Putting the FBTR to the litmus test

Published in The Hindu on May 1, 2008

IGCAR is taking up yet another challenge. The scientists are putting the reactor to the litmus test of automatically shutting down at the very first instance of a fuel leakage.

“We want to take one subassembly [that contains the fuel pins] beyond the 1,55,000 MW days/tonne burn-up till the clad [metal casing] fails,” said Dr. Baldev Raj.

Scientists feel that they would be able to increase the burn-up by another 9,000 MW days/tonne before the clad gives way. The post irradiation examination (PIE) of the fuel indicates that it has already reached the natural end of its life. But the metal casing (clad) has not given way.

The fuel undergoes continuous fission and it swells. It then comes in contact with the metal casing leading to stress build-up at the casing.

The casing ruptures after some time, unable to accommodate the swelling fuel. “There are specific instruments to detect clad [metal casing] failure. These instruments were checked for their responses recently by putting fuel pins with perforated clad [to simulate failed clad] in the core, and these instruments responded well,” said Dr. P.V. Ramalingam, Director of Reactor Operation and Maintenance Group, IGCAR.

Will the metal casing failure leading to fuel leakage not cause problems? “The clad is the first barrier, the primary sodium system is the second, and the reactor containment building is the last barrier,” said Dr. Ramalingam. “So when the clad fails, it is only the first barrier that would have failed. The fission products released would be contained in the sodium system barrier.”

When this happens, the systems are supposed to detect it and shut down the reactor.

The temperature would then drop and the cracks in the clad would get sealed. “The contamination will be only minimal,” said Dr. Ramalingam.