PWR AND WWER MOX BENCHMARK CALCULATION BY HELIOS

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Fig. 3: MOX - UOX WWER-440 geometry. MOX WWER-440 Assembly UOX WWER-440 Assembly Pu/(U+Pu+Am) = 4.42 % Geometry: Gd-2 assembly Burn up of UOX assembly: (24 GWd/tHM + 31 GWd/tHM) final 55 GWd/tHM Burn up of MOX assembly: app. 42 GWd/tHM Red - high (5.516 % Pu) Blue - medium (4.334 % Pu) Pink - low (2.856 % Pu) 2.2 MOX FUEL ASSEMBLIES, INFINITE LATTICE The profiled MOX fuel assemblies of the PWR 900, WWER-1000 and WWER-440 are shown on fig. 4, 5 and 6. Boundary conditions were set in HELIOS 1.10 for infinite lattice calculation for all of the studied assemblies. The final burn up was proposed to the same value as in super cell - 42 GWd/tHM. Fig. 4: MOX PWR assembly. Fig. 5: MOX WWER-1000 assembly. Fig. 6: MOX WWER-440 assembly.
2.3 MOX FUEL COMPOSITIONS The listed initial MOX composition is a representative of the realistic UOX fuel irradiated in a mixed MOX - UOX LWR core [1]. This MOX fuel consists of a typical plutonium vector for material derivated from reprocessing of thermal reactor UOX fuel. Plutonium isotopic composition, corresponding to the three Pu content zones, is given in Tab. 1 and uranium isotopic composition in Tab. 2. Tab.1: Plutonium isotopic composition in fresh MOX fuel [1]. Nuclide Isotopic Composition [Atom.%] Pu-238 0.8 Pu-239 66.7 Pu-240 20.6 Pu-241 7.5 Pu-242 2.9 Am-241 1.5 Tab.3: Initial MOX fuel content [1]. Tab.2: Uranium isotopic composition in fresh MOX fuel [1]. Nuclide Isotopic Composition [Atom.%] U-234 0.002 U-235 0.22 U-236 0.004 U-238 99.77 Pu content in the zone Plutonium Content, w/o Pu(total) + Am/[U+Pu+Am] High 5.6 Medium 4.4 Low 2.9 Plutonium from reprocessed fuel is usually fabricated into the MOX fuel as soon as possible to avoid problems with the decay of short-lived Pu isotopes [2]. In particular, Pu-241 (halflive 14.29 years [5]) decays to Am-241 which is a strong gamma emitter, giving rise to a potential occupational health hazard. It is so if separated Pu, over five years old, is used in a normal MOX plant. The Am-241 level in stored Pu increases about 0.5 % per year with corresponding decrease in fissile value of the Pu [2]. Content of Pu-238 (half-live 87.7 years [5]) is increased in high-burn up fuel. It is a strong alpha emitter and a source of spontaneous neutrons. Pu-239, Pu-240 and Pu-242 are long-lived and hence little changed with prolonged storage [2]. 2.4 UOX FUEL COMPOSITIONS For the calculations, the adjacent UOX fuel assemblies are modeled as already burned. They have an initial enrichment of 3.25 w/o and have reached a burn up of 24 GWd/tHM [1].
Page 1 and 2: PWR AND WWER MOX BENCHMARK CALCULAT
Page 3: Fig. 1: MOX-UOX PWR geometry. Fig.
Page 7 and 8: Tab. 4: Weight concenrations [%] in

PWR AND WWER MOX BENCHMARK CALCULATION BY HELIOS

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