Increment of capacity of casks for LWR spent fuel transport. (2) Simulation of neutron transport in BWR fuel assembly

Numerical simulations of neutron multiplication and transport inside / outside a BWR fuel assembly stored in light water pool were conducted taking account of pin-wised nuclide composition. As the results, neutron leakage ratio from the assembly is found insensitive to the burn-up of the fuel as well as a PWR UO2 fuel assembly. With the ratio, we can evaluate total neutron yield in the assembly by counting number of neutron absorption outside the assembly. Since the total neutron yield is a good indicator of burn-up of fuel, we can confirm the declared burn-up of a fuel assembly and take burn-up credit to its storage and transports. (author)