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LER 90-006-00:on 900321,discovered That Nuclear Svc Water Sys Assured Makeup Source to Containment Valve Injection Water Sys Surge Chamber 2A Would Not Provide Adequate Flow. Caused by Clogged pipe.W/900430 Ltr
	ML20042F474
Person / Time
Site:	Catawba
Issue date:	05/03/1990
From:	Glover R, Owen T; DUKE POWER CO.
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	LER-90-006, LER-90-6, NUDOCS 9005080369
	Download: ML20042F474 (8)
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lhake Power Company 00

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J DUKEPOWER April 30, 1990 l Document Control Desk U. S. Nuc1 car Regulatory Consnission [

Washington, D. C. 20555 ,

Subject:

Catawba Nuclear Station Docket No. 50-413 LER 414/90-06 Gentlement i f

Attached is Licensec Event Report 414/90-06 concerning TECHNICAL SPECIFICATION VIOLATION DUE TO LOSS OF ASSURED MAKEUP TO CONTAINMENT VALVE INJECTION WATER SYSTEM DUE A DEFECTIVE PROCEDURE. ,

Thin event was considered to be of no significance with respect to the hculth and safety of the public.

Very truly yours, ;

7 a o -/7e To B. Owen .

Station Manager kob\LER-NRC.TBO xc: Mr. S. D. Ebnoter American Nuclear Insurers Regional Administrator, Rogion 11 c/o Dottio Sherman, ANI Library U. S. Nuclear Regulato? Commission Tho Exchange, Suito 245 101 Marietta Stroot,. N4, Suite 2900 270 Farinington Avenue Atlanta, GA 30323 Farmington, cT 06032 i

M f. M Nuclent Consultants Mr. K. Jabbour 1221 Avenucc of the Americas U. S. Nuclear Regubtory iCommission New York, NY 10020 Office of Nuclear Reactor Regulation Washington, D. C. 20555 INPO Records Conteir Suite 1500 Mr. W. T. Orders 1300 Circle 75 P.urkway NRC Resident Inspector Atlarita, GA 303T3 Catawba Nuclear Station 9005080369 900503 ~

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On March 21, 1990, at approximately 1500 hours0.0174 days 0.417 hours 0.00248 weeks 5.7075e-4 months , with Unit 2 in Mode 1, Power Operation, it was discovered while performing PT/2/A/4200/62, RN to NW Piping Flush, that the Nuclear Service Water (RN) System assured makeup source to the Containment Valve Injection Water (NW) System Surge Chamber 2A would not provide adequate flow. Previous test results indicate this condition occurred between the June 26, 1989 and September 23, 1989 tests. Subsequent investigation revealed that RN to NW piping was clogged with sediment thereby reducing flow.

System piping and components have been cleaned, tested and returned to service.

) This incident is attributed to a Defective Procedure due to inadequate acceptance criteria. Acceptance criteria established for minimum flow will be incorporated into Unit 1 and 2 test procedures, and testi ig frequency will be increased. In addition, an evaluation will be performed on similar tests to determine the need for acceptance criteria or trending programs.

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0l0 0l 2 or 0 l7 BACKGROUND The Containment Valve [EIIS:V] Injection Water [EIIS:JM] (NW) System is designed to inject water between the two seating surfaces of selected gate valves used for Containment Isolation. The injection pressure is higher than Containment design peak pressure during a Loss of Coolant Accident (LOCA). This will provent leakage of the Containment atmosphere through the gate valves, thereby reducing potential offsite dose following a postulated accident.

The NW System consists of two independent, redundant trains; one supplying A train valves and the other supplying 8 train valves. This separation of trains peuvents the possibility of Containment isolation valves not sealing due to a single failure. Each train contains a surge chamber which is filled with water and pressurized with nitrogen. Makeup water is provided from the Demineralized Water [EIIS KJ) (YM) Storage Tank for testing and adding water to the surge chambers during normal plant operation. Assured makeup is prcvided from the essential header of the Nuclear Service Water [EIIS:BI] (RN) System. An automatic swap to RN occurs after an ST (Containment Isolation) Signal when the aurge chamber water level drops below the low-low level setpoint or when nitrogen pressure drops below the low-low pressure setpoint. )

F The RN System serves as the ultimate heat sfnk for heat loads in the Auxiliary

[EIIS:NF] and Reactor [EIIS:NH] Buildings other than the secondary (steam) side of the station. The RN System also serves as the assured source of makeup water for several safety related systems, including NW. RN is a raw water system which uses Lak6 Wylie or the Standby Nuclear Service Water Pond (SNSWP) as the supply.

Tecnnical Specification 3.6.6 states that both trains of the Containment Valve Injection Water System shall be OPERABLE in Mode 1, Power Operation, Mode 2, Startup, Mode 3, Hot Standby, and Mode 4, Hot Shutdown. With one train of NW inoperable, required action is to restore the inoperable system to OPERABLE status within 7 days or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

Periodic test PT/1,2/A/4200/62, RN to NW Piping Plush, is performed quarterly to remove clams from the RN to NW Surge Chambers supply line. This line contains normally closed valve 2NW8A (NW Surge Chamber 2A RN Supply Isolation) with vent valve 2NW118 (NW Surge Chamber 2A RN Supply Vent) downstream. The test method consists of isolating the surge chamber, opening 2NW8A and 2NW118, and establishing flow throtch the vent valve. The length of time needed to flush one gallon of water int:, a container is measured and recorded. The piping

[EIIS: PSP] is then flushed for 15 minutes before returning the system to its ;

original condition. This process is repeated for the resp e.lw B train components.

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[ EVENT DESCRIPTION On March 21, 1990, while Unit 2 was in Mode 1, power Operation, Periodic Test PT/2/A/4200/62, RN to NW Piping Flush, was performed. After completing the test, Operations noted, at approximately 1500 hours0.0174 days 0.417 hours 0.00248 weeks 5.7075e-4 months , that A train flow was significantly less than B train flow. The time necessary to obtain one gallon of flow from A train was 103 seconds while the time for B train was only 6 seconds. Subsequent investigation by Operations revealed that the two previous tests indicated similar results (performed on September 23, 1989 and December j 21, 1989). Work requests had been initiated by operations after each test to I investigate and repair vent valve 2NW118 for flow blockage. Equipment history I records for 2NW118 and the Train B vent valve (2NW117) indicated to operations i that clogging and/or valve internals problems created low flow during prev bus tests. The work request written following the December 21, 1989 test was assigned a low priority and had not been worked as of March 21, 1990. The Operations Unit Managers group was contacted and agreed to have this work request completed the next week during other scheduled A Train work activities.

Due to equipment history records. vent valve 2NW118 was considered by operations as the source of flow blockage.

On P.a c h 23, 1990, Operations originated several work requests to break cu.nections in the RN to NW supply line to investigate for possible blockage.

On March 29, vent valve 2NW118 was removed from the system and cleaned. The valve was found to be clogged with mud and debris. Also on March 29, W RN to NW supply line was disconnected and cleaned at several locations. A w atantial amount of mud and debris was also found in this section of piping.

On March 30, operations initiated Problem Investigation Report (pIR) 2-C90-0110 due to the clogged RN to NW supply line.

On April 2, after reviewing test results, Design Engineering concluded that RN could not have supplied adequate makeup flow to the NW Traia A Surge Chamber at the indicated flow rate and that Unit 2 was probably in violation of T/S 3.6.6.

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l This condition was resolved by cleaning the RN to NW supply lines on March 29, 1990.

l CONCLUSION l

The Operations periodic Test Procedure, pT/1,2/A/4200/62, does not contain acceptance criteria to irdicate if adequate flow exists during the flushing process. Therefore, this incident is attributed to a Defective Procedure due to incomplete information. As a result of this event, Design Engineering developed-acceptance criteria to indicate minimum RN to NW flow based on RN essential i header pressure for use during future tests. pT/1,2/A/4200/62 will be revised j to incorporate thia data, j i

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0l0 0l4 or 0l7 Following system cleaning, Operations determined that the flow blockage existed due to sediment buildup at the inlet to valve 2NW8A (NW Surgo Chamber 2A RN Supply Isolation), which is normally closed. The piping upstream of this valve is filled with stagnant RN water which is susceptible to sediment buildup. The

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blockage that existed at vent valve 2NW118 compounded the low flow measurements recorded while completing PT/2/A/4200/62. Thus, the procedure is also deficient due to the specified test method of measuring flow at the vent valve. Actual RN to NW Surge Chamber flow was not measured and cannot be determined.

PT/1,2/A/4200/62 will be revised to require flow to be measured between the last in-line valve and the surge chamber. This will indicate actual RN to NW flow during future tests.

A contributing cause of this event is attributed to the less than adequato understanding by Operations of previous test results which indicated a substantial difference in flow rate between the trains of NW. The System Expert was not consulted nor involved in the review of these data. This time difference between trains was noted by Operations and attributed to clogging of 2NW118. Each time 2NW118 was taken apart it was found to be significe.ntly clogged. An inappropriate action occurred when it was assumed that the total reason for the low flow was clogging of 2NW118 and that sufficient flow did exist from RN to the NW surge chamber. Because of this assumption, low priority was assigned to the work requests for cleaning 2NW118. The System Expert was not consulted in the assignment of work request priority. As corrective action, Operations staff personnel will be reminded of the importance of involving the assigned System Expert in reviewing problems.

Another contributing cause of this event is less than adequate implementation of the recommendations made by the Asiatic Clam Tack Force to ensure acceptable performance of raw water systems. Review and trending of the results of the NW flush test were not performed. As corrective action, a review will be performed to evaluate the remainder of the raw water system flush program to ensure adequate implementation of the Task Force's recommendations.

An extensive review of RN and NW piping configurat.v was conducted to determine if A train is more susceptible to flow blockage th.. 3 train. There were no differences identified that would indicate this condition.

A review of the OEp database for the previous 24 months revealed no other incidents where raw water system interaction with safety systems caused a 4 Technical Specification (T/S) violation. Therefore, this is not considered to f be a recurring event. However, 25 months ago, LER 413/88-15 was written due to the degraded performance of the Unit 1 Auxiliary Feedwater [EIIS:BA) (CA) System )

and required Hot Shutdown of both Units due to Asiatic clam infestation in the RN System. Corrective actions initiated as a result of this incident were {

1 extensive, and no related T/S violations had occurred up to this incident.

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1) The Unit 2 Train A RN to NW Supply Line and valve 2NWil8 were cleaned and flushed to meet acceptance criteria provided by Design Engineering.

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2) The Unit 2 Train B and both Unit 1 trains of RN to NW were flushed to check for flow blockage. No problems were noted during this process.

, 3) Design Engineering developed acceptance criteria for minimum RN to NW flow based on RN essential header pressure for use during future

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PTANNED

1) Operations test procedures will be revised.to incorporate data from Design Engineering for use as acceptance criteria for minimum flow.

The test method will also be changed to require flow measurement to be

, taken between the last in-line valve and the surge chamber. In addition, the test frequency for the RN to NW Piping Flush will be ;

increased from quarterly to monthly as an interim measure, until l results are further evaluated. i

2) A review will be performed to evaluate the raw water system flush and flow monitoring program relative to the' recommendations of the Asiatic Clam Task Force. ,

3) Operations will communicato with Operations staff the need to involve the assigned System Expert in reviewing problens. Lessons learned <)

from this event will be provided to operations staff to emphasize this point.

SAFETY ANALYSIS The NW surge chambers are normally maintained with a pressurized volume corresponding to 72% level, or approximately 67 gallons. Upon receipt of a phase A Containment Isolation signal, the chamber outlet isolation valve would open to inject water into the cavity between the seating surfaces of certain 4 gate valves used tor containment isolation. One noted difference'between a !

system test and actual system operation is that the cavities of the majority of the valves served would already be filled with water at a pressure higher than i Containment design pressure, thereby minimizing depletion of the surge chamber. i Based on the maximum allowable valve seal injection flow rate of 1.21 g:n (Unit ;

2-Train A), it can be expected that with no chamber makeup provided, the '

available surge chamber volume of 67 gallons would be depleted in approximately

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LtR NUMttR 461 PACE (3) vtan S$4y(A4 .Q848,Q Catawba Nuclear Station, Unit 2 rsx, tu ma. eu. e ea.o .m w ec r.~ au ei on 0l5l0l0l0l q 1l4 S0 --

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0l0 0[6 or ol7 55 minutes. The most recent actual leakage test results have indicated an injection flow rate to be approximately .23 gpm, which would yield a chamber depletion time of approximately 291 minutes following an actuation of the NW System. It is therefore reasonable to assume that adequate sealing of the affected containment isolation valves would have been provided for at least 291 minutes. Symptoms indicating isolation of assured NW makeup would not be evident at least until low-low chamber level was reached, set to occur at 25%

level and approximately 152 minutes into an accident. '

At the low los chamber level setpoint with the Containment Isolation signal present, automatic makeup from RN would normally occur. With that source unavailable, the contents of the surge chamber would in fact be depleted, but j not before control room computer alarms would be received for surge chamber low ;

level and pressure. position status of the RN supply isolation valve (2NW-BA or l 2NW-61B) would indicate OpEN cn the computer at the low-low level signal. ;

Analog computer indication of chamber level, as well as control board gauges of pressure and level are also available to the Operator. Indication of low surge ;

chamber level and pressure, open status for the RN supply isolation valve, and normal RN essential header pressure would be evidence of either a closed valve or blockage in the supply line to the surge chamber. These symptoms could j

, reasonably be expected to be evident on both trains and at different times due to a difference in train leakage rates.

With the situation recognized, manual makeup of a limited volume from the Makeup !

Domineralized Water [EIIS:KJ) (YM) System, coordinated with the proper nitrogen '

overpressure from the available nitrogen supply, would have remained as a viable but limited option. The limitation of resorting to YM in an accident situation it in view of the 30-day capacity and minimum pressure requirement placed on the NW surge tank assured makeup.

A review of previous test results indicate the RN to NW supply line was clear of obstruction on March 24, 1989. The time required to obtain the one gallon sample was 7 seconds on this date.

l The data from the test performed June 26, 1989 (27 seconds) indicates that some amount of blockage existed at that time. Due to the test method of measuring flow at the vent valve, the location of this blockage cannot be determined. It is reasonable to assume that blockage existed in the vent valve and in the supply line. Therefore, to assure conservatism, the Unit 2 Train A RN to NW supply line will be assumed inoperable starting June 26, 1989. At the next tust i date, September 23, 1989, the data (130 seconds) further indicates system ;

inoperability. The supply line was cleaned, tested, and returned to service on March 29, 1990, therefore the time frame addressed in this safety Analysis is June 26, 1989 to March 29, 1990. !

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Technical Specification 3.6.6 requires that both NW trains are operable during Modes 1, 2, 3, and 4. Catawba Unit 2 operated in these Modes almost exclusively during the time period in question, with A Train potentially inoperable. Due to redundancy provided by IN Train B, 2njection water would have been available to

, ensure Containment isolation. However, IN Train B was also inoperchle at intermittent times during this period due to train related testing or work activities (D/G 2B RN Train B, IN Train 2B). During these short, intermittent periods of time, both trains of NW were inoperable, periods of Train B IN inoperability were limited by the Tech Spec Action Statement time limits applicable to the system causing inoperability. The longest period permitted is 7 days (for the NW system). The maximum single duration of inoperability of both trains of NW is assumed to be 7 days.

The postulated event in concern is a LOCA at a time between June 26, 1989 and March 29, 1990 when NW Train B was inoperable. The low probability of a large break LOCA (7E-4) is further reduced during the approximate 9 month period in questisn. The probability of this postulated event is significantly reduced by the short periods of time that NW Train B was inoperable. Due to the cumulative effect of these conditions, the overall probability of the postulated event is reduced to approximately 7.5E-5.

If the postulated event were to occurr (a LOCA with both NW trains inoperable),

seal injection flow would have been available until depletion of the surge chamber. After this tine, with no makeup assumed, offsite dose limits specified in 10CFR100 could have been exceeded due to increased leakage outside j Containrent.

During the period of time in which Train A NW is considered to have been potentially inoperable, an accident requiring operation of the NW did not occur.

Thus, there were no radiological consequences as a result of this incident and the health and safety of the public were not affected.

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ML20042F474

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