ML19325E325

Forwards AEOD/E908, Excessive Valve Body Erosion at Brunswick. Study Initiated as Result of Valve Body Erosion on 881214.Info Notices 83-55 & 89-001,NRC Bulletin 88-004 & Generic Ltr 89-13 Issued to Address Issue

ML19325E325
Person / Time
Site:	Brunswick
Issue date:	10/20/1989
From:	Novak T NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Rossi C Office of Nuclear Reactor Regulation
References
AEOD-E908, GL-89-13, IEB-88-004, IEB-88-4, IEIN-83-05, IEIN-83-5, IEIN-89-001, IEIN-89-1, NUDOCS 8911060236
Download: ML19325E325 (2)

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October 20, 1989

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MEMORANDUM FOR: Charles E. Rossi. Director Division of Operational Events Assessment, NRR l

James E. Richardson, Director I

Division of Engineering Technology, NRR l,

FROM:

Thomas M. Novak, Director i

Division of Safety Programs, AEOD l

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SUBJECT:

SOME OBSERVED EROSION FAILURES MAY NOT BE t

ADDRESSED BY PROPOSED MONITORING PROGRAMS l

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j A review of erosion induced failures from 1980 through 1988 is enclosed (E. J. Brown, " Excessive Valves Body Erosion at Brunswick," AEOD/E908, September 29,1989). The study was initiated as a result of a valve body erosion eveht at Brunswick Unit 1 on December 14, 1988.

In the report, we conclude there is a broad range of erosion induced problems, including cavita-i tion induced valve body erosion, valve essembly degradation due to vibration, pipe support damage due to vibration, piping erosion downstream of throttled valves, severe degradation of pumps in the service water system and RHR service water system, low-flow-related damage to pumps in other systems, and i

corrosion / erosion fouling that may adversely impact heat transfer capability of service water system heat exchangers or piping rather than pump or valve operability.

The NRC has issued several generic communications addressing these issues.

These include Information Notices83-055, 89-001,89-008;Bulletin 88-04; and Generic Letter 89-13. The Information llotices identify the technical concerns l

involving valve assembly vibration, piping support vibration, pump and valve erosion, and low flow pump erosion, but they don't include specific action.

I Bulletin 88-04 requests that licensees investigate parallel pump operation for dead-heading during miniflow operation and the adequacy of the miniflow line.

l Generic letter 89-13 essentially concentrates on heat exchangers in service water systems.

It appears there are two efforts established to address these problem areas.

First, the BWR Owners Group (BWROG) has established an effort to cover " target" l

valves in systems such as RHR, HPCI, RCIC, and HPCS as well as two RHR survice water system valves. This effort will concentrate on valve cavitation, but will i

l act address pump degradation due to low-flow conditions. The second effort involves licensee response to Generic Letter 89-13 pertaining to service water l

. systems. This review, too, will not address low-flow operation of pumps.

Further, during NRC staff meetings with the BWROG, there were indications from 0\\

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L a HUMARC representative that they would review these erosion concerns'with

-separate PWR Owners Groups. We are not aware that generic PWR reviews have

<t; evolved from this pr< cess,

.i hs Therefore, it appears that low-flow-induced degradation of pumps will'not be' i[

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' covered by either the BWROG effort or Generic Letter 89 13. This degradation cannot be detected by inservice testing programs in accordance with Section XI of the ASME Code. Thus, the only warning is pump failure.

In addition, the industry effort for. review of PWR system erosion does not seem to have resulted in a generic review of plants. We believe that NRR should pursue both. low-flow pump damage and PWR plant monitoring issues, i

s original a:

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2homas M. Novah Thomas M. Novak, Director Division of Safety Programs, AE0D

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MEMORANDUM FOR: Jack E. Rosenthal, Chief AE0D/E908 i

Reactor Operations Analysis Branch Division of Safety Programs, AEOD THRV:

Matthew Chiramal Chief i

Engineering Section i

Reactor Operations Analysis Branch Division of Safety Programs, AE00 l

4 FROM:

Earl J. Brown Engineering Section Reactor Operations Analysis Branch l

Division of Sefety Programs, AE0D SUCJECT:

EXCESS!YE VALVf. BODY EROSION AT BRUNSWICK t

A copy of a technical review report on excessive valve body erosion at Brunswick i

is enclosed for your information.

i The re) ort indicates there is a broad scope of erosion related problems that could Tave an adverse impact on safety related system operation or availability.

The problems include cavitation induced valve body erosion, valve assembly i

piping support damage due to vibration, pi)ing degredation due to vibration erosiondownstreamofthrottledvalves,severedegradationofpumpsintie f

service water system and RHR service water system low flow related Jamage to pumps in other systems, and corrosion / erosion fouling that may adversely impact heat transfer capebility of service water system heat exchangers er piping rather than pu:np or valve operability. The intustry action by the BWR i

owners group will ' cover target" valves, but not pumps. Thus, it a) pears that low flow damage mechanisms for pumps may not be adequately covered )y eithet the BWR owners group or Generic Letter 89-13 for Service Water Systems.

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w{ B-Earl J. Brown i

Engineering Section l

Reactor Operations Analysis Branch u

Division of Safety Programs, AEOD

Enclosure:

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AEOD TECHNICAL REVIEW REPORT i

Q, is UNIT:

Brunswick 1 TH REPORT NO.: AEOD/E908 L

DOCKET NO.: 50-326 DATE: September 29, 1989 LICENSEE:

Carolina Power and Light Company EVALUATOR / CONTACT:

E. J. Brown NSSS/AE:

General Electric /UE&C f

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SUBJECT:

EXCESSIVE VALVE BODY EROSION AT BRUNSWICK j

j EVENT DATE: December 14, 1988 I

SUMMARY

L Excessive valve body erosion was discovered in the LPCI injection valve, l

E11-F0178, at Brunswick Unit 1.

The licensee investigation indicated that valve i

throttling was a major contributor to the erosion. A review of previous AE0D reports, the Sequence Coding and Search System, and NPRDS identified four previous AEOD reports that addressed erosion events and more than 200 other erosion events. The event date indic6te a pattern of erosion damage and i

degradation of components in several safety systems (RHR, HPCI, RCIC, service water, and RHR service water). The primary causes appear to be cavitation related to either throttling devices such as valves, orifices, and reducers or low flow conditions. An NRC information notice, IN 89-01, was issued on the j

valve erosion event and Generic Letter 89-13 was issued on service water i

system problems.

ItagpearsthatactionbytheBWRownersgroupwill i

concentrate on " target valves in various systems. However, it appears that low flow damage mechanisms for pumps may not be adequately covered by either i

the CWR owners group action or Generic Letter 89-13 for service water systems.

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Also, it is not clear that industry efforts to monitor PWR plants have evolved as anticipated.

DISCUSSION On December 14, 1988, the licen:;ee discovered excessive erosion of the valve body downstream of the seat during disassembly of the LPCI injection valve, E11-F017B, for Brunswick Unit 1.

The valve disassembly was being conducted as part of the plant long term maintenance program. The valve body had erosion pockets with a mininum wall thickness of 1.7 inches. The original wall thickness was between 3.5 and 4 inches.

Inspection of the identical valve, E11-017A, on the other LPCI train revealed a wall thickness of 1.4 inches in the same area of the valve body.

Preliminary investigation by the licensee j

indicated that a major contributor to the erosion of these valve bodies could be l

the throttling operation of the valves. The licensee discovered erosion in l

other throttle valves in the LPCI system. NRC Information Notice IN 89-004 (Ref.1)wasissuedonthisevent.

1 The effort to ascertain the extent of this problem included a review of i

previous AEOD reports, a search of the SCSS LER database, and'a search of the NPRDS equipment failure database. This review identified three engineering j

evaluation (EE) reports that addressed erosion and effects of valve throttling in nuclear plants and one case study that included erosion as a degradation i

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mechanism. The three EE reports are:

"Hisuse of Valve Resultin Damage to the Valve Assembly (and Pipe Supports," E31 Erosion in Nuclear Power Plants," E416 Ref. 3); and ' pump Domage Due to Low flow Cavita-i tion,"E807(Ref.4). The case study report was: " Service Water System f ailures i

and Degradations in Light Water Reactors, C801 (Ref. 5). The LER search using l

l the Sequence Coding Search System (SCSS) identified 64 valve erosion events from 1980 through 1988. The NPRDS search identified over 140 events covering l

the period from 1985 to 1988.

t AE00 Reports AEOD/E315 This report was an evaluation of two events involving operation of the residual heat removal system (RHR) in the shutdawn cooling mode at the Susquehanna Unit 1 plant. The F017B valve (the st.me valve with erosion at Brunswick) was used to throttle flow in the shutdown cooling mode of the RHR system. This valve was observed vibrating severely. The packing was lost, the position t

indicator had fallen off, the 6djacent pipe hanger had two broken welds, and another pipe hanger had cracked welds. Several pipe hanger wd d cracks were observed on the other train also, four months later the valve iisc separated from the stem. The investigation found that RHR flow for the shutdown cooling mode could be distributed as a minimum 1/4 heat exchanger flow and 3/4 bypass flow. This flow distribution in c.ombination with a very low level of decay heat l

created a situation in wnich it was desirable to reduce flow through the RHR l

heat exchanger, but this could only be accomplished by throttling valve F0178.

The report suggested that an infcrmation notice be issued.

IE IN 83-055 (Ref. 6) was issued on the event.

It was concluded that the severe damage to the LPCI system injection valve, F017B, was directly related to RHR system flow limitations that result from a combination of system design, configuration, flow control, and the low level of decay heat. The report sugge',ted that NRR review l

system operation for compatibility of valve assembly design and qualification including frequency of operation and vibration, together with the adequacy of the shutdown cooling node system flow control.

AE0D/E416 This study was an evaluation of more than 140 reports involving erosion in There were 31 reports about valves p(umps.. valves, heat exchangers, and piping.a report may inclurie several valves HTGR. The erosion events involved both steam and water systems. The erosion problems included wear through the wall of valve bodies, deterioration of rubber seets, and wear of retaining devices. A major finding was that " erosion events appear related to the specific water source with suspended solids (raw water,radwaste,etc.),theuseofthrottlingdevices(valvesandorifices),or l

l a combination of these effects." This study also indicated that piping erosion i

events were related to use of thro +tling devices such as valves, orifices, and l

reducers. Approximately 40 percent of the 60 piping erosion reports were related to flow throttling. Thus, if valve throttling is used, the program to monitor erosion should include toth the valve and downstream piping, u

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The report concluded that constructive actions to address erosion problems could include:

(1) cognizance of the phenomenon for certain systems and sites, (2) identification of specific plant equipment and l

configurations that may be susceptible to erosion, and (3)physica implementation of monitoring programs to detect degradation of equipment (pumps, valves, heat I

exchangers,andpiping).

AEOD/E807 Erosion and vibration resulted in failure of an emergency service water pump at Susquehanna Unit 1.

Subsequent disassembly of the pump revealed that the i

bottom portion of the pump suction bell had separated from the body and had fallen into the pump pit.

inspection of the residual heat r moval service water pumps revealed cavitation damage similar to that found in the service J

water pumps. The cavitation was caused by flow recirculation due to operating the pumps at low flow rates. The RHR$W pumps had been operated at less than 50 percent flow most of the time. A search of operational experience database fties identified similar pump degradation from low flow operation at Vermont

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Yankee, H. B. Robinson 2, Turkey Point 3. Haddam Neck, and a foreign plant.

The study concludes that operation of centrifugal pumps at low flow conditions for extended periods of tine can cause cavitation damage from flow recirculation, f

The cavitation erodes the impeller and the internal pump casing wall. The low t

flow conditions could occur during >erformance of the inservice surveillance tests by restricting flow through tle mini flow bypass line, or running the i

NRC pumps in a low flow mode for a system designed for a wide range of flows.

Bulletin 88-04 (Ref. 7) addressed the miniflow test configuration. NRC Informa-tion Notica 89-008 (Ref 8) was issued to highlight pump damage caused by low-flow operation.

AEOD/C801 This report was a comprehensive review and evaluation of service water system I

failures and degradations observed in LWRs from 1980 to 1987. The causes of failuresanddegradationsincludevariousfoulingmechanisms(sediment deposition, biofouling, corrosion and erosion, pipe coating failures, calcium carbonate,. foreign material and debris intrusion); single failure and other design deficiencies; flooding; multiple equipment failures; personnel and procedural errors; and seismic deficiencies. Of 980 operational events during this period, 276 were deemed to have potential generic safety significance.

l A majority (58 percent) of the events involved system fouling. The fouling mechanisms included corrosion and erosion (27 percent), biofouling (10 percent),

foreign material and debris intrusion (10 percent), sediment deposition (9 percent), and pipe coating failure and calcium carbonate deposition (1 percent).

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The recommendations from the study were:

.(1) Conduct, on a regular basis, performance testing of all heat exchengers which are cooled by the service water system and perform a safety function to verify heat exchanger heat trarsfer capability.

(2) Require licensees to verify that their service water systems are not vulnerable to a single failure of an active component.

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, (3) Inspect, on a regular basis, important portions of the piping of the service water system for corrosion, erosion, and biofouling.

L (4) Reduce human errors in the operation, repair and maintenance of the service water system.

GenericLetteer89-13(Ref.9)wasissuedJuly 18, 1989 to address the issues identified in Case Study C801.

LER SCSS Search All LERs were searched using the automated database (SCSS) to identify those LERs in which the words " erosion" and " valves" both a) pear. Sixty-four LERs from 1980 through 1988 were identified. About half tse events identified by this search occurred after our 1984 study of erosion, E416. These events did not appear to include excessive wear similar to that reported at Brunsw;ck, in general, the data was similac.to that reviewed in the E416 study. There were many events with valves that failed leak rate tests due to erosion of the disc. This was corrected by lapping. Other reported causes were erosion due to steam cutting, and expansion of a small leak from a gasket, "0" ring, or steam packing.

NPRDS Search The search strategy for the HPRDS was to identify valves with normal / abnormal It was further refined with a narrative search for the word " erosion."

wear.

There were over 140 reports identified from 1985 through 1988 for all safety c16sses (1, 2, 3, and 4). The type of reported erosion was similar to that in the AE0D studies and the recent SCSS review. There were no narrative descrip-tions that indicated erosion as extensive as that at Brunswick Unit 1.

However, there were reports that identified other valves % the RHR system with erosion damage. Son.e of the valves were F015B (this vehe S in series with F0178),

I f024B (RHR test line control valve), 1001-28A and B (outboard isolation valves),

and 1001-36A (RHR pump test line). Thus, the events reported to NPRDS illustrate i

erosion patterns similar to those previously identified in the AE00 reports E315 E416, and E807.

Industry program The BWR Owners Group (BWROG) has established an effort to address valve erosion l

due to cavitation induced by valve throttling. The BWROG objective is to

" Provide a guidance document for individual utilities to estab?ish and implement a valve assessment / inspection program in order to eliminate valve erosion pro-blems." The BWROG program is a multistep process including meeting with NRC staff to present the plan, schedule, and discuss results prior to final disposi-tion for use by licensee; surveying all BWROG participating utilities to identify safety-related valves used for throttling; request / collect data on cavitation erosion; identify methods used by utilities to eliminate erosion problems; and prepare a BWROG Guidance Report.

Information about the program was presented to ACRS on April 27, 1989.

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I' Based on data reviewed to date, the effort has identified approximately 15 or l

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16 " target" valves in PWR safety-related water o stems. The appropriate i

number of valves depends on whether the BWR has HPCI or HPCS. The approach

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addresses eight valves in the RHR system, two in the RHR service water system, l

two in the core spray system, one to three in the HPCI/HPCS sy:tems, and one l

in the RCIC system, for 1 systems other than RHR, the " target" valves are l

test return valves except for two heat exchanger flow control valves.

l AEOD staff have participated with NRR during the BWROG presentations. The previously cited AEOD reports E315. E416, and E807 were identified for industry information. The concerns expressed by AE00 were that cavitation induced damage nas exhibited a broader scope than simple valve body erosion.

In addition to i

valve body erosion, the AE00 studies have identified cavitation induced damage as valve assembly degradation due to vibration piping support damage due to vibration, piping erosion downstream of throttled valves, severe degradation of pumps in the service water system and the RHR service water system, and low l

flow related damsge to pumps in other systems.

It is our understanding that the BWROG program will be limited to " target" valve body erosion. Further, it was indicated by the BWROG that pumps will not be eddressed and, if service water pumps are a concern, they should be covered as part of any NRC action related to service water systems, in addition, a representative from NUMARC indicated i

that efforts to address erosion in PWR plants would be reviewed with the various owners groups. Wearenotawareofsubsequentaction(afterApril1989) by any PWR owners group.

i OVERVIEW i

The AE00 reports have identified a relatively broad scope of erosion relatet l

service water system, and RHR service water problems involving the RHR system system.

TheproblemsincludecavItationinducedvalvebodyerosion, valve assembly degradation due to vibration, piping support damage due to vibration, I

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piping erosion downstream of throttled valves, severe degradation of pumps in the service water system and RHR service water system, low flow related i

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damage to pumps in other systems, and corrosion / erosion fouling that may adversely impact heat transfer capability of service water system heat exchangers or piping rather than pump or valve operability. NRC generic i

communications that pertain to these issues include Information Notices83-055, 89-001 and 89-008;Bulletin 88-04, and Generic letter 89-13.

Itappearsthattherearetwoeffortsestablishedtoaddressthesegroblem areas.

First, the BWROG has established an effort to cover

• target valves in systems such as RHR, HPCI, RCIC, and HPCS as well as two RHR service water system valve. This BWROG effort appears to be a thorough effort that will concentrate on valve erosion and cavitation but will not address other components. Presumably, if valve savitation is reduced, there is the potential e

for beneficial reduction in vibration problems with piping supports and valve assembly operation.

l The second effort involves licensee response to Generic Letter 89-13 pertaining to service water systems. As previously indicated, the corrosion / erosion aspect of this effort appears to emphasize fouling that may impact heat transfer capability rather than degradation of components such as pumps and valvee.

Thut, it would seem that low flow pump erosion may not receive appropriate monitoring to address the concerns identified in E807 (Ref. 4).

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-flOINGS j

1.

AE00 studies have identified a broad scope of cavitation related component damage. These include valve body erosion, valve assembly degradation due to vibration, piping support damage due to vibration, piping erosion downstream of throttled valves, severe degradation of pumps in the service water system and RHR service water system, low flow damage to pumps in other systems, and service water system failures and degradations involving fouling rscchanisms that include corrosion and erosion.

I 2.

The conclusions, suggested actions, and recumendations in AE00 reports i

E315, E416, E807, and C801 appear to be re w o.Sle approaches to minimize l

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effects of this damage in the future.

3.

NRC has issued several generic communicatioc.4 addressing these erosion issues. These 4::uments are Information Notices83-055, 89-001 and 89-008;Bulletin 38-04; and Generic Letter 89-13.

4.

The EWROG effort appears to be a thorough effort pertaining to erosion of

" target" valves. NRR is following this effort. We understand the effort will not include monitoring of pumps.

5.

It does not appear that any formal effort has been established by PWR owners groups to review these erosion issues.

6.

The damage mechanism to centrifugal pumps under low flow conditions identifiedinE807(Ref.4)doesnotappeartobeappropriatelyaddressed by eithcr the BWROG action or Generic Letter 89-13.

-CONCLUSIONS The event data from 1980 through 1988 exhibit a consistent pattern of erosion damage and degradation of omi.cncnts in several safety related systems.

The primary causes appear to be cavitation related to either throttling devices tuch L3 valves, orifices, and reducers or low flow conditions. This results in either long term erosion wear or a more immediate destructive vibration problem. However, the root causes leading to erosion or cavitation damage appear related to system flow limitations with special concern at low flows relative to full system capacity. A combination of system design, configuration, flow control and low flow requirements conspi n to cause equipment damage. The conclusions, suggested actions and reco:mencations in AE0D reporte r315, E416, E807, C801, and the NRR Generic Letter 89-13 appear ufeful to moni'n danage and degradation due to erosion.

However, it appears that flow dawge mechanisms for pumps may not be adequately addressed by either the BWROG or GL 89-13.

Also, it is not clear that industry efforts to monitor PWR plants has evolved as anticipated.

REFERENCES 1.

U.S. Nuclear Regulatory Commission, NRC Informatior Jotice No.89-001, Valve Body Erosion," January 4, 1989.

U.S. Nuclear Regulatory Commitsion, E. J. Brown, " Misuse cf "alve Resulting in Vibration and Damage to the Valve Assembly and pipe Supports, "AE00/E315, July 7, 1983.

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U.S. Nuclear Rtgulatory Comission, E. J. Brown, " Erosion in Nuclear Power Plants," AEOD/E416, June 11, 1984 4.

U.S. Nuclear Regulatory Comission, C. Hsu, " Pump Dmage Due to Low Flow Cavitation," AE00/E807, October 18, 1988.

5.

.U.S.. Nuclar Regulatory Comission, P. Lan and E. Leeds, " Service Water System failures and Degradations in Light Water Reactors," AEOD/C801, August 1988..

6.

U.S. Nuclear Regulatory Commission, IE Information Notice 83-055,

" Misapplication of Valves by Throttling Beyond Design R6cge," August 22, 1983.

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U.S. Nuclear Regulatory Commission, NRC Bulletin No. 88-04, " Potential Safety-Related Pump Loss," May 5, 1988.

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U.S. Nuclear Regulatory Comission, NRC Information No.89-008, " Pump Damage Caused by Low-Flow Operations," January 26, 1989.

9.

U.S. Nuclear Regulatory Commission, J. G. Partlow to All Licensees. " Service Water System Problems Affecting Safety-Related Equipment (Generic Letter 89-13)," July 18,1989.

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