ML20198E147
| ML20198E147 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/18/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198E136 | List: |
| References | |
| NUDOCS 9812230348 | |
| Download: ML20198E147 (6) | |
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1 UNITED STATES s
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 30eedHlo01
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 222 TO FACILITY OPERATING LICENSE NO. DPR-65 NQflTHEAST NUCLEAR ENERGY COMPANY THE CONNECTICUT LIGHT AND POWER COMPANY THE WESTERN MASSACHUSETTS ELECTRIC COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 DOCKET NO. 50-336 I
1.0 INTRODUCTIOE By letter dated July 2,1998, Northeast Nuclear Energy Company (NNECO/the licensee) proposed a license amendment that would allow changes to the Millstone Nuclear Power Station, Unit 2 (MNPS-2), Updated Final Safety Analysis Report (UFSAR). NNECO has examined the service water system (SWS) coatings and has determined that the protective coatings could degrade or fail in modes that have not been previously analyzed and that the utilization of the coatings is not fully riescribed in the MNPS-2 UFSAR.
Specifically, NNECO proposes to modify the UFSAR descriptions of the SWS and certain associated components to reflect the utilization of various protective coatings not presently
. identified. In particular, UFSAR Section 9.7.2.4," Service Water - Availability and Reliability,"
would be modified to f eflect the utilization of protective coatings and liners in the piping and components of the SWS, and would also describe the use of procedures, preventive maintenance, surveillance, and inspections to detect and correct protective coating degradation. UFSAR Table 9.7-2, " Service Water System Components," would be modified to detail the use of protective cocnings in the various types cf SWS piping. UFSAR Table 9.4-1,
" Reactor Building Closed Cooling Water System Components," would also be updated to indicate the application of protective coating in the reactor building closed-cooling water (RBCCW) heat exchanger channel heads.
NNECO has determined that the requested changes constitute an unreviewed safety question as defined in Title 10 of the Code of Federal Reaulations (10 CFR) Section 50.59, and that a change to the UFSAR is required through an amendment to Facility Operating License No.
DRP-65 pursuant to 10 CFR 50.90.
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2.0 BACKGROUND
l The SWS for MNPS-2 originally consisted of cement-lined cast iron main supply headers that were repaired in 1992 with cured-in-place epoxy composite liner. Between 1988 and 1993, essentially all of the epoxy-lined piping upstream of safety-related components was replaced with polyvinyl chloride (PVC) lined piping. The purpose for these coatings and linings is to protect the piping from seawater corrosion and/or erosion. Two degradation failure modes are I
possible and have been observed. The first is where material flakes off in small pieces or breaks into small pieces after it flakes off. This is typical of brittle coatings like epoxy. The second is where large sheets of material flake off and remain in large slieets. This is typical of more flexible materials such as PVC. At the time of installation, failure of the PVC liner was not considered to be credible. However, PVC degradation and failure have been observed and may have more significant consequences than have been previously evaluated.
in recent years, NNECO has experienced liner failures where large pieces of coating material have been identified. In 1995, a 2-square foot piece of PVC was found in the channel head of the RBCCW 'A' heat exchanger. In 1997, a 70-square-inch piece of PVC liner was found in the 'B' emergency diesel generator (EDG) engine cooler duplex strainer. A month later, a 30-square-inch piece of liner was found in the same location. The potential for the failure of the PVC liner material was not considered credible during the original design or during subsequent design changes and, thus, it was not evaluated. However, the observed degradation and failures, as previously noted, could have significant consequences.
2.0 EVALUATION As previously noted, protective coatings were used to protect intemal pipe surfaces from seawater corrosion and/or erosion. Large bore piping was either cement-lined cast iron pipe or epoxy-coated carbon steel pipe. The coatings have degraded over time end most of the epoxy-coated pipe has been replaced with PVC lined pipe. Also, the original cement-lined pipe has been repaired with cure-in-place epoxy composite liners. Epoxy-based materials have also been used to repair degraded or damaged linings and to protect the channel heads of the RBCCW heat exchangers.
Operability of SWS components is monitored using various temperature and flow alarms in the l
control room, scheduled periodic surveillance of service water pump differential pressure and service header flow, scheduled periodic surveillance of tube-side pressure differential and service water flow for SWS heat exchangers, scheduled periodic cleaning of the EDG engine cooler duplex strainers, RBCCW heat exchangers and vital chillers, and verification of RBCCW heat exchanger differential pressura during operator rounds.
The RBCCW heat exchangers require the highest service water flow and are most likely to be l
impacted by the failure of lining material upstream. There is a standby RBCCW heat exchanger that can be put into operation while a fouled RBCCW heat exchanger is examined and cleaned, which allows the affected train to remain operable. The heat exchangers' differential pressure and flow measurements are compared with acceptance criteria during l
each shift, if the acceptance criteria is not satisfied, actions are specified to identify any degradation and take appropriate corrective actions in the early stages of development. Once l
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per month an additional differential pressure and flow surveillance is performed and every 3 months the channel head interior is visually examined.
The NRC staff has determined that these actions provide reasonable assurance that lining degradation will not impair the RBCCW heat exchanger safety function.
The EDG engine coolers and duplex strainers experience only trickle flow during normal operation (i.e., EDGs in standby status); hence, it is unlikely that released lining will block these components under these conditions. However, during EDG operation and periodic flow testing, there is sufficient flow that could cause blockage. The strainers are about 10 feet upstream of the EDG engine coolers and the strainers are more likely to become blocked than the engine coolers. Strainer differential pressure is monitored hourly and low SWS flow to the coolers and strainers will alarm in the control room. If blocked, the strainer basket will be swapped and cleaned to establish proper flow. In addition, the strainers are swapped and cleaned once a month.
There is about 10 feet of lined pipe between the duplex strainer and the EDG engine coolers.
If this liner fails, the strainer will not protect the engine coolers. Monthly flow surveillance will provide the necessary information to indicate that the liner has failed in this area. Also, semiannual channel head visual inspections provide an additional means of detecting lining degradation.
The NRC staff has determined that flow surveillance and visual inspection will allow detection j
and corrective action to be taken for any degradation in the EDG engine coolers and duplex strainers and that it is unlikely that lining degradation in the short section of pipe will impair the operation of the EDG engine coolers before it is also detected and corrected.
The attemating current (ac) switchgear room cooling coils receive low flow from the SWS.
However, only a small flow area blockage could cause the design basis limits to be exceeded.
Biweekly flow surveillance and the monitoring of the ac switchgear loom temperature during each shift will ensure that released lining debris will be detected and corrected. Attemative means of cooling the affected switchgear rooms have been proceduralized, which allows time to eliminate any flow restriction without impairing the operability of the vital switchgear.
The vital chillers receive trickle flow during normal operation and blockage is unlikely during normal operation. During accidents, the chillers provide chilled water to vital direct current switchgear rooms and have full SWS flow. The vital chillers have monthly flow surveillance combined with biweekly flow surveillance of the cooling coils and ac switchgear room temperature monitoring. As noted above, attemative means of cooling the affected switchgear rooms have been proceduralized.
The NRC staff has determined that any failure of the linings in the SWS will be detected and corrected in a reasonable time and will not impair the operation of the ac switchgear room cooling coils and vital chillers.
Each SWS train has one turbine building closed-cooling water (TBCCW) isolation valve and l
one EDG engine cooler bypass isolation valve that are designed to isolate under most accident
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conditions to ensure that adequate flow is available for the safety-related heat exchangers. A
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j 4-test was performed that resulted in PVC material being entrapped in an isolation valve that prevented complete closure of the valve. However, these valves are stroke tested on a quarterly basis and any entrapped lining material would be identified at that time. Also the valves are isolated each time a differential pressure and flow surveillance is performed on the EDG engine coolers and the failure of the valves to completely isolate would be detected by a reduced flow measurement. In addition, these isolation valves could become restricted while in the open position, which would likely reduce flow to the TBCCW heat exchangers or through the EDG engine cooler bypass. These valves could be restricted in the open position reducing SWS flow to the TBCCW heat exchangers that could lead to an elevated temperature on the shell side that would likely result in a high temperature alarm in the control room. However, the
.TBCCW heat exchangers are not required for safe shutdown or long-term cooling and flow through the diesel bypass line does not serve any safety-related function.
The NRC staff has determined that it is unlikely that failure of the linings in the SWS would go undetected or would result in an unsafe condition if a TBCCW isolation valve or an EDG engine cooler bypass isolation valve would become restricted by entrapment of PVC material.
Blockage of flow restricting orifices downstream of the RBCCW heat exchangers is unlikely due to the large crifice aperture. No other safety-related flow restricting orifices are suscepble to blockage due to liner failure because they or located downstream of heat
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exchangers in piping where protective coating is not utilized. Liner material could become entrapped in open butterfly valves upstream of EDG engine coolers and in flow control valves downstream of RBCCW heat exchangers. Blockage of these valves is unlikely due to their large available flow area. Blockage of any of these components would be detected by EDG engine cooler low flow control room alarms and the RBCCW heater exchanger differential pressure and flow surveillance which is conducted during each shift.
The NRC staff has determined that blockage due to liner fai!ure is unlikely in flow restricting orifices, open butterfly valves upstream of EDG engine coolers or in flow control valves downstream of the RBCCW heat exchangers and, if it did occur, it would be readily detected and corrected.
Blockage of butterfly valves upstream of switchgear room cooling coils and vital chillers could result from failure of the liner. This would cause the ac switchgear room temperatures to gradually increase that would be detected during operator rounds performed during each shift or result in low flow that would be detected during the biweekly differential pressure and flow surveillance.
The NRC staff has determined that any blockage of butterfly valves upstream of switchgear room cooling coils and vital chillers by liner failure would be detected and corrective action taken in a timely manner.
Fbw elements upstream of the EDG engine cooleis protrude into the flow stream. The flow 1
elements have holes in the leading and trailing edges that are used to determine flow rate. If paint chips or PVC blocked the leading edge holes, the sensed dynamic pressure could be artificially low. This would in tum produce a low flow indication and alarm in the control room, l
which would trigger an investigat!on.
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' The NRC staff has determined that blockage of these flow elements would be detected and that corrective action would occur in a timely manner.
Pressure instrumentation does not perform a control function during accident mitigation, however, it is important during normal operation of the SWS and in the early detection of lining problems since many of the previously discussed pressure and flow measurements rely on this instrumentation. Because the pressure instntmentation lines are static lines, which are perpendicular to flow, it is unlikely that they will become blocked. In addition, these lines are periodically blown down as part of the instrument and controls preventive maintenance program.
The NRC staff agrees that it is unlikely that these lines would become blocked and that the periodic blowdowns would correct any blockage.
Degradation of the lining could lead to corrosion and/or erosion of the SWS piping and could eventually lead to system leakage. If leakage does occur, it will be detected during operator I
walkdowns and will be corrected using station procedures for code and non-code repairs as appropriate. In addition, flaps of degraded PVC material not fully released could interfere with flow in the SWS. The reduction in flow in large bore piping would be small; however, in relatively small bore piping in the EDG engine cooler supply and discharge piping could be affected. Low flow in these areas would produce a low flow indication and alarm in the control room or would be identified in the monthly differential pressure and flow surveillance.
The NRC staff agrees that flow reduction caused by liner flaps would be detected and corrected in a timely manner.
Epoxy chips could become lodged within heat exchanger tubing resulting in localized turbulent flow and possible tube wall degradation. This degradation is expected to occur over a long period of time. Eddy current testing is performed on all safety-related heat exchangers during each refueling outage and would identify erosion damage before it advances through wall. If a leak were to occur, it would be detected prior to becoming significant. The means used to detect leakage include loss of RBCCW inventory, coffer dam water level alarm, elevated ac switchgear room temperature, EDG engine lube oil and jacket water sampling and analysis, and periodic chemical analyses of closed-cooling water.
The NRC staff has determined that the above measures are adequate to detect any significant leakage and measures could be taken to isolate and repair the leak.
3.0
SUMMARY
The NRC staff has determined that the proposed changes to UFSAR and commitment to the actions previously described will provide reasonable assurance that any degradation or failure of the SWS protective coatings will be detected and corrected in a timely manner. Therefore, the NRC staff finds that the proposed revisions to UFSAR Section 9.7.2.4, " Service Water-Availability and Reliability," which will reflect the utilization of protective coatings and liners in the piping and components of the SWS, and describe of the use of procedures, preventive maintenance, surveillance, and inspections to detect and correct protective coating degradation; Table 9.7-2, " Service Water System Components," which will detail the use of l
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. protective coatings in the various types of SWS piping; and Table 9.4-1, " Reactor Building Closed Cooling Water System Components," which will indicate the application of protective coating in the RBCCW heat exchanger channel heads, are acceptable. The changes are described in Attachment 3 of the licensee's submittal.
4.0 ST. ATE CONSULTATION in accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment clianges a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The amendment also relates to changes in recordkeeping, reporting, or administrative procedures or requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. ' The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (63 FR 43206 dated August 12,1998). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9) and (10). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commis:: ion's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: J. Davis Date: December 18, 1998
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