WHY PREFER UN-SAFE REACTORS INSTEAD OF SAFER MODELS?

Prof.T.Shivaji Rao,

Director, Centre for Environmental Studies,

Gitam University, Visakhapatnam-530 045

American experts have recently developed such safe reactors for which the probability of a serious accident is zero, that is, a reactor whose safety depends not on the active intervention of safety systems (which with some degree of probability can fail) but on physical principles that insure the reactors safety without mechanical or human intervention but upon immutable physical principles that even in an emergency could not be abrogated.

Enlightened nuclear and environmental experts have been warning the industry and the Governments to renounce the current generation of reactors stating that no matter how extensive the safety measures are the reactor machines are disasters “waiting in the wings”. In fact General Atomics, an American firm is building a modular high-temperature gas-cooled reactor in Idaho-falls to produce tritium for nuclear weapons and to serve as a basis for a civilian reactor that would generate electricity. In the case of this new reactor proposed in Idaho for ensuring full safety, the designers deliberately restrict the core size and reactor out-put to 140 Mega-watts

In fact a large reactor built in Colorado before the advent of the modular-designs has utterly failed as its Helium circulator has broken down frequently. The secret of the safe reactor lies in its sand-grain sized fuel particles encapsulated in multi-layered glassy carbon spheres that trap radio-active fission products but transmit heat while remaining intact upto 3300^oF. Since the maximum temperature that the fuel grains can attain in the spheres is limited to about 3000^oF , the Uranium fuel cannot melt through the spheres under any kind of an accident. But the pressurized water reactors proposed to be built at Koodankulam in Tirunelveli district of Tamil Nadu are inherently unsafe. In these reactors fuel rods of about half-inch thickness attain temperature of 4100^oF at the core while the casing temperature is maintained at 650^oF by the cooling water. If the pipe breaks and water supply fails for just a few seconds, the hot fuel can destroy the metal casing which begins to break at 1800^oF and melts at 3370^oF. Although back up systems such as the emergency core cooling system and concrete containment are expected to ensure that no radio-activity will escape into the outside environment during an accident, still core-melt accidents did occur at Three Mile Island and Chernobyl plants. While the maximum fuel temperature of 3000^oF is less than the fuel casing failure temperature of 3300^oF in a safe reactor, the maximum fuel temperature of 4100^oF is more than twice the fuel casing failure temperature of 1800^oF in an inherently unsafe reactor.