| 摘要 |
<p>PROBLEM TO BE SOLVED: To exclude the effect of<13> N gas produced by activation during monitoring offgas taken out of reactor and existing in a large quantity and determine abnormality of fuel rod. SOLUTION: On both sides of a gas chamber 12 in which offgas is introduced, a first detector 16 and a second detector 18 are provided. For each annihilation of a positron emitted from<13> N, two annihilationγ-rays are emitted in directions opposite to each other, which are simultaneously detected by both the first detector 16 and the second detector 18. Such a specific annihilationγ-rays are eliminated by anticoincidence count, so that theγ-rays from rare gas are measured with good sensitivity. In an operation part 54, each of species concentration is operated based on the spectrum. In a determining part 56, abnormality of fuel rod is determined and the degree of leakage is determined, based on the concentration ratio of at least two species with different half lives.</p> |
