PFBR: novel steel reduces power generation cost

Published in The Hindu on March 12, 2009

The Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam has achieved a major breakthrough that would allow it to generate power at 30 paisa per unit less 4-5 years after the Prototype Fast Breeder Reactor (PFBR), which is under construction, is commissioned.

The PFBR is expected to be commissioned in September 2010, and the cost of a unit of power at the time of commissioning will be Rs.3.22 per unit.

Increased burn-up

“We have developed advanced steel that will allow us to increase the burn-up [the amount of energy extracted from a unit mass of fuel] of the mixed oxide fuel by 100 per cent,” said Dr. Baldev Raj, Director of IGCAR.

The current burn-up target for the mixed oxide fuel that will be used in PFBR is 1,00,000 MWdays/tonne. The new steel would allow the burn-up to be increased up to 2,00,000 MWdays/tonne.

Dr. Raj had told this Correspondent last year (The Hindu, May 1, 2008) that the Centre was working to develop a new kind of steel that would allow it to increase the burn-up.

Unlike in the case of the mixed carbide fuel used in the Fast Breeder Test Reactor (FBTR), the physical and chemical changes that the oxide fuel undergoes during irradiation do not affect the steel that encases it.

So scientists looked at improving the steel so that it does not get damaged by high energy neutron bombardment inside the reactor.

The significance

In essence, it would mean that the new kind of steel (in which the fuel is kept) that the scientists have developed would allow better utilisation of fuel by extracting more energy from a given quantity of fuel.

“The bigger a reactor, the greater would be the leverage of high burn-up, and this would result in more reduction in unit cost of power,” he said.

The IGCAR scientists, along with the Hyderabad based Nuclear Fuel Complex and Advanced Materials Research Centre, Hyderabad, have used nanosized yttria element dispersed in steel to produce this special product.

The special yttria steel does not undergo swelling and creeping even under continuous high energy neutron bombardment at high temperature.

Changing the dynamics

This becomes possible as yttria changes the dynamics of the defects produced by neutron irradiation. Certain physical changes that causes steel to swell are thus prevented. This allows increased extraction of energy from a unit mass of fuel.

The scientists have studied the microstructure and other characteristics of the steel. The actual testing would begin soon. “We would put the steel in the FBTR [for testing] in a few months’ time,” Dr. Raj said.

“Since it would take about 6-7 years to reach 2,00,000 MWdays/tonne burn-up in the FBTR, we will do an accelerated testing in an accelerator.”

Testing in an accelerator is expected to start soon. They would have the results in three months’ time.

The biggest challenge, according to the Director, was to extrude the new steel into a tube without introducing any physical weaknesses such as cracks and porosity.

Now that the scientists have succeeded in developing steel that will allow the burn-up to be doubled, are they working on producing an even better one? Though it may be possible to develop better steel, the challenge lies elsewhere.

The limiting factor

According to Dr. Raj, the limiting factor would come from reprocessing of the spent fuel that has undergone more than 2,00,000 MWdays/tonne burn-up and a shorter cooling period.

Fuel removed from a reactor cannot be reprocessed immediately as it would be hot and would have residual radioactivity. Hence it should be allowed to cool down.

“It is not a challenge to reprocess spent fuel up to 2,00,000 MWdays/tonne burn-up,” he said.

Other advantages

Apart from the better utilisation of fuel and thus reducing the cost of power generation, increasing the burn-up would translate to lesser fuel being used and thus reduced nuclear waste production.