Neutronics criticality safety analysis

VII.63. The use of INF isotopics in the criticality safety analysis means that any computational methods used to predict the isotopics should be validated, preferably against measured data. The reduced reactivity in INF is due to the decrease in fissile inventory and the increase in parasitic, neutron absorbing nuclides (non-fissile actinides and fission products) that build up during bumup. Broadhead [V11.23] and DeHart [V11.24] provide information to help identify the important nuclides that affect the reactivity of PWR irradiated fuel. The INF nuclides that can be omitted from a safety analysis are the parasitic absorbers that can only decrease k jj further if included in the analysis. Neutron absorbers that are not intrinsic to the fuel material matrix (gases, etc.) must also be eliminated. 

The assumption in criticality safety analysis that considers the reduction in reactivity due to changes of fissile material, and/or increase in fission product neutron absorbers in spent fuel that has occurred as a result of use in a nuclear reactor. 

Safety-analysis capabilities are contained within the Nuclear Facility Operations and Nuclear Technology Programs organizations. These organizations produce Safety Analysis Reports for both reactor and nonreactor nuclear facilities, primarily in TA-V. Other organizations provide specialized safety-analysis support in the form of mechanistic accident-progression analysis, heat transfer, structural analysis, neutron transport, nuclear criticality safety, and other areas upon request. 

An essential part of the crihcality safety analysis is to ensme that the computer code accurately predicts the effective multiplication factor. Therefore, the computer code is benchmarked against experimental data, using critical experiments that encompass the pertinent design parameters of the canister basket. The most important parameters are (1) the enrichment, (2) the geometrical spacing between fuel assemblies, (3) the boron loading of the fixed neutron absorbing panels, and (4) the soluble boron concentration in the water. 

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