Measurement and evaluation of hydrogen yield in the transportation of the breached fuel with wet type transport cask

Wet type casks such as NFT type transport casks are mainly used for the transportation of spent fuel in Japan. The hydrogen yield within the cask due to coolant (water in the cask) radiolysis must be considered for these types of casks. In the past, we has measured hydrogen concentration in the gas phase part of the cask after the transportation of fuel with intact cladding, and it was verified that the hydrogen gas concentration in the cask is sufficiently lower than the 4% hydrogen gas concentration limit of flammability.1) As we had an opportunity to transport a fuel assembly containing a breached fuel rod with Damaged Fuel Can (DFC) in NFT type transport cask, the concentration of hydrogen in the gas phase part of the DFC after transportation was measured. The measured concentration of hydrogen gas in the DFC (approx. 0.2%) was sufficiently lower than the 4% hydrogen gas concentration limit of flammability. Moreover, these measured values were equivalent to results of calculation based on previous study.