Operating pumps on minimum flow

The Nuclear Regulatory Commission (NRC) regulations in Appendix A to 10 CFR 50 require that components important to safety be designed and tested to quality standards commensurate with the importance of the safety functions to be performed. The NRC regulations in 10 CFR 50.55a reference the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code for criteria to conduct inservice testing of pumps. The ASME Code allows the performance of pump inservice testing using mini flow bypass loops. Operating experience and studies performed for the Nuclear Plant Aging Research Program (NUREG/ CR-4597, Vols. 1 and 2) showed that a leading cause of pump problems and failures is associated with hydraulic instability phenomena induced by low-flow operation. The NRC staff issued Information Notice (IN) 87-59 to alert all licensees to two miniflow design concerns identified by Westinghouse. The first potential problem discussed in this IN involves parallel pump operation. If the head/capacity curve of one of the parallel pumps is greater than the other, the weaker pump may be dead-headed when the pumps are operating at low-flow conditions. The other problem relates to potential pump damage as a result of hydraulic instability during low-flow operation. In NRC Bulletin 88-04, dated May 5, 1988, the staff requested all licensees to investigate and correct, as applicable, the two miniflow design concerns. The staff also developed a Temporary Instruction, TI 2515/105, dated January 29, 1990, to inspect for the adequacy of licensee response and follow-up actions to NRC Bulletin 88-04. Oak Ridge National Laboratory has reviewed utility responses to Bulletin 88-04 under the auspices of the NRC's Nuclear Plant Aging Research Program, and participated in several NRC inspections. Examples of actions that have been taken, an assessment of the overall industry response, and resultant conclusions and recommendations are presented