Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
