ML20196H280

TS Proposed Change 214 to License DPR-28,revising & Clarifying Terminology Re Certain RPS Scram Bypass Permissives

ML20196H280
Person / Time
Site:	Vermont Yankee
Issue date:	06/24/1999
From:	Wancyzk R VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20196H285	List: ML20196H280 ML20196H288
References
BVY-99-85, NUDOCS 9907060199
Download: ML20196H280 (10)

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.- s VERMONT YANKEE y NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, Vf 05301-7002 (802) 257 5271 June 24,1999 BVY 99-85 U.S. Nuclear Regulatory Commission ATfN: DocumentControlDesk Washington, D.C. 20555 '

Reference:

(a) Licensee Event Report 98-022, Rev.1, dated February 24,1999

Subject:

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

Technical Specifications Proposed Change No. 214 Turbine Control Valve and Turbine Sten Valve C!eere Scram Bynass Pursuant to 10CFR50.90, Vermor.t Yankee (VY) hereby proposes to amend Facility Operating License, DPR-28, by incorporating the attached proposed change into the VY Technical Specifications. The proposed change revises and clarifies terminology concerning certain reactor protection system (RPS) scram bypass permissives. The specific changes involve the bypassing of the turbine control valve fast

. closure and turbine stop valve closure RPS functions during low power conditions. Due to potentially confusing current Technical Specification terminology, which may have contributed to the condition discussed in Reference (a), VY proposes clarifying the Technical Specifications to preclude potentially nonconservative operation.

Attachment I to this letter contains supporting information and the safety assessment of the proposed change.: Attachment 2 contains the determination of no significant hazards consideration. Attachment 3 provides a marked-up version of the current Technical Specification pages with the changes noted.

Attachment 4 is the retyped Technical Specification pages incorporating the changes. .

1 VY has reviewed the proposed Technical Specification change in accordance with 10CFR50.92 and I

- concludes that the proposed change does not involve a significant hazards consideration. VY has also determined that the proposed change satisfies the criteria for a categorical exclusion in accordance with 10CFR51.22(c)(9) and does not require an environmental review. Therefore, pursuant to 10CFR51.22(b),

no environmental impact statement or environmental assessment needs to be prepared for this change.

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' ' , B'VY 99-85 / Page 2 VERMONT YANKEE NUCLEAR POWER CORPORATION If you have any questions on this transmittal, please contact Mr. Thomas B. Silko at (802) 258-4146.

Sincerely, VERMONT YANKEE NUCLEAR POWER CORPORATION

/viven Robert J. Wan y- v[/

Director of Sa and Regulatory Affairs STATEOF VERMONT ) 4 h NNOg WINDHAM COUNTY , .g;,

NOTAm Then personally appeared before me, Roben J. Wanczyk, who, being duly sworn, did tate ti t he is Director bf Safety and Regulatory Affairs of Vermont Yankee Nuclear Power Corporation, that he i a orf4BulGxe ,te and file the foregoing document in the name and on the behalf of Vermont Yankee Nuct we orati , an that the statements therein are true to the best of his knowledge and belief.

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I A A L .L L Sally A. Sandstrum, Notary Public My Commission Expires February 10,2003 Attachments cc: USNRC Region 1 Administrator USNRC Resident inspector- VYNPS USNRC Project Manager- VYNPS Vermont Department of Public Service l

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VERMONT YANKEE NUCLEAR POWER CORPORATION

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Dgogket No.50-27i BVY 99-85 1

4 Attachment i Vermont Yankee Nuclear Power Station Proposed Technical Specification Change No. 214 Turbine Control Valve and Turbine Stop Valve Closure Scram Bypass Supporting Information and Safety Assessment of Proposed Change I

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BVY 99-85 / Attachment I / Page i VERMONT YANKEE NUCLEAR POWER CORPORATION l'

INTRODUCTION The proposed amendment modifies terminology used in Technical Specifications (TS) Sections 2.1.E,

. 2.1.F,3.1.1 and the related Bases. The intent of these changes is to clarify the basis for the turbine control valve (TCV) fast closure and turbine stop valve (TSV) closure scram bypass permissives. The analytical basis for the bypass setpoint rightly corresponds to a fraction of reactor rated thermal power (RTP) and not other measures of power, for instance, " turbine power." The current use of terminology in the TS relating to " power" may be potentially confusing. RTP is precisely defined in the TS Definitions section

and corresponds to the proper basis for the subject scram bypass permissives.

He proposed changes will improve the TS and enhance plant safety by avoiding unclear or ambiguous terminology, which could potentially lead to noncorservative operation.

Background

The VY nuclear steam supply system supplier notified boiling water reactor operators (via GE SIL 423) of the potential for erroneous instrumentation setpoints controlling the bypass of RPS signals on TCV fast closure and TSV closure. The subject Service Information Letter identified that a nonconservative first stage turbine pressure (FSTP) setpoint had been established at another facility because, "the personnel responsible for defining the instrument setpoint were incorrectly led to believe that the basis was 30% of rated turbine power instead of the correct basis of 30% of rated reactor thermal power." The SIL concluded: "The preferred specification is in percent of rated thermal power and is 30% for most plants.

The alternate specification is a pressure value in psig at the turbine first stage. If the latter specification is chosen, it should correspond to 30% of rated reactor thermal power or lower (or to the appropriate basis for the plant)."

This lack of clarity may have contributed to a similar situation that occurred at VY, as discussed in LEl?98-022, Rev.1, dated February 24,1999. To avoid confusion and the potential for erroneous setpoints with consequent nonconservative operation concerning the bypan of RPS signals, VY is proposing certain changes to the Technical Specifications and its Bases.

Discussion of Analvtical Basis for Scram Bvoass Setooint l l

At power, closure of the TSVs and fast closure of the TCVs result in the loss of a heat sink that produces I reactor pressure and power transients that must be limited immediately. Therefore, a reactor scram is i initiated at the start of TSV closure and TCV fast closure in anticipation of the transients that could result l from the valves' closure. For these events the reactor scram provides protection of the fuel and (in  !

combination with the, safety and relief valves) pressure vessel overpressure protection.

To preclude spurious shutdowns and improve plant availability, the TCV fast closure and TSV scram signals are automatically bypassed at low power. This automatic bypass is a design basis assumption in the transient analyses for VY. At such low power levels the pressure rise associated with the TSV and TCV closure events is not as rapid or as large as at higher power levels. Since margins to fuel thermal limits and reactor coolant pressure boundary limits are large at low power levels, the TCV fast closure or i TSV closure scrams are unnecessary. The diverse high neutron flux or high vessel pressure scrams are adequate to terminate the transients at low power levels. The scram bypass power level is currently limited by the transient analysis to operation at or below 32.2% RTP. This is the reactor power level at .

which sufficient fuel thermal margin is available to allow bypass of the TSV and TCV based trips and '

! place reliance on the neutron flux or high pressure scums to terminate over-pressure events.

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( BVY 99-85 / Attachment 1/ Page 2

, The turbine control ' alve v fast closure and turbine stop valve closure scram bypass is controlled by four (4) pressure switches (two per trip system), designated PS 5-14A through D, which sense turbine first stage pressure. These switches have a setpoint, which is slightly lower than the analytical limit, that automatically removes the scram bypass when the turbine first stage pressure exceeds a preset value corresponding to 530% of reactor RTP. The lower operational limit provides additional consenatism by maintaining the TSP'and TCV trips functional to a lower power than required by the analysis. The analysis supponing FSTP bypass setpoint contains conservative inputs and suitable allowances for

' instrument drift and uncenainties.

Discussion of Claanaes Because ofinconsistencies in terminology and lack of clarity of certain terms mlated to the bypaa feature for TSV and TCV closure scrams, changes are being proposed to clarify certain Technical Speci cations and Bases. These changes are meant to preclude an erroneous scram bypass.

Main turbine first stage pressure is used to automatically control the RPS bypass of TCV fast closure and TSV closure scram signals. The FSTP at which the RPS bypass is permitted corresponds to $30% of reactor RTP. This setpoint is conservative relative to the analytical limit of 32.2% of RTP.

" Rated thermal power" is defined in Section 1.0 of the Vermont Yankee Technical Specifications as "a steady state power level of 1593 thermal megawatts." Use of this term and the associated definition provide clarity and specificity such that erroneous application of the scram bypass can be avoided.

Soccific Channes Change #1:

On page 10 of the current Technical Specifications, in Section 2.1.E, insert the phrase,"when operating at

. greater than 30% of Rated Thermal Power" such that the revised Specification now reads: " Turbine stop valve scram shall, when operating at greater than 30% of Rated Thermal Power, be less than or equal to 10% valve closure from full open." This change adds clarity to this trip function, since it may be l' bypassed at low power, but is required to be operable when operating at greater than 30% of rated thermal power. Since the term, " rated thermal power" is already defined in the Definitions section of the Technical Specifications, the applicability of this trip function is now unambiguous.

Change #2:

On page 10 of the current Technical Specifications, in Section 2.1.F. change the phrase, ".. 30% of full power" to ".'. 30% of Rated Thermal Power." While technically not incorrect, the current Specification is l being changed to make it clear that the relevant " power" is reactor thermal power (and not, for example, l- turbine power). Since the term, " rated thermal power" is already defined in the Definitions section of the p Technical Specifications,'the applicability of this trip function is now unambiguous. Since the actual L scram signal bypass is controlled by sensing turbine first stage pressure, it could have been erroneously concluded that the bypass is based on turbine power.

Change #3:

On page 17 of the current Technical Specifications, replace the last sentence of Bases 2.1.E from, "This scram is bypassed when turbine steam flow is below 30% of rated, as measured by turbine first stage pressum." to "This scram' signal may be bypassed at 5 30% of reactor Rated Thermal Power." The analytical basis for the scram bypass setting is reactor thermal power. 30% of turbine power might occur 1

B'VY 99-85 / Attachment I / PJge 3

. VERMONT YANKEE NUCLEAR POWER CORPORATION l

-at reactor power levels greater than 35% of reactor rated thermal power, which exceeds the analytical basis. Herefore it could be nonconservative to operate with this signal bypassed at 30% turbine power.

Change #4:

Also, on page 17 of the current Technical Specifications, add an identical concluding sentence at the end

' of Bases 2.1.F as was done in Change #3 above. The sentence is: "This scram signal may be bypassed at 5 30% of reactor Rated Thermal Power." The basis for this statement is the same as Change #3 above.

The scram functions of TCV fast closure and TSV closure must be enabled when reactor thermal power exceeds 30% of rated thermal power.

Change #5: .

On page 24 of the current Technical Specifications, replace Note 10 of Table 3.1.1 from, "A turbine stop valve closure and generator load rejection bypass is permitted when the first stage turbine pressure is less than 30% of normal (220 psia)" to now state," Turbine stop valve closure and turbine control valve fast

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closure scram signals may be bypassed at 5 30% of reactor Rated Thermal Power." In this context, the term," generator load rejection," is synonymous with turbine control valve fast closure.

This change more correctly states the basis for the scram signal bypass. Gince the analytical basis for the bypass is related to reactor thermal power, the proposed change precisely states this basis. To interpret this bypass as 30% turbine power could be nonconservative. Additionally, other factors could cause turbine first stage pressure to be less than normal. Such other factors include (1) feedwater heater out of service; or (2) turbine bypass valves open. Under such conditions, it is still necessary to maintain the scram functions active above 30% of reactor RTP. Although the scram bypass is automatically controlled by sensing FSTP, it is preferable to express this restriction in terms of reactor rated thermal power rather than FSTP. This is because FSTP may be non-conservatively affected by operational variances, even though the FSTP setpoint is based on RTP.

The parenthetical, single value "(220 psia)" has been deleted. It is unnecessary to retain a value for the FSTP setpoint in Technical Specifications since it is a derivative of the value of reactor rated thermal power used in the transient analyses.

Change #6:

On page 30 of current Technical Specifications, in Bases Section 3.1, insert the following as the new, third paragraph:

Turbine stop valve (TSV) closure and turbin c< trol valve (TCV) fast closure scram signals may be bypassedat S 30% ofreactor Rated Tin w Power since, at low thermalpower levels, the

. margins tofuel thermal-hydraulic limits andreactorprimary coolant boundarypressure limits are large and an immediate scram is not necessary. This bypassfunction is normally  !

accomplished automatically bypressure switches sensing turbinefirst stage pressure. The l turbinefirst stagepressure setpoint controlling the bypass ofthe scram signals on TCVfast j

. closure and TSVclosure is derivedfrom analysis ofreactorpressurization transients. Certam ,

operationalfactors, such as twhine bypass valves open, can influence the relationship between l turbinefirst stagepressure andreactor Rated Thermal Power. However, above 30% ofreactor Rated Thermal Power, these scramfunctions must be enabled. l

VERMONT YANKEE NUCLEAR POWER CORPORATION BVY 99-85 / Attachment I / Page 4

. This new paragraph provides the basis for the allowable bypass of scram signals. It also explains the source of the bypass signal and provides caution regarding operaticcal events which could potentially lead to nonconservative operation if the bypass is not removed above 3U3 of reactor rated thermal power.

The change more clearly states the intent that the TSV closure and TCV fast closure scram functions be enabled when reactor thermal power exceeds 30% of RTP. This assures that the RPS bypass that is effectuated by the measure of turbine first stage pressure properly corresponds to the analytical basis of RTP and is not permitted outside prescribed limits.

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VERMONT YANKEE NUCLEAR POWER CORPORATION

. . i Docket No. 50-271 BVY 99-85 l

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.. Attachment 2 i Vermont Yankee Nuclear Power Station l

Proposed Technical Specification Change No. 214 j Turbine Control Valve and Turbine Stop Valve Closure Seram Bypass Determination ofNo Significant Hazards Consideration i

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VERMONT YANKEE Nuct: AR POWER CORPORATION BVY 99-85 / Attachment 2 / PJge 1

. Pursuant to 10CFR50.92, VY has reviewed the proposed change and concludes that the change does not involve a significant hazards consideration since the proposed change satisfies the criteria in 10CFR$s t 2(c).

1. The operation of Vermont Yankee Nuclear Power Station in accordance with the proposed l amendment will not involve a significant increase in the probability or conseauences of an accident oreviousiv evaluated.

l l The proposed change clarifies the basis for the reactor protection system bypass of the turbine stop valve l closure and turbine control valve fast closure scram signnis. Consideration of the bypass function itself only applies to certain pressurization transients and not accident analyses.

The change properly states the basis for the scram bypass and relates it to reactor thermal power and

_ precludes potential misinterpretation of the basis for the bypass setpoint. Turbine power lags reactor l power over the range of concern. Therefore, changing terminology related to " power" to mean " reactor power"instead of" turbine power"is conservative. Accordingly, this change can not be less restrictive.

The low power (TSV closure and TCV fast closure) scram signal bypass does not initiate or mitigate any accident considered in the Updated Final Safety Analysis Report. This function is enabled at higher power to mitigate the effects of the pressurization transient which results from ~1SV closure or TCV fast closure. This change will not alter assumptions relative to the initiation or miti;;ation of any accident event.

This change will not involve a significant increase in the probability or consequences of an accident previously evaluated since there is no physical alteration of the plant configuration or relaxation of setpoints or operating parameters.

! 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 oreviously evaluated.

The reactor protection system bypass of the turbine stop valve closure and turbine control valve fast closure scram signals is not conridered an initiator of any accident. This change to clarify the basis for applicability of the bypass does r at create any new or different kind of accident since it does not involve any change in the physical con'<iguration of the plant, nor relaxation of setpoints or operating parameters. ,

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VY has determined that the proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated because the change merely adds a more restrictive  ;

interpretation to current terminology.  !

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3. The operation of Vermont Yankee Nuclear Power Station in accordance with the nroposed amendment will not involve a significant reduction in a margin of safety.

The change involves reducing the potential for misinterpreting the basis for the reactor protection system bypass of the turbine stop valve closure and turbine control valve fast closure scram signals and consequent potential for nonconservative operation of the plant. As a result, the potential for operation of )

the plant in an unsafe condition is reduced, thereby maintaining the margin of safety.

VY. has determined that the proposed change does not involve a significant reduction in a margin of safety since operation of the plant consistent with analytical bases of operation is further assured.

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I- Conclusion .

On the basis of the above, VY has determined that operation of the facility in accordance with the

l. . proposed change does not involve a significant hazards consideration as defined in 10CFR50.92(c), in that it: (1) does not involve a significant increase in the probability or consequences of an accident previously evaluated; (2) does not create the possibility of a new or different kind of accident from any accident previously evaluated; and (3) does not involve a significant reduction in a margin of safety.

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