The Hindu : Mixed oxide fuel introduced into FBTR

Online edition of India's National Newspaper
Sunday, Jul 27, 2003

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Mixed oxide fuel introduced into FBTR

By R. Prasad

CHENNAI JULY 26. The Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam has used a mixed oxide fuel containing the isotope U{+2}{+3}{+3} (Uranium 233) for the first time in the world. A sub-assembly containing 37 pins with mixed oxide fuel was introduced into the Fast Breeder Test Reactor (FBTR) six days ago.

This gains importance as the 500 MW Prototype Fast Breeder Reactor (PFBR) will be fuelled by the mixed oxide fuel (30 per cent Po and 70 per cent U{+2}{+3}{+3}).

Indigenously prepared mixed carbide (70 per cent plutonium and 30 per cent natural Uranium) is being used as a fuel in the FBTR. The mixed oxide fuel is introduced in the reactor to understand its irradiation performance before it is used in the PFBR.

"All along only Po and U{+2}{+3}{+3} have been used in Fast Breeder Reactors and this is the first time U{+2}{+3}{+3} is being used," said S.B. Bhoje, Director, IGCAR.

"This is mainly to take advantage of the huge thorium resources that India has." Another sub-assembly is expected to be introduced into FBTR next year.

The mixed oxide fuel introduced (annular pellets) has a hole in the centre. The hole is specially meant to reduce any risk arising due to fuel melting. Heat being maximum at the centre of the fuel pellet, any melting that occurs starts from the centre. The melted fuel flows down the hole and thereby any possible clad failure is averted.

A hole is formed naturally in the centre even if a solid fuel without a hole is used. This happens as the 8-10 per cent porosity present in the fuel starts migrating towards the periphery leaving a hole in the centre.

"But we need to wait for the hole to be formed and this takes three days. And when a new sub-assembly containing fuel without a hole is introduced into a reactor we need to slowly increase the linear heat rating to the designed rating and wait for a hole to be formed.

``This means we would be running the reactor at below the designed heat rating. And the net result is that we would end up losing money every time a new sub-assembly is introduced. This can be avoided by using fuel with a hole in the centre," Mr. Bhoje explained.

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