IE Information Notice No. 86-02: Failure of valve operator motor during environmental qualification testing

On August 30, 1985, the General Electric Company (GE) reported to the NRC that they had experienced test anomalies of the Reliance, class RH, ac motors during EQ testing of a Limitorque fast-acting SMB-3-150 valve motor operator for its Gulf States Utilities (River Bend) and Niagara Mohawk (Nine Mile Point 2) BWR customers. These motors have magnesium rotors. Magnesium rotor motors have previously undergone EQ testing by Limitorque (PWR Qualification -- Project 600456A) without failures. However, during the current testing, three motors failed during the 100-day design-basis-event (DBE) test. General Electric recommends that licensees determine the plant-specific applications of magnesium motors subject to harsh environment, the adequacy of long-term cooling could be evaluated assuming failure of the magnesium rotor MOVs a few days after the DBE. Some systems may allow for the operator to position the valve to its safety position immediately following the DBE instead of waiting for automatic actuation, while other systems may require realignment to a standby mode after initial core cooling. In addition to operator training, it may be prudent to disconnect some of the valve actuation logic following safety positioning to prevent valve realignment without operator initiation