| 摘要 |
PROBLEM TO BE SOLVED: To determine abnormality of a fuel rod by measuring fission product rare gas with good sensitivity under the existence of<13> N gas produced by activation, during monitoring of offgas extracted from a reactor. SOLUTION: In a gas chamber 12, offgas is introduced andγ-ray radiated from a gas chamber 12 is detected by a detector 14. In this case, for reducing theγ-rays of 511 keV produced by the annihilation of positrons emitted from<13> N, a reduction filter 20 is provided. The offgas spectrum is measured in a spectrum measuring part 30, and the concentration of each of species is operated in an operation part 32. In a determining part 34, determining of fuel abnormality is made. Also in a determining part 34, the degree of leakage is determined, based on the concentration ratio of at least two species having different half lives from each other.
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