Power coefficient anomaly in JOYO

not registered; not registered; not registered; Yamamoto, Hisashi*

This report describes the Power Coefficient Anomaly in JOYO, which occurred in 75MW Power Ascension Test, Summer 1979. The substance of this anomaly was the non-reproducible power coefficient during the initial power-up from 50MWt to 75MWt and the permanent reactivity loss of -40 cent in isothermal condition. And this anomaly was accompanied the time-dependent changes of power coefficient and the recovery of the reactivity which were never obserbed before. The cause of this anomaly has not been identified perfectly yet, but the investigation about the cause has reached the stage to focus two candidates as the cause of the anomaly (1. the elongation of ruel stuck 2.the inclination outward of fuel subassembies), as the results of various approaches to the Anomaly, that is, analyses, plant experiments and fuel post-irradiation tests. Now, the effort of accumulation and investigation of data and analyses is continued in JOYO.