Burnup Trusted System Technology Application In The Pressurized Water Reactor Spent Fuel Storage Pool

In general, when doing analyses of criticality safety of spent fuel transport or storage, one assumption is that the compositions of the spent fuel are same as the fresh fuel. Using the "fresh fuel" assumption can simplify the analysis of criticality safety and associated administrative controls. But this assumption is very conservative, which limits the efficiency of the transport and storage of the spent fuel. The concept of taking credit for the reduction in nuclear fuel reactivity due to burnup of the fuel is referred to as "burnup credit". It can greatly improve economic efficiency of the transport and storage of the spent fuel.This paper describes the analytical methods for applying burnup credit in the spent fuel pools for pressurized water reactor (PWR). The analyses of criticality safety of the spent fuel pool on burnup credit concept consists of two steps: at first, to calculate isotopic concentrations, and then to do the safety analyses of criticality about the spent fuel pools basing the isotopes concentrations obtained at the first step. There are some problems must be considered: to select and validate a computer code system to calculate isotopes concentrations in spent fuel by irradiation in the reactor core and subsequent decay; to select and validate a computer code system to predict the sub-critical multiplication factor of a spent fuel pool (safety analyses of criticality of a spent fuel pool); to establish bounding conditions for the isotopes concentration and criticality calculations to ensure the results of the safety analyses of criticality to be conservative; to generate a clear spent fuel assemblies loading criteria (to meet the criticality criteria of the safety analyses) for a special spent fuel pool. This paper has done a series of analyses on those problems. Specially, detail analyses on the effect of axial burnup heterogeneity have carried out in this paper. Finally, the methodology for applying burnup credit in the calculation work is presented, which uses the computer code system of scale4 and the computer code of MCNP4.In the last chapter of the thesis, a preliminary safety analyses of criticality is done on the spent fuel pool of Daya bay nuclear power plant using the selected computer code system and the method which is gotten before. The objective of this part is to show a clear calculation process of the burnup credit technology.Although the burnup credit technology is of great economic benefit, if it is used into practice, high level technology and administrative controls are needed. For example, the nuclear power plants are required to provide the reliable burnup values; the records of the irradiation history of each fuel assembly must be kept; there must be a device for burnup measurement of assemblies; all the analysis must be supported by the appropriate experiment data, and so on.