ML20207Q209
| ML20207Q209 | |
| Person / Time | |
|---|---|
| Issue date: | 12/16/1986 |
| From: | Leeds E NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20207Q205 | List: |
| References | |
| TASK-AE, TASK-T609 AEOD-T609, NUDOCS 8701270015 | |
| Download: ML20207Q209 (10) | |
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AE00 TECHNICAL REVIEW REPORT
LICENSEE: Multiple LWRs Evaluator /
Contact:
E. Leeds
SUBJECT:
FOREIGN MATERIAL AND DEBRIS IN SAFETY-RELATED FLUID SYSTEMS ;
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SUMMARY
On January 1, 1985, with the Pilgrim reactor operating at 22% power, the "n
- standby liquid control system (SLCS) relief valve lifted at approximately '
l 600 psi as opposed to its setpoint of 1425 psi during surveillance testing.
l Although, the cause for the "A" SLCS relief valve lifting below its setpoint l could not be determined, investigation found debris floating in both the main and test SLCS tanks. The system was subsequently declared inoperable. This study was performed to assess the generic implications and potential safety ;
! significance of the effect of foreign material and debris on safety-related '
i systems.
The study found that formal written procedures are commonly used at nuclear ,
power plants to minimize the introduction of foreign material and debris into l l safety-related fluid systems during system maintenance and modification !
t activities and that these procedures appear to be generally effective. The l study also found that a limited number of operating events have been 1 l attributed to foreign material and debris contamination during maintenance or
! modification and that there is relatively minor safety significance associated with these events. The study concludes there is limited risk significance which can be associated with the effect of foreign material and debris on !
safety-related fluid systems. Therefore, it is suggested that no further AEOD review on this subject be taken at this time.
DISCUSSION ;
i Introduction i On January 1, 1985, with the Pilgrim reactor operating at 22% power, the "A" standby liquid control system (SLCS) relief valve lifted at approximately 600 psi (compared with a required setpoint of 1425 psi) during surveillance testing (Ref.1).
Although the "B" SLCS train had been successfully tested, the SLCS was declared inoserable because debris was found floating in both the main and test SLCS '
tanis. The SLCS main and test tanks were drained and cleaned and both SLCS l l
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- This document supports on going AE00 and NRC activities and does not represent the position or requirements of the responsible NRC program office.
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relief valves were retested. The "A" relief valve was bench tested several times and lifted at the required setpoint on each test. The cause for the "A" SLCS relief valve initially lifting below its setpoint could not be determined. The "B" relief valve was bench tested and lifted within specifications but lower l than its setpoint. The valve was disassemblert for inspection and pieces of a rubber glove were found between the valve's blowdown adjusting orifice and
- plunger. The entire SLCS was then air blown and/or flushed in sub-sections to ensure that the debris had been cleared from the system. The system was then successfully surveillance tested and declared operable.
A review conducted by the licensee (Boston Edison) found that both the test tank cover and the main tank manway had been opened during a recently completed recirculation pipe replacement and refueling outage. The licensee postulated that while the tanks were open, debris either fell or was inadvertently thrown into the tanks. The corrective actions taken to prevent recurrence were to place locking mechanisms on the test tank cover and bolt the manway cover to the top of the main tank.
A study was initiated to evaluate the Pilgrim event and other similar reported occurrences to determine their causes and potential safety implications and to assess the potential safety significance of foreign material and debris contaminating safety-related fluid systems. The scope of the study was limited to events in which the debris or foreign material was most likely introduced during maintenance activities or through inadequate plant housekeeping. The study also reviewed the regulatory guidance for maintaining fluid systems free of debris, the extent to which procedures were used to 'ninimize the introduction of foreign material and debris during system maintenance or modification and the apparent effectiveness of these procedures.
Regulatory Guidance The requirements for the establishment, implementation and maintenance of writ-ten procedures for a broad range of nuclear plant activities is specifically addressed in the " Administrative Controls" section of the technical specifications of every operating light water reactor (LWR). The requirements for implementation of procedures involving specific activities referenced in the technical specifications include those listed in Appendix "A" of Regulatory Guide 1.33-1978, " Quality Assurance Program Requirements." However, Appendix "A" of Regulatory Guide 1.33 is not intended to be an inclusive compilation of all ,
required procedures and the Guide endorses the American National Standards Institute (ANSI) Standard N18.7 which contains criteria for administrative controls for operating nuclear power plants. ANSI Standard N18.7 provides specific guidance for the control of work activities and environments that can affect the quality of important systems / components of nuclear power plants.
Specifically, paragraph 5.2.10. " Housekeeping and Cleanliness Control," provides I
the following guidance:
Ouring maintenance or modification activities, certain portions of ,
safety-related systems may be subject to potential contamination with !
foreign materials. To prevent such contamination, control measures, l including measures for access control, shall be established. Imme- '
diately prior tt closure an inspection shall be conducted to assure cleanliness and the result of such inspection shall be documented.
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Furthermore, the ANSI guidance continues:
Measures for minimizing the introduction of foreign materials during maintenance or modification, or cleaning following maintenance or modification of radioactively contaminated systems or of equipment in high radiation fields require special consideration.
The guidance for the control of work activities, conditions and environments at nuclear plants under construction is provided in ANSI Standard N45.2.3-1973,
" Housekeeping During the Construction Phase of Nuclear Power Plants," and pro-vides methods acceptable to the NRC staff to comply with the pertinent quality assurance requirements of Appendix B to 10 CFR 50, " Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants" (Ref. 2).
To summarize, both ANSI Standards N18.7 and N45.2.3 provide regulatory guidance for the implementation of procedures to minimize the introduction of foreign material or debris during system maintenance or modification at nuclear plants under construction and during operation.
Analysis of Operational Data To perform the study, a search of the Sequence Coding and Search System (SCSS)
Licensee Event Report (LER) data base from January 1981 through February 1986 was conducted. The LER data base was searched for events in which foreign mate-rial and debris impacted on the operation of safety-related systems at light water reactors. A summary of each of the events collected from this search is presented in Appendix A. The summary information for each event includes the plant name, the event date and a brief description of the event. The event description includes the event cause (if reported) and the corrective actions taken to prevent recurrence.
Twelve LERs in which foreign material / debris affected the operation of safety-related systems at various LWRs were found and evaluated for this study. Eight of the events occurred at pressurized water reactors (PWRs) and four events occurred at boiling water reactors (BWRs). More than one event was reported at only two plants, Hatch and Surry. At Hatch, two events involving debris in safety-related systems were reported, one at each unit. Both of the Hatch events appear to have occurred because of similar maintenance performed on both units' RHR service water systems in May,1982 and both events were discovered during post-maintenance testing. At Sarry, two events involving debris in safety-related systems were also reported in 1982. However, the events at Surry occurred ten months apart and involved different systems at each unit. Since the events of 1982, no events involving the introduction of debris or foreign material into safety-related systems have been reported for either Hatch or Surry.
Although the events evaluated in the study occurred at ten different plants and involved seven different systems, the event reports contained a number of similarities concerning the cause of the events, the method of discovery and the corrective actions taken to prevent recurrence. In seven of the twelve events, the licensees specifically stated that the debris / foreign material was
most likely introduced into the system (s) during maintenance and modification activities. In nine of the events, the effect of the debris / foreign material on the system was discovered during required post-maintenance and surveillance testing. Finally, in five of the events, the licensees' corrective actions in-cluded a specific review or modification of existing procedures used to prevent the introduction of debris / foreign material into equipment.
Of the twelve events evaluated, only two events occurred in which the respec-tive licensees declared the systems involved to be inoperable: (1) the January 1, 1985 event at Pilgrim, and (2) an event at Salem-1 involving the high head safety injection pumps which occurred on July 16, 1984. In both the Pilgrim and Salem-1 events, foreign material was introduced into the systems during maintenance activities and was subsequently discovered during post-maintenance and surveillance testing. The Salem-1 event was specifically addressed in a report prepared by the Office for the Analysis and Evaluation of Operational Data (AE00) which found that high pressure safety injection pumps could be susceptible to abrasive foreign material in the pumped fluid (Ref. 3). The report on the Salem-1 event suggested that the Office of Nuclear Reactor Regu-lation (NRR) consider expanding the scope of Generic Issue 38, " Potential Re-circulation System Failure as a Consequence of Ingestion of Containment Paint Flakes or other Fine Debris," to evaluate the potential loss of the high pres-sure recirculation system during small-break LOCA mitigation for PWRs.
- The system components affected in all twelve events evaluated were pumps and valves. The debris /forei events and in one event (gn materialdebris Salem-1), caused degraded actually pump caused performance pump failure. inInfive the remaining six events, debris prevented valves from opening or closing completely (four events) and caused relief valves to lift below their setpoints (two events).
Two generic issues presently under investigation by the Generic Issues Branch of the Division of Safety Technology concern the affect of debris on safety-related pumps at LWRs. These two generic activities are: (1) Generic Issue 38,
" Potential Recirculation System Failure as a Consequence of Ingestion of Con-tainment Paint Flakes or Other Fine Debris," and (2) Unresolved Safety Issue (USI) A-43, "Centainment Emergency Sump Performance." The effect of foreign material on RHR and core spray system (CSS) pumps for BWRs and RHR and contain-ment spray pumps for PWRs is being addressed in Generic Issue 38. A review of most pump designs used in BWR safety systems and some PWR safety injection sys-tems in regard to their susceptibility to damage by debris ingestion is being addressed in USI A-43.
Compliance with Regulatory Guidance The LERs describing debris / foreign material events at four of the ten plants evaluated in this study (Arkansas Nuclear One, Hatch, Monticello and Palisades) included references to procedures already in effect to prevent the introduction of foreign material into safety-related systems. The resident inspectors at four additional plants involved in this study (Pilgrim, Salem, San Onofre and Surry) were contacted to determine if procedures intended to minimize the intro-duction of debris into safety-related systems are in effMt at these plants.
The resident inspectors confirmed that Pilgrim, Salem, San Onofre and Surry have all implemented these procedures and usually adhere to them. Therefore, it appears highly likely that all LWRs under construction and in operation have in some way implemented the regulatory guidance described in ANSI Standards N18.7 and N45.2.3. Furthermore, considering the amount of system maintenance and rrodifications that take piece at nuclear power plants, it appears from the general lack of operational data ti.e.,12 events reported during 4 years of operation at over 80 nuclear powei plants) that these procedures are generally effective at preventing foreign material and debris from contaminating safety-related systems.
FINDINGS AND CONCLUSIONS The analysis and evaluation of operational data involving the impact of foreign material and debris on safety-related systems can he summarized by the following findings and conclusions:
(1) Both ANSI Standards N18.7 and N45.2.3 provide regulatory guidance for the implementation of procedures to minimize the introduction of foreign ma-terial and debris during system maintenance and modifications at nuclear plants under construction and in operation.
(2) Considering the amount of system maintenance and modifications that take place at nuclear power plants, it appears from the general lack of opera-tional data (i.e.,12 events reported during 4 years of operation at over 80 nuclear plants) that existing administrative controls and procedures are effective in minimizing the introduction of foreign material and debris into safety-related systems.
(3) Required post-maintenance testing and system surveillance tests appear to provide a " safety-net" that will detect and identify any system abnormali-ties caused by foreign material and debris contamination before a demand situation (i.e., accident condition) exists.
(4) Current generic activities (i.e., Generic Issue 38 and USI A-43) are investi-gating the effect of debris and foreign material on BWR and PWR safety system pumps.
(5) The operational data evaluated in this study seems to indicate that there is limited safety significance involved in events caused by debris and foreign material contaminating safety-related systems.
Based on these findings and conclusions, no further AE0D action concerning foreign material and debris contamination of safety-related systems appears necessary at this time.
REFERENCES
- 1. Boston Edison Company, Docket No. 50-293, Licensee Event Report 85-001.
- 2. Regulatory Guide 1.39, " Housekeeping Requirements for Water-Cooled Nuclear Power Plants," Revision 2, September, 1977.
- 3. Robert G. Freeman, " Engineering Evaluation Report: Failure of Safety-Related Pumps due to Debris," AE0D/E512, September 4,1985.
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APPENDIX A Plant Document No. Name Event Date Event Description
- 1. ANO-1 LER 85-001 During a surveillance test, an emergency feedwater pump failed to develop required 01/07/85 flow and discharge pressure. Subsequent investigation found foreign material in the pump's balance drum, causing excessive drum clearances. It is believed that the foreign material was introdaced into the system during outage related modifications.
The foreign material was removed, the balance drum clearances were properly set, and the pump was satisfactorily re-tested. The procedures used to ensure system cleanliness during maintenance are being reviewed for adequacy.
- 2. Hatch-1 LER 82-043 During a surveillance test, an RHR service 05/05/82 water pump failed to develop required flow and discharge pressure. Subsequent investigation found that debris had entered the pump and lodged in the impeller. The source of the debris was attributed to maintenance work performed on the system and the breakdown of the traveling water screens. The debris was removed from the pump impeller and the pump was successfully re-tested. Procedures for securing mater-ials during maintenance activities are being reviewed for adequacy.
i 3. Hatch-1 and 2 LER 82-046 On May 10, 1982 at Unit 2 and on May 19, 05/10/82 1982 at Unit 1, during scheduled inservice inspections, an RHR service water pump at each plant failed to develop required flow and discharge pressure. Subsequent investigation found that debris had lodged in each pump's impeller. The source of the debris was attributed to the accidental dropping of materials into the systems during maintenance activities and a break-down of the traveling water screens. The debris was removed and each pump was suc-cessfully re-tested. Corrective actions included improving methods of securing materials and tools used for maintenance ,
and repairing the traveling wat.e screens.
7 FOREIGN MAT DEBRIS 04/29/86
Plant Document No. Name Event Date Event Description
- 4. McGuire-2 LER 83-002 While moving a temporary incore detector 03/01/83 during initial fuel loading, the rope holding the detector cable fell into the reactor vessel and was drawn into 'C' loop hot leg. The cause of the event was personnel error as plant procedures pro-hibit loose material in the vicinity of the open vessel. The rope was subse-quently found wrapped around the 2A RHR pump impeller hub and removed. The per-sonnel involved were counseled.
- 5. Monticello I.E. During normal plant operation, a surveillance Inspection test indicated a reduction in the head Report capacity of the #14 RHR pump. Subsequent 50-263/ investigation found that a mophead was 85-08 lodged in the suction of the pump. It is LER 83-005 believed that the mophead entered the RHR 02/16/83 system during the previous maintenance outage. The mophead was removed and the pump was satisfactorily re-tested. The licensee has implemented formalized final inspections of maintenance projects to prevent similar events from occurring.
- 6. Palisades LER 82-012-01 During testing, a Safety Injection and 04/23/82 Refueling Water (SIRW) Tank outlet valve failed to close. The outlet valve in the redundant SIRW tank suction line remained operable. The inability of a SIRW outlet valve to close could affect the operability of the associated high pressure safety injection pump. Inspection of the solenoid valve in the air line for the SIRW outlet valve found a piece of teflon tape lodged in the solenoid valve. The tape prevented the solenoid valve from closing completely, thereby maintaining opening air pressure on the SIRW outlet valve. The solenoid valve was cleaned and proper maintenance techniques were reviewed with maint0 nance personnel.
- 7. Pilgrim-1 LER 85-001 During surveillance testing, the 'A' SLCS 01/01/85 relief valve lifted at approximately 600 psi as opposed to its setpoint of 1425 psi. Investigation discovered debris ,,
floating in both the main and test SLCS tanks and the SLCS system was subsequently 04/29/86 8 FOREIGN MAT DEBRIS
4 Plant Document No. Name Event Date Event Description declared inoperable. After draining and cleaning the SLCS tanks, both the 'A' and
'B' SLCS relief valves were retested.
The 'A' relief valve was bench tested several times and lif ted at the required setpoint each test. The cause for the
' A' SLCS relief valve initially lifting below its setpoint could not be determined.
The 'B' relief valve was bench tested and lifted within specifications but lower than its setpoint. The valve was dis-assembled and pieces of a rubber glove were found between the valve's blowdown adjusting orifice and plunger. The entire
_ SLCS was then air blown and/or flushed in sub-sections to verify that the debris had been cleared from the system. Finally, the system was successfully surveillance tested. Apparently, both the test tank cover and the main tank manway were open at certain times during the recently com-pleted recirculation pipe replacement and refueling outage. It was postulated that while the tanks were open, debris either fell or was thrown into the tanks. The licensee's long term corrective action was f to place locking mechanisms on the test tank cover and bolt the manway cover to the top of the main tank.
- 8. Salem-1 LER 84-017 During a surveillance test, a charging 07/16/84 pump seized after running for 30 seconds.
The licensee attributed the seizure of the pump to metal filings found lodged between the impeller and wearing rings.
Metal filings were also found in the suc-tion lines of all three charging pumps and were determined to be the by products of maintenance work performed on the pumps' common vent line header. Corrective ac-tion.s included repairing the charging pump 'and flushing the charging system.
- 9. San Onofre-3 LER 84-014 With the reactor at 100% power, a charging 04/15/84 pump surveillance test was conducted fol-lowing maintenance on the pump. However, when the charging pump was started, charg-~~
ing flow to the reactor coolant system did not increase as expected. The pump was stopped and investigation found that the pump's discharge relief valve had 04/29/86 9 FOREIGN MAT DEBRIS
Plant Document No. Name Event Date Event Description lifted below its normal setpoint. The valve was removed, disassembled and inspected. Dearis was found under the valve's disc and nozzle and was attributed with causing the valve to lift below its setpoint. The valve was cleaned, reassem-bled, bench tested and reinstalled.
- 10. Surry-1 LER 83-048 With the reactor operating at 76% power, 10/24/83 the discharge pressure of the 'B' charging pump component cooling pump decreased to the setpoint which initiated the automatic start of the redundant component cooling purrp. Investigation found that the level control valve for the component cooling pump head tank would not fully open to maintain sufficient level in the tank because of malfunctioning float. The float provides level feedback to a valve controller which modulates valve position.
Debris in the tank interfered with the float's proper operation. The debris in the tank was removed and the valve con-troller was adjusted to ensure proper operation.
- 11. Surry-2 LER 82-009 With the reactor operating at 100% power, 01/28/82 the lubricating oil temperature began increasing for 'C' charging pump. Invest-igation found that a. foreign object lodged in the body of the service water tempera-ture control valve reducing the cooling water flow to the lube oil heat exchanger.
The temperature control valve was disassem-bled and the foreign object was removed.
The valve was reassembled and the system was returned to normal.
- 12. Turkey Point-3 LER 82-013-01 During a monthly surveillance test, 'C' 09/17/82 AFW pump failed to run for the required 15 minutes. It was determined that the auxiliary steam turbine pressure control valve did not close completely. Disassem-bly of the valve revealed two pieces of foreign material under the valve seat, preventing proper closure of the valve.
The source of the foreign material was
not determined. The valve was repaired and the turbine control system was adjusted.
04/29/86 10 FOREIGN MAT DEBRIS