Gas leakage detection method and gas leakage detection apparatus in horizontally-installed canister

A gas leakage detection apparatus in a horizontally-installed canister comprising a basket containing spent nuclear fuel inserted in the canister, the gas leakage detection apparatus comprising:

• a first temperature sensor configured to measure a temperature TB at a canister bottom portion to be one end portion in a lateral direction in a horizontally-installed attitude of the canister that is horizontally installed and housed inside a concrete silo, a third temperature sensor configured to measure a temperature TSB at a canister side surface lower portion located below a horizontal plane passing through a center of the canister in the horizontally-installed attitude, a second temperature sensor configured to measure a temperature TT at a canister lid portion to be the other end portion in the lateral direction in the horizontally-installed attitude, and a fourth temperature sensor configured to measure a temperature TST at a canister side surface upper portion located above the horizontal plane passing through the center of the canister in the horizontally-installed attitude;
• a monitoring unit configured to monitor measurement values of the first temperature sensor, the second temperature sensor, the third temperature sensor, and the fourth temperature sensor to identify changes in movement of inert gas inside the canister warmed by the spent fuel, where a direction of flow of the warmed inert gas is restricted by a wall of the basket, such that the inert gas moves along the wall of the basket in a lateral direction and heat of the spent fuel is transferred to the canister side surface by heat conduction via the basket;
• and
• a gas leakage determination unit configured to determine occurrence of leakage of the inert gas inside the canister based on temperature changes between monitored measurement values for each of the temperatures TB, TSB, TT, and TST.