The Indian Atomic Energy Regulatory Board (AERB) ordered the shutdown of Nuclear Power Corporation of India’s (NPCIL’s) Kakrapar 1 on 22 April. The move follows an uncontrolled power rise on 10 March, which was provisionally rated at level 2 on the International Nuclear Event Scale. An AERB statement said: “The event reflected certain weaknesses in safety culture at the plant and need for improving safety practices.”
The power rise occurred when the 235MWe PHWR was undergoing online refuelling and the power supply for the system adjusting rods failed. Unfortunately, a system to add boron to the moderator in an emergency was ‘inhibited’ to avoid activation during slight variations in power levels during refuelling. The AERB considered that to be an erroneous operator action.
The reactor power increased from 70% to 98% before tripping. The AERB considers the 98% trip point too high and a level of 90% more appropriate.
Kakrapar staff and NPCIL were asked to carry out investigations into the causes of the
incident. Results and analyses by expert groups were considered by the AERB safety review committee for operating plants on 31 March and again on 21 April, but the exact reasons for the reactor power rise could not be established. The AERB decided to shut down the unit “as a measure of abundant caution,” while the station and NPCIL carry out further detailed investigations.
According to the January issue of COGnizant – the monthly magazine published by Candu Owners Group (COG) – Kakrapar 1 was declared the best performing Pressurised Heavy Water Reactor (PHWR) among the 32 such type of reactors operating across the world. The unit moved into first place at the end of September 2002 on the basis of a gross capacity factor of 98.4% during the preceding 12 months.