ML19318A062

Confirms 800508 Telcon W/E Blackwood Re Substantial Safety Hazard Notification Per 10CFR21.Discusses Westinghouse Charging Pump Operation & Interim Mods for 3-loop & 4-loop, Operating & Nonoperating Plants

ML19318A062
Person / Time
Site:	Summer
Issue date:	05/08/1980
From:	Anderson T WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
Shared Package
ML19318A060	List: ML19318A059 ML19318A062
References
NS-TMA-2245, NUDOCS 8006180404
Download: ML19318A062 (9)

Text

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Westinghouse Water Reactor mmieenenown Electric Corporation. . . Divisions .... .

65 Pmseurgh PennsyNa.13 M2'O I

.. May 8,1980-

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.... NS-TMA .2245

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Mr. V. Stello, Director - - -

Office of Inspection and Enforcement - -

U. S. Nuclear Regulatory Commission ,

1717 H Street ,. . . , . .

Washington, D...C. 20555 .._...........li_~..~... . .- . . . . . , . . . . . . . .... . .

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Subject:

Centri ~ fugal ' Charging Pump 0'peration Fo'lYowinh Secondary Side ' '

High Energy Line Rupture - -

Dear. Mr. Stellot -

-l This letter is to confim the telephone conversation of May 8,1980 between Westinghouse and Mr. Ed Blackwood of Division of Reactor Operations Inspection, Office of Inspection and Enforcement, regarding notification made pursuant to

. Tit 1.e 10 CFR Part 2.1.. . ._ , . . . , _ _ , , ,

' A review of the Westinghouse Safety Injection (SI) Termination Criteria following a secondary side high energy line rupture (feedline or steamline rupture at high initial power levels) has revealed a potential for conse-quential dad. age of one or more centrifugal charging pumps (CCPs) before the SI temination criteria are satisfied and CCP operation terminated.

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Such consequential damage may adversely impact long-term recovery operations for the initiating event and is not pemitted by design criteria. This concern exists for plants which utilize the CCPs as Emergency Core Cooling System (ECCS) pumps,.where.the CCPs are automatically started, and where the CCP miniflow isolation valves are automatically isolated upon' safety injection initiation. Attachment A identifies plants potentially subject to this -

concern. A summary of the concern and recommendations follow. .

Following a secondary side high energy line rupture and associated reactor trip, Reactor Coolant System (RCS) pressure and temperature initially cecrease.

Safety injection is actuated and the CCPs start to increa.se RCS inventory.

Reactor Coolant System pressure and temperature subsequently increase due to the loss of secondary inventory, steamline and feedline isolation, RCS inventory addition and reactor core decay heat generation. The accident scenario may vary with rupture size and specific plant design, but it will develop into a RCS heatup transient with accompanying increase in RCS pressure.

.As RCS pressure increases, the pressurizer power-operated relief valves (PORVs) are designed to limit RCS pressure to 2350 psia. Although these

. valves are nomally available, they are not designed as safety-related equip-ment. It can be postulated that, due to either loss of offsite power, 800'6180h .

Mr. V.'Stello -

May 8. 1980 -

NS-THA-2245 -

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adverse environment inside containm'ent, the pressurizer PORY in manual

- mode, or the PORY block valve in a closed position, due to PORV leakage, the pressurizer PORVs may not!be' operable. As a result of the RCS. heatup and inventory increase, the RCS pressure could rise to the pressurizer s safety val,ve setpoint of 2500 psia within approximately 200 seconds and remain at that pressure until transient " turnaround.". Transient " turn-around" can occur between 1800 and 4200 seconds depending on operator action

.and available equipment. During the initial portion of thi.s transient, the.

SI cermination criteria may not be satisfied.

• Consequently, the RCS pressure can reach' the pressurizer safety valve relief pressure before CCP operation is terminated. During this period, the minimum flow required for CCP opera-tion must be satisfied by flow to the RCS since the CCP miniflow isolation

. valves are automatically closed on' safety injection initiation. This requires that the CCPs be able to deliver their minimum required flow to the RCS at the safety valve setpoint pressure.

To evaluate this concern, Westinghouse has developed a calculational method

- and has reviewed typical- CCP head vers'us flow performance curves and other -- -

representative plant parameters. The calculational method considers the effects of safety valve relief setpoint accuracy, RCS piping resistance,.ECCS piping resistance, number of CCPs operating, technical specification allowable CCP head degradation, and uncertainties associated with in' plant verification testing. The analyses for two CCP operation, the best estimate condition, is similar to the analysis for one CCP operation except that the flowrate used '

, to determine ECCS piping line loss must ensure the minimum, flow through each pump. For example, at a specific required head, the pump with the higher I developed head may be required to deliver greater than the minimum flow in -

1 order to permit the lower head pump to meet the minimum flow requirement.

This generic evaluation indicates that sufficient flow to satisfy CCP minimum, flow requirements to avoid pump degradation may not be ensured for a secondary

. system'high energy.line rupture under the conditions descri_ bed above. . . .

Based on the generic evaluation, Westinghouse recommends that operating plants perform a plant specific evaluation to assess this concern. Attachment B provides the Westinghout.e calculational method and a sample calculation which

can be used in this evaluation. Based on Westinghouse generic review, satis-factory results may not be obtained. Should a plant specific concern be identified, the following recommendations have been developed and can be tailored- to specific plant applications for the interim until necessary design -

< modifications can be implemented. The interim modifications consist of system alignment and operating-procedure changes to provide backup to the pressurizer PORVs in ensuring that CCP minimum flow requirements are satisfied. In conjunc-

. tion with the interim modifications, it is recommended that plants, (a) review the pressurizer PORV operations to maximize the availability of these valves i

to' limit challenacs to the pressurizer safety valves, and (b) review the -

maintenance operat. ions and technical specifications for the backup (i.e., third)

, charging pump .to maximize its availability for long-term recovery from a j secondary side' rupture. These recommendations, in ccmbination with the interim L .

Mr. v . .ms i s w ,

. . . NS-TMA-2245 modifications described below, are considered sufficient to address this con-cern in the interim un.til necessary design modifications can be implemented.

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... . . j Interim Modi fica tion. I . . . . ... .. . ..._. .. . .. . . .. . . . . . . ... .. ...

. . . . This interim modif.ication is. preferred and requires that cargponent cooling . . .. . ...

wat2r be supplied to the seal water heat exchanger foTlowing safety injection initiation in order to provide cooling for CCP miniflow.

1 Verify that CCP.miniflow.'eturn r is aligned directly.to the CCP suction , , . . . ,.

l during normal'opbration' w'ith the alternate return path to the volume l control tank isol,ated (lodk closed). ,

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2. Remove the safety injection initiation automatic closure signal from ~

the CCP miniflow isolation valves. . .

3. Modify plant emergency operating procedures to instruct the operator to: ,

a. Close the CCP miniflow isolation valves when the actual RCS -

l pressure drops to..the calculated pressure for manual reactor coolant pump trip. .

b. Reopen the CCP miniflow isolation valves should the wide range .

' RCS pressure subsequently rise to greater than 2000 psig.

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Interim Modification II-This modification is an alternative for plants in which component cooling ,

water is not supplied to .the . seal water heat exchanger following safety .. . l injection initiation. Since miniflow cooling is not provid'ed, this alterna- '

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l iiive directs minif'lo'w to"'th'e Volume control tank to permit the CCP minimum flow requirements to be satisfied with cool uncirculated water. The volume l control tank acts as a surge tank to collect miniflow following safety injection initiation with excess flow directed to a holdup tank'via the volume control tank relief valve.

1. Align the CCP miniflow to the volume control tank during normal opera-tion with the miniflow return path direct to the CCP suction isolated (lock closed). Verify that the volume control tank relief valve and discharge line capacity exceeds the miniflow requirements of all CCPs plus the , reactor coolant pump seal return fidw.

2. Same as Interim Modification I, Item 2.

3. Same as Interim Modification I, Item 3. .

4 M

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gg, V. Stello Maff8,1980 ,

N5+TMA-2245 p eJ on tho generic evaluatio'n, Westinghouse has initiated efforts to perform a,

. ,,tional plant specific analyses for non-operating plants and to develop

-[.,,gn nodl(Ications to resolve any identified concerns. The modifications '

. de doigned to safety-related st'andards and will be compatible with

',,ungheuse SI termi. nation cr,itaria and standardized technical specifications.

. .eu n: quire further inforina't' ion, please call ' Ray S ro (412-373-4189) of my ,

. cr. .. . . .

.pp .

Very truly yours.

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- T. H. Anderson, Manager -

Nuclear Safety Department

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AiTACHMENTA OPERATING PLANT 3 .

3-Loop

• 4-Loop Beaver Valley 1 Cook 1 & 2 '

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Farley 1 ,

'S la em 1 & 2 Trojin Surry 1 & 2 ,

North Anna 1 & 2 Zion 1'a 2 .

Sequoyah 1

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NON-OPERATING PLANTS ,

' Beaver Valley 2 Braidwood 1 & 2 Farley 2

• Byron 1 & 2 ,

Shearon Harris 1, 2, 3 & 4 Calloway 1 & 2 Virgil Summer .

Catawba 1 & 2 Comanche Peak &2 Diablo Canyon 1 & 2 Jamesport 1 & 2 Haven Marble Hill 1 & 2 McGuire 1 & 2

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Millstone 3 Seabrook 1 & 2

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Sequoyah 2

- Sterling Vogtle 1 & 2 Watts Bar 1 & 2 Tyrone Wolf Creek

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- MINIMUM CENTRIFUGAL CHARGING PUMP FLOW .

- DURING TWO PUMP PARALLEL SAFETY INJECTION OPERATION In order to ensure that minimum pump flow is maintained during parallel

• safety injection operation of two centrifugal charging pumps (CCPs),

Westinghouse provides below a sample calcuiation utilizing actual plant l

data and determines what actua'l CCP developed head at the miniflow flowrata must be available. - -

t .

Step 1: Individually detennine the developed head of each CCP at the mini-1 - flow flowrate of 60 gpm from field test data. (two pumps for '

l 4-loop plants and three pumps for 3-loop plants)

. Sample: Maximum developed head pump ,

i 2571.4 psid = 5940 ft. 0 60 gpm l

l Minimum developed head pump l

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2554.1 psid = 5900 ft. 0 60 gpm l

. Step 2: Correct the pump head for testing error. Add tne appropriate error in determining the above measured developed head, i.e.,

- instrument error plus reading error, to the maximum developed -

head and subtract this error from the minimum developed head.

Sample: Pressure instrument accuracy of + 0.5 percent x span of measuring instrument of 3000 psig = 15 psi (35ft.ofhead),plus10 psi (23ft.) reading accuracy = 58 ft.

.The resultant CCP developed heads at miniflow which can be supported are a maximum developed head of 5998 ft. for the maximum head pump, and a minimum developed head of 5842 ft. for the minimum head pump.

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e .-,- n g s, -- * - ----,---,--,,,,-e >m--

Step 3: Determine total CCP flow. Construct a pump curve "or the maxi- -

mum head pump that is parallel to the actual "as-built" vendor

, pump curve and passes through the above determined; developed

. head at the miniflow flowrate which is the measured developed ,.

. head plus the determined measurement accuracy. (Seeattach- ,

. .' ment Figure 1.) .

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. Use this head versus flow curve to determine the flow delivered \

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by the maximum head pump (strong pump) at the developed head of the minimum head pump (weak pump) at the miniflow flowrate .

(i.e.,5842ft.asdeterminedinStep1). ,'- " " * ' - , ,,

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. Sample: As illustrated in Figure 1, the delivere'd flow of the ..

strong pump at 5842 ft. is 150 gpcz. Therefore, the total flow from both CCPs which guarantees that the . .. ..

weak CCP will be delivering at least 60 gpm is 210 gpm (150gpm+60gpm). .

Step 4: Determitie Injection Piping hiead Loss. The head loss due to

' friction in the safety' injection /RCP seal injection piping is determined as follows: .

- ' The ah is e' qual to the strong CCP developed head at runout . . . .; . ..',

f flow. This resistance is established during the CCP flow balance testing which limits CCP flow to the runout limit.

The injection piping resistance (k) is equal to the developed ,

head of the strong CCP at its runout flow divided by the (runoutfl'owrate)2 ,

e.g* k = developed head'(runout Q flowrate)2 (550 gpm) = k = 1500 ft. 2 k = 4.96 x 10-3 ft./gpm2

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. 'The resistance of the injection piping (Ahf), at the total CCP flow required to maintain 60 gpm through the weak CCP is: .

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3 ft.29PM.) (210 gpm)2 =.,219 .. ft. -

Ahg = kQ -.2-or Ah.f*.(4.96x10- .

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Step 5: Detennine head loss through the Reactor C'oolant System. ,

'. Conside'r that the r,eactor coolant pumps are operating, therefore, the pressure drop. from th'e CCP cold leg injection nozzles through -

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the reactor vessel'to the pressurizer surge line off the hot leg at full RCS flow are to be included. This pressure drop is , .

approximately 50 psid (116 ft.) for 4-loop plants and 48 psid

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- (111 ft.) kor 3-1o03 plants. This pressure. drop must be overcome , , , , ,

4 by the CCPs in order to d.eliver flow to the' RCS at the hot leg /

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pressur'izii friessure. .

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Step 6: De'tennine the elevational head between the RWST and the pressurizer safety valves.

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e.g. RWST 'el'evation -

- 160 ft.

CCP suction elevation .- 100 ft.

RCS cold leg injection nozzle elevation - 126 ft. . . . . , . .

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187 ft.

PressurWer safety valve elevation -

RWST 'to CCP suction - 60 ft.

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minus CCP suction to RCS -

(-26 ft.)

minus RCS to pressurizer safety valves (61 ft. assuming a full pressurizer) I corrected for density difference -

(-44 ft.)  !

-10 ft. l 1 .

Thus, in this example the CCPs must provide an additional 10 ft.

of elevational head. ,

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.' . ATTACHMENT B

. t ., Calculate the pressurizer safety valve relief pressure. .

e.g. . relief pressure = safety val nominal relief pressure

+ 15 setting tolerance ,

relief pressure = 2485 psig + 25 psis = 2510 psig (5798 ft.)- -

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2etermine the maximum RCS pressurizer pressure at which 60 gpm minimum flow is.. maintained through the weak CCP. .

Maximum RCS pressure = (CCP developed head at total CC.P flowrate) - ,

(injection piping head loss) - (head loss through RCS) - (eleva-tionheadloss) '

Maximum RCS pressure = 5842 ft. - 219 ft. - 116 ft. .10 ft. = l 5437 ft. = 2380 psig Cs: paring this pressure to the pressurizer safety valve relief

rtssure (Step 7) of 2510 psig, it is evident that the 60 gpm flew required for the weak CCP will not be maintained.

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