachloride is transformed to vapor with electric heating and then electrons are injected in the vapor and U+ ions are produced. These ions are accelerated to high speeds by an electric field and are passed through a magnetic field. Their trajectories are circular perpendicular to the magnetic field and 235U and 238U are collected in collector pockets as the following diagram.

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Figure 9: Physics of Electromagnetic Enrichment [19]

The biggest drawback of the process, besides the energy consumption, is that less than half of the uranium tetrachloride is transformed to ions and in the collection process, only half of them are collected.

4.2.2 Gaseous Diffusion Enrichment

The theory behind this enrichment process is that the heavier molecules travel slower than lighter ones. Inside a chamber, the UF6 is compressed and forced through porous semi-permeable membranes. The 235U molecules have a higher probability to pass through the membrane since they are faster than the 238 U ones. This process is constantly repeated through many chambers in cascade form. Every stage has three parts. The diffuser, the compressor and the heat exchanger. The depleted UF6 is selected from one end of the cascade series and the enriched UF6 from the other end. The advantages of this method of enrichment are that it can handle large quantities of gas UF6 but the separation amount is very small.

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Figure 10: Gaseous Diffusion Enrichment [19]

The separation factor α2 is calculated to be the square root of the division of the molecular weights of 238UF6 and 235UF6.

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Although about 25% of the enrichment capacity of the worlds uranium enrichment is done by diffusion, this method is becoming gradually obsolete since it requires high level of energy and is been replaced by the centrifuge enrichment method. A plant of 10,000,000 SWY per year needs electric power of 2700 Mw. Compared with a centrifugal plant this is 15 times more.

The required stages in a diffusion plant is 30 times more than a centrifuge plant and also the time required to achieve equilibrium is also extremely high. The time in a diffusion plant is months and in a centrifugal plant is hours.

4.2.3 Aerodynamic Nozzle separation

This process was used in West Germany and South Africa and it is based in the theory of directing a mixture of compressed UF6 and Helium H2 along a curved wall so the heavier 238U molecules move out of the wall compared with the 235U ones. The deflection ends in and edge where the heavier and lighter outputs are of enriched 235U and H2 are collected [43].

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Figure 11: Aerodynamic Nozzle separation [43]

The process is energy consuming and creates many tails so it is not preferred today.

4.2.4 Laser Enrichment

This method is the future of uranium enrichment in the nuclear industry since it has low costs, low energy requirements and smaller waste in the form of tails. This method is being accomplished in molecular or atomic level.

The atomic method is the Atomic Laser Isotope Separation (AVLIS) in the USA and the SILVA in France, but the method had no scientific results and was abandoned in favor of SILEX (Separation of Isotopes by Laser Excitation), also known as GLE or global laser enrichment, which mainly uses UF6[26].

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Figure 12: Laser enrichment Process [27]

SILEX operates in molecular level. This method is based on the physics of photo-ionization. In this method, a laser of high power is tuned in the frequency of 235U and is aimed at the gaseous metal oxide making the electrons of 235UF6 to excite from the laser power. The ionized 235 UF6 is collected in to a plate which is negatively charged. Silex is estimated to produce 2000 tU per year by the year 2020 [37].

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Figure 13: Physics of Laser Enrichment [26]

A pulsed CO2 laser with a wavelength of 10.8 μm is switching its wavelength to 16 μm and through reflecting mirrors is directed to diluted UF6, which is cryogenically cooled and comes out with supersonic speeds out of a nozzle. The 16-μm wavelength is absorbed by the 235 UF6 which is excited in its vibration frequency and is enriched but not from the 238UF6. The process is repeated until the required enrichment level is achieved [26]. This method requires very little energy compared with the enrichment by diffusion and centrifuge enrichment.

Another method of laser enrichment is CRISLA. The whole process is done in chambers in low temperatures to create coagulation of the gas, which is not ionized. The laser process is the same as SILEX and 235U has its electrons excited by a high-power laser tunes in the same frequency as the 235U. This condensation makes the depleted substance to remain in the chamber and the enriched one in 235 U is taken out of the system.

The biggest problem with Laser enrichment comes with nuclear proliferation risks.

The laser units are very small with 1m length and the space required is also very small 20m x15m (300 m2) with the ability to produce 32.5 Kg of enriched uranium. Laser systems to enrich uranium are not regulated yet and this poses a major concern in the nuclear proliferation potential almost the same level as centrifugal and plutonium regulations.

4.2.5 Centrifuge Enrichment

This kind of enrichment is based in the laws of physics of centripetal acceleration and the fact that objects with higher mass will move at a faster rate than the ones with the lower mass. This means that the heavier molecules will move towards the wall of the container while the lighter ones will not.

The actual gas centrifuge casing varies in size. Most of them are 4-5 meters tall but some of them can be as 12 meters tall and 20 cm in diameter. Inside the casing is the cylindrical rotor and an electric motor. The rotor rotated at 5,000 – 7,000 rounds per minute in early versions but it can now exceed 60,000 rpm in the new type Zippe centrifuges [23]. The centripetal force created is much stronger than the gravitational force 104 times. In the casing, there is one input and two output lines. The input line is the feed and the two outputs are the depleted and the enriched gas. The input feed of the UF6 is pressurized at 1mba and the output lines take the product to other centrifuged to continue the process [2].

Abbildung in dieser Leseprobe nicht enthalten

Figure 11: Centrifuge Rotor Layout [28]

The centrifuge rotor is comprised of the following subsystems:

1) Casing

2) The rotor itself

3) Power supply and electric motor

4) Vacuum system

5) The suspension / bearing system

6) The bellows

In order to minimize resistance and friction the rotor is operating inside vacuum.

The gas centrifuge is regulated by an electronic converter with an input of 50-60 Hz and an output of a higher frequency. Since the speed of the rotor is proportional to the frequency output the converter feeds the device with AC of variable frequency around 1 KHz and the required rpm are created. The design is reliable, is evolving constantly and problems of the past like resonance frequencies are long gone.

The rotation causes the 235U atoms to concentrate in the center and the 238U towards the walls of the chamber. The enriched product is axially drawn off by a thermal gradient.

The collection is done inside the chamber by vents in the wall and the center that collect the two products.

4.2.6 Centrifuge Rotor construction

The rotor is made from strong materials like titanium, maraging steel, aluminum alloys, and various composites that use carbon fibers, aramid or glass to boost its strength. The rotor must have a certain length to avoid vibrations and to maintain a good balance to avoid suspension and bearing failure. The rotor is installed in a casing to avoid the domino effect (if a rotor fails not destroying the adjusted ones) [33].

The rotor has a peripheral speed different than the rotational speed, which characterizes the strength of the rotor, depending on the density “ρ” and tensile strength “σ”and signifies the maximum strength of the rotor. The peripheral speed is given by the following equation:

Abbildung in dieser Leseprobe nicht enthalten [34]

Since the peripheral speed is the product of the circumference of the rotor and the rotational frequency, we can have the same result with a smaller radius and higher rotational speed compared with a rotor with a large radius and low rotational speed.

Peripheral speed is a very important factor. A change in peripheral speed by 10% will result an increase in separation by 46% [34]. The isotope separation is proportional to the fourth power of the peripheral speed.

The speed depends on the alloys that the rotor is made. The following table gives the maxim speeds that the rotor can hold, depending on the construction material:

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Table 1: Peripheral Speed according to construction material [34]

Balancing is also an important factor. This is because if there is a difference between the mass axis and the geometrical axis a rotating radial load is created. Thus, vibrations are created due to the fact that while the rotor is rotating around its center of mass the geometric center and the bearings are pushing it towards the center. This is the dynamic unbalance of the rotor creating two types of synchronous whirls. The conical and the cylindrical whirl. These whirls have to be balanced in construction of the rotor.

If we have an unbalanced force we have resonances creation which are called rigid body critical speeds. These are the cylindrical and conical critical speeds which are given by the following equations [34]:

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In the equations “m” is the mass of the rotor, “s” is the bearings stiffness, “p” is the polar inertia and “i” is the half bearing separation.

Balance can be achieved by decreasing the bearings stiffness or with a shaft bearing design which is flexible thus lowering the natural frequency.

If a rotor is too long it experiences, at higher frequencies, flexural critical speeds due to longitudinal vibrations. If the rotor has a lot of resonance frequencies it will have high risk of mechanical failure so the effort is centralized in having the maximum separation before the critical frequency is reached.

If the critical speed cannot be avoided then bellows are inserted or optimization on the dumbing of the bearings or bypassing the critical speed accelerating at the critical point.

The output of a single centrifuge, with today’s technology, is 30 grams of high-enriched uranium and four separative work units SWU per year. More advanced centrifuges can produce 40 SWUs per year but this also depends on the degree of enrichment feed and the amount of the processed uranium.

As a rule, the production 20-25 Kg per year of highly enriched uranium can be achieved with 850-1000 centrifuges with speeds of 400 m/sec, which is enough quantity to create a single nuclear weapon [33].

4.2.7 Cascading

The output feed of the enriched gas is the feed of the next centrifuge by various methods. These processes are the serial one, the parallel and the symmetrical. This process is called cascading.

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Figure 15: Serial-Parallel Cascading [19]

The serial connection is not a very efficient one since a large quantity of uranium is wasted in tails (depleted output). It is reported that if 10 centrifuges are used in serial cascade with an input of 10,000 Kg of UF6 and an initial enrichment of 0.711% the final product will be 2.66 Kg with enrichment at 0.81%, which means a lot of wasted uranium [2].

The parallel connection is better than the serial but still not very efficient. It is reported that connecting 10 centrifuges in parallel and a feed of 10,000 Kg of UF6 the final product will be 4.36 Kg with enrichment of 0.92% still a waste of Uranium.

Abbildung in dieser Leseprobe nicht enthalten

Figure 16: Symmetrical Cascading [19]

In the symmetrical connection, the depleted product from any centrifuge is recycled in the previous centrifuge and this is done to all machines. This kind of connection does not follow a typical pattern and it is tailored made to fit the need of every customer, so the design of every connection is different [19].

In the symmetrical cascade, the number of the centrifuges decreases as the enrichment proceeds to the end so the process is also called tampered cascade.

To construct the best cascade, we must consider two characteristics. To have the same separation factor for every stage, never mix gases of different enrichment levels to minimize the energy consumption.

Another method is the asymmetrical cascade (also called two up- one down cascade) and the waste is send two stages back and the product goes in the next stage. This method is not used in gas centrifuges and is used in aerodynamic nozzle separation.

If we have an initial feed of 11,038 Kg of UF6, and 2633 centrifuges we can produce 83 Kg of low enriched uranium with 4.3% enrichment and depletion tails of 0.28% with a total production of 1,025 Kg per year.

If we compare the centrifuge cascade method with the gas diffusion method, the capability of isotope separation in gas diffusion is greater but the capacity is much smaller. The number of stages required is also much smaller. To achieve the same level of enrichment 10 to 20 centrifuge cascades correspond to thousands in diffusion cascades [1].

The cascades are also designed to operate continuously and they cannot shut down or be slowed with a single switch. Their life expectancy is 25 years and their efficiency are measured in the percentage of depleted uranium tails they produce with the Russian cascades at 0.10% and Western ones at 0.18% to 0.22%.

4.2.8 Advantages Disadvantages of Enrichment Methods

The basic methods of enrichment are the gaseous diffusion, the Gas Centrifuge, the laser enrichment and lately re-enrichment from withdrawal of old nuclear weapons. The other methods are primarily used for scientific purposes.

The gas centrifuge idea was first introduced in 1919 and was explored during the Manhattan Project but was abandoned in favor of Gaseous diffusion and electromagnetic enrichment because in short term had more chances to succeed. The Soviet Union though in the 50’s proved to be the best and more reliable method that gaseous diffusion and soon after all countries turned to Gas centrifuge.

Lately the new method of laser enrichment is explored and tested with very promising results.

The following table gives the percentage on enrichment methods used worldwide in certain years and an estimation for the 2020.

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Table 2: Percentage and Timeline of Enrichment Methods [16]

Diffusion methods of enrichment, which was very popular in the past, has decreased dramatically. In the year 2000 the supply source was 50% diffusion, 40% centrifuge and 10% recycling of high enrich uranium of atomic weapon. In 2010 the diffusion was 25%, the centrifuge 65% and recycling of atomic weapons still 10%. In 2015 in western states diffusion had dropped to 0%, centrifuge 100% and atomic weapon recycling 0%. With the new technologies of laser enrichment, it is projected that by the year 2020 diffusion will be obsolete in all countries the laser will be 3%, centrifugal at 93% and recycling of atomic weapons again at 4% (due to life expectancy of US weapons at that time) [16].

If we compare the three enrichment methods we conclude that the Gaseous diffusion enrichment is the costliest with cost per SWU ($ 180) and also it is very energy consuming. The only advantage it has is that it can be easily identified by the Atomic agencies due to its large energy consumption so it is characterized with low proliferation risk.

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Figure 17: Comparison of Gaseous Diffusion-Gas Centrifuge-Laser methods of Enrichment on Cost per SWU, Energy Cost, and Proliferation Risks [37]

The Gas centrifuge enrichment method is more efficient with less cost per SWU ($ 100) and about half the energy cost required for gaseous diffusion. The proliferation risk is higher because the energy requirements can resemble energy consumption by any small factory so it is easier for a country to cover its centrifuge program and escape from the IAEA inspections.

Finally, the Laser Enrichment is the best method in all aspects. Its cost per SWU is down to one third of the gas centrifuge ($ 30), its energy cost is also at one third of the gas centrifuge but the proliferation risk is extremely high because of the small size of the laser construction and its small energy consumption, almost impossible to be identifies by the Atomic inspections.

4.3 Reprocessed Uranium Enrichment

The nuclear fission that takes place in a nuclear plant creates plutonium 239U in addition to depleted uranium 238U and two new isotopes 232U and 236U, which is collected in to mixed oxide fuel (MOX) with 3% to 6% plutonium 239U. The isotope 236U is wasting neutrons and this higher enrichment of 235U is required.

The uranium collected in the used nuclear fuel (RepU) can be re-enriched by special plants that separate the plutonium from uranium by dissolving it with nitric acid. Then the solution reacts with tributyl phosphate creating an oily solution separating the two products, and then by washing them with water to get the final extraction [2].

The plutonium salvaged can be used for fuel for special reactors like the Magnox reactors in Great Brittan or CANDU reactors. This process though is very dangerous since it can create the fissile plutonium material needed for an atomic weapon. Countries that are not under the IAEA watchdog can easily salvage enough plutonium for fission of an atomic device, like North Korea [16].

The isotope 236U creates a problem in reprocessing, since it is a neutron absorber and so the created fuel must be in higher enrichment status than normal fuel (4.6% enrichment compared with 4.4% before) and the recycle can be made only once.

The kind of fuel that can be repressed is low burnup and low enriched called RepU. An extraction of 1659 tons of enriched reprocessed fuel in two plants was made from 16,000 tons of RepU [16].

In all enrichment methods, we have depleted uranium tails of 0.3% that can contain 42% of the isotope 235U. Tails also contain 88% of the original mass feed [20] and it is stored in cylindrical steel containers with depleted UF6 with are subject to corrosion and eventual release, after many years, of the UF6. For that reason, many countries, which don’t know what to do with their tails and have some kind of environmental concern, are sending them to Holland and Russia for re-enrichment despite the fact that this process is very expensive.

In the US 60,000 tons of nuclear waste have been produced so far and this number in increasing by 2,000 tons per year. It is estimated that to reprocess 2,000 tons per year two reprocessing factories are needed with a cost of $ 20 billion and a cost of $ 3 to $ 4.5 billion operating cost per year. That is the reason reprocessing plants are not build and radioactive debris is buried in shallow tranches. It’s all about money [38].

4.4 Reprocessing Expired nuclear Weapons

Under an agreement signed between the US and Russia the lateral would disarm some of its nuclear weapons and reprocessed then from highly enriched uranium to low enriched uranium (down blending). The program was called “From Megatons to Megawatts”. This LEU was finally bought by the US in a deal costing $ 12 billion and it is estimated that ½ of the nuclear fuel used by the US nuclear factories today comes from dismantled nuclear weapons.

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The Russian HEU though was not pure. It contained other isotopes too as high concentrations of 234U, 232U and 236U and chemical impurities. The method used was lowering the impurities with radiochemical processes and increasing the dilution factor by combining the 234U with uranium of higher yields producing 1.5% Low enriched Uranium [40].

Table 3: Method of Down blending High Enriched Uranium (HEU) to Low Enriched Uranium (LEU) [40]

It must be noted that the whole process requires much more energy and costs more that creating Low enriched uranium from simple enrichment but it is good measure in the destruction of old warheads.

5. ENRICHMENT IN MIDDLE EAST COUNTRIES- ISRAEL/IRAN

5.1 History of Enrichment in Middle East Countries

When enrichment reaches the 85% grade of 235U the initial required grade for the creation of an atomic weapon is created. The grade is connected with the critical mass required for detonation, which means if the enrichment is increased to 97% a very small weapon can be designed ready to equip the head of a small missile (Higher enrichment- Smaller warhead).

In an ideal world, uranium enrichment is under scrutiny and the watchdog of IAEA. Nuclear plants use fuel coming to them from respected companies in various countries, like Canada, Japan, and Australia etc. who properly regulate the market of nuclear fuel. This means that the created plutonium after the fission in the nuclear plant goes back in the depleted tails back to the reprocessing plant. The problems arise when the countries want to create their own nuclear fuel under the inspection of the IAEA or not. The required enrichment, as was mentioned is 4-5% for nuclear plants, 20% for scientific reactors (which create medical isotopes) and higher than 85% for nuclear weapons. Some states like Iran, North Korea and Israel have their own enrichment plants some of which are under the IAEA control and some are not.

There is a problem of inspection and control of centrifugal plants especially if a state wants to build a clandestine plant, which requires only 160 W/m2 and can disguise as a typical industrial facility very hard to detect with IR imaging. If it were an older diffusion plant, it would require 10,000 W/m2, easy to be identified.

It is also important to notice that the enrichment effort per ton of uranium feed is not linear. As enrichment increases the effort SWU decrease dramatically. To reach 4% enrichment 800 SWU are required with a production of 130 Kg out of the ton. For a 20% 1150 Separate Work Unit (SWU) required with a 26 Kg product and 1250 SWU for 5.6 Kg for 95 % enrichment [4].

This means that a state can claim it is manufacturing 20% enriched 235U for medical or scientific research that can be easily converted to 95% with little effort so safeguards become ineffective.

The problem began after Pakistan decided to create its own atomic weapons program following India’s first atomic weapon test. One of Pakistan’s scientists who was working in the past for Urenco in Holland decided to sell in the black market blue prints and old centrifuge parts [21]. Some countries like North Korea, Libya and Iran took advantage of this and began developing their own centrifugal enrichment program. Libya, after the fall of the regime abandoned its nuclear program. North Korea is under negotiations with the US for its nuclear program and Iran has signed the JCPOA treaty to be inspected by IAEA. Iran from the early 60’s pursued the nuclear technology and despite its revolution by 2006, Iran had its first 164 centrifugal cascade in place and with a constant increase in numbers. Today these centrifuges have been revised to IR-2M, IR-4, and IR-6 and one IR-8 (for 20% enrichment) which are much more effective [4].

Of course, the JCPOA treaty regulates only two items out of 100 to create a centrifuge. The bellows and the rotors. All other components are free to purchase. So, if the 98 items are stockpiled it is easy to create more centrifuges. The JCPOA treaty also limited the supplies of 235U and the capabilities to create plutonium 239U.

5.2 Israel’s Nuclear Program

5.2.1 History of Israel’s nuclear program

Israel from the foundation of the country in 1948 had problems with its neighbors, which always wanted the end of the country and was constantly in high alert to avoid this. Many scientists at that time migrated to Israel and one of them Erns Bergmann became the founder of the Israel’s Atomic program. To achieve this, Israel contacted the French, who were at the time in close scientific cooperation regarding nuclear technology and in 1953 requested assistance in building a nuclear reactor. By the year 1956, an initial understanding was signed. The French at that time worried about the cooperation between Egypt and the Soviet Union so it was decided to modify the initial understanding from an 18 MW research nuclear reactor to further facilities including plutonium 239U separation. The nuclear reactor finally was at that time 3 times that of the original size with reports by the year 1986 estimated its size at 125-150 Mw. This reactor was not used to produce steam for turbines but instead it was used for plutonium production. This cooperation with France was so close that Israeli scientist helped France in resolving some of its own nuclear technical problems with a French company building plutonium separation plants at the same time together in France and Israel[15].

Finally, the reactor EL-102 type was built in the site of Dimona with underground facilities of unknown use. This caused tensions between Israel and USA who demanded inspections in the site that started in 1962 and ended 1969 but only for installations above the ground. The French not only helped the Israelis with their scientists in creating the site but also provided Israel with hardware technology and nuclear test explosion data.

5.2.2 Israel’s nuclear fuel and Dimona plant

The reactor needed fuel and since it was unregulated, the fuel should be purchased from the open market. In 1965, the US government initiated an investigation led by the FBI, CIA and the Atomic Energy commission, on the loss of 200 pounds of HEU uranium from a small fabrication plant in Apollo Pennsylvania. According to some sources [31] this uranium went to Israel. Extra Uranium and heavy water was supplied from Norway, France and the US. After the 1967, war Israel obtained 200 tons of Yellow cake from Antwerp Belgium and in the mid 70’s 600 more tons from South Africa.

Since Israel had mining deposits of phosphates in Negev desert, it designed a method to extract Uranium out of the phosphate.

According to an Israeli scientist, named Vanunu (who worked for a certain period in Dimona plant) Israel was extracting by irradiation of the nuclear fuel 40 Kg of plutonium per year (before his arrival in Dimona plant in 1977) and at l the time of him, being there the facility produced 1.17 Kg of 239U per week. Since Vanunu worked there for 8 years that means that, a production of 320 Kg could be achieved. According to the same person, proven by photographs in London Sunday Times, in Dimona was an underground facility for nuclear weapons construction that produced solid 4.4 Kg 239U spheres for nuclear bombs, beryllium neutron deflectors and copper hemispheres to seal the plutonium inside. At the same time, the facility produced deuterium and tritium, necessary components for a thermonuclear hydrogen bomb [32].

5.2.3 Israel’s Nuclear Capacities and Weapons

It must be noted that Israel never admitted of having nuclear weapons but according to Jane’s Intelligent report Israel is in possession of more than 200 tactical nuclear weapons in artillery shells, aerial bombs and tactical nuclear missiles like Jericho 2 and Jericho3 [31].

The range of Israel’s missile range is in figure 18. Jericho 2 is a medium range ballistic missile (MRBM) with a range of 1,500-3,500 Km and Jericho 3 is an intermediate range ballistic missile (IRBM) with a range of 4,800-6,500 Km [30].

Its capacity and stockpiles are, according to the same sources, 0.84±0.15 tons of Weapons grade 239U and 0.3 ±0.12 tons HEU 235U.

Israel never signed any treaty as non-proliferation of nuclear weapons treaty (NPT) or Missile Technology Control Regime (MTCR) or Fissile Material Cutoff treaty (FMCT). It is refusing any inspection in its nuclear facilities from the United Nation and is opposing calls for a Middle East WMD Free Zone based on reasons of national interests. To assure worldwide concerns Israel has declared not to be the first one to introduce nuclear weapons in the Middle East.

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Figure 18: Ballistic Jericho 2-3 missiles and their estimated range [30]

5.2 Nuclear Program and Uranium enrichment in Iran

5.3.1 History of Iran’s Nuclear Program

Iran’s nuclear program started in the 50’ in the Shahs regime. The Shah believed that oil supply would run off one day so he pledged for the construction of 23 nuclear power plants. Iran signed various agreements from nuclear factories to enrichment facility with many countries [12]. One of the agreements was with President Ford for the construction of a complete reprocessing plutonium facility and so Iran would be sufficient in the complete fuel cycle from mining, enrichment, fuel construction, and reprocessing with plutonium extraction. The agreement was never fulfilled.

In 1979 after the Iranian revolution, the program was set in to a new base. Agreements were signed with France, Argentina and the Soviet Union for technical cooperation and scientific expert exchange. In 1987 agreements were signed with Pakistan for training and in 1990 with China for a miniature neutron source n reactor (MNSR) [8]. In the 2000’s Iran’s nuclear program was investigated by IAEA after claims that a nuclear bomb program was in place.

5.3.2 Iran’s Centrifuge facilities and plants

By 2010, Iran had installed in the power enrichment plant in Natanz two cascades of centrifuges of the IR-1 type consisting of 164 mushiness each in tandem pairs. The country then used these cascades to produce 20% enriched Uranium Hexafluoride UF6 [17].

Centrifuge IR-1 is the same as the P-1 centrifuge created by Pakistan after the blue prints of a Pakistani scientist who was working in the past for Urenco in Holland decided to help his country in the pursue of nuclear weapons but unfortunately for money reasons decide to sell in the black market blue prints and old centrifuge parts. This came as a necessity for Pakistan after the realization that its rival, India, had detonated a test nuclear device [10].

The IR-1 cascade is in a tandem design with the output tails created by cascade1 are recycled in cascade 2 [22]. The whole process consists of five stages as follows:

1. With “A” we denote the feed of Cascade 2
2. With “B” we denote the product of Cascade 2
3. With “C” we denote the initial feed of Cascade 1
4. With “D” we denote the feed in cascade 1
5. With “E” we denote the total product stage

The flow with the tails generated by the cascade 1 are recycled in cascade 2, according to Figure 12

The numbers in figure signify the tandem configuration and the total number of the centrifuges.

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Figure 12: Iran's Cascade flow with the tails generated by cascade 1 recycled in cascade 2[22]

This configuration is producing 20% enriched UF6 with a minimal waste of 0.7% of 235U. This kind of centrifugal had problems as its Pakistani equivalent of P1. The problem was vibration causing the tandem to shut down in order not to break. So, Iran stared to enhance its centrifuges and create newer models as IR-2, IR-4, IR-5, and later IR-8 [10].

If this cascade is to be used to level up the enrichment to 85%, ready for a nuclear weapon, it is believed that per cascade, 2.5 Kg of UF6 could be produced and if the cascade worked constantly 37Kg of HEU UF6 (25Kg HEU 235U) at 85% enrichment could be produced in 15 months. Of course, this would require Iran to have in reserve 300 Kg of 20% enriched product. By 2013, the stockpile of 20% enrichment UF6 was 182 Kg but the required reserve was achieved a few years later and has not change, not even after the signed treaty between IRAN and IAEA.

By the year, 2011 Iran had operational 136 modified IR-2 centrifuges in cascade and 27 IR-4. These two types of centrifuges are identical in length and in diameter. They are derived from the Pakistani P-2 centrifuge. The IR-2 rotor has two sections inside made of Carbon fiber and its bellows are made from maraging steel. The difference of IR-4 with IR-2 is that it has connections bellows made also by carbon fiber. This is due to sections and the inability of Iran to purchase enough maraging steel for the production of the centrifuges and so had to develop a design based in Carbon Fiber. This of course resulted in a higher rate of failure.

The output of both types is, for each machine 5 SWU per year that is much better than the initial IR-1 in the Natanz facility that had only 0.75 SWU per year per machine [23]. To make the comparison 4000-5000 IR-1 centrifuges are equivalent to 1000 IR-4/IR-5 centrifuges [36].

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Figure 13: Iran's cascade centrifuges in Natanz facility [42]

5.3.2 Joint Comprehensive Plan of Action (JCPOA) agreement

Until the JCPOA agreement was signed, Iran had increased its centrifuges to 19,000 and after the treaty had reduced them to 6000 but unfortunately the IEAE cannot say how many centrifuges are in storage and how many parts are in inventory.

So today 2018, following the treaty, Iran has 5060 IR-1 centrifuges in 30 cascades operational in Natanz. The rest 16,000 IR-1 and 164 IR-2 and IR-4 are put in to storage. The second enriched plant at the location of Fordow (which is an underground facility to avoid air strikes) had limited its centrifuges to 2,800-3,000 from the initial 9,000 but non-operational until required to operate again at Iran’s convenience!

The treaty also required Iran to stop research and development in enhancing its IR-2, IR-4, IR-5, IR-6, IR-7 and IR-8 centrifuges[7]. To facilitate IAEA to measure the output of its existing IR-1 and not to build a reactor that can produce weapon graded plutonium 239U, for a period of 15 years and to facilitate inspections by the UN and IAEA inspectors in its operational facilities. If the inspectors report there were any suspicious facilities, the country would need a request for inspection 24 days prior to the visit (enough time to dismantle and hide any equipment)[36].

Another part of the agreement was to reduce the inventory of LEU (2.7% to 3.5% 235U of UF6) to 300 Kg from an initial of 12,000Kg and to switch all of its 20% enriched UF6 to 5% LEU fuel plates.

The treaty seems solid but has some points that should be addressed. It is obvious that the nuclear capabilities of the country have greatly reduced after the treaty.

Iran’s nuclear capabilities before and after the JCPOA agreement are presented in Appendix in Figures 20 and 21 including a timeline in Figure 23 of the same agreement.

In those figures, we see a significant change in the quantities of uranium and plutonium in Iran and a significant decrease in the number of he centrifuges. In addition, under the JCPOA treaty, Iran cannot make more centrifuges but the agreement has a fault.

If we investigate, the single IR-8 centrifuge Iran is allowed to have under the JCPOA treaty then it is unexplained the fact that at least six IR-8 rotor assemblies are under stock and more bellows and tubes are manufactured. More IR-6 and IR-6s assemblies are also manufactured and put in stock for spare parts. So there is a possibility that all parts and filament wirings were not declared and these can be used in short time to produce more centrifuges [6].

In Appendix, Figure 23, the time for Iran to produce weapon-graded uranium is presented. The required enrichment from 0.7% to 3.5% 235U enrichment requires 9,000 centrifuges and a time of 4.5 to 7 months. To go to the next level of 20 % enrichment 1,312 centrifuges are required. Then from 20 % to 60% enrichment 465 centrifuges and finally to weapons grade 90% enrichment only 128 centrifuges are required with the whole process lasting 2.2 to 3.5 months [41].

Iran’s nuclear facilities are presented in the appendix figure 24.

The total number of centrifuges Iran actually possesses is under scrutiny and what is actually known is only how many centrifuges are operational. In addition it is very important to note that under the treaty the restrictions on the number of centrifuges stop after 10 years and the restriction on enrichment 5 years after that. It is estimated; by the American government, that by the mid 20’s Iran could be back in its nuclear capabilities because by 2025 there will be an end in limiting the heavy water reactors construction and an end on the upper limit in the stock of HEU. That is the reason of the withdrawal of US from the treaty despite the fact that now Iran is complying with the restrictions.

Here arises a question on why the US government signed the treaty in the first place. The reason is that at that time, the Iranian nuclear program had to stop and this could be done with only two ways. Either stop the enrichment process and the nuclear factories (already working!!) with bombs or with the treaty. Since the strategic analysts predicted that even with the maximum bomb efficiency destroying some enrichment facilities of Iran, after the bomb destruction, the program would be back in track in a period of four years but this time aiming it efforts in creating bombs. Therefore, the best solution at that time was to sign the treaty.

It remains a fact that having nukes is a necessity for regimes like North Korea and Iran because that is the way of the sustainability of their regime.

6. CONCLUSIONS

Enrichment of uranium 235U creates products for either fuel in nuclear plants or medical and scientific purposes. Enrichment is done through various methods but the most acknowledged today is enrichment by centrifuging which can create enrichments up to 97% and enrichment by laser being the most promising for the future. The best results in the centrifuge enrichment are achieved if the centrifuges are constructed in cascading mode and its results are based in several methods with various outputs and efficiency. The other two methods, enrichment by gas diffusion and electromagnetic enrichment are becoming slowly obsolete.

The new trend in enrichment is laser enrichment with low energy consumption and low SUW but also high in proliferation risks.

Reprocessed uranium enrichment can be also done but with high cost and energy consumption. Unfortunately, countries with nuclear plants prefer the method of dumbing their nuclear waste in shallow tranches creating a huge environmental problem.

Reprocessing of uranium and plutonium in expired nuclear weapons is also in favor today, despite the high cost because the US wants to destroy as many of the old Russian nuclear weapons as possible.

The enrichment, although regulated by the IAEA, is very hard to be monitored. Either states do not sign the nonproliferation agreement in distribution of atomic weapons or they avoid clear inspection to determine their nuclear capability. The IEAE is constantly monitoring those states but the reality is that if a country aims to build nuclear weapons, it will, despite the monitoring. The only way to achieve this is with constant pressure and sanctions with doubtful results since sanctions are a good excuse to retreat from IAEA inspections, and so accelerating an already existing program.

In the Middle East, there are two key players. Israel and Iran. The other countries that had initiated a nuclear research and development program like Iraq and Libya have stopped their advances for different reasons. Iraq had stopped after the destruction of the reactor in the construction phase by an Israeli air strike and the Libya because the Regime had fallen.

Israel, with the Dimona reactor and the plutonium reprocessing under the plant, is claimed to have nuclear capabilities and weapons on missiles and smaller air and artillery bombs. Israel has not signed the nonproliferation of atomic weapons treaty and is not under the IAEA inspections, for reasons of national security, but has pledged not to be the first one to use nuclear weapons in the region. The possession of nuclear weapons, according to Israel is a necessity in maintaining the Jewish state.

Iran since the Shah regime always was in the nuclear path and after the Iranian revolution, the path was a necessity for the regime to maintain its integrity. Agreements were placed with various countries in constructing nuclear plants and enrichment facilities. The preferred method was centrifugal enrichment. The process was low energy consuming, proven constructions (with blue prints in the open market) after the leak of Pakistanis centrifugal plants and easy to hide resembling like normal industrial facilities.

Imposed sanctions proved a major drawback in the program so Iran decided to sign the JCPOA treaty limiting its capabilities but at the same time permitting the acquirement of essential nuclear components in the open market.

In addition to the nuclear components, for the enrichment facilities, the market opened for other parts too, for missile construction and micro components that would minimize an atomic weapons size, ready for installation in a missile’s warhead, devices for missile accuracy and detonation components for nuclear fission inside a nuclear warhead.

The JCPOA agreement did limit Iran’s breakout time for the creation of weapon grade material for the construction of a nuclear weapon but at the same time permitted the procurement of material impossible to get under the previous sanctions.

US withdrawal from the agreement did not limit the trade with other countries like China, Russia, the European Union so it is with doubtful results beside the fact that US can impose sanction in foreign companies dealing in the future with Iran leading to tensions with these countries.

It is believed that Iran not only has centrifuges in stock but it also possesses the necessary equipment stock to build new ones at a convenient time and reduce the time line in creating a bomb in short time.

Iran’s statement end of May 2018 that Iran was ready to fulfill its enrichment plans without limitations in matter of months should not be taken lightly.

Unfortunately, matters like these are not resolved by scientific means but solely by political ones.

It is a fact that if a country that already possesses the nuclear knowledge in enrichment and construction of a nuclear weapon want to build it there is nothing to stop it in the long end.

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[44] Aerodynamic enrichment nozzle.svg available: https://commons.wikimedia.org/wiki/File:Aerodynamic_enrichment_nozzle.svg

Appendix

Abbildung in dieser Leseprobe nicht enthalten

Figure 14: Iran’s nuclear capabilities before the JCPOA agreement [36]

Abbildung in dieser Leseprobe nicht enthalten

Figure 22: Iran’s nuclear capabilities after the JCPOA agreement [36]

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Figure 15: Time line of the JCPOA agreement [35]

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Figure 24: Time required for weapons garded uranium to be produced and number of required centrifuges [35]

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Figure 16: Nuclear installations in Iran [11]

Details

Pages
22
Year
2018
Language
English
Catalog Number
v437753
Institution / College
University of California, Santa Cruz
Grade
4
Tags
uranium enrichment methods implications middle east countries

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Title: Uranium Enrichment Methods and Implications on Middle East Countries