Restoring environmentally qualified equipment health after a boric acid event

A crack in the control rod drive mechanism weld at the reactor vessel closure head led to a long-term boric acid exposure event inside a midwest pressurized water reactor. Although detrimental effects of boric acid exposure have been demonstrated for carbon steel bolts and other support devices, the long-term effects on electrical equipment are less certain. The uncertainty in continued viability of the environmentally qualified (EQ) equipment located inside containment necessitated a re-evaluation of the accident mitigation capability of the various containment equipment exposed to the long-term boric acid event. This paper reports on the comprehensive approach for the development and implementation of compensatory measures undertaken to assure the health of EQ equipment following an extended boric acid exposure event.