Architecture and management of a geological repository - Andra

3 – High Level Long-Lived WasteResearch carried out at the CEA, especially on behalf of the French nuclear power programme, and theroutine operation and maintenance of its facilities, are other sectors that have produced a wide range ofwaste. Most of this waste, made up of intermediate-level solid and liquid effluent waste, has beenconditioned using immobilisation materials and packages of various types and geometry.Finally, activities linked to national defence produce intermediate-level technological waste.For the repository studies, the package inventory (in terms of type and quantity) includes all wastealready produced as well as waste that may be produced through operating existing nuclear facilities.With regard to future production, this implies the need to formulate waste production and conditioninghypotheses, especially concerning management of nuclear power plants.Currently 58 pressurised water reactors, commissioned between 1977 and 1999, are operated toproduce electricity. The tonnage of nuclear fuels removed from these reactors over their totaloperating period is estimated at 45,000 metric tons of heavy metal (tHM). This estimation is based ona combination of hypotheses concerning (i) the average lifetime of units (forty years), (ii) powerproduction (16,000 terawatt-hours total production), (iii) the gradual increase of the "burnup" ratio offuels in the reactors 18 . The fuel types considered and the corresponding average burnup ratio is asfollows:- three generations of uranium oxide fuels: UOX1, UOX2, UOX3, irradiated respectively at33 gigawatt-days per metric ton of fuel (GWd/t), 45 GWd/t and 55 GWd/t, on average;- fuels containing recycled uranium (URE) irradiated on average at 45 GWd/t;- mixed uranium oxide and recycled plutonium oxide fuels (MOX) irradiated at 48 GWd/t onaverage.On this basis, four nuclear fuel management scenarios were selected for the studies. The principlebehind these scenarios is to include various possible industrial strategies without singling out any ofthem for special priority. This process makes it possible to consider a very wide range of waste typesand examine the technical aspects of the various packages.The first three scenarios, designated as S1a, S1b and S1c, correspond to continued reprocessing ofspent fuels removed from EDF reactors. Scenario S1a supposes that all these fuels (UOX, URE andMOX) are reprocessed. This scenario includes the hypothesis of incorporating fission productmixtures and minor actinides from UOX and MOX fuels in glass. Also, for study purposes, it isassumed that a very small part of the plutonium from reprocessed UOX fuels is incorporated in somepackages. This scenario therefore covers a variety of vitrified C package typologies. In scenarios S1band S1c, MOX fuels are not reprocessed, allowing the hypothesis of their direct disposal to beexplored. Scenarios S1b and S1c have been separated in order to study, in scenario S1b, the possibilityof increasing the waste concentration in glass, compared with the packages currently produced; thisgreater concentration would result in a slightly greater release of heat from the packages. Finally, afourth scenario, designated as S2, which supposes that reprocessing is stopped, is used for theexploratory study of direct disposal of UOX and URE fuels, as well as the MOX fuels considered inscenarios S1b and S1c. In this scenario the fuels are considered to be waste, which, we should recall, isnot the case at present.To be able to estimate the quantity of waste produced, scenarios S1a, S1b and S1c are based on thefollowing distribution of various types of fuels removed from existing reactors: 8,000 tHM of UOX1(33 GWd/t), 20,500 tHM of UOX2 (45 GWd/t), 13,000 tHM of UOX3 (55 GWd/t), 800 tHM of URE(45 GWd/t) and 2,700 tHM of MOX (48 GWd/t). In scenarios S1b and S1c, the direct disposal studyconcerns all the 2,700 tHM of spent MOX fuels.18The burnup of a nuclear fuel assembly expresses the energy produced in the reactor by the fissile material that it contains (uranium oxideor mixture of uranium and plutonium oxides)DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM75/495