ML20005E720
| ML20005E720 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 12/31/1989 |
| From: | Padovan L NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20005E714 | List: |
| References | |
| AEOD-E910, IEIN-88-023, IEIN-88-23, NUDOCS 9001100186 | |
| Download: ML20005E720 (7) | |
Text
{{#Wiki_filter:a 4 r AEOD/E910 ENGINEERING EVALUATION REPORT t POTENTIAL FOR GAS BINDING OF HIGH HEAD SAFETY INJECTION PUMPS RESULTING FROM INSERVICE TESTING OF VCT OUTLET ISOLATION VALVES December 1989 o L P Prepared by: L. Mark Padovan i i Office for Analysis and Evaluation of Operational Data U.S. Nuclear Regulatory Commission o$21jjjfCK06 s93 pas 05000344 r P PDR a m
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SUMMARY
l Trojan nuclear plant personnel discovered that by openin one manual " bypass" valve around the volume control tank (VCT) outlet isolation va ves during inservice both high head safety injection pumps could potentially be rendered testing,le due to hydrogen gas binding, if a safety injection signal occurred while inoperab t i the bypass valve was open. Upon completion of testing, should the manual bypass valve be inadvertently left in the open position, both trains of high head safety injection could be unknowingly rendered inoperable for an extended period of time. i DESCRIPTION OF OCCURRENCE l On October 30, 1989, during inservice testing of the VCT outlet isolation valves at the Trojan nuclear plant, plant personnel discoverud that the procedurally specified opening of one manual " bypass" valve around the motor operated VCT outlet isolation '~ valves could render both high head safety injection pumps inoperable if a safety l injection signal occurred while testing was in process (Ref. 1). Upon completion of testing, should the manual bypass valve be inadvertently left in the open position, i both trains of high head safety injection could be unknowingly rendered inoperable for an extended period of time. The test procedure involved timed opening and closing of VCT outlet isolation valves M0-ll2B and MO-ll2C (see Figure 1). In order to maintain charging pump suction from the VCT during testing to permit normal plant operation, the test procedure specified opening manual isolation valve 8484. With this valve open, upon receipt of a safety injection signal, the VCT would remain aligned to the high head safety injection pumps. If VCT hydrogen cover gas pressure was sufficiently high, pump suction could be areferentially provided from the VCT, even though the pump suctions were aligned to tie refueling water storage tank. Hydrogen gas could then be entrained into the high head safety injection pumps, rendering both of them inoperable. ANALYSIS AND EVALUATION l At the Trojan plant, three charging pumps have the capability of taking suction from l the VCT. One pump is a positive displacement pump (PDP) which can be used to perform reactor coolant system hydrostatic testing, and normally functions to i automatically maintain pressurizer level and reactor coolant pump seal injection. The other two pumps are high head centrifugal charging pumps which provide the same normal function as the PDP, but also are engineered safeguards components, providing high head safety injection during a loss of coolant accident or main steam line break. Upon receipt of a safety injection signal, both high head centrifugal charging pumps are started, the normal charging path isolates, and flow from the charging pumps is aligned to the boron injection tank with seal injection flow to l the reactor coolant pumps still being maintained. Additionally, valves M01120 and M0 ll2E open to supply charging pump suction from the refueling water storage tank, l and valves MO 112B and M0 ll2C close to isolate the VCT from the charging pumps. Valve 8484 is normally locked closed, and valve 8482 is normally open to provide a flow path for the reactor coolant pump seal water return heat exchanger. During performance of Periodic Operating Test (P0T) 2-3 at Trojan, valve 8484 is opened to provide a flow path around the VCT outlet isolation valves. This alignment allows valves MO-ll2B and M0-ll2C to be timed open and closed while charging pump suction remains supplied from the VCT. However, this valve configuration also defeats the
P automatic capability to isolate the VCT upon receipt of a safety injection signal. If VCT hydrogen cover gas pressure was sufficiently high, suction to the pumps could i be preferentially provided from the VCT, even though the pump suctions were aligned to the refueling water storage tank. Hydrogen gas could then be entrained into the high head safety injection pumps, rendering both of them inoperable. For a large break LOCA, with an initial VCT pressure of 15 to 45 psig, the licensee calculated the pumps would become inoperable within 1 to 19 minutes of initiation of the safety injection signal. FINDINGS AND CONCLUSIONS I The potential exits for a common mode failure to disable both high head safety injection pumps, by opening a manual " bypass" valve around the VCT outlet isolation valves during testing. This situation can be exacerbated by inadvertent failure to close the valve after testing is completed. Should the manual bypass valve be inadvertently lef t in tne open position, both trains of high head safety injection could be unknowingly rendered inoperable for an extended period of time. Inservice test procedures, surveillance test procedures, and operating procedures should be reviewed to determine if precautions should be added to inform plant personnel of the potential to disable the high head safety injection pumps when opening the manual " bypass" valve around the VCT outlet isolation valves. Alternately, the procedures could be modified to assure pump suction is taken from the refueling water storage tank, rather than from the VCT through the bypass valve. REFERENCES
- 1. Trojan Nuclear Plant Licensee Event Report 89-21 *High Head Safety Injection Inoperable on loss of Volume Control Tank Isolation Capability Due to Procedural Error," Docket No. 50-344, Portland General Electric Company, November 29, 1989.
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1 i UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 i i January, 1990 NRC INFORMATION NOTICE NO. 88-23, SUPPLEMENT 2: POTENTIAL FOR GAS BINDING OF HIGH-PRESSURE SAFETY INJECTION i PUMPS UPON RECEIPT OF A SAFETY INJECTION SIGNAL. i i addressees: All holders of operating licenses or construction permits for pressurized water reactors (PWRs).
Purpose:
The purpose of this information notice is to alert addressees to potential problems resulting from transport of hydrogen from the volume control tank (VCT) to the safety related high pressure safety injection pumps during testing of VCT outlet isolation valves, potentially rendering both trains of high head safety injection inoperable. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid t 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 Trdan nuclear plant, plant personnel discovered that the procedurally specified opening of one manual " bypass" valve around the motor operated VCT outlet isolation valves could render both high head safety injection pumps inoperable if a safety injection signal occurred while testing was in process. Should the manual bypass valve inadvertently be left in the open position after completion of surveillance testing, both trains of high head safety injection could be unknowingly rendered inoperable for an extended period of time. The test procedure involved timed opening and closing of VCT outlet isolation valves MO-112B and MO-ll2C (see Figure 1). In order to maintain charging pump suction from the VCT during testing to permit normal plant operation, the test procedure specified opening manual isolation valve 8464. With this valve open, upon receipt of a safety injection signal, the VCT would not be automatically isolated from the suction the high head safety injection pumps. If VCT hydrogen cover gas pressure was sufficiently high, suction of the pumps could be preferentially provided from the VCT, even though the pump suctions were aligned to the refueling water storage tank. Hydrogen gas could then be entrained into the high head safety injection l pumps, rendering both of them inoperable. Discussion: Opening of one manual " bypass" valve around the motor operated VCT outlet L
~. - IN 88-23, Supp. 2 January, 1990 Page.2 of 2 isolation valves could render both high head safety injection pumps inoperable if a safety injection signal occurred while testing was in process. This situation can be exacerbated by inadvertent failure to close the valve after testing is completed. Should the manual bypass valve be inadvertently left-in the open _ position, both trains.of high head safety. injection could be unknowingly. rendered inoperable for an extended period of. time, Actions taken by. licensees to avoid or correct the described situations include reviewing inservice test. procedures, surveillance test-procedures, and! operating procedures to determine if precautions should be added to inform plant personnel of ' the potential to disable the high head safety injection pumps when opening the manual " bypass" valve around the VCT outlet -isolation valves. - Alternately, licensee. procedures were found to specify that pump suction is to be taken from the refueling-water storage tank, rather than from the VCT through the bypass valve during testing. This.inforration notice requires no specific action or written response. If you have any question-Sut the information in this notice, please contact the technical contac ced below or the appropriate NRR project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation 4 Technical
Contact:
L. Mark Padovan, AE00 (301) 492-4445
Attachment:
List of Recently Issued NRC Information Notices 1 l
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