ML20078P859

Forwards Revised Position on 15 Closure Requirement for Primary Containment Vent & Purge Isolation Valves & Justification for Interim Operation,In Response to NRC

ML20078P859
Person / Time
Site:	LaSalle
Issue date:	11/07/1983
From:	Schroeder C COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
7562N, NUDOCS 8311090197
Download: ML20078P859 (4)

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'N Commonwealth Edison 4 ) oni First Natiorcl Pl za. Chicago. Illinois O ' Addr:ss RIply to: Post Office Box 767 Chicago, filinois 60690 November 7, 1983 Mr. Harold R. Denton, Director Of fice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

LaSalle County Station Units 1 & 2 Primary Containment Vent and Purge Isolation Valve Closure Times NRC Docket Nos. 50-373 and 50-374 References (a): Letter from C.W. Schroeder to H.R.

Denton dated October 6, 1983.

(b): Letter from A. Schwencer to D.L.

Farrar dated October 18, 1983.

Dear Mr. Denton:

In Reference (a), Commonwealth Edison committed to modify or replace the ten Vent and Purge isolation butterfly valves per unit to result in a closure time of 15 seconds or less. We agreed to complete these changes prior to the startup following the respective first refueling outage for each uilit.

In Reference (b), the NRC clarified their position on the acceptable closure time for the purge and vent isolation valves. They now require that these valves close within 15 seconds from the onset of a LOCA. The NRC also requested our justification for the interim operation of both units until the valve modifications are completed. Attached is our response to Reference (b).

To the best of my knowledge and belief the statements contained herein and in the attachment are true and correct. In some respects these statements are not based on my personal knowledge but upon infor-mation furnished by other Commonwealth Edison employees and consultants.

Such information has been reviewed in accordance with Company practice and I believe it to be reliable.

If there are any further questions in this matter, please contact this office.

Very truly yours, 8311090197 831107 PDR ADOCK 05000373 P PDR 9_* u/vlas C. W. Schroeder Nuclear Licensing Administrator 1m cc: NRC Resident Inspector - LSCS T. Novak - NRR

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Attachment CECO's Revised Position on the Primary Containment Vent and Purge Isolation Valves To ensure that we will meet the 15 second closure requirement defined in Mr. A. Schwencer's letter of October 18, 1983, Commonwealth Edison will replace the existing eight 26" and two 8" vent and purge butterfly isolation valves on each unit with valves that can close in 10 seconds or less and do not require AC power to close. We also agree to revise the technical specification for both units, as shown on the attached marked up page, to incorporate this requirement. For Unit 2, this should be incorporated prior to license issue. For Unit 1, this will be included in the major update of Unit 1 Technical Specifications to reflect changes made in Unit 2 Technical Specifications. This will allow a 5 second time delay from the onset of the pipe rupture to when the valves receive the isolation signal. Our analysis and test results indicate that this time delay will only be about one second. The margin provided by requiring valve closure within 10 seconds also precludes the need for routine surveillance of instrument response time in this situa-tion, and therefore no Technial Specification changes to Table 3.3.2-3, are required.

Commonwealth Edison does not plan to modify or replace the other vent and purge isolation valves. Although they require AC power to operate, they can close in 5 seconds or less and are only 2" or 1.5" in size. Including the entire 13 second time delay alowed in the FSAR for the diesel generators to start and energize the bus, these valves will be fully closed within 18 seconds from the onset of the accident. The total blowdown through these valves after 15 seconds is insignificant when realistic source terms are used. These times are also conservative because the test results show that the diesel generators will energize the bus within 11 seconds and that most of these valves close within 4

, seconds. Therefore, modifying or replacing these 2" and 1.5" valves will l not increase safety, i

l Decreasing the valve closure time for the replacement butterfly i valves will not affect our schedule for completing this work. As stated l

in our letter of October 6, 1983, we plan to replace these valves prior to startup following the respective first refueling outage on each unit.

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We believe that operating either unit until the valve modifica-tions are completed will not significantly decrease the level of safety.

These butterfly valves will be open for only a small fraction of time during this interim period, and therefore, the probability of an accident occurring while one of these valves is open is extremely small. We only intend to use these butterfly valves in accordance with Technical

' Specification 3.6.1.8. When used for inerting or de-inerting the primary containment, per Technical Specification requirement 3.6.6.2, this action must be completed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after thermal power exceeds 15% or cannot be started unless thermal power will be reduced below 15% of rated within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. In addition, we will not be routinely inerting the Unit 2 drywell and suppresssion chamber until the startup tests are finished, in accordance with the license exemption and Technical Specification 3/4.10.5. Thus the number of outages that will require these valves to be opened during this period will be minimal.

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TABLE 3.6.3-1 (Continued) g PRIMARY' CONTAINMENT ISOLATION VALVES

?

m MAXIMUM i

ISOLATION TIME e VALVE FUNCTION A.MD NUMBER VALVE GROUP (a) (Seconds) 5

[ Automatic Isolation Valves (Continued)

8. Containment Vent and Purge Valves # 4 o

IVQ026 < 199 /O IVQ027 7 100 / 0 *

• IVQO29 7 100 /o " "

1VQO30 7 IM / O " "

IVQO31 7 190 / O " ~

IVQO32 2 1+ f w IVQO34 7 196 / O "

1 IVQ035 55 m IVQO36 < IM- / 0 , ,

4

• IVQ040 7 100 / O ~"

IVQ042 7 99 /O" 1VQ043 I 90 /O'#

IVQ047 iM S IVQ048 iM f IVQ050 7 43 F IVQ051 5M .f IVQ068 <5

9. RCIC Turbine Exhaust Vacuum Breaker 9 NA Line Valves 1E51-F080 1E51-F086

10. LPCS, HPCS, RCIC, RHR Injection Testable Check Bypass Valves (9) 2 NA 1E21-F333 1E22-F354 1E12-F327A, B, C

, 1E51-F354 1E51-F355 S f[Ond}

Tf ese va/ves SAall have o m axim en allowab/t isola / ten 1/ t 0f 0 '

un tii startup follo wmy the first refuelmy outaje.

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