ML20207A715

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Review & Assessment of Water Hammer Occurrences,CY81-CY85
ML20207A715
Person / Time
Issue date: 06/25/1986
From: Serkiz A
Office of Nuclear Reactor Regulation
To:
Shared Package
ML20207A713 List:
References
FOIA-86-862, REF-GTECI-A-01, REF-GTECI-PI, TASK-A-01, TASK-A-1, TASK-OR NUDOCS 8607160404
Download: ML20207A715 (10)
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Review and Assessmert of Water Hammer Occurrences CY 1981 through CY 1985 A. W. Serkiz NRR/DSR0/RSIB 6/25/86

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. BACKGROUND Safety concerns associated with water hammer occurrences in nuclear power plants were evaluated in the course of resolving Unresolved Safety Issue (USI) A-1, " Water Hammer." The staff's technical findings were reported in NUREG-0927, Revision 1. The findings noted that the total elimination of water hammer was not feasible due to design and operation 61 conditions encountered. These. findings also noted that safety implications associated with w'ater hammer were less severe than previously hypothesized. These findings were based on water hamer occurrences from CY-1969 to CY-1981 (approximately 150 water hammers had been reported during that period), and evaluation of underlying causes and levels of damage (i.e., mostly damage to pipe hangers and supports).

Since the resolution of USI A-1 in March 1984 (see SECY-84-119), water hammer occurrences have continued, although the frequency of occurrence has been low.

The water hammer occurrence at San Onofre Unit 1 on November 21,1985(see NUREG-1190), which was the result of grossly failed check valves in the feedwater system, has prompted a re-examination of water hammer with particular attention to water hammer occurrences since 1981. The discussion which follows deals with these reported water hammers in the CY-1981 to CY-1985 period and the safety implications associated with these occurrences.

Reassessment of water hammer occurrences:

Figure 1 shows the number of water hammer occurrences reported via LER's, etc.,

as a function of calendar year (CY). There were 148 such events reported in the 1969 to 1980 time frame; an additional 40 occurrences were reported from CY-1981 to CY-1985. Figure 2 illustrates the cumulative reactor operating history (i.e., cumulative reactor years) for U.S. nuclear plants. These data were used to calcul c e the water hammer frequency of occurrence shown in Figure 3. The frequency of occurrence averaged from CY-1969 to CY-1980

l Water Hammer Evaluation Number of Occurences Per Calendar Year PWRs And BWRs 12 -

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Figure 3. Water Hanner Occurrence Frequency (nortnalized to CY) l l r - _ _ .

- e is 0.29 occurrences per reactor year for the total plant population, and Thus, water hammer 0,13 events per reactor year from CY-1981 to CY-985.

occurrence frequency has decreased during a time span where cumulative BWRS have reactor operational time has nearly doubled (see Figure 2).

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The plants that reported water hammers from CY-1981 through CY-1985 are There were listed in Table 1, along with occurrence data, reference LER, etc.

18 water hamer occurrences in BWRs and 22 water hammer occurrences in Tables 2 and 3 provide an overview of the systems incurring a water hamer, underlying causes, and related findings for BWRs and PWRs in the CY-1981 through CY-1985 period. The underlying causes are the same as those reported in NUREG-0927 Revision 1, with approximately 1/3 of the reported events being without identified underlying causes.

The underlying causes identified in NUREG-0921 were voided lines, steam-water entrapment and faulty procedures. These are the same causes identified in the New plants (i.e., post CY-1980) are not the review of the CY-1981-1985 data.

This is not surprising since a new principal contributors (see Table 1).

generation of operators is now operating the older nuclear plants and a new learning cycle is being consumated. The LER information available did not provide a means for assessing the contribution attributable to new plant operational staff.

Water hammer occurrence in the feedwater systcm will result in the highest loads due to potential for steam and cold water to come in contact and produce a condensation-induced water slug. The 1972 water hamer at Indian Point 2, which ruptured a feedwater line, and the November 21, 1985 water hamer at San Onofre Unit 1, which did extensive damage to piping supports and introduced a crack into the Loop B feedwater piping (see NUREG-1190), are the

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most severe water hammers to have occurred in PWR feedwater systems. .

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-7 CONCLUSIONS The water hammer occurrences and underlying causes reported for the CY-1981 through CY-1985 period are the same (i.e., piping voiding and operational related) as the prior water hammer occurrences (CY-1969 through CY-1980) and their unde:-lying causes. No new phenomena have been identified. Prior to the SONGS-1 event in November 1985, check valve failures have not been a reported cause, with the exception of the stuck open check valve at Salem-2 in 1984 (see Table 3)'. Water hammer frequency of occurrence has decreased (see Figure 3) although the number of operational reactor years has nearly doubled since CY-1980 (see Figure 2).

Based on this review of the more recent water hammer events, there does not appear to be a need to reopen the USI A-1, " Water Hammer." The water hammer occurrence at San Onofre-1 on 11-21-85 was due to grossly failed check ~

valves which allowed for backflow of steam from the stean generators and a condensation-induced water hammer when cold AFW was introduced into the feedwater piping (see NUREG-1190).

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  • 8-Table 1: ReportedHammerOccurrencesReported(CY81toCY85)

Water Hamer LER -

Date Plant Typ_e No. System HPCI  :

03/28/81 Brunswick 1 BWR 325/81-034 04/14/81 Brunswick 1 BWR 324/81-046 RHR Nine Mile Point 1 BWR 220/81-031 RCIC 07/04/81 Dresden 2 BWR 237/81-057 HPCI 09/03/81 Dresden 2 BWR 237/82-061 CCSW 10/05/81 10/28/81 Hatch 2 BWR 366/81-104 HPCI Arnold BWR 331/82-008 LPCI 01/21/82 02/19/82 Arnold BWR 331/82-014 RHR Cooper BWR 298/83-006 RHR 05/09/83 06/04/83 Fitzpatrick BWR 333/83-053 RHR 04/19/84 Cooper BWR 298/84-007 SBGT .

09/06/84 Brunswick 1 BWR 325/84-023 CSS 09/08/84 Grand Gulf 1 BWR 416/84-042r SSWS Brunswick 2 BWR RHR 11/27/84 324/84-014' '

12/07/84 Brunswick 1 BWR 325/84-034 MSS 293/85-008: HPCI i 03/31/85 Pilgrim 1 BWR 04/27/85 Susquehanna 2 BWR 388/85-016 RHR 05/18/85 Pilgrim 1 BWR 293/85-012 HPCI San Onofre 2 PWR-CE 361/82-165 SG 088 12/09/82 Maine Yankee PWR-CE 309/83-002 FW #2 SG 01/25/83 Clavert Cliffs 2 PWR-CE 318/84-720 Main Feedwater 04/21/84 Emerg FW' System 05/08/85 Waterford 3 PWR-CE PN0/V86-21 08/13/85 Arkansas Nuclear 2 PWR-CE 368/85-017 SG 10/04/85 San Onofre 2 PWR-CE 361/85-049 SDCS San Onofre 1 PWR-WE 206/81-008 SG B 05/04/81 Indian Point 2 PWR-WE 247/81-023 SG 21 10/14/81 Turkey Point 3 PWR-WE 250/82-007 SG 3C 05/29/82  :

09/06/82 Robinson 2 PWR-WE 261/82-012 CVCS 10/07/82 Diablo Canyon 1 PWR-WE 275/82-009 ASW SYS ,

03/27/83 McGuire 1 PWR-WE 369/83-016 RHR

, 04/07/83 McGuire l' PWR-WE 369/83-018 RHR

10/06/83 Salem 2 PWR-WE 311/83-057 AFWS 12/05/83 Summer 1 PWR-WE 395/83-138 FW 04/06/84 Salem 2 PWR-WE 322/84-015 MFW 08/05/84 McGuire 2 PWR-WE 370/84-017 CVCS/RHR 02/17/85 Diablo Canyon 1 PWR-WE 275/85-011 FW BYPAS Salem 2 PWR-WE 311/85-005 SG Feed Pump 04/17/85 04/29/85 McGuire 2 PWR-WE 370/85-009 Main Steam 05/18/85 Diablo Canyon 1 PWR-WE 275/85-014 AFW 11/21/85 San Onofre 1 PWR-WE 206/85-107 MFW w -- - - - -. . - , . . .

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Table 2: Overview of Reported BWR Water Hammer Events Kumber of Reported Underlying Additional System Events Causes Comments RHR System:

Shutdown Cooling 4 Procedures (1) Isolation valve (y)

Mode Voided lines (3) . leakage LPCI Mode ,1 Unknown Pool Cooling Mode 1 Unknown Steam Condensing 1 Unknown Mode HPCI System 5 Design & Procedures (2)

Steam-Water Entrapment (1)

Voided lines (1)

Voidedlines(1)

Main Steam System 1 Steam-Water Entrapment Inadequate DraiAing Procedures Core Spray 1 Unknown Isolation Condenser 1 Steam-Water Entrapment Inadequate DragingProcedures Service Water Systems ,_3_ Voidedlines(3) Procedures (2)

Total 18 9

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Table 3: Overview of Reported PWR Water Hammer Events ,

Number of Underlying Systems Events Causes Coments Feedwater 4 Unknown (1) Stuck opcn

- steam-bubble Check valve at collapse (1) Salem-2 4/6/84

-Voidedlines(1)

- Procedures (1)

Steam Generator 4- Unknown (1) Line voiding occurred Water Hamer Procedures (2) due to check valve Voided lines (1) leakage at SONGS-1 11/21/85 RHR 3 Voided lines (3) Inadequate procedures (1)

IsolationValveleakage(1)

Design Deficiency (1)

SG Blowdown 3 Volided lines (1) Isolation valve leakage (1)

Piping Procedures (1)

Unknown (1)

CVCS 2 Voided line (1) Maintenance error (1)

Steam bubble collaspe Steam supply 3 Steamwater(3) Drain pot operation (2) to auxiliary Entrapment Failed heat tracing (1) feedwater Main steam 1 Steam water entrapment Operator error Steam supply 1 Steam water entrapment Drain Pot operation to main feed pump Service Water J Voided lines i

Total 22 4

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