PHWR Fuel Fabrication - Indian Experience

Abstract

With the decision of the Indian Department of Atomic Energy (DAE) to opt for Heavy Water Reactor system for nuclear power generation, and consistent with the policies of the Department for self-reliance and self-sufficiency, work was taken up in early sixties on development of technology on Zircaloy-clad UO₂ fuels. Pilot scale production facilities were set up at Trombay to evolve the technology of UO₂ powder production and fuel element fabrication. As per the decisions taken at that time for the first PHWR - RAPP-I(Rajasthan), half the initial charge of fuel had to be made in India and the other half to be provided by Canada. This, in fact, has been the real base for power reactor fuel development programme in India. The fuel-Zircaloy-clad natural UO₂-was successfully made with imported zircaloy tubes and hardware for the first half charge fuel.

The experience thus gained has been put to use for designing and building a large-scale fuel fabrication facility. The Nuclear Fuel Complex (NFC) thus came into existence in early 70's to manufacture PHWR fuel with an initial capacity of 100 tonnes of finished fuel per year. Facilities were also established at NFC for production of BWR fuel, zircaloy tubing and hardware required for the fuel; and Zircaloy coolant and calandria tubes required for the reactors.

NFC produces Zircaloy-clad natural UO₂ fuel for PHWRs at Kota (Rajasthan), Kalpakkam (Tamil Nadu) and Narora (Uttar Pradesh) - starting from indigenous magnesium diuranate concentrates from UCIL (Uranium Corporation of India Limited - another unit of DAE) for production of UO₂ pellets, and zircon beach sands from IRE (Indian Rare Earths Limited - another unit of DAE) for production of Zircaloy fuel and hardware. The magnesium diuranate (yellow cake) is processed through ADU route to produce ceramic grade uranium oxide powder which is pelletised and the pellets are loaded in zircaloy tubes and resistance welded with end caps to form elements. 19 elements appended with spot-welded wires/pads are assembled into bundles with zircaloy end plates. The technology of attachment of spacer pads was developed by both brazing and welding routes. However, welding route is preferred to avoid toxicity from beryllium used in the brazing process. About 42,000 Nos. of fuel bundles have been made so far for use in P H W R reactors. The fuel production plants are being expanded to meet the increased requirements of fuel towards the planned nuclear power program me, namely 10,000 MWe by year 2000 AD.

Over the years several design changes and process improvements have bee:, introduced in the fuel viz., sub-divided fuel like 22 element bundles; substitution of zircaloy wires by strip pads as appendages; introduction of short-height chamfered pellets etc. The fuel produced has shown an excellent in-reactor behaviour as judged by the very low failure rates. With the development of computer codes for fuel design and management and with the establishment of fuel design and testing capabilities both in-pile and out-of-pile, the "total fuel" capability has been established leading to self-sufficiency in this vital area of nuclear technology.

This paper primarily details our experience in fuel manufacture and inspection; and also highlights operational experience.