Performance Monitoring of Zircaloy-4 Square Fuel Channels at Taps - 1&2 / NPCIL

Tarapur Atomic Power Station is a twin unit Boiling Water Reactors. The rated initial capacity of each unit was for 210 MWe. Subsequently due to Secondary Steam Generator tube leak problem, the units were de-rated to 160 MWe in the year 198485. The station has completed 36 years of successful commercial operation. TAPS reactor fuel channels are made of Zircaloy -4, material. These are used along with 6x6 array nuclear fuel assemblies. The fuel channels need to be discharged once it reaches an optimum exposure limit and based on the surveillance programme, which monitors the channels performance. There are 284 fuel assemblies in each reactor. The fuel channel has a square cross section and it surrounds the fuel assembly. The channel is secured to the fuel assembly by means of channel fastener assembly. The fuel channel length is 158.625" and wall thickness is 0.060". NFC has indigenously developed fuel channels for TAPS and these are at various stages of exposure in both the reactor cores. The performance review of these channels was carried out by the expertise from TAPS-Site, NPCIL-ED and RED, BARC. The two major factors, which af1ect fuel channels performance, are (a) Bulge and (b) Bow. The phenomenon of longitudinal bow occurs due to the neutron flux gradient across the channels faces. Studies made on this subject by General Electric (GE) indicated that this channel def1ection occurs at a slow rate. Therefore, fuel channels surveillance programme is essential to check the irradiated fuel channels performance in order to replace the fuel channels once it reaches the optimum exposure limit. To estimate the useful life of irradiated fuel channels, channel def1ectionfbulge measurement inspection system and methodology was developed jointly by TAPS and Centre for Design and manufacture (CDM), BARC. This system was successfully deployed at TAPS. This paper briefly describes the developmental efforts made by Nuclear Fuel Complex (NFC), Hyderabad, NPCIL-Fuel Group, Engineering Directorate, RED/BARC, CDM/BARC.