In-core instrumentation device

Purpose: To improve the inspection accuracy for the power distribution to thereby enhance the inspection performance for the safety of fuels by making the disposing interval of the detectors for the inspection of the power distribution more closer at the lower portion of the reactor core. Constitution: In a BWR type reactor, as shown in axial distribution, a peak tends to appear at the lower portion of the reactor core due to the void effect. Further, upon power level change, transient phenomena is caused in which a large distortion is resulted particularly, in the lower portion of the power distribution. In view of the above, the number of local power inspection monitors is further increased at the lower portion of the reactor core. The density of the inspection points with respect to equally divided portions in the height of the reactor core can thus be made more closer at the lower portion of the reactor core thereby enhance the inspection performance. (Kawakami, Y.)