Restoring health to containment EQ equipment after a boric acid release event

Abstract

A recent long term boric acid release event at a Midwest PWR power station necessitated re-assessment of the continued viability of the plant's Environmental Qualification (EQ) Program equipment located inside Containment. The event was found to be caused by a small crack in a Control Rod Drive Mechanism weld at the Reactor Vessel Closure Head. Although short term effects of boric acid exposure have been demonstrated as acceptable over the years through numerous EQ testing and test reports, the longer term effects (in this case perhaps as long as six to eight years) were considered unknown in terms of future accident mitigation capability. To address this issue, a Discovery Action Plan was developed to assess and restore the Containment's EQ Program health. This Discovery Action Plan included criteria for screen-out of equipment with no susceptibility to boric acid corrosion, a categorization methodology for remaining equipment based on potential for boric acid ingress and other types of susceptibility, and inspection procedural details. This paper reports on the comprehensive approach for the development of the Discovery Action Plan and the successful results of the associated inspection program.0-7803-8257