ML20217C449

Proposed Change 201 to License DPR-28,modifying Util Licensing Basis by Limiting Time Large Purge & Vent May Be Open to 90 H Per Yr

ML20217C449
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	03/20/1998
From:	Reid D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20217C455	List: ML20217C449 ML20217C459
References
BVY-98-43, NUDOCS 9803270028
Download: ML20217C449 (19)

Text

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ERMONT ANKEE j

NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, VT 05301-7002 (802) 257 5271 March 20,1998 BVY 98-43 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555

Subject:

Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)

License Amendment Request, Proposed Change No. 201 Containment Puras and Vent Pursuant _to 10CFR50.90, Vermont Yankee Nuclear Power Corporation (VY) hereby requests to amend Facility Operating License, DPR-28.

This license amendment request proposes to modify VY's licensing basis by limiting the time the large (18") purge and vent valves may be open to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year. Adoption of the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year limitation is in accordance with the guidance of Standard Review Plan Section 6.2.4 " Containment Isolation System" and Branch Technical Position CSB 6-4 " Containment Purging During Normal Operations", and negates the need for performing dose consequence analysis and mechanistic effects analysis associated with a LOCA concurrent with purge and vent operations. Approval of this license amendment will restore VY's ability to purge and vent (inert and de-inert) the primary containment during plant operations to support personnel entry for maintenance and inspection of equipment. In addition, it will allow performance of rated temperature and pressure inspections of the reactor coolant system (RCS) during plant startups which provide additional margin for safe operation of the unit by verifying all RCS boundaries that have been interrupted during the refueling outage have been returned to an operable condition.

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/ of this letter provides supporting information and the safety assessment of the proposed change.. Attachment 2 is the determination of no significant hazards considerations. provides envisioned changes to the Technical Specification Bases to reflect the new licensing basis following approval of this license dY amendment request.

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VY has reviewed the license amendment request in accordance with 10CFR50.92 and

concludes ' that the proposed change does not involve a significant _ hazards consideration.- VY has also reviewed the proposed license amendment against the icriteria of 10CFR51.22 for environmental considerations and concludes that the

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VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nucle r Regul: tory Commission BW 98-43 \\ Page 2 proposed changes will not increase the types and amounts of effluents that may be released offsite since it proposes to reduce the amount of time the purge and vent valves may be open. Thus, W concludes that the proposed changes are eligible for categorical exclusion from the requirements for an environmental impact statement in accordance with 10CFR51.22(c)(9).

The Plant Operations Review Committee and the Nuclear Safety Audit and Review Committee have reviewed the license amendment request and concur with the above determinations. Pursuant to 10 CFR 50.91(b)(1), we have provided a copy of this license amendment request and the associated analysis regarding a no'significant hazards consideration to the appropriate State of Vermont representative. W requests that the NRC issue this license amendment by April 28,1998 in order to support rated temperature and pressure RCS system leakage inspections following completion of our upcomirg refueling outage.

This license amendment will enhance operational safety and efficiency by clarifying the licensing basis with regard to purge and vent operations, and will not jeopardize the public health and safety of the public.

If you have any questions on this transmittal, please contact Mr. Thomas B. Silko at (802) 258-4146.

Sincerely,

- VERMONT YANKEE NUCLEAR CORPORATION

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Donald A. Reid Senior Vice President Operations g, 644,o,n -

,w Nk STATE OF VERMONT

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Then personally appeared before me Donald A. Reid, who, being duly sworn, dd state that he i r

Pe operations of Vermont Yankee Nuclear Power Corporation. that he is duly authorized to execute and file go f

document in the name and on the behalf of Vermont Yankee Nuclear Power Corporation. and that the state rein are ue i

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to the best of his knowledge and belief.

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Sa'ity A. Sand 6trum, Notary Pubic My Commission Expires February 10,1999 Attachments cc:

USNRC Region 1 Administratnr USNRC Resident inspector-WNPS USNRC Project Manager-WNPS Vermont Department of Public Service

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VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 BVY 98-43

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Vermont Yankee Nuclear Power Station License Amendment Request Containment Purge and Vent Supporting information and Safety Assessment of Proposed Change March 1998

VERMONT YANKEE NUCLEAR POWER CORPORATION

U.S. Nuclerr Regulatory Commission BVY 98-43 \\ Attachment 1 \\ Page 1 Vermont Yankee Nuclear Power Station License Amendment Request Containment Purge and Vent Supporting Information and Safety Assessment of Proposed Change INTRODUCTION During a review of industry events, Vermont Yankee (VY) determined that the potential exists during primary containment inerting and deinerting operations at power to overpressurize the Standby Gas Treatment System (SBGT) filter train housings in the unlikely event of a LOCA. While the SBGT system will isolate automatically from the primary containment on a LOCA signal, it was determined that the potential for 6 overpressurization existed. The potential overpressurization could challenge secondary containment in the event of a LOCA concurrent with containment inerting and deinerting activities. Since a LOCA is postulated (while the RCS is pressurized) in the hot shutdown condition, startup and run modes, administrative controls have been implemented to prevent purge and vent evolutions during these periods to ensure the integrity of the SBGT trains. This license amendment proposes to resolve this concern by modifying our current licensing basis, which allows for continuous purge and vent operations, to a 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year limitation.

BACKGROUND In a letter dated November 29,1978', the Staff identified generic concerns of purging r

and venting of containment to all operating reactor licensees and requested our response to these concerns. Of particular concern within this letter was the ability to satisfy design and licensing basis radiological consequences during purge and vent operations. To satisfy this concern, VY had to propose a Technical Specification restriction to the purging and venting of primary containment to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, or, ensure that unlimited purging during power operation was justified.

The extent of the need for purging was not fully anticipated in the original design and licensing of VY. For examplo, the need to maintain an inerted containment was not originally planned. Accordingly,~ the Staff identified that an acceptable resolution to the

. purge and vent questions was different for plants with construction permits issued prior

. to July 1,1975'. The intent of the options for these plants was to (1) limit operation of 3

' Reference USNRC Letter to VYNPC, dated November 29,1978, " Containment Purging During Normal Plant Operation".

8 Per Standard Review Plan Section 6.2A, plants with construction permits issued prior to July 1,1975,

- BTP ltems B.1.c and B.5.a, regarding the size of the purge system used during normal plant operation iand the justification by acceptable dose consequence analysis, may be waived if the appfK: ant r'

VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclerr Regulatory Commission BW 98-43 \\ Attachment 1 \\ Page 2 the pu,rge and vent valves to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year (during hot shutdown condition, startup and run modes), thus negating the need to postulate a LOCA coincident with purge and vent operations, or (2) demonstrate that the radiological consequences of a LOCA while purging are within the 10 CFR 100 guidelines.

W originally adopted the second option, which, following several docketed exchanges resulted in the issuance of Amendment No. 91 to the license in October,1985'. This Amendment found acceptable our evaluation of the radiological consequences of a postulated LOCA during purge and vent operations.

However, similar to analysis performed by other licensees, the mechanistic effects associated with a LOCA concurrent with purge and vent operations were not fully considered (reference LER 97-005'). Accordingly, VY's current belief that the correct resolution to this issue is to limit purge and vent operations to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, thus redefining our licensing basis such that a LOCA is not postulated during this 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> period. This option is consistent with Standard Review Plan (SRP) Section 6.2.4 " Containment isolation System" 5 INERTING and DE-INERTING OPERATION The Atmospheric Control system is used to supply nitrogen (inerting) to the containment or air (de-inerting). The term ' purge' is the process of discharging air or gas from containment in such a manner that replacement air or gas is required to purify containment. The term ' vent' or ' venting' is the process of discharging air or gas from containment in such a manner that replacement air is not provided or required.

During startups, the primary containment atmosphere is required by Technical Specifications to be replaced with nitrogen within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of entering the run mode.

This time frame has been determined to be acceptable by the Staff since the probability of a LOCA occurring during the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following a startup is low enough that this

" window" when primary containment is not inerted is justified. To inert the drywell, AC-8 (18")is opened and nitrogen is supplied by the nitrogen purge supply via VNP-23 (refer to the figure below). During this time, AC-7A (18") is open allowing air to be directed outside via AC-6, to the SBGT, or via AC-7 to the reactor building exhaust duct.

Similarly, to inert the suppression chamber, AC-10 (18") is open and AC-7B (18") is open.

During periods when primary containment integrity is required, one volume (either the drywell or suppression chamber) is inerted at a time.

commits to limit the use of the purge system to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year while the plant is in the hot shutdown condition, startup and run modes of operations.

Reference USNRC letter to the WNPC, dated October 28,1985, NW 85-221.

Reference WNPC letter to USNRC dated September 5,1997, BW 97-113,

• Reportable Occurrence No. LER 97-005, Rev.1'.

While W was licensed prior to the issuance of the SRP, benchmarking current license amendment requests against it is a viable means to demonstrate acceptability.

VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nucleir Regulatory Commission

- BW 98-43 \\ Attachment 1T Page 3

- The Technical Specifications allow for the primary containment atmosphere to be de-inerted within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to shutting down. This time frame has been determined by the Staff to be acceptable since the probability of a LOCA occurring during the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to a shutdown is low enough that this " window" when primary containment is not inerted is justified. De-inerting is accomplished by supplying fresh air via r.C-9 to either AC-8 or AC-10. Similar exhaust paths are provided as for the inerting process. Again, during periods when primary containment integrity is required, one volume (either the drywell or suppression chamber) is de-inerted at one time.

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The process of inerting and de-inerting takes approximately 10 to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to accomplish. It is this small time frame during startups and shutdowns that the potential exists to damage the SBGT system if a LOCA is postulated.

Since an inerted containment prevents personnel access, the containment is inerted as late as possible in plant startup and de-inerted as early as possible during plant shutdown. This allows for necessary inspections beneficial to nuclear safety such as maintenance activities and the inspection of the RCS integrity during plant startups and shutdowns.

Consistent with the allowed time frame for having primary containment de-inerted while at power, the probability of a LOCA occurring during a 10 to 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> period following a startup or prior to a shutdown, is low enough that these " windows" when purge and vent

- operations are aIlowed is justified. The subject license amendment request will modify our licensing basis by adopting a total 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year limitation on the above discussed evolutions. During this 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> period, the modified licensing basis-will

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VERMONT YANKEE NUCLEAR POWER CORPORATION

. U.S. Nucle:r Regul: tory Commission BW 98-43 \\ Attachment 1 \\ Page 4 1

negate, the need for performing dose consequence analysis and mechanistic effects analysis associated with.a LOCA concurrent with the above discussed evolutions.

Similar to the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> window for having primary containment de-inerted, W believes that the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> window, which essentially envelopes the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> window, is justified.

Normal plant operations (other than inerting and de-inerting) will have AC-8 and AC-10 closed and nitrogen will be supplied to the drywell via the 1" nitrogen makeup supply.

The differential pressure maintained between the drywell and torus will allow the nitrogen to " bubble over" into the suppression chamber. A normally open AC-6B (3")

allows for venting. A normally closed AC-6A (3") is periodically opened for performance of.surveillances such as monthly torus to drywell vacuum breaker tests. Procedurally,.

when AC-6A is open, AC-6 and AC-7 are closed to prevent overpressurization of the SBGT system or the reactor building ductwork, should a LOCA occur. For this and-similar analyses performed, a spurious opening of AC-6 or AC-7 (one of the closed containment-isolation valves) is not assumed as a failure simultaneous with a postulated LOCA. Analyses demonstrate for normal plant operation system alignments, including surveillances such as those described above, that SBGT integrity would be maintained if a LOCA was postulated. Therefore, during normal plant operations the 90

. hour clock does not apply. Accordingly, opening of the 18 inch atmospheric control isolation valves AC-7A, AC-78, AC-8, and AC-10 will be limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per calendar year (except for performance of the subject valve stroke time surveillances -

in which case the appropriate corresponding valves are closed to protect equipment should a LOCA occur).

This restriction will apply whenever primary containment integrity is required. Simply stated, the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> clock will apply anytime purge and vent evolutions can not assure the integrity of the SBGT trains or related equipment.

DESCRIPTION OF PROPOSED CHANGE This license amendment request proposes to modify W's licensing basis by limiting the time the large (18") purge and vent valves may be open to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year. The adoption of this 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> limitation option negates the need for performing dose consequence analysis and mechanistic effects analysis associated with a LOCA concurrent with purge and vent operations. This proposed change is in accordance with the guidance of Standard Review Plan (SRP) Section 6.2.4 " Containment isolation System" and Branch Technical Position CSB 6-4 " Containment Purging During Normal Operations".

While this proposed. change does not necessitate a change in W's Technical Specifications,' a license amendment is warranted since the change involves a new methodology for evaluating purge and vent evolutions. SRP 6.2.4 recommends that the commitment to limit the use of the purge and vent valves to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year be incorporated into the Technical Specifications. However, during the development of

.NUREG 1433 improved " Standard Technical Specifications General Electric Plants, BWR/4," Revision 1, it was agreed that the 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> should not be located within TS

VERMONT YANKEE NUCLEAR POWER CORPORATION

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U.S. Nucle:r Regulatory Commission BW 98-43 \\ Attachment 1 \\ Page 5 and in, stead _should be located in a licensee controlled document. Accordingly, W proposes to locate the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> limitation in TS bases sections 3.7.A and 3.8.L.

Since this proposed change will affect the methodology for evaluating purge and vent evolutions, the Final Safety Analysis Report (FSAR) should be revised. Accordingly, L upon approval of this license amendment, W will initiate a FSAR change to document the revised methodology.

SAFETY ASSESSMENT Vermont Yankee (W) determined that the potential exists during primary containment inerting and 'deinerting operations at power to overpressurize the SBGT filter train housings in the unlikely event of a LOCA.

While the SBGT system will isolate automatically from the primary containment on a LOCA signal, it was determined that the potential for overpressurization existed. This license amendment request serves to resolve this issue by limiting operation of the purge and vent valves to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year (during hot shutdown condition, startup and run modes), thus negating the need to postulate a LOCA coincident with purge and vent operations. This proposed solution is consistent with the guidance. of Standard Review Plan (SRP) Section 6.2.4

" Containment isolation System" (revision 2) and Branch Technical Position CSB 6-4

" Containment Purging During Normal Operations"(revision 2).

SRP 6.2.4, section II.n. states "... guidance on the design and use of containment purge systems which may be used during the normal plant operating modes (i.e., startup, power operation, hot standby and hot shutdown) is provided in Branch Technical Position CSB 6-4. For plants... which the Safety Evaluation Report for construction permit application was issued prior to July 1,1975, [W's safety evaluation report for construction was issued July 11, 1967] the methods described in Section B, items B.1.a, b, d, e, g [ sic], f, and g, B.2 through B.4, and B.5.b, c, and d of Branch Technical Position CSB 6-4 should be implemented. For these plants, BTP ltems B.1.c and B.S.a, regarding the size of the purge system used during normal plant operation and l

the justification by acceptable dose consequence analysis, may be waived if the applicant commits to limit the use of the purge system to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year while the plant is in the startup, power, hot standby and hot shutdown modes of operations."

The following is W's position regarding each of the BTP ltems:

B.1. The on-line purge system should be designed in accordance with the following criteria:

VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission BW 98-43 \\ Attachment 1 \\ Page 6

a. Ger,ieral Design Criterion 54' requires that the reliability and performance capabilities of containment isolation valves reflect the importance of safety of isolating the systems penetrating the containment boundary. Therefore, the performance and reliability of the purge system isolation valves should be consistent with the operability assurance program outlined in Branch Technical Position MEB-2, " Pump and Valve Operability Assurance Program." (Also see SRP Section 3.10.) The design basis for the valves and actuators should include the buildup of containment pressure for the LOCA break spectrum, and the supply line and exhaust line flows as a function of time up to and during valve closure.

Response: The purge and vent valves have satisfactorily been demonstrated to close against the buildup of containment pressure in the event of a design basis accident.

7 This is documented in the Staffs Safety Evaluation Report dated May 22,1984 entitled

" Demonstration of Containment Purge and Vent Valve Operability". It is noted that notwithstanding the intent of this license amendment, W will continue to ensure the ability of the purge and vent containment isolation valves to close against the buildup of containment pressure in the event of a design basis accident. W satisfies the intent of this BTP ltem.

b. The number of supply and exhaust lines that may be used should be limited to one supply line and one exhaust line, to improve the reliability of the isolation function as required by General Design Criterion 54, and to facilitate compliance with the requirements of Appendix K to 10 CFR Part 50 regarding the containment pressure used in the evaluation of the emergency core cooling system effectiveness and 10 CFR Part 100 regarding offsite radiological consequences.

Response: As a result of the concern, which this license amendment request will resolve, the purge and vent procedure currently does not allow for the purge and vent valves to be -open when in the hot shutdown condition, startup and run modes.

However, the purge and vent procedure does contain a caution / note (which would apply following approval of this license amendment) which states "To prevent bypassing the torus (suppression pool) during a DBA LOCA, only one 18" supply valve, AC-8 or AC-10, and one 18" vent valve, AC-7A or AC-7B, may be open at a time. The drywell and torus must be purged /inerted separately when containment is required." W satisfies the intent of this BTP ltem.

' References to the general design criteria (GDC) have been retained in the quoting of the SRP and BTP, However, it is noted that the GDC do not apply to Vermont Yankee. Reference SECY-92-223 dated September 18, 1992 which articulates that the staff will not apply the GDC to plant with -

construction permits issued prior to May 21,1971. At the time of promulgation of Appendix A to 10 CFR Part. 50, the_ Commission stressed that the GDC were not new requirements and were promulgated to more clearly articulate the licensing practice in effect at the time. Each plant licensed before the GDC.were formally adopted was evaluated on a plant specific basis, determined to be safe, and licensed by the commission.

F Reference USNRC letter to VYNPC dated May 22,1984, NVY 84-108, " Containment Vent Valve Operability".

VERM '3NT YANKEE NUCLEAR POWER CORPORATION U.S. Nucle:r Regul tory Commusion BW 98-43 \\ Attachment 1 \\ Page 7

c. The size of the lines should not exceed'about eight inches in diameter, unless

' detailed justification for larger line sizes is provided, to improve the reliability and performance capability of the isolation and containment functions as required by General Design Criterion 54, and to facilitate compliance with the requirements of Appendix K to 10 CFR Part 50 regarding the containment pressure used in evaluating the emergency core cooling system effectiveness and 10 CFR Part 100 regarding the offsite radiological consequences.

Response: Per SRP 6.2.4, this does not apply to W.

d. As required by General Design Criterion 54, the containment isolation provisions for the purge system lines should meet the standards appropriate to engineered safety features; i.e.', quality, redundancy, testability and other appropriate criteria, to reflect the importance to safety of isolating these lines. General Design Criterion 56 establishes explicit requirements for isolation barriers in purge system lines.

Response: The purge and vent valves are designed and maintained as safety class 2 and are subject to the periodic-testing requirements of the Inservice Testing and Appendix J programs. Thus, the purge and vent valves meet the standards appropriate for an engineered safety feature for quality, redundancy and testability. W satisfies the intent of this BTP ltem.

e. To improve the reliability of the isolation function, which is addressed in General Design Criterion 54, instrumentation and control systems provided to isolate the purge system lines should be independent and actuated by diverse parameters; e.g.,

containment pressure, safety injection actuation, and containment radiation level.

Furthermore, if energy is required to close the valves, at least two diverse sources or energy shall be provided, either of which can effect the isolation function.

Response:.The purge and vent valves receive an isolation signal on high drywell pressure or low reactor water level. Each of these diverse signals are a one out of two taken twice logic. In addition, these valves also receive an isolation signal on high radiation in _the reactor building ventilation or a high radiation signal on the refuel floor.

' Each trip logic receives trip signals from redundant channels. All relays in the trip logic areide-energize to actuate. The' instrumentation and logic for these isolations are

. safety related.

iThe isolation valves.are air operated and controlled by an energized solenoid. Each valve 'will fail closed on loss' of air or if the solenoid de-energizes. Additionally, these Lyalves have been shown to be able to close against the dynamic effects of a LOCA.

.W satisfies the intent of this BTP ltem.

' VERMONT YANKEE NUCLEAR POWER CORPORATION '

U.S. Nucle:r Regulatory Commhion BW 98-43 \\ Attachment 1 \\ Page 8 z

f. Purge system isolation valve closure times,-including instrumentation delays, should '

not exceed five seconds, to facilitate compliance with 10 CFR Part 100 regarding offsite radiological consequences.

Response:. The purge and vent valves that perform a primary containment iso!ation function have a Technical Specification maximum closure time of 10 seconds.

Consistent with SRP 6.2.4, this time does not include the time to reach actuation signal

- setpoints'or instrument delay times. While this time is greater than that recommended by the BTP, it has been reviewed and determined to be acceptable. This is based upon the following factors:

A valve closure time of 10 seconds is consistent with the assumption documented within the Staffs October,1985' SER for License Amendment No. 91 regarding the radiological consequences of a postulated LOCA during purge and vent operations. (reference response to BTP ltem B.5.a)

This time frame does not impact the emergency core cooling system's (ECCS) effectiveness as a result of a possible reduction in containment backpressure since accident generated containment backpressure is not credited in ECCS performance. (reference response to BTP ltem B.5.c)

The purge and vent valve closure time trend data shows that the actual closure time for all of the valves has routinely been less than four seconds.

The exception is AC-8 which has an average closure time of 4 to 5 seconds (the highest recent result was 5.33 seconds in October 1996). Therefore, reducing the maximum valve closure time allowed by Technical Specifications to 5 seconds would result in marginal, if any, physical improvements to the purge and vent valves.

A 10 second closure time will ensure primary containment isolation, even if a single failure were postulated, prior to any LOCA-induced fuel damage.

Reducing the maximum closure time to 5 seconds would not prevent the subject concern of SBGT integrity in the unlikely event of a LOCA occurring during purge and vent operations.

Accordingly, W believes that the Technical Specification maximum allowed stoke time of 10 seconds is justified and does not warrant change. VY satisfies the intent of this BTP ltem.

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Provisions 'should be made to' ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

• : Reference footnote no. 3.

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VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclair Regulatory Commission BW 98-43 \\ Attachment 1 \\ Page 9' Response: In a letter dated May 21,1981', W informed the Staff of the results of an evaluation which concluded that debris screens were not necessary. In a subsequent SER'",- which referenced.our May 21,1981 letter, the Staff documented that the

operability of the purge and vent valves has satisfactory been demonstrated.

B.2. The purge system should not be relied on for temperature and humidity control within the containment.

Response: Use of the purge and vent valves are not relied on for temperature and humidity control within primary containment. W satisfies the intent of this BTP ltem.

. B.3. Provisions should be made to minimize the need for purging of the containment by providing containment atmosphere cleanup systems within the containment.

' Response: Containment atmospheric cleanup is not an issue at W. Purge and vent operations of primary containment via the 18" lines are only required for inerting and de-inerting activities associated with plant startup and shutdown. W satisfies the intent of this BTP ltem.

B.4. Provisions should be made for testing the availability of the isolation function cnd the leakage rate of the isolation valves during reactor operation.

Response: The purge and vent valves are subject to the periodic testing requirements of the Inservice Testing program. In addition, each primary containment atmospheric control (PCAC) system penetration has to have two in-series, redundant, safety class, isolation valves that are leak tested in accordance with the requirements of the appropriate edition of Appendix J as referenced by the Technical Specifications. The following information lists the four PCAC penetrations along with their isolation valves:

Penetration 1 Isolation Valve (s) 2*' isolation Valve (s)

X-25 AC-6A/7A AC-6/7 X-26 AC-8 AC-9/23 X-205 AC-10 AC-9/23 X-218 AC-6B/7B AC-6/7 All of the PCAC butterfly valves are leak tested in the accident direction at P. (44 psig).

- The valves have been leak tested every refueling outage. The frequency of future tests Reference VYNPC letter to USNRC, dated May 21,1981, FVY-81-83, " Additional information on Containment Purge and Vent Valves".

'8 i. Reference footnote no. 7.

-VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclerr Regulatory Commission BW 98 43 \\ Attachment 1 \\ Page 10

.will be,in'accordance with 10CFR50 Appendix J. W satisfies the intent of this BTP ltem.

B.5.

The following analyses should be performed to justify the containment purge system design:

a. - An analysis of t. e radiological consequences of a loss-of-coolant accident. The h

analysis should be done for a spectrum of break sizes, and the instrumentation.and setpoints that will actuate the' purge valves closed should be identified. The source term used in the' radiological calculations should be based on a calculation under the terms of Appendix K to determine the extent of fuel failure and the concomitant release of fission products, and the fission product activity in the primary coolant. A pre-existing i

iodine spike should be considered in determining primary coolant activity. The volume lof containment in which fission products are mixed should be justified, and the fission products from the above sources should be assumed to be released through the open purge valves during the maximum interval required for valve closure. The radiological consequences should be within 10 CFR Part 100 guideline values.

Response: Per SRP 6.2.4, this does not apply to W. However, as documented in the i

Staff's Safety Evaluation Report (SER) of Amendment No. 91 to the !icense in October, 1985", the radiological conseituences of a postulated LOCA during purge and vent operations were found acceptable. As was common for the time, this evaluation did not include a mechanistic effects analysis associated with a LOCA concurrent with purge and vent operations. The SER documented certain assumptions associated with the evaluation of the radiological consequences of a LOCA concurrent with purging and venting. These assumptions included a more restrictive Technical Specification limit on primary coolant dose equivalent iodine, primary coolant mass release via the 18" purge valve assuming choke flow and a purge valve closure time of 10.5 seconds. Following approval of this amendment, W does not anticipate requesting a return to the original (higher) primary coolant dose equivalent iodine limits. W satisfies the intent of this BTP ltem.~

b. An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related equipment; e.g., fans, filters, and ductwork, located

'beyond the purge system isolation valves against loss of function from the environment

_ created by the escaping air and steam.

Response: During normal plant operation, the postulation of a LOCA will not impact structures and safety-related equipment; e.g., fans, filters, and ductwork, located beyond the purge and vent isolation valv_es. During this time frame, which constitutes

approximately 99% of the year, the ability of structures and safety-related equipment to

" Reference footnote no. 3.-

VERMONT YANKEE NUCLEAR POWER CORPORATION

' U.S. Nuclair Regulatory Commission BW 98-43 \\ Attachment 1 \\ Page 11 perform their safety related function will remain unchanged.

During the maximum allowed 90' hour period, the purge and vent valves will remain capable of isolating primary containment. This license amendment proposes to limit total purge and vent operations to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, thus negating the need for a mechanistic effects analysis.

c. - An analysis of the reduction in the containment pressure resulting from the partial loss' of containment atmosphere. during the accident for ECCS backpressure determination.-

Response:.The PCAC valves have a very fast closure time. This time frame will have little impact on containment backpressure. W's current containment analysis and ECCS pump performance analysis do not credit accident generated containment backpressure. If future n'eeds require crediting backpressure, it is not envisioned that the impact of purge and vent operations will be postulated. This is justified due to the small impact that purge and vent operations have on containment backpressure and due to the low probabi!ity of a LOCA concurrent with purge and vent operations. This would ~also be consistent with the licensing basis for which this license amendment intends to modify. W satisfies the intent of this BTP ltem.

d. The maximum allowable leak rate of the purge isolation valves should be specified on a case-by-case basis giving appropriate consideration to valve size, maximum allowable leakage rate for the containment (as defined in Appendix J to 10 CFR Part 50), and where appropriate, the maximum allowable bypass leakage fraction for dual containments.

Response: The purge and vent vcaves are included in the Appendix J program. The valves satisfy the subject requirements of that program. W satisfies the intent of this BTP ltem.

Based upon the above, this license amendment request to modify W's licensing basis by limiting the time the large (18") purge and vent valves may be open to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year is justified. The 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year limitation is in accordance with the guidance of Standard Review Plan Section 6.2.4 " Containment Isolation System" and Branch Technical Position CSB 6-4 " Containment Purging During Normal Operations", and would negate the need for performing dose consequence analysis and mechanistic effects analysis associated with a LOCA concurrent with purge and vent operations.

Approval of this license amendment will restore W's ability to purge and vent (inert and de-inert) the primary containment during plant operations to support personnel entry for

maintenance and inspection of equipment in addition, it will allow' performance of rated temperature and pressure inspections of the RCS during plant startups which provide additional margin for safe. operation of the unit by verifying all RCS boundaries that

- have been interrupted during the refueling outage have been returned to an operable condition.

VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 BVY 98-43 Vermont Yankee Nuclear Power Station License Amendment Request Containment Purge and Vent Determination of No Significant Hazards Consideration 1

March 1998

VERMONT YANKEE NUCLEAR POWER CORPORATION J

U.S. Nucle:r Regulatory Commission BVY 98-43 / Attachment 2 / Page 1 Vermont Yankee Nuclear Power Station License Amendment Request Containment Purge and Vent Determination of No Significant Hazaros Consideration Pursuant to 10CFR50.g2, Vermont Yankee Nuclear Power Corporation (VY) has rev! owed the proposed changes and concludes that the changes do not involve a significant hazards consideration since the proposed changes satisfy the criteria in

' 10CFR50.g2(c).

1.

The anaration of Vermont Yankee Nuclear Power Station in accordance with the proposed amendment. will not involve a sianificant increase in the probability or consecuences of an accident previousiv evaluated.

No physical change is being made to any systems or components that are credited in the safety analysis, therefore there is no change in the probability or consequences of any accident analyzed in the Final Safety Analysis Report.

The proposed change will not affect the ability of the purge and vent valves to isolate primary containment. The ability to isolate primary containment remains unaffected by the proposed amendment.

VY's current licensing basis allows for unlimited purge and vent operations, but thi:: does not ensure the integrity of the SBGT system. The proposed change will assure the integrity and operability of the SBGT system if a design basis accident occurs. This is accomplished by restricting the use of each 18 inch containment vent and purge flow path during any period that primary containment integrity is required.

The restrictions imposed by the license amendment request on tha opening of the purge and vent valves will limit the period of time that a potential off-site release flow path exists. Consequently, the probability that a potential release path exists coincident with a breach of the primary coolant system will be reduced, providing additional assurance that a release of radiotetive gases to the environment will be avoided.

Allowing limited use of the purge and vent valves during periods when primary containment integrity is required reduces the probability of an accident by allowing personnel access to primary containment for the maintercme and inspect'on of equipment.

In addition, it will allow performance o. rated

' temperature and pressure inspections of the reactor coolant system (RCS) during plant startups which provide additional margin for safe operation of the unit by' verifying all RCS boundaries' that have been interrupted during the refueling outage have been retumed to an operable condition, N

g a

.a

. VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nucle:r Regulatary Commission

+

BVY 98-43 / Attachment 2 / Page 2 2.

The operation of Vermont Yankee Nuclear Power Station in accordance with the proposed amendment. will not create the possibility of a new or different kind of accident from any accident previousiv evaluated.

The proposed change does not establish a new mode of operation for the purge and vent valve system, only the extent to which the system may be used. The proposed change imposes additional restrictions on the operations of the containment purge and vent valves. Additional restrictions for operation of these valves does not create the possibility for a new or different kind of accident from any accident previously evaluated.

Additionally, the proposed change does not affect the ability of the containment purge and vent valves to mitigate previously evaluated accidents during the modes they are credited. The purge and vent valves, if open during an accident will maintain the ability to close against the postulated differential pressure.

3.

The operation of Vermont Yankee Nuclear Power Station in accordance with the proposed amendment. will not involve a sianificant reduction in a marain of safety.

Currently, TS allows unlimited use of containment purge and vent isolation valves. The proposed change will assure the integrity and operability of the SBGT system. This is accomplished by restricting the use of each 18 inch containment purge and vent flow path during periods when primary containment integrity is required. The more restrictive requirements reduce the probability of an accident concurrent with purge and vent operations.

Theiefore, based on the above evaluation, VY has concluded that these changes do not involve a significant hazards consideration.

VERMONT YANKEE NUCLEAR ^ POWER CORPOR ATION l'

Docket No. 50-271 BW 98-43 Vermont Yankee Nuclear Power Station License Amendment Request Containment Purge and Vent Envisioned Changes to Technical Specification Bases to Reflect New Licensing Basis Following Approval of the License Amendment Request March 1998

VERMONT YANKEE NUCLEAR POWER CORPORAa' ION U.S. Nucle:r Regulatory Commission BVY 98-43 / Attachment 3 / Page 1 INSERT A The use of the 18" purge and vent flow path isolation valves AC-7A (16-19-7A), AC-78 (16-19-78), AC-C (16-19-8); AC-10 (16-19-10) has been restricted to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.

Normal plant operations (other than inerting and de-inerting) will have AC-8 and AC-10 closed and nitrogen will be supplied to the drywell via the 1" nitrogen makeup supply.

The differential pressure maintained between the drywell and torus will allow the

nitrogen.to " bubble over" into the suppression chamber. A normally open AC-6B (3")

- allows for venting. A normally closed AC-6A (3") is periodically opened for performance of.surveillances such as monthly torus to drywell vacuum breaker tests. Procedurally, when AC-6A is open, AC-6 and AC-7 are closed to prevent overpressurization of the SBGT system or the reactor building ductwork, should a LOCA occur. For this and similar analyses performed, a spurious opening of AC-6 or AC-7 (one of the closed containment isolation' valves) is not assumed as a failure simultaneous with a rAJiated LOCA. Analyses demonstrate for normal plant operation system alignments, indading surveillances such as those described above, that SBGT integrity would be maintained if a LOCA was postulated. Therefore, during normal plant operations the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> clock does not apply. Accordingly, opening of the 18 inch atmospheric control isolation valves AC-7A, AC-7B, AC-8, and AC-10 will be limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per calendar year (except for performance of the subject valve stroke time surveillances -

in which case the appropriate corresponding valves are closed to protect equipment should a LOCA occur).

This restriction will apply whenever primary containment integrity is required. Simply stated, the 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> clock will apply anytime purge and vent evolutions can not assure the integrity of the SBGT trains or related equipment.

la i