The Department of Atomic Energy (DAE) and the Nuclear Power Corporation of India Ltd. (NPCIL) plan to use slightly enriched uranium (SEU) in the future 700 MWe Pressurised Heavy Water Reactors (PHWRs) instead of the current technology of using natural uranium as the fuel in all the PHWRs of Indian nuclear programme until now.

This was stated was by R. N. Jayaraj, Chief Executive Officer of the Nuclear Fuel Complex (NFC) in Hyderabad, in a presentation made at a two-day India International Nuclear Symposium (IINS), which concluded here on Thursday.

The IINS was organised by the London-based World Nuclear Association (WNA).

Natural uranium contains only 0.7 per cent of the fissile isotope Uranium-235, the rest being the fertile isotope Uranium-238, which gets converted to Plutonium-239 in the reactor by neutron absorption. The SEU, which is being proposed to be used in future 700 MWe PHWRs, will contain 1.1 per cent of U-235.

The Light Water Reactors (LWRs) of the type being built at Kudankulam and the types that are likely to be supplied by other foreign vendors use low enriched uranium (LEU), which has 3 to 5 per cent U-235 enrichment.

The advantage of using SEU, according to Mr. Jayaraj, is the higher nuclear burn-up that can be achieved.

Burn-up is a measure of the amount thermal energy that is extracted from a given amount of nuclear fuel. The burn-up achieved with natural uranium in the present Indian PHWRs is about 6700-7000 megawatt-days (MWd)/tonne (t) of uranium-oxide.

The burn-up that is achievable with SEU in PHWRs would be about three times this value (about 21,000 MWD/t), Mr. Jayaraj said.

Use of SEU in Indian PHWRs was tested in one of the Indian reactors, according to reliable sources in the NPCIL. The physics and energy production characteristics have been extensively studied by introducing few elements of SEU in some fuel bundles in the reactor core. The 700 MWe contains 4704 fuel bundles, each containing 37 fuel elements each.

The results are apparently very promising and it is felt that SEU can now be introduced as a significant fraction of the fuel make-up in PHWRs, even up to 40 per cent based on appropriate regulatory approvals from the Atomic Energy Regulatory Board (AERB), NPCIL sources said.

One of the key arguments in favour of this approach is that, if SEU can now be procured from international market, why not make the best use of it in safeguarded PHWRs of the Indian programme.

Envisaging an imminent approval of the regulatory authorities, the NFC has already drawn up plans to produce SEU fuel bundles from the year 2018. It has projected a requirement of about 10,000 bundles of SEU in the beginning, which could grow up to 55,000 bundles by 2030.

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