ML20042E088

Forwards Addl Info Re 891011 Tech Spec Change Request 89-09 to Reduce Number of Suppression chamber-to-drywell Vacuum Breakers Required to Be Operable

ML20042E088
Person / Time
Site:	Limerick
Issue date:	04/09/1990
From:	Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20042E089	List: ML20042E088 ML20042E090
References
NUDOCS 9004200071
Download: ML20042E088 (5)

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3 a PHILADELPHIA ELECTRIC COMPANY '

.i NUCLEAR GROUP HEADQUARTERS 955-65 CHESTERBROOK BLVD, WAYNE PA 19087 5691 I ' "I " *""

April 9, 1990 Docket Nos. 50-352 50-353 License Nos. NPF-39 NPP-85 l

U.S. Nuclear Regulatory' Commission '

Attn Document Control Desk Washington, DC 20555

SUBJECT:

Limerick Generating Station, Units 1 and 2 Technical Specifications Change Request No. 89-09,

" Reduction of the Number of Suppression Chamber-to-Drywell Vacuum Breakers Required to be Operable,"

Response to-Request for Additional Information j

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Dear Sir:

i Philadelphia Electric Company (PECo) submitted Technical (

Specifications Change Request (TSCR) No. 89-09 for the Limerick .A Generating Station (LGS), Units 1 and 2, by letter dated October 11, 1989.= This TSCR proposed to reduce the number of reactor containment suppression chamber-to-drywell: vacuum breakers required to be operable. On-December 15,.1989, a conference call was held with-j representatives of the NRC, PECo, and:the LGS Architect-Engineer (Bechtel Corporation) that performed the original and current vacuum breaker analyses. During this conference call, the NRC' requested additional-information. The requests, which were~ confirmed with the NRC,-and our responses are provided in Attachment 1, " Response'to NRC Request for Additional Information on. LGS Inadvertent: Spray Actuation 4

(ISA) Analysis." Attachment 2, " Description of Limerick Inadvertent l Spray Actuation Analysis," prepared by Bechtel Corporation provides the following additional information.

1.0 Description of Inadvertent-Spray-Actuation Analysis 2.0 Discussion of Two and Three Vacuum Breaker Flow Path Study 3.0 Comparison of the Final Safety Analysis Report (FSAR) and the ISA' analysis 4.0 References, Figures 9004200071 900409 a gDR ADOCK 03000352 '

PDC '

U S. Nuclocr Rrgulctory Commicolon' April 9, 1990 Documant Control D3;k Page 2 The information in Attachments 1 and 2 is taken from previously completed analyses which provided the justification for our October 11, 1989 TSCR. The analyses are based on assumptions more limiting than the design basis and therefore represent the most limiting accident-scenario for specifying-the suppression chamber to drywell vacuum breaker requirements. .The analyses show that with a minimum of two vacuum breaker assemblies operating, during the accident scenario, the Limerick Generating Station drywell negative pressure stays below the design negative pressure limits.

Should you require further information, please do not hesitate to contact us.

Sincerely yours,

?

. CW ,1 G. A. Hunger, Jr.

Manager Licensing Section Nuclear Services Department Attachments cc: T. T. Martin, Administrator, Region I, USNRC a T. J. Kenny, USNRC Senior Resident Inspector, LGS T. M. Gerusky, Director, PA. Bureau'of Radiological Protection ]

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RESPONSE TO NRC REOUEST FOR ADDITIONAL INFORMATION ON LGS INADVERTENT SPRAY ACTUATION (ISA)' ANALYSIS Ouestion la: Provide a description of, the vacuum breaker valves based on actual' valve. test data as to-opening times-(inertia) and flow capacity.

Response: In the ISA computer analysis,*the vacuum relief flow was calculated based on steady state theoretical flow equations of compressible critical and non critical flows. To produce results which are conservative in comparison with the test data,' the parameters in the theoretical flow equation were conservatively { chosen in two areas:

. 1) A' conservative valve opening pressure was selected. In the test, there was measurable flow at around 1.0 psi differential.

pressure across the two valves in series. . In .the ISA computer analysis the opening pressure used is 2.81 psid. No flow is .

assumed' to occur until the differential presrura from wetwell' 1 to drywell (1'.e. across the vacuum breaker assembly) is greater -

than 2.81 psi.

2) Similarly, based on review of the-test data, /4 conservative pressure differential. of 4.48 psi for the fully open valves (wetwell to drywell) was selected.

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A lin nr' valve opening j '

characteristic was assumed, which results in,less mass flow -

as a' function of differential pressure than the' test results demonstrate'will flow through.the two valves in series.

The ' inertia of the valve disk was not : considered in .the ' flow  !

calculation. . Neglecting of. the inertia. isijustified since the ISA transient is-fairly slow. The modeling of the vacuum breakers is such that they- open as a function'of differentia 1' pressure only ,

and take about six seconds to open. The. test data shows that, 1

except for the initial 20' opening,- the effect of disk inertia is l insignificant. The delay of valve opening through the~use'of a .

j very conservative opening pressure, and the use of conservative J linear ramp opening, is more than adequate to compensate for any a effect of valve inertia.  !

I For additional details see the attached Description of the LGS.ISA l Analysis Section 1.1.

l Ouestion 1b: At what AP does the valve actually start to open (e.g. ,1.81 psid) . j Response: In the computer analysis, the valves are assumed to begin to open when the differential: pressure across the vacuum breaker assembly 1 (two valves in series) reaches 2.81 psi. Test data indicates that (

measurable flow will actually occur at approximately 1.0 psid. j

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Ouestion Ic: Provide a description of the length of time it takes the valve to i start opening (e.g. 15 to 16 seconds) and how long it takes to j fully open, i i

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Response: .Since the: opening of the valves is.'a function of-differential pressure across the valves,. the length'of time it takes for the valves to . fully, open depends- on the- drywell' and. wetwell depressurization transient.- In-the case of the calculation-for two operating vacuum. breaker assemblies, the valves start to open at.approximately 15 seconds and reach the fully open position:at-approximately 21 seconds into the transient. In the case of the calculation for the three operating vacuum breaker assemblies, the valves never reach'the fully:open= position since the flow of noncondensible gases through. the vacuum breaker assemblies is J

!. sufficient to keep the differential pressure between the wetwell- ,

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-and drywell below that required to fully open the valves.  !

l Because conserystive values for valve opening pressure and fully open differential pressure are used in the calculation, the vacuum breakers will actually open- sooner than is shown in .the calculation, and a less severe drywell - depressurization would' result.- .

-Question Id: Provide a' description of the assumed temperatures in the system, including water sprays.

Response'; At - the initiation of the ISA ' event, ' the following temperature .

parameters are used:

drywell: 258.33-F 0 j' wetwell: 50.00 F '!

service-water:- 40.00.F spray: 47.60 F ,

The d:ywell tempsrature is the saturation temperature corresponding to a drywell pressure 'of 34.436 psia. The;drywell pressure-is- d equal to the sum of the wetwell noncondensibles and; vapor space pressures (which include the noncondensibles carried from - the-  ;

drywell), plus the hydrostatic submergence: pressure of-the 12'.25 '

foot depth of suppression pool water outside the downcomer. l i

- The initial spray water temperature of 47 6 F is calculated based .j '

l on a RHR service water temperature of .40'F, RHR suction (suppression pool) water temperature of 50 F and an RHR heat exchanger effectiveness of 0.249. For additional . details see the attached Description of the LGS ISA Analysis, Sections 1.2'and 1.3.

Question 2: What are the~ basis assumptions used in the transient analysis-for two vacuum breaker flow paths?

,i Response: The ISA computer model itself includes . conservative. basis assumptions which are described in the attached Description of the

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l Limerick ISA Analysis. -In addition, conservative ' assumptions were i .{

made regarding initial conditions and other parameters in order to maximize the negative pressure in. the- drywell, These assumptions are described below:

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'1. All drywell noncendensibles are assumed to be swept from'the drywell- prior -to- the -ISA event. A small quantity of

.noncondensibles is discharged from the primary containment

_ prior to purge valve closure, which_ conservatively minimizes?

the quantity of the noncondensibles available to return to' the drywell. The remainder = of- the noncondensibles are carried to -

the wetwell by steam' flow.

2. ' The' vetwell_ traporature , -including suppression pool: water, is t assumed to be 50 F.

'3. The RHR service water temperature is assumed to be 40 F. This ~

minimum service water temperature will cool the RHR spray flow '

even further and result. in very conservative drywell depressurization.

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4. One RHR loop-spray flow rate of 9500 gpm is assumed.

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5. Conservative vacuum breaker flow characteristics 'are used,. as1 described in the. response to_ Question:la.

These assumptions are discussed in more detail- in the attached Description of the LCS ISA Analysis.

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