Fissile material reprocessing

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

Nuclear fuel reprocessing was first undertaken with the sole purpose of recovering plutonium, for weapons use, from uranium irradiated in nuclear reactors. These reactors, called the production reactors, were dedicated to transmuting as much of the uranium as possible to plutonium. From its original scope of recovering exclusively plutonium, with no attempts to either recover or recycle uranium, nuclear fuel reprocessing has since grown into a much more sophisticated and complex operation with expanded scope. It is now called upon to separate uranium and plutonium from the fission products, and to purify these elements to levels at which these fissile materials can be conveniently recycled for reuse. The present scope also extends to fission products separation and concentration. 

The other main type of HLW are the liquid and sludge (a mixture of liquid, suspended colloids, and solids) that resulted from reprocessing to reclaim fissile material, either for weapons pro-... 

The diagram in Figure 16.1 shows two possible paths for this cycle, that is, with and without fuel reprocessing. The majority of reactors in the world and all U.S. reactors operate with a once-through cycle without reprocessing. Some countries, particularly France, do fuel reprocessing with reuse of the plutonium from spent fuel. The portions of the cycle, that precede the introduction of the fissile material into the reactor are referred to as the front end of the cycle, while the back end includes those steps that occur after the removal of the fuel from the reactor. The details of this cycle and the chemistry involved are discussed below. 

Hippel, F. 2007. Managing spent fuel in the United States The illogic of reprocessing. Research Report No. 3, International Panel on Fissile Materials. 

Mixtures of uranium and plutonium may be used instead of weakly enriched uranium in thermal reactors and are applied in fast breeder reactors, which are operated with the aim of producing more fissile material than is consumed by fission. The main fissile nuclide is Pu, which is continuously reproduced according to reaction (11.4) from In fast breeder reactors operating with about 6 tons of Pu and about 100 tons of U a net gain of fissile Pu may be obtained. The bum-up is about 10 MW d per ton of fuel, and reprocessing with the aim to recover the plutonium is expedient. 

Diversion of spent or extensively irradiated fuel for clandestine chemical extraction of fissile material in a reprocessing facility this scenario is technically more demanding and time-consuming than the one mentioned above because of the high level of radioactivity from the fuel which is involved. However, it is of particular concern at about 15 research reactors under IAEA safeguards due to large accumulated quantities of spent fuel, and it is of importance at more than 100 others. 

The starting materials for uranium nuclear fuels are uranium compounds from natural uranium deposits and fissile material separated by reprocessing from spent uranium fuel rods. 

Aqueous reprocessing methods have been developed to effect an efficient and thorough separation of fissile elements from the contaminating fission products in spent fuel( l). While these processes may be altered to yield a proliferations-resistant product by coprocessing or by the addition of radioactive material that will contaminate the clean fissile material, it still is necessary to safeguard some of the process steps to ensure that material useful in nuclear weapons will not be diverted (3). The safeguard requirements and the ease of subversion of such provisions make many versions of the conventional processes subject to unacceptable proliferation risks. 

Although the retention of selective fission products in fissile materials may not adversely affect the performance of fuel in a reactor, the intensity of the gamma radiation is such that the fissile material must be handled, transferred, and fabricated remotely. As a result, it is both technically difficult to divert the fissile material and fabricate a weapon, and nearly impossible to do so without detection. The levels of residual radioactivity in the product of some of the pyrochemical or dry processing methods is close to that found in spent unreprocessed fuel and hence the reprocessed product presents a risk to proliferation only trivially less than that of spent fuel. Pyrochemical and dry processing methods can be used that will... 

Besides being proliferation resistant, the other advantages of fuel cycles using AIR0X reprocessing are (1) extension of uranium reserve by recycling the fissile material in spent fuel,... 

Most of the present nuclear reactors have been burning solid fuel elements of either normal or enriched uranium. Thus far, it has been necessary to reprocess fuel in order to recover valuable fissionable or fissile material. It is possible that fuel elements will be developed for future reactors which can be burned to the point where it is not economically justifiable to recover fissionable materials. Obviously, this depends upon the value of these materials. Such a procedure would provide an optimum solution to the major part of the waste disposal problem. The fission products would still be locked in the fuel element, simple disposal techniques could be employed, and in fact, spent fuel elements would probably have secondary uses as radiation sources. 

High-level waste from reprocessing to reclaim fissile materials for weapons... 

The used fiiel elemmts may later be reprocessed to recover the remaining amount of fissile material as well as any fertile material or regarded as waste fertile atoms are those which can be transformed into fissile ones, i.e. " Th and U, which through neutron capture and jS-decays form fissile and Pu, respectively. The chemical reprocessing removes the fission products and actinides other than U and Pu. Some of the removed elements might be valuable enough to be isolated although this is seldom done. The mixed fission products and waste actinides are stored as radioactive waste. The recovered fissile materials may be refabricated (the U may require re-enrichment) into new elements for reuse. This "back-end" of the nuclear fuel cycle is discussed in Chapter 21. 

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