Radioactive gas measurement apparatus and failed fuel inspection apparatus

A failed-fuel detection system comprising:

• a sampler for sampling a radioactive gas containing a nuclide to be measured and a positron emitter nuclide passing through a nuclear reactor fuel housed in a nuclear reactor;
• and
• a radioactive gas measurement apparatus for measuring a radiation generated from the radioactive gas sampled by the sampler, wherein the radioactive gas measurement apparatus comprises:
• a radiation measurement cell comprising an inlet pipe connected to the sampler and a discharge pipe, the radiation measurement cell introducing and discharging a radioactive gas containing a nuclide to be measured and a positron emitter nuclide through the inlet pipe and the discharge pipe;
• a radiation detector for measuring a radiation generated from the radioactive gas;
• and
• a radiation collimator allowing the radiation measurement cell to communicate with the radiation detector and setting a predetermined radiation measurement geometry condition between the radiation measurement cell and the radiation detector, and wherein
• as the predetermined radiation measurement geometry condition, an inner wall area of the radiation measurement cell which the radiation detector views through the radiation collimator is set equal to or less than a half of a total inner wall area of the radiation measurement cell.