Year
2013
File Attachment
314.pdf490.52 KB
Abstract
Concerning gamma shielding materials used for a transportable storage cask, technical and economical comparison was performed at PATRAM 2010 between a single wall cask which uses carbon steel for gamma shielding, and multi-wall cask which uses lead for gamma shielding. As the next step of the comparison study, neutron shielding materials for the transportable storage cask are compared on both technical and economical viewpoints. One of the main neutron sources in spent fuels is Cm-244 and Cm-242. The neutrons are produced at their decay process. The other one is fission neutrons, which are produced at fission reaction of fissile materials in the spent fuels. The former neutrons are acting as a primary source of the fission reaction. As generation of both Cm-244 and Cm-242 in the spent fuels increases by the involution of the fuel burn-up, neutron source intensity of high burn-up fuels becomes stronger. Moreover, the half life of Cm-244 is longer comparing to those of dominate gamma sources in the spent fuel, neutron source is sometimes main radiation source for the shielding design of the transportable storage cask, which will contains high burn-up and longer cooling time spent fuels comparing to a transport cask. The typical neutron shielding materials used for the transportable storage cask are water and resin. Water is economical material and good for neutron shielding because it contains lots of hydrogen atom. However, careful consideration shall be paid against vapour pressure when water temperature becomes higher, which affect very much to structural design. Resin is solid and also contains lots of hydrogen atom. No consideration is necessary for pressure as water, but degradation by high temperature shall be considered during long storage period. Assuming water and resin as the neutron shielding materials, comparative study is carried out on material property, the influence to the cask design and manufacture, and economy. To make the comparison simpler, forged steel mono-wall cask is selected in this study.