A study for leak testing in the fuel handling facility "JOYO"

Ito, Hideaki; not registered; not registered; Okubo, Toshiyuki

The fuel handling facility in "JOYO" must maintain an argon atmosphere and be gas tight; this prevents the oxidation of sodium adhering to a fuel assembly and leakage of radioactive gases. Periodic leak testing of the double O-ring gas seal had been performed at increasing pressure to assure its specified leak tightness. The problem with this method was that it took a long time to obtain an accurate measurement. The leak testing methods for the fuel handling facility, the reactor containment vessel, and other vessels were all reexamined. As a consequence, it was determined that alternative devices and methods for improving the leak rate measurements should be studied. Four methods of leak testing were evaluated; the present increasing pressure method, helium leak testing, decreasing pressure method, and a liquid nitrogen decreasing pressure method. A new automatic leak measurement device was used in these evaluations. The results of the utilization and limitations of the four methods of leak testing are summarized as follows. (1) The decreasing pressure leak testing method was efficient with regard to accuracy and stability for use in the fuel handling facility. (2) The automatic leak measurement device used a statistical calculation to measure the leak rate stability and it met the specified measurement requirements. (3) The leak rate measuring time was reduced by half with this new device and it could also simultaneously examine other objects.