EMBRITTLEMENT

On July 31 the NRC unanimously rejected the Union of "Concerned" "Scientists" obstructionist petition to shut down the Massachusetts Yankee Rowe nuclear plant due to embrittlement of the pressure vessel, ruling that the public faces no undue risk by next April, when the plant will be shut down for refueling..

Embrittlement of metals by a stream of neutrons is a phenomenon that has been known for decades [AtE Nov 81] and though press reports would never let you suspect it, every nuclear plant monitors it carefully. It is most critical at the seams where the steel pressure vessel is welded: in circles at the top, bottom and middle of the cylindrical vessel. It is minimized by design, which keeps the neutron flux density low. (Flux density is analogous to pressure in a water jet; by broadening the stream, one can reduce the pressure without lowering the rate of water delivery.)

If the brittleness threatens to approach the limit set by the ASME (Amer. Soc. of Mech. Eng.) standard, the utility has two choices of reducing the flux fuel management (placing the partial-ly spent fuel rods with lower flux on the outside, near the walls of the pressure vessel) and shielding (placing metal shields between the fuel and the walls of the pressure vessel). This will slow the embrittlement, but not eliminate it. If the embrittlement threatens to exceed the ASME standard, the toughness (ductility) of the pressure vessel can be restored by annealing, i.e., by heating it, in place, to a temperature at which the metal's internal stresses and brittleness are removed, and then letting it cool slowly.

None of this was mentioned or explained in any corrugation of the Great American Brainwashboard. But all of them (including the W.St.J.) gave publicity to the angry statements by the UCS, which, as always, is well-heeled enough to appeal the decision. Its "scientist" Robert Pollard, for example, whined that the "NRC had once again let economics overrule public safety."

In fact, of course, if the NRC's judgment were to be wrong, the utility would pay a fearful price (TMI cost the owner utility more than $2 billion); to the contrary, if Pollard wants to talk economics, he makes a living by badmouthing nuclear power, and as one who has debated him in the 1970s, I have my doubts if this lightweight ex-NRC clerk could earn much in any other occupation.