ML19257A199

Submits Info Re NRC 791109 Interim Position for Containment Purge & Vent Valve Operation.Normal Online Purging of Containment Not Routine Operation.Isolation for Purge & Vent Sys Provided by Butterfly Valves

ML19257A199
Person / Time
Site:	Vermont Yankee
Issue date:	12/27/1979
From:	Johnson W VERMONT YANKEE NUCLEAR POWER CORP.
To:	Ippolito T Office of Nuclear Reactor Regulation
References
WVY-79-148, NUDOCS 8001020453
Download: ML19257A199 (4)

Text

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VERMONT Y AN KEle NUCLEAR POWER CORPOR ATION SEVENTY SEVEN GROVE STREET RUTLAND, VEIO10NT 05701 *f 9 148 ENGINEERING OFFICE December 27, 1979 TURNPIKE RO AD WESTDORO, M ASSACHUSETTS G1501 TELEPHONE 617-366-90ll United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention: T. A. Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors Refercnces: (a) License No. DPR-28 (?oniet No. 50-271)

(b) USNRC Letter to YAEC dated November 9,1979; Containment Purging and Venting During Normal Operation (c) USNRC Letter to YAEC dated November 29, 1978 (d) USNRC Letter to YAEC dated September 27, 1979

Subject:

Purge and Vent Valve Operability Reference (b) provides the !.LC's " interim position for containment purge and vent valve operation pending resolution of isolation valve operability". As discussed in Reference (b), this interim position was developed following discussions with valve manufacturers, who reported that their valves may not close against the ascending differential pressure and the resulting dynamic loading of a design basis LOCA.

In light of the information contained in Reference (b), and information obtained from the manufacturer of our purge and vent valves, Vermont Yankee submits the following information:

1. Normal on-line purging of the Vermont Yankee containment (drywell) is not a routine operation. Typically, the only time '

on-line purging is conducted is just prior to an extended outage, i.e. refueling, when work is to be done inside the drywell. This controlled purging allows drywell airborne activity levels to be reduced to minimize radiation exposures and improve working conditions.

The necessity for VY to continuously vent is related to the requirement to maintain a differential pressure between the drywell and the suppression chamber. VY has been operating with the torus /drywell differential pressure as a result of an Order issued by the NRC staff on February 13, 1976. It was concluded in that Order that maintaining a differential pressure of >l.7 psi between the drywell and torus provides adequate assurance 1663 139 8001020 453

United States Nuclear Regulatory Commission December 27, 1979 Attention: T. A. Ippolito, Chief Page 2 that containment integrity will not be jeopardized by upward motions resulting from hydrodynamic forces from the most severe loss of coolant accident. (Ref: Mark I Containment Short Term Program) Limiting Conditions for Operation and surveillance requirements for the drywell/ torus differential pressure control.

system were incorporated into the facility Technical Specification by Amendment 50.

The differential pressure control scheme, currently being employed by the plant, requires a positive pressure in the drywell (typically 1.8 to 1.9 psi) and essentially atmospheric pressure in the torus. In order to keep the torus near atmospheric pressure, and thus maintain the required AP, a continuous vent is necessary to compensate for air in-leakage from the drywell. As previously explained to the NRC staff, the air in-leakage is primarily through the Containment Air Monitoring System and the torus vent header drain lines.

2a. Containment isolation for the purge : nd vent system at Vermont

. Yankee. is provided by butterfly valves as illustrated below.

(Sal 6-19-6A, 6B, 7A, 7B, 8, 9, 10, 23 and SB6, 7)

. To Stack VERMOhT YATr2Z FURCE & VENT SYSTEM 33 g f Frem e RB Exhaust M; i C N -

2A O d 16-19-100 RRU-18 16-19-101 1-156-10 3A 4A g 3" IIPCI-13 INSTRmENT 6" r l

]h Fan I ]1 , AIR SB-7 3"4 8" '

SUPPL %

16-19-23 SB-6 16-20-20 .p 1"-AC-17 -

16-20-22B 18"-AC-5 L"-AC-18 g 16-20-22D 16-19-9 16-19-7A 6"-AC-15 I? I 1 15" AC-14A 18"-AC-2 h

16-19-6A 3"-AC-8 16-19-3

~

i 16-20-22A Y 16-19-10 6 r

1 1 20"-AC-13 16-19-7B VACURt RELIEF 013"-AC-4 1663 140 ,-

United States Nuclear RegulaLcry Commission December 27, 1979 Attention: T. A. Ippolito, Chief Page 3 Administrative controls have been implemented to ensure that valves associated with the purge operation remain in the closed position during reactor power operation until we have assurance from the manufacturce that they are capable of closing against the prescribed forces. (SB16-19-7A, 7B, 8, 9, 10, 23 and SB-7)

The Technical Specifications and current venting scheme requires only one valve greater than 3 inches to be maintained in the open position, 8"-SB-6.

An evaluation was performed by the valve manufacturers to determine the maximum allowable opening. The evaluation was based on data generated during recent flow tests and inputs specific to the Vermont Yankee situation, i.e.

containment pressure response and geometry. The results of this evaluation are as follows:

1. Calculations done for calve SB-6 confirm that the valve will close from any disc position in the time required by Technical Specifications.

2. The resulting dynamic loadings from the postulated ascending pressures associated with the LOCA will not damage critical valve parts.

3 Based on test data, the manufacturer has informed us that there is no limited disc opening which would result in a continuous valve closure force from the postulated fluid dynamic. forces of DBA-LOCA.

Taking into account that 1) the torque coefficients used for these calculations have been recently verified by test, 2) the conservatisms in the calculations and 3) the enhancement to safety resulting frca the AP operation, we feel that there is sufficient justification for allowing venting operations, as described above, to continue.

2b. As a result of questione raised in Reference (c), Vermont Yankee reviewed the circuitry associated with the valves listed above and determined that any one manual override, maintenance operation, or test to verify operational availability, will not impair the func'cional ability of the isolation control system to respond correctly to essential monitored variables.

In addition, we examined whether sufficient physical features were provided to facilitate adequate administrative controls of the manual override features, and that the use of each such manual override is adequately annunciated in the plant control room. From this examination, Vermont Yankee Identified a few manual override features in safety actuation signal circuits that do not in all respects meet the requirements identified above. During the 1979 refueling outage additional physical features (key lock switches and annuciation) were installed to provide station operators with these features.

I663 14l

United States Nuclear Regulatory Cor: mission December 27, 1979 Attention: T. A. Ippolito, Chief Page 4 We trust this information adequately addresses your it: mediate concerns.

We plan to continue working with the valve manufacturer as necessary to address the other purge and vent valves and the guidelines for demonstration of operability as required by Reference (d). If you should desire additional information, please contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION

.$ IVX1 W. P,. Johnson Vice President RJW/dep COMMONWEALTil 0F MASSACllUSETTS)

)ss.

COUNTY OF WORCESTER )

Then personally appeared before me, W. P. Johnson, who being duly sworn did state that he is a Vice President of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to exueute and file the foregoing request in the name and on the behalf of Vermont Yankee Nuclear Power Corporation, and that the statements therein are true to che best of his knowledge and belief.

[

Robert 11. Groce Notary Public g

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.E *, My CommissiJn Expires September 14, 1984

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