United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-23, Supplement 2: Potential for Gas Binding of High-Pressure Safety Injection Pumps During a Loss-Of-Coolant Accident

                                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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