carbide fuel reprocessing.....

FBTR: ‘We don’t see any problems with reprocessing’

The carbide fuel that had reached a burn-up of 1,55,000 MW days/tonne was reprocessed

Easy task: Unlike the carbide fuel, reprocessing the oxide fuel that will be used in the PFBR should not be difficult, says Dr. Baldev Raj, Director of IGCAR, Kalpakkam. The Kalpakkam based Indira Gandhi Centre for Atomic Research (IGCAR) has squeezed the most out of the uranium-plutonium mixed carbide fuel in the Fast Breeder Test Reactor (FBTR).

The fuel has proved its capability to light up a 100 watts bulb continuously for 14,880 hours for 620 days using just one gram of the fuel.

Technically speaking, the carbide fuel had reached the maximum burn-up of 1,55,000 MW days/tonne some time ago without any failure of fuel. Burn-up is the cumulative amount of energy that can be extracted from a unit mass of the fuel.

So the higher the burn-up, the greater is the amount of energy that can be extracted from a given amount to fuel.

Closing the fuel cycle

And in what may be termed as closing the fuel cycle, the IGCAR scientists have successfully reprocessed the spent fuel that has undergone 1,55,000 MW days/tonne burn-up.

Reprocessing is very important as only about 17 atoms per cent of the fuel would have undergone fission to produce energy.

So reprocessing helps to extract the valuable plutonium and separate the fission products from the spent fuel. The reprocessed plutonium is refabricated as fuel.

Reprocessed fuel

It was in 2005 that IGCAR reprocessed the fuel that had undergone 1,00,000 MW days/tonne burn-up.

‘Fast breeder’ reactor, as the name indicates, breeds or produces more plutonium than what it consumes for producing energy. This is what gives it the name “breeder.”

So perfecting the reprocessing technology is a must to extract the unspent plutonium for use in a new reactor.

There are other advantages as well. Reprocessing goes a long way in removing the long lived fission products (actinides) and in the process it makes waste management much easier.

Many challenges

For all its advantages, reprocessing is fraught with many challenges, especially when the fuel has undergone higher burn-ups.

Dissolving the 1 lakh MW days/tonne burn–up fuel with nitric acid, among other steps, was done without much of a problem.

“Our assessment was right about the additional challenges of reprocessing the fuel [that has undergone 1,55,000 MW days/tonne burn-up],” said Dr. Baldev Raj, Director of IGCAR.

“There was more radioactivity, more problems with shielding, the separation process, maintenance and degradation of solvents. But there were no surprises.” An additional challenge came in the form of handling the fuel that has undergone a shorter cooling.

Shorter cooling

“We reprocessed the fuel after just 18 months cooling period. This is comparable to commercial reactors,” he said. It may be recalled that the 1 lakh MW days/tonne burn-up fuel was reprocessed after six years of cooling.

“Today we can say that we don’t see any problems with fuel reprocessing,” he said confidently. So he is thirsting for more challenges. “We would like to reduce the cooling period from 18 to 12 months,” Dr. Raj noted.

Experience gained

While IGCAR has gained much experience and hence confidence in reprocessing the mixed carbide fuel used in the fast breeder test reactor, the PFBR would have a mixed oxide fuel.

So will its experience with carbide fuel help in reprocessing the oxide fuel to be used in the PFBR? “Reprocessing [mixed] carbide fuel is difficult unlike [mixed] oxide fuel. We don’t see any difficulty,” said the Director, sounding confident.