| I. Materials > The Uranium-Plutonium Chain > Management of Irradiated Fuel |
II. PERSPECTIVES FOR THE FUTURE:
France does not have a long-term program for managing fuel that is not designated for reprocessing. Since EDF does not plan to reprocess all its fuel, the question of the future of irradiated fuel is in need of resolution.
For the future, the possibilities for increasing storage capacity include the densification of storage in present pools. In 2003 Cogéma received authorization to increase the capacity of pools at La Hague by densification. However, such an increase can only be a short-term solution. A long-term solution is being studied in the framework of law no. 91-1381 of 30 December 1991 concerning research on the management of radioactive wastes and law no. 2006-739 of 28 June 2006 concerning sustainable management of radioactive materials and wastes.
Law of 30 December 1991
The 1991 law directly concerns the management of “high-activity, long-lived wastes.” The law is presently interpreted as applying to irradiated, unreprocessed fuel as well as to reprocessing wastes that are said to belong to category C. By that law, Parliament asks that “the Government address each year to Parliament a report stating the advancement of research . . . and of work which is being carried on simultaneously for
--[Axe 1] “research on solutions allowing the separation and transmutation of long-lived radioactive elements present in the wastes”;
--[Axe 2] “study of the possibilities of reversible or irreversible disposal in deep geological formations, in particular by means of the construction of underground laboratories”;
--[Axe 3] “study of methods of packaging and of long-term surface storage of the wastes.”
“At the end of a period that will not exceed fifteen years from the promulgation of the present law the Government will send to Parliament an overall report evaluating this research, accompanied by a bill authorizing, if found appropriate, the creation of a storage center for high-activity, long-lived wastes.”
According to this law the CEA is responsible for research on Axe 1 and Axe 3; and Andra, on Axe 2. The National Evaluation Commission for research on the management of radioactive wastes (CNE), instituted by law 91-1381 underlined the necessity of the CEA’s and Andra’s coordinating their efforts.
LAW OF 28 JUNE 2006
At the end of the fifteen years specified above, research on deep underground burial was insufficient to allow the government to send to Parliament a bill authorizing the creation of a storage facility. The new law passed authorized continuation of the research on all three axes set forth in the earlier law and set forth a procedure for authorization of a deep underground disposal facility. The law transferred responsibility for research on Axe 3 from the CEA to Andra.
[[The information below on Axe I and Axe II presents the status of research in 2002. We are in the process of compiling an update.--September 15, 2008 ]]
In 1991, the CEA inaugurated the program Spin (Séparation, incinération), which had two parts, Actinex and Puretex. Actinex included a group of long-term studies aiming at the separation-transmutation of long-lived elements, such as the actinides and fission products found in reprocessing wastes [CNE 95; Bataille 96]. Puretex grouped research tending to decrease the volume and activity of waste, in particular secondary wastes from reprocessing [Bataille 96]. Today the CEA groups a part of the program Puretex and the program Actinex-separation in a program called “Séparations poussées” (advanced separations). (The CNE remarks that the programs Puretex and Actinex “should, in all logic, not appear as such in future documents and presentations to assure their readability.” [CNE 00]).
II.A.1. SEPARATION
Today, 99% of fission products, 99.7% of minor actinides, and 0.2% of plutonium remain in the solution to be vitrified after reprocessing and are destined to be disposed of deep underground. The objective is to “separate then extract the elements whose lifetimes are likely to exceed that of the underground disposal centers.”
The CEA is studying the separation of neptunium, americium, curium, technetium, iodine, and cesium. The three elements named first, which are minor actinides, “represent the essential of the long-term radiotoxic waste inventory.” The three last, fission products, have been selected, because they are characterized by a long life, a quite great abundance in irradiated fuel, and potential mobility because of their relatively elevated solubility and their relatively low capacity to attach themselves to solid materials [Bernard 00].
Neptunium, technetium, and iodine can be treated with greater or less efficiency in contemporary reprocessing plants by adaptations of the Purex process. Neptunium can be recovered without major modification of the Purex process. The adaptation of the Purex process used for technetium 99 separates only the part of the technetium that is in the form of a solution. The solid part, which represents about 10 to 15% of the technetium, remains unchanged. As to iodine 129, the process used today allows recovery of only 97% of that radionuclide. The CEA is carrying out research on the possibilities of improving the separation of technetium and iodine [CNE 00].
The separation of americium, of curium, and of cesium has necessitated the development of a new chemistry of separation, having as objective the design of very selective synthetic molecules.
--The Diamex process would separate minor actinides and lanthanides from the other fission products.
--The Sanex process would separate the lanthanides from a mixture of americium and curium.
--The Sesame process would separate the americium from the curium [Bernard 00].
--The Calixarène program would separate cesium by means of “calixarène” molecules from the solutions of fission products produced by the Purex and Diamex processes [CNE 00].
For the separation of the minor actinides technetium, iodine, and cesium, the CEA plans a demonstration of the scientific feasibility (validation of the basic concepts) in 2001 and demonstration of the technical feasibility starting in 2005 or earlier. The scientific feasibility of Diamex was demonstrated in 1994 [CNE 00].
In the context of the “Advanced separations” program, the CEA is also studying reprocessing by the dry method, a means that was abandoned in the eighties. The CEA is at present interested in the non-aqueous method for the treatment of special fuels and the targets used for transmutation. The procedures are called pyrochemical (reactions at a high temperature). For reprocessing, the pyrochemical reactions take place in melted salts. From now to 2006, the CEA intends to acquire “the maximum data concerning the chemistry and electrochemistry of the elements constituting fuel and irradiated targets, in melted chlorides and fluorides and in biphase melted fluoride systems-melted metals. It is a program of evaluation.” The CEA intends to pass, probably after 2006, to demonstrative experiments, in the shielded cells of Atalante (Marcoule), on targets irradiated in Phénix [CNE 00].
II. A. 2. TRANSMUTATION
During transmutation operations, the researchers try to “change the case” of an element in the periodic classification by submitting it to an intense flux of neutrons, to transform it, either into a short-lived element, or into a stable, therefore non-radioactive, element.
The CEA is studying transmutation, chiefly for actinides and some long-lived fission products, by using
--critical reactors (PWRs and fast neutron reactors)
For critical reactors, the CEA carries out 1) studies on the neutronics of transmutation and scenarios designed to improve nuclear data and calculation systems and 2) “experimental studies on fuel and targets that have allowed the definition of families of new types of fuel adapted to transmutation” and the carrying out of irradiation tests in the Phénix rector [Bernard 00].
--hybrid systems. Hybrid systems include a) an accelerator of high-intensity protons; b) a source of spallation (a thick target composed of a heavy material in which the phenomenon of spallation occurs-ie heavy nuclei struck by high-energy protons emit neutrons); and c) a subcritical nuclear reactor. In a hybrid system, the neutrons furnished by the accelerator via the source of spallation cause and maintain the chain reaction in the subcritical reactor.
In regard to hybrid systems, the research group Gédéon (CEA, CNRS, Andra, EDF, and Framatome) have launched several programs. The IPHI project has as its goal the construction at Saclay of an injector of high-intensity protons. The Megapie project is designed to develop and experiment on a spallation target. The CEA, the CNRS, and German, Belgian, Italian, and Swiss researchers are collaborating on this project [CNE 00]. Experimentation will take place in Switzerland. The Muse experiments, conducted in the Masurca reactor at Cadarache, use “a neutron generator, placed in the middle of a mass simulating the environment of a spallation source in a hybrid system” [Bernard 00].
A CEA-CNRS group has been given the responsibility of establishing a dossier as the first stage of the possible launching of a European demonstration of a hybrid system with fast neutrons. French researchers presently seem to favor a linear accelerator with a superconducting cavity; a spallation target in liquid lead-bismuth; and a coolant of helium gas. The CNE would like to know if these options would suit the industrial companies and other European partners.
Researchers evaluate by means of scenarios separation-transmutation’s performance potential. Since 1998, they have been studying five families of scenarios: three using current technologies: parks consisting of PWRs, fast reactors, or PWRs and fast reactors; and two using hybrid systems: 1) a mixed PWR park with UO2 fuel and hybrid systems to transform plutonium, minor actinides, and long-lived fission products and 2) a “ ‘double-level’ park in which PWRs and fast neutron reactors are used for the multirecycling of plutonium, and hybrid systems for the transmutation of minor actinides and long-lived fission products” [Bernard 00].
Work on transmutation has been hindered since Superphénix shut down, by the lack of reactors in which to carry out tests. The Phénix reactor will not go into operation again until 2001, and must stop operating in 2004. “It is likewise necessary for the future reactor Jules Horowitz to contribute to this research, in particular in regard to fast neutrons.” This cannot occur until after 2006 [CNE 00].
Problems
Christian Bataille remarked in 1996: “When one bombards a target with neutrons, the desired reaction is never the only reaction that occurs, and the effect of parasite reactions can sometimes remove all interest from the operation.” The capture of neutrons can end in the creation of long-lived radionuclides. Transmutation reactors can also produce short-lived fission products that disintegrate into long-lived fission products.
It is for these reasons among others that certain long-lived radionuclides cannot be transmuted into short-lived isotopes or into stable isotopes. Among these radionuclides are carbon 14, strontium 90, uranium 238, and cesium 135. Uranium, which represents 94% of the mass of irradiated fuel, cannot be a candidate for transmutation, because the capture of neutrons by uranium 238 leads to the creation of plutonium 239.
The transmutation scenarios require large parks of reactors as well as installations for the fuel production and reprocessing. If each of the reactors of a park that annually produces 400 TWh has a power of 1000 MWe, it is possible to reduce the amount of plutonium and minor actinides by a factor of four, by using one fast neutron reactor for five PWRs, or seven to eight fast neutron reactors in total and by mutirecycling plutonium. It is possible to reduce the plutonium and minor actinides by a factor of 50 to 120 by using one breeder reactor for three to four PWRs, and by multirecycling plutonium and “incinerating” the minor actinides [Bataille 98].
That necessarily means a very long-term project. “A reactor park would go through three phases: (1) a transition phase for making the actinides reach equilibrium […] (2) an equilibrium phase during which the production of the actinides is equal to their destruction and (3) finally a transition phase during which the actinides are progressively destroyed.” For three scenarios presented to the CNE by the CEA using proven reactors (PWR and fast neutron reactors), phase one would last between 50 and 100 years, and phase three would necessitate between 150 and 250 years in order to reduce the equilibrium inventory by a factor of 10 [CNE 00].
A transmutation program, particularly if it depends on reprocessing by the aqueous method, generates large quantities of secondary waste, and would presumably expose workers to ionizing radiation. The CNE has remarked that “it seems initially unavoidable that advanced reprocessing would lead to new type B wastes”; and the CEA’s scientific council signaled in a 1990 report that “for the short term consequences, the separation-transmutation of the actinides represents an increase in doses, but especially an increase in the number of people exposed.”
The cost of an advanced transmutation program would be prohibitive.
A transmutation program, whatever its scope, would not eliminate the need for a deep-underground disposal site. Certain isotopes that cannot be transmuted will necessitate a disposal solution. Moreover, according to the CNE, category B waste, the volume of which will amount to 100,000 cubic meters in 2020, must be disposed of in a deep-underground facility.
II.A.3. PACKAGING
As a complement to the separation-transmutation path, the reference strategy, the CEA is studying the separation-packaging path “for separated radionuclides that cannot be transmuted” [Bernard 00]. For example, “the separation of cesium is part of the Separation-Conditioning concept” [CNE 00]. For these radionuclides, the CEA is studying and developing new packaging matrices. The study and the development of these matrices as well as the demonstration of their long-term performance are conducted in axe 3 [Bernard 00].
Andra is in charge of studying reversible disposal in a deep geological formation. In 2004 it put into operation an underground laboratory in the clay at Bure (Meuse) (See the chapter “Waste storage”)
For axe 3 of the law, the CEA has launched two major research programs entitled respectively “treatment and packaging of wastes” and “long-term storage.”
The first of these programs includes the project “New packaging matrices” (NMC), begun in 1997, which studies the packaging of separated radionuclides and high activity waste from classic reprocessing without advanced separation.
The second program is composed of three distinct projects, entitled respectively “Long-term behavior of packaging” (CLTC), a project initiated in 1998; “Acceptance and characterization criteria” (CAC), initiated in 1999; and “Very long-term storage,” initiated in 1997. The CLTC program includes the study of the evolution of irradiated fuel in dry storage, which is the subject of the subprogram Precci of EDF and the CEA (Research program on the long-term evolution of packages of fuel) [CNE 00].
The CEA has proposed a dozen families of preliminary concepts for one or several EtLD [CNE 99]. The Commission has given priority to studies on irradiated fuel [CNE 00]. According to the CNE, the researchers are still studying:
--a design composed of a network of galleries buried between 30 to 50 meters below the surface of the ground, for “irradiated fuel, B and C wastes”;
--a surface or half-buried installation;
--a concrete bunker, possibly half-buried, cooled by natural ventilation, like Cascad at Cadarache;
--a concrete bunker, possibly half buried, providing centralized storage for material with strong thermal density and having an evolutionary system of cooling
--a regional depository for irradiated fuel under shelter, modular and strictly surface. It would receive standardized packages of irradiated fuel [CNE 00].
An EtLD would guarantee the preservation and recovery of packages “for periods of less than 300 years.” According to Daniel Iracane, in charge of the CEA’s “long-term storage” section, this type of “storage site is not designed to become final” [Iracane 00]. However, the CNE notes that “there are no physical or technical reasons that prevent this type of storage, periodically renewed, from being prolonged during centuries or even thousands of years” if society is capable of carrying out the necessary surveillance [CNE 00].
According to a calendar approved by the Government, “the first engineering studies should establish the requirements by 2002, in order to carry out the preliminary studies, which should be ready for specific sites in 2005” [CNE 99]. The government has not yet officially begun looking for sites for an EtLD. Daniel Iracane states that “it is the selection of a future industrial disposal site that is delicate.”
The CNE considers that the EtLD concept “is conceivable for C wastes (high activity) or irradiated UOX fuel.” Nevertheless, a very long-term disposal site for MOX fuel would “necessitate a special study, we can already foresee major difficulties, tied to its heavy thermal load” [CNE 00].
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