The Spent Fuel Containers Criticality Calculation Under Different Circumstances

KBS-3spent fuel canister is used for geological disposal of spent fuel in Sweden, it’scomposed by the ductile cast iron lining and the composition of copper shield。Castiron lining provides mechanical strength to support, and the copper shield prevent thecorrosion of containers。When the canister is damaged, due to the high levelradioactive waste contain fissile materials, such as Pu-239, U-233, etc., in thesituations that the groundwater go into the canister, because water is good moderatorand coolant, the fast neutrons of the average energy of2Mev will be slowed to bethermal neutrons, fissile materials under the effect of the thermal neutron will occurfission chain reaction, the it will release about200Mev energy one time, while twoor three neutrons are released。If effective multiplication factor Keffis used to say theself-sustaining fission chain reaction’s conditions, when Keff<1,it’s said that thesystem is subcritical; when Keff=1, said the system is critical; when Keff>1, said thesystem is supercritical. When the system is subcritical or critical, it is controllable,and it will not cause harm to the surrounding environment and the residents; when thesystem is supercritical, it is not controllable,and it is very dangerous, so thecalculation of criticality safety should be paid attention。In this paper, it’s used the MCNP program to simulate and calculation Keffvaluein case that is in air that pressure water reactor spent fuel container is safe, anddamaged and water infusion condition. Pressurized water reactor spent fuel containersin geological disposal repository, packaging container integrity and in the normal safebentonite, water intrusion bentonite but not damaged packaging container andpackaging container breakage of groundwater into the dip it in some cases to verify the value of Keff, spent fuel containers criticality safety. At the same time It’s studiedon water infusion quantity and neutron energy spectrum of changes, the followingconclusions obtained through analysis：1.If a single container under normal conditions is considered, pressurized waterreactor spent fuel container’s Keffvalue is around0.13762, in the event of immersioncases, Keffvalue will increase, but still will be less than0.71, so even if the containersare broken and groundwater immerse, the device is safe and effective.2.Through the study of spent fuel containers of water into the leaching amount onthe neutron spectrum effect, it’s clear that the neutron can be detected by the detectorneutron are concentrated in the low energy, the probability of others could be detectedis very small.3.If the water immersion of spent fuel containers enlarge, there will be more fastneutrons be slowing down to low energy neutron, in the low energy region due to theresonance absorption phenomenon that in some places the neutron flux density is verysmall, in the remaining section of the neutron energy probability than into theleaching water hours significantly greater.