Patent Number: 
Section: claims

1. A gas leakage detection method in a horizontally-installed canister comprising a basket containing spent nuclear fuel inserted in the canister, the method comprising:monitoring each of 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 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 temperature TT at a canister lid portion to be the other end portion in the lateral direction in the horizontally-installed attitude, and 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, wherein the monitoring identifies 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; anddetermining occurrence of leakage of the inert gas inside the canister based on changes between temperatures of monitoring points for each of the temperatures TB, TSB, TT, and TST. 2. The gas leakage detection method in a horizontally-installed canister according to claim 1, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference between one or both of the temperature TB at the canister bottom portion and the temperature TSB at the canister side surface lower portion and one or both of the temperature TT at the canister lid portion and the temperature TST at the canister side surface upper portion. 3. The gas leakage detection method in a horizontally-installed canister according to claim 1, wherein the temperature TB at the canister bottom portion is a temperature at a center of the canister bottom portion, the temperature TSB at the canister side surface lower portion is a temperature at a bottom portion of the canister side surface to be a lowermost portion in the horizontally-installed attitude, the temperature TT at the canister lid portion is a temperature at a center of the canister lid portion, and the temperature TST at the canister side surface upper portion is a temperature at a top portion of the canister side surface to be an uppermost portion in the horizontally-installed attitude. 4. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTBT (where ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion. 5. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 6. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. 7. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT4 (where ΔT4=ΔTBT+ΔTSBST) obtained by adding the temperature difference ΔTBT (ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion to the temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. 8. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT3GR (where ΔT3GR=ΔTBT+ΔTBST) obtained by adding the temperature difference ΔTBT (ΔTBT=TB−TT) between the temperature TB at the canister bottom portion and the temperature TT at the canister lid portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 9. The gas leakage detection method in a horizontally-installed canister according to claim 2, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT3R (where ΔT3R=ΔTSBST+ΔTBST) obtained by adding the temperature difference ΔTSBST (ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 10. 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; anda 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. 11. The gas leakage detection method in a horizontally-installed canister according to claim 2, wherein the temperature TB at the canister bottom portion is a temperature at a center of the canister bottom portion, the temperature TSB at the canister side surface lower portion is a temperature at a bottom portion of the canister side surface to be a lowermost portion in the horizontally-installed attitude, the temperature TT at the canister lid portion is a temperature at a center of the canister lid portion, and the temperature TST at the canister side surface upper portion is a temperature at a top portion of the canister side surface to be an uppermost portion in the horizontally-installed attitude. 12. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTBT (where ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion. 13. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 14. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. 15. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT4 (where ΔT4=ΔTBT+ΔTSBST) obtained by adding the temperature difference ΔTBT (ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion to the temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. 16. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT3GR (where ΔT3GR=ΔTBT+ΔTBST) obtained by adding the temperature difference ΔTBT (ΔTBT=TB−TT) between the temperature TB at the canister bottom portion and the temperature TT at the canister lid portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 17. The gas leakage detection method in a horizontally-installed canister according to claim 3, further comprising determining occurrence of leakage of the inert gas inside the canister when there is a change in sum ΔT3R (where ΔT3R=ΔTSBST+ΔTBST) obtained by adding the temperature difference ΔTSBST (ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. 18. The gas leakage detection method in a horizontally-installed canister according to claim 1, wherein the monitoring further identifies heat transferred from the spent fuel to the bottom of the canister and to the side surface lower portion of the canister by heat conduction.