CRACKS AND CRACKPOTS

So another nuclear disaster threatens: The metal pressure vessel, several inches thick and housing the core, could crack when the hot water leaks out and the cold water of the emergency cooling is injected. The NRC has listed 13 plants where precautionary measures must be taken, and the great antinuclear humanitarians are once more fervently hoping for the Grand Catastrophe to arrive at long last.

But once more, they drool in vain.

It has been known for decades that metals become brittle in years of irradiation by neutrons. By 1970, the AEC issued Safety Guide 2, Thermal Shock to Reactor Pressure Vessels, ordering data collection, research, and surveillance programs to make sure the pressure vessel would not crack if cold water had to be injected.

There have been no surprises in the way metals are gradually embrittled by years of irradiation; the new point is that in some reactor designs the neutron flux out of the core (at the points where it is not "screened" by fuel bundles) is greater than expected, causing faster aging of the metal in the places exposed to it. Thus, the injected water would have to be ever warmer (over the years) to keep above the point where thermal shock might embrittle the pressure vessel in an emergency.

For future reactors, the remedy is simple: absorbers for the stream of neutrons where too many leave the core.

As for the present, even if nothing were done, it would simply mean a shorter useful reactor life. But there are remedies. The heat transfer in those 13 plants will be measured and analyzed to see whether operating conditions must be changed. If so, the reactor can be run in conditions (of temperature and pressure) that will avoid brittleness even with cold safety injection water. Alternatively, the injection water can be kept warm. And finally, the entire core could be removed during an extended outage, and the pressure vessel annealed with infrared heat to restore the metal's ductility for another 15 to 20 years.

Annealing was, in fact, a solution suggested in the AEC's 1970 safety guide. The trouble is its cost, which is mainly the cost of the replacement power the utility has to buy during the three months or so of the overhaul (the type of cost inflicted on utilities by antinuclear litigation and regulatory delays). Do we solve problems or use them for propaganda?