Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
January 31, 1990
Information Notice No. 88-23, SUPPLEMENT 2: POTENTIAL FOR GAS BINDING
OF HIGH-PRESSURE SAFETY
INJECTION PUMPS DURING A
LOSS-OF-COOLANT ACCIDENT
Addressees:
All holders of operating licenses or construction permits for pressurized
water reactors (PWRs).
Purpose:
This information notice supplement is intended to alert addressees to
potential problems resulting from the transport of hydrogen from the volume
control tank (VCT) to the safety-related high-pressure injection (HPI) pumps
during testing of the VCT outlet isolation valves. Both trains of high
pressure injection could possibly be rendered inoperable during this
operation. It is expected that recipients will review the information for
applicability to their facilities 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:
On October 30, 1989, during inservice testing of VCT outlet isolation valves
at the Trojan Nuclear Plant, plant personnel discovered that both
high-pressure injection pumps could be rendered inoperable if a safety
injection signal (SIS) occurred while the manual "bypass" valve around the
motor-operated VCT outlet isolation valves is opened (as specified by
procedure). The test procedure involved timed opening and closing of VCT
outlet isolation valves MO-112B and MO-112C (see Figure 1). In order to
maintain HPI pump suction from the VCT during testing, the test procedure
specified locking open manual valve 8484, bypassing the isolation valves.
An SIS causes MO-112D and MO-112E to open to align the HPI pump suction to
the refueling water storage tank (RWST). An SIS also causes MO-112B and
MO-112C to close after MO-112D and MO-112E are open to isolate the VCT from
the HPI pumps' suction. If a safety injection signal is received while
valve 8484 is open, the VCT would not be automatically isolated from the
suction of the HPI pumps. If VCT hydrogen cover gas pressure were
sufficiently high, suction of the pumps could be preferentially provided
from the VCT, even though the pump suctions were aligned to the RWST.
Hydrogen gas could then be entrained
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IN 88-23, Supplement 2
January 31, 1990
Page 2 of 2
into the HPI pumps, rendering them inoperable and possibly causing pump
damage. The inservice test of MO-112B and MO-112C is performed quarterly.
The total time manual bypass valve 8484 was open was 15 to 30 minutes each
quarter.
Discussion:
The licensee evaluated a number of flow and pressure conditions that might
occur following an SIS to determine when the VCT would be drained and the
cover gas ingested into the HPI pumps' suction when the VCT isolation valves
are bypassed. Conditions during a large-break loss-of-coolant accident
(LOCA), a small-break LOCA, and a main steamline break were examined. The
licensee determined that following a small-break LOCA, with low initial VCT
pressure, the HPI pumps could continue to operate for up to 2 hours before
gas entrainment would occur. However, for a large-break LOCA with an
initial VCT pressure of 15 to 40 psig, the HPI pumps might be made
inoperable by gas binding after as little as a minute of operation. Similar
results were determined for a main steamline break.
The likelihood of HPI pump failure from VCT cover gas injection following an
SIS would be exacerbated by inadvertent failure to close the 8484 valve
after testing is completed. If the manual bypass valve were inadvertently
left in the open position, both HPI trains could be unknowingly rendered
inoperable for an extended period.
Test procedures for other valves are being reviewed by the licensee to
determine if similar problems exist. At another utility, the VCT isolation
valves are tested with the bypass line closed and the isolation valves in
the RWST line to the HPI pump suction open to provide suction flow to the
HPI pumps when the VCT isolation valves are cycled.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: L. Mark Padovan, AEOD
(301) 492-4445
Walton Jensen, NRR
(301) 492-1190
Attachments:
1. Figure 1, Charging System Overview
2. List of Recently Issued NRC Information Notices
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