ML20236W228

Forwards Response to Request for Addl Info for Resolution of GL 96-06, Assurance of Equipment Operability & Containment Interity During Design Basis Accident Conditions, Per NRC

ML20236W228
Person / Time
Site:	LaSalle
Issue date:	07/30/1998
From:	Dacimo F COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-96-06, GL-96-6, TAC-M96825, TAC-M96826, NUDOCS 9808050162
Download: ML20236W228 (6)

Text

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Commonw ealth lilimn 1:ompany 1.aSalle Generating Station 2601 North 21st Road i

.~

Wrvilles, 11. 6134 l-9757 Tcl N15-357C61 i

l l

J July 30,1998 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Commonwealth Edison Company (Comed) Response to Nuclear Regulatory Commission Request for Additional Information - LaSalle Station Units 1 and 2 (TAC Nos. M96825 and M96826), dated May 11,1998 LaSalle County Nuclear Power Station, Units 1 and 2 Facility Operating Licenses NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374 Referencee: 1.

NRC Generic Letter 96-06, " ASSURANCE OF EQUIPMENT OPERABILITY AND CONTAINMENT INTEGRITY DURING DESIGN BASIS ACCIDENT CONDITIONS", dated September 18,1996 2.

Licensee Event Report #96-020-00," POTENTIAL WATER HAMMER CONCERNS OF RESIDUAL HEAT REMOVAL SERVICE WATER SYSTEM DIVISION 2 PIPING," dated January 16,1997 3.

J. Hosmer Letter to U. S. NRC, Response to Generic Letter 96-06, " ASSURANCE OF EQUIPMENT OPERABILITY AND CONTAINMENT INTEGRITY DURING DESIGN BASIS ACCIDENT CONDITIONS",

dated January 28,1997 l

g I

4.

NRC letter to O. Kingsley, " REQUEST FOR i

ADDITIONAL INFORMATION - LASALLE STATION, UNITS 1 AND 2 (TAC NOS. M96825 AND M96826)",

.g

.,tiJ dated May 11,1998 Reference 1 (GL 96-06) included a request for licensees to evaluate cooling water systems that serve containment air coolers to assure that they are not l

vulnerable to waterhammer and two phase flow conditions for design basis 9000050162 900730 DR ADOCK 0500 3 A Unicom Company

acciderits. References 2 and 3 included a commitment to review the chilled water system, prior to startup of LaSalle Units 1 and 2, to determine if the system is susceptible to waterhammer or two phase flow. Reference 4 requested additional information from Comed in regards to the GL 96-06 issues.

The attachment to this letter provides the chilled water system waterhammer susceptibility assessment and the response to the request for additional information.

it there are any questions or comments concerning this letter, please refer them to Harold D Pontious, Jr., Regulatory Assurance Manager, at (815) 357-6761, extension 2383.

Res

lly,

()k*

Fred R. Dacimo Site Vice President LaSalle County Station Attachment cc:

C. A. Paperiello, Acting NRC Region 111 Administrator M. P. Huber, NRC Senior Resident inspector - LaSalle D. M. Skay, Project Manager - NRR - LaSalle

]

F. Niziolek, Office of Nuclear Facility Safety - lDNS 1

i

(

f

i ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR RESOLUTION OF GL 96-06 ISSUES AT LASALLE 1 & 2 i

I QUESTION 1 Describe measures that have been taken to assure that plant operators will not use the containment /drywell coolers as an option during accident conditions.

(

RESPONSE TO QUESTION 1

{

LaSalle General Abnoimal Procedure LGA-VP-01," Primary Containment Temperature Reduction," has been revised to remo/e the option to use the chilled water system for providing additional drywell temperature reduction in a post Loss-of-Coolant Accident (LOCA) environment.

QUESTION 2 Implementing measures to assure that waterhammer will not occur, such as prohibiting post-accident operation of the affected system, is l

an acceptable approach for addressing the waterhammer concern.

However, all scenarios must be considered to assure that the vulnerability to waterhammer has been eliminated. Confirm that all I

scenarios have been considered, including those where the affected containment penetrations are not isolated (if this is a possibility), such that the measures that have been established are adequate to prevent

[

the occurrence of waterhammer during (and following) all postulated accident scenarios.

RESPONSE TO QUESTION 2 References 2 and 3 included a commitment (NTS 373-180-96-020.05LER for Unit 1 and NTS 373-180-96-020.06LER for Unit 2) to review the chilled l

water system, prior to startup of LaSalle Units 1 and 2, to determine if the system is susceptible to waterhammer or two phase flow. The review has l

concluded that such susceptibility does not exist in the operational / shutdown modes, but does exist in the LOCA accident mode. Due to the high temperature experienced in the drywell following a LOCA, voids may be created in the isolated lines as the system vents through the relief valves to prevent overpressurization. Similarly, during a Loss-of-Offsite-Power (LOOP) coincident with a LOCA the flow through the system will cease and the water in the lines will expand as it is heated. Due to the potential voiding, opening the containment isolation valves and/or starting the chilled l

water pumps post-LOCA could result in a waterhammer event. Reference 3 j

explains that the containment isolation valves for the chilled water system l

are automatically isolated on a Group 11 isolation (ie, high drywell pressure or low reactor level). In the unlikely event that the Group 11 isolation should i

fail, LGA-01, "RPV Control," requires verifying isolations occurred properly.

1

ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR RESOLUTION OF GL 96-06 ISSUES AT LASALLE 1 & 2 As noted in the response to Question 1, the option of using the chilled water system post-LOCA by allowing the reopening of the containment isolation valves and restarting the chilled water pumps has been eliminated to preclude waterharnmer. On this basis, the response to further questions is not required.

QUESTION 3 i

If a methodology other than that discussed in NUREG/CR-5220,

" Diagnosis of Condensation-Induced Waterhammer," was used in l

evaluating the effects of waterhammer, describe this alternate methodology in detail. Also, explain why this methodology is l

applicable and gives conservative results (typically accomplished through rigorous plant-specific modeling, testing, and analysis).

l Note: This question is only applicable to those event scenarios where the occurrence of waterhammer has not been eliminated (see l

question 2, above).

l l

RESPONSE TO QUESTION 3 I

l Not applicable l

QUESTION 4 i

For both the waterhammer (if appilcable as discs:ssed in the note l

following question 3, above) and the two-phase ilow analyses, provide the following information:

i a.

Identify any computer codes that were used in the waterhammer and two-phase flow analyses and describe the methods used to i

benchmark the codes for the specific loading conditions involved (see Standard Review Plan Section 3.9.1).

l b.

Describe and justify all assumptions and input parameters (including those used in any computer codes) such as l

amplifications due to fluid structure interaction, cushioning, j

speed of sound, force reductions, and mesh sizes, and explain why the values selected give conservative results. Also, provide justification for omitting any effects that may be relevant to the analysis (e.g., fluid structure interaction, flow induced vibration, erosion).

2

ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR l

RESOLUTION OF GL 96-06 ISSUES AT LASALLE 1 & 2 l

c'.

Provide a detailed description of the " worst case" scenarios for l

waterhammer and two-phase flow, taking into consideration the complete range of event possibilities, system configurations, and parameters. For example, all waterhammer types and water i

slug scenarios should be considered, as well as temperatures,

(.

pressures, flow rates, load combinations, and potential component failures. Additional examples include:

the effects of void fraction on flow balance and heat e

transfer; the consequences of steam formation, transport, and e

accumulation; I

cavitation, resonance, and fatigue effects; and e

erosion considerations.

e Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves," helpful in addressing some aspects of the two-phase flow analyses. (Note: it is important for licensees to realize that in addition to heat transfer considerations, two-phase flow also involves structural and system integrity concerns that must be addressed).

I d.

Confirm that the waterhammer and two-phase flow analyses included a complete failure modes and effects analyses (FMEA) for all components (including electrical and pneumatic failures) that could impact performance of the cooling water system and confirm that the FMEA is documented and available for review, or explain why a complete and fully documented FMEA was not performed.

e.

Explain and justify all uses of " engineering judgment".

RESPONSE TO QUESTION 4 Not applicable QUESTION 5 i

Determine the uncertainty in the waterhammer (if applicable as discussed in the note following question 3, above) and two-phase flow analyses, explain how the uncertainty was determined, and how it was accounted for in the analyses to assure conservative results.

3

ATTACM'"A T v

F RESPONSE TO REQUEST FOR W. ONAL INFORMATION FOR RESOLUTION OF GL 96-Ob le8UES AT LASALLE 1 & 2 i

RESPdNSE TO QUESTION 5 Not applicable QUESTION 6 Confirm that the waterhammer (if applicable as discussed in the note following question 3, above) and two-phase flow loading conditions do 1

not exceed any design specifications or recommended service conditions for the piping system and components, including those stated by equipment vendors; and confirm that the system will l

continue to perform its design-basis functions as assumed in the j

safety analysis report for the facility, and that the containment isolation l

valves will remain operable.

RESPONSE TO QUESTION 6 I

Not applicable QUESTION 7 Provide a simplified diagram of the affected system, showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.

RESPONSE TO QUESTION 7 l

l Not applicable QUESTION 8 L

l Describe in detail any modifications that have been made or are l

planned to resolve the waterhammer and two-phase flow issues discussed in GL 96-06.

l l

RESPONSE TO QUESTION 8 Not applicable f

I 4