Application of High Burnup 9x9 Fuel Model Bundles for Spent Fuel Transport Package Systems

Year
2016
Author(s)
Yoshiyuki Fujita - Back-End Transport Industry Working Group, World Nuclear Transport Institute, Remo House, United Kingdom
Hirotaka Nojima - Nuclear Fuel Transport Co., Ltd., Tokyo, Japan
M. Matsumoto - Nuclear Fuel Transport Co., Ltd., Tokyo, Japan
Takehiro Isono - Toshiba Corporation Energy Systems & Solutions Company, Isogo Nuclear Engineering Center
Tetsuro Takeshita - Toshiba Corporation Energy Systems & Solutions Company, Isogo Nuclear Engineering Center
File Attachment
F2028.pdf279.79 KB
Abstract
It is generally assumed in the criticality safety design of spent fuel transport packages that extremely conservative virtual spent fuel, such as fuel having the composition of fresh fuel without taking into account the effect of burnable poisons, is loaded into transport packagings. However, when this assumption is applied to highly enriched fuel for high burnup, it is excessively conservative for creating the criticality safety design for transport packages.Meanwhile, in the actual design of BWR fuel, a neutron multiplication factors in each core during the early stage of burnup are suppressed by means of gadolinium, which is a burnable poison. Currently, BWR fuel in Japan is designed so that infinite multiplication factors (kinf) in cold state loaded core systems during the whole burnup period do not exceed 1.3.Accordingly, criticality safety assessments can be performed which have the appropriate tolerance for transport packages with virtual fuel bundles taking into account this characteristic designed to have a kinf of 1.3 in cold state loaded core systems (model bundles).This paper describes criticality safety assessments conducted for NFT-38B spent fuel transport package systems with high burnup 9x9 fuel assumed to be the virtual fuel based on the traditional assumption and assumed to be model bundles. We compared the effective multiplication factors (keff) of the traditional virtual fuel bundles and that of the model bundles. The keff value of the traditional virtual fuel under accident conditions exceeded 0.95, which is the aim sought for criticality safety. Meanwhile, the keff value of the model bundles under accident conditions was sufficiently smaller than 0.95. Moreover, we verified representativeness of the model bundle for the package systems by comparing it with existing fuel. Therefore the application of model bundles can be expected for rational subcritical safety assessments of transport packages for high burnup 9x9 spent fuel.