Safety up gradation during refurbishment and recommissioning of pressurized water loop in Cirus

Cirus is a 40 MW(th) research reactor in Bhabha Atomic Research Centre, Trombay, Mumbai. One of the six 4 inch I.D. lattice positions of Cirus is having Zircaloy-2 Test Section of Pressurised Water Loop (PWL) which is an in pile facility to test experimental fuel assemblies under simulated power reactor conditions. The system was commissioned in 1972 and has since been extensively used for irradiation of PHWR and BWR fuels including MOX fuel. Cirus reactor was shut down in year 1997 for extensive refurbishment as part of its life extension programme. Opportunity was utilised and Pressurised water loop was also subjected to detailed inspection and refurbishment. A theoretical assessment of degradation of the structural integrity of the zircaloy-2 pressure tube as a result of hydrogen pick up related problems was done by Reactor Engineering Division of BARC and subsequently it was subjected to detailed ISI using Eddy Current and Ultrasonic testing method. A new Uninterrupted Power Supply system was incorporated which has made irradiation of test fuel assembly up to 400 KW power possible in Cirus PWL without exceeding thermal safety limits during power supply transients. After refurbishment and safety up gradation, PWL was commissioned and operated satisfactorily. This paper describes the experience gained in refurbishment, safety up gradation and commissioning of the system. (author)