05000315/LER-1999-013, :on 990327,safety Injection & Centrifugal Charging Throttle Valve Cavitation During LOCA Could Have Led to ECCS Pump Failure.Caused by Inadequate Original Design Application of Si.Throttle Valves Will Be Developed

:on 990327,safety Injection & Centrifugal Charging Throttle Valve Cavitation During LOCA Could Have Led to ECCS Pump Failure.Caused by Inadequate Original Design Application of Si.Throttle Valves Will Be Developed

ML17325B642
Person / Time
Site:	Cook
Issue date:	06/01/1999
From:	Orourke B INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17325B641	List: 05000315/LER-1999-013, :on 990327,safety Injection & Centrifugal Charging Throttle Valve Cavitation During LOCA Could Have Led to ECCS Pump Failure.Caused by Inadequate Original Design Application of Si.Throttle Valves Will Be Developed
References
LER-99-013, LER-99-13, NUDOCS 9906080148
Download: ML17325B642 (3)

LER-1999-013, on 990327,safety Injection & Centrifugal Charging Throttle Valve Cavitation During LOCA Could Have Led to ECCS Pump Failure.Caused by Inadequate Original Design Application of Si.Throttle Valves Will Be Developed

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(6) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x)
3151999013R00 - NRC Website

text

E NRC Form 366 U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

L(CENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVEOSYOMB)IO.31~104 EXP)REB 06r30)2001 ESTSJATED SVRDEN PER

RESPONSE

TO COMPLY WITH TIES MANDATORY INFORMATIONCOLLECDON RECVESP. 50JJ HRS. REPORTED lESSONS lEARHEDARE INCORPORATED VITO THE UCENSINO PROCESS AND FED SACK 'TO INDVSTRY.

FORWARD COMNBPS REOARDVIO SVRDEN ESTSIATE TO THE INFORMATION AND RECORDS MANAOEMENT SRANCH IT%

FSSL V.S.

NVCLEAR REOVIATORY COLSSSSON, WASHSIOTON, DC 2N554NI. ANDTO THEP~

REDVCTION PRO/ECt O1100100, OFACE OF MANAOEMENT AJID SVOOET, WASISNOTON, DC 20MS FACIUTYNAME(I)

Cook Nuclear Plant Unit 1 DOCKET NUMBERt2) 05000-315 PAOE IS) 1 of3 TITLE(4)

Safety Injection and CentNugat Charging Throttle Valve Cavitation During LOCA Could Lead to ECCS Pump Failure EVENT DATE {6)

LER NUMBER {6)

REPORT DATE (7)

OTHER FACILITIESINVOLVED(6)

MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REVISION NUMBER MONTH

'DAY YEAR ACIUTYNAME D.C. Cook, Unit 2 FACIUTYNAM 05000-316 NUM R

03 27 1999 1999 013 00 06 01 1999 OPERATING MODE (9)

POVlER LEVEL(10) 0 20.2201 (b) 20.2203(a)(t) 20.2203(a)(2N) 20.2203{a) {2)(ii) 20.2203(a)(2)(ui) 20.2203(a)(2)(iv) 20.2203(a)(2)(v) 20.2203(a)(3)(I) 20.2203(a)(3)(9) 20.2203(a)(4) 50.36(c)(1) 50.36(c)(2)

UCENSEE CONTACT FOR THIS LER (12) 50.73(a)(2)(l) 50.73(a)(2)(6) 50.73{a)(2)(iii) 50.73(a)(2)(lv) 50.73(a)(2)(v) 50.73(a)(2)(vti) 50.73(a)(2)(viii) 73.71 50.73(a)(2)(x)

OTHER SPPCEF in AIJSVect IJeNAN 01 n NRC Form MEA TELEPHONE NUMBER0IcIvde Area Code)

THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR li: (Check one or more) (11)

Ms. Brenda W. O'ourke, Compliance Engineer (616) 465-5901 x2604 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT {13)

COMPONENT MANUFACTURER REPORTABLE TO EPIX COMPONENT MANUFACTURER REPORTABLE TO EPIX SUPPLEMENTAL REPORT EXPECTED 14 X

YES IfYes, corn lete EXPECTED SUBMISSION DATE NO EXPECTED SUBMISSION DATE 15 12 YEAR 01 1999 Abstract {Umitto 1400 spaces, I.e., approximately 15 single-spaced typewritten lines) (16)

On March 27, 1999, during development of an Emergency Core Cooling System (ECCS) thermal hydraulic flow analysis model, Engineering concluded that preliminary hydraulic flow analysis results indicated that the Unit 1 Safety Injection (Sl) and Centrifugat Charging (CC) throttle valves could potentially experience cavitation during a LOCA. Specifically, during a LOCA, large differential pressures created across the Sl and CC throttle valves would result in cavitation and possible mechanical erosion of the valves and downstream piping. During post-LOCA conditions, throttle valve erosion could lead to a pump runout condition and subsequent failure ofthe ECCS pumps.

Radiography performed to determine valve position showed the valves to be less open than predicted by the hydraulic analysis.

This condition could result in LOCA generated debris becoming lodged in the throttle valve, resulting in reduced flowto the reactor core. Similar conditions exist for the Unit 2 Sl and CC throttle valves.

During continuing evaluation, plant personnel concluded that the conditions were reportable on May 4, 1999, and a 4-hour notification was made to the NRC in accordance with 10CFR50.72, for a condition that resutted in the plant being in an unanalyzed condition, and for any event or condition that alone could have prevented the fulfillmentof the Sl or CC system safety function needed to mitigate the consequences of an accident.

The preliminary cause is inadequate original design application of the Sl and CC throttle valves. Because five ofthe six Unit 1 throttle valves were found to be less than 44 percent open, these vatves could be assumed to be partially or fully plugged with debris although the amount of plugging would depend on the nature and geometry ofthe debris. However, partial or full plugging could render the systems not capable of performing their intended safety function during the recirculation phase of a LOCA event. As part ofthe evaluation, a permanent solution forthe cavitation-induced erosion and potential debris plugging willbe devetoped to restore conformance with the plant design basis and to support ECCS operability. Possible modifications are currently under review and the method selected willbe implemented prior to restart of each unit. A supplement to this LER willbe provided upon completion of the condition evaluation.

9906080i48

'T)9060i PDR ADQCK 050003i5 8

PDRU.S. NUCLEARREGULATORYCOMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

~

TEXT CONTINUATION FACILITYNAME(1)

Cook Nuclear Plant Unit 1 DOCKETNUMBER(2) 05000-315 YEAR 1999 LER NUMBER (6)

SEQUENTIAL NUMBER 013 REVISION NUMBER 00 PAGE (3) 2 of 3 TEXT (Ifmore space is required, use additional copies ofNRC Form (366A) (17)

Conditions Prior to Event

Unit 1 was in Mode 5, Cold Shutdown Unit 2 was in Mode 5, Cold Shutdown Descri tion of Event On March 27, 1999, during development of an Emergency Core Cooling System (ECCS) thermal hydraulic flow analysis model, Engineering concluded that preliminary hydraulic flow analysis results indicated that the Unit 1 Safety Injection (Sl)[BQ] and Centrifugal Charging (CC)[SJJ throttle valves [FCVJ could potentially experience cavitation during a LOCA.

Specifically, during a LOCA, large differential pressures created across the Sl and CC throttle valves would result in cavitation and possible mechanical erosion ofthe valves and downstream piping. Throttle valve erosion during post-LOCA conditions could cause the valves to allow excess flowthrough the Sl and CC pumps, which could lead to a pump runout condition and subsequent failure ofthe ECCS pumps.

The preliminary flow analysis also predicted that the Sl and CC throttle valves would be less open than previously determined during evaluation of an industry event in 1995.

In addition, actual valve stem measurements concluded that the Sl and CC throttle valves were less open than predicted by the preliminary flow analysis.

As a result, radiography was performed on April8, 1999, fortwo Sl throttle valves to better assess their position. Radiography results also concluded that the throttle valves were more closed than'predicted by the hydraulic analysis, and also showed indications of possible valve erosion. With the throttle valves found less open, debris generated in containment during a LOCA could potentially become lodged in the throttle valves, resulting in reduced flowto the reactor core. Similar conditions exist forthe Unit 2 Sl and CC throttle valves.

During continuing evaluation ofthe identified conditions, on May 4, 1999, plant personnel concluded that these conditions were reportable to the NRC.

Cause of Event

The preliminary cause is inadequate original design application ofthe Sl and CC throttle valves. Atthe time of original plant design, this throttle valve design was commonly used throughout the industry forthe same throttling application.

However, it was not recognized that these valves are susceptible to mechanical cavitation damage as a result of high differential pressures across the valve.

Opportunities to identify this potential condition were missed during previous evaluations of industry events regarding the potential for post-LOCA ECCS pump runout damage due to throttle valve degradation.

Anal sis of Event In accordance with the requirements of 10CFR50.72(b)(2)(i) and 10CFR50.72(b)(2)(iii)(D), a 4-hour notification was made to the NRC for a condition that resulted in the plant being in an unanalyzed condition, and for any event or condition that alone could have prevented the fulfillmentofthe Sl or CC system safety function needed to mitigate the consequences of an accident.

As such, this LER is being submitted in accordance with the requirements of 10CFR50.73.

UFSAR Section 6.2 states that the primary function ofthe ECCS is to provide cooling water to the reactor core in the event of a LOCA. The ECCS system consists ofsix ECCS pumps: two Centrifugal Charging pumps, two Residual Heat Removal (RHR) pumps, and two Safety Injections pumps.

The subject throttle valves are installed on each of the four CC pump lines to the reactor coolant loops and on the discharge side of each Sl pump.U.S. NUCLEARREGULATORYCOMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

~

TEKF CONTINUATION FACIUTYNAME(1)

Cook Nuclear Plant Unit 1 DOCKETNUMBER(2) 05000-315 YEAR 1999 LER NUMBER (6)

SEQUENTIAL NUMBER 013 REVISION NUMBER 00 PAGE (3) 3of3 TEXT (Ifmore space ls required, use additional copies ofNRC Form (366A) (17)

The operation of the ECCS following a LOCA consists oftwo distinct phases:

1) the injection phase during which reactivity is controlled, initial cooling of the core is accomplished, and coolant lost from the primary system is replenished, and 2) the recirculation phase, in which long term core cooling is provided during the accident recovery period. Long term core cooling is provided, in part, by the Sl and CC systems that deliver coolant water from the containment recirculation sump back to the reactor coolant system.

Following a LOCA event, any debris that was generated in containment willbe filtered through a 0.25-inch square mesh screen [BP](SCN] prior to entering the containment sump to prevent foreign material from entering the ECCS system.

V The preliminary results ofthe ECCS hydraulic flow analysis were used to calculate the potential cavitation damage to the Sl and CC throttle valves under various ECCS system operating configurations.

The most limiting operating configuration assumes the throttle valves to be wide open to simulate the maximum erosion condition. The flow analysis concluded that with the throttle valves wide open, cavitation would likely occur and the Sl pumps would be in a runout condition, while both CC pumps would remain available.

For the case where only one CC pump is running, analysis results conclude that the single CC pump would go to the runout condition, in addition to both Sl pumps. For this configuration, calculations indicate that the Sl valves would be in a choked flow condition, which could cause cavitation-induced erosion ofthe valves and/or downstream piping. In addition, the CC throttle valves were calculated to be in the incipient damage range, which is the level at which cavitation is considered sufficient to result in erosion damage.

Westinghouse letter NSAL-96-001, "Erosion of Globe Valves in ECCS Throttling Applications," indicates that even with throttle valve erosion, the CC and Sl pumps should remain operable long enough to allow the operators to use the RHR pumps for long term cooling. However, no formal analysis has been performed to validate the impact this condition has on long term ECCS post-LOCA operation.

Information received from the valve manufacturer requires the throttle valves to be approximately 44 percent open to ensure debris would not become lodged in the valve. Because five ofthe six Unit 1 throttle valves were found to be less than 44 percent open, these valves could be assumed to be partially or fullyplugged with debris although the amount of plugging would depend on the nature and geometry ofthe debris.

However, partial or full plugging ofthe Sl and CC throttle valves could render the systems not capable of performing their intended safety function during the recirculation phase of a LOCA.

Corrective Actions

A permanent solution forthe cavitation-induced erosion and potential debris plugging of the throttle valves willbe developed to restore conformance with the plant design basis and to support ECCS system operability. Possible modifications are currently under review and the method selected willbe implemented prior to,restart of each unit.

As part ofthe Restart effort, an improved operating experience program is being developed.

In addition, the Expanded System Readiness Review project teams are evaluating operating experience information to assess whether applicable industry issues have been adequately addressed for applicability to D.C. Cook.

The adequacy of the systems to perform their safety and accident mitigation functions is being reviewed during the discovery process at D.C. Cook under a number of system assessments and programmatic assessments to support the Restart Plan. These include the Expanded System Readiness Review (ESRR) and the Licensing Basis Review. Identified deficiencies are being addressed under the Corrective Action Program.

The evaluation for this condition has not been completed.

Based on the results ofthe completed evaluation, information regarding the safety significance, and corrective and preventive actions willbe provided in an update to this LER.

Previous Similar Events

None

~ NRC FORM 366A (6-1998)