United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-59: Potential RHR Pump Loss

                                                       IN 87-59

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                November 17, 1987


Information Notice No. 87-59:  POTENTIAL RHR PUMP LOSS

Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is provided to alert addressees to potential problems 
with safety injection pumps having common recirculation lines.  It is expected 
that recipients will review the information for applicability to their facili-
ties and consider actions, as appropriate, to avoid similar problems.  
However, suggestions contained in this information notice do not constitute 
NRC requirements; therefore, no specific action or written response is 
required.

Description of Circumstances: 

Westinghouse Electric Corporation has notified all utilities with 
Westinghouse-designed nuclear steam supply systems of two concerns they have 
identified regarding the design of the minimum flow (miniflow) recirculation 
line configuration for the residual heat removal (RHR) pumps which also 
function as low pressure safety injection (LPSI) pumps.  The first concern 
involves the potential for dead heading one of two RHR pumps in systems that 
have a common miniflow recirculation line serving both pumps.  The second 
concern involves the adequacy of the miniflow recirculation line capacity even 
for single pump operation.  In addition, Westinghouse has stated that these 
concerns might also be applicable to high pressure safety injection pumps.

Discussion:

A small-break loss-of-coolant accident causes a safety injection signal to be 
generated, which starts both RHR pumps and for some plants, circulates coolant 
through a common miniflow recirculation line until the reactor coolant system 
(RCS) is depressurized to below the pump shutoff head; the point at which the 
RHR pumps can deliver coolant to the RCS.  The flow resistance of the miniflow 
line is great enough that during recirculation the RHR pumps are operating 
close to their shutoff head.  Thus, even modest degradation of one pump can 
result in it being dead headed by the other pump.  Westinghouse has stated 
that an RHR pump supplied by one vendor can, under certain conditions, operate 
dead headed for a maximum of only 10.4 minutes without resulting in pump 
damage.  For this reason, generic emergency operating procedures for 
Westinghouse reactors require that a dead headed pump be stopped.  To avoid 
loss of safety margin, it is important that this action be taken before pump 
damage is sustained.

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                                                            November 17, 1987
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Westinghouse indicates that, traditionally, the design criteria for miniflow 
lines have been based on the need to limit the temperature rise in the pumped 
liquid and pump casing.  However, that design criteria should include 
consideration of the potential for pump operation at conditions close to the 
pump shutoff head.

The NRC staff believes that this issue may be relevant to all water-cooled 
reactor designs, regardless of the pump application or the NSSS manufacturer.  
This is based on the belief that miniflow lines have traditionally been de-
signed for only 5% to 15% of pump design flow, while some pump manufacturers 
are advising that their pumps should have minimum flow capacities of 25% to 
over 50% of best efficiency flow for extended operation.

The information herein is being provided as an early notification of a poten-
tially significant matter that is still under consideration by the NRC staff. 
If NRC evaluation so indicates, specific licensee actions may be requested.

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contact listed below or the Regional Administrator of the appropriate regional 
office.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation


Technical Contact:  Roger W. Woodruff, NRR
                    (301) 492-7096


Attachment:  List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013