ML20079Q642

Application to Amend License DPR-28,revising Tech Specs to Reflect Change in Main Steam Line Low Pressure Isolation Setpoint While in Run Mode,From 850 to 800 Psig Per NUREG-0737,Item II.K.3.16

ML20079Q642
Person / Time
Site:	Vermont Yankee
Issue date:	01/23/1984
From:	Heider L VERMONT YANKEE NUCLEAR POWER CORP.
To:	Eisenhut D Office of Nuclear Reactor Regulation
Shared Package
ML20079Q644	List: ML20079Q642 ML20079Q650 ML20079Q659
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.16, TASK-TM FVY-84-5, NUDOCS 8402010282
Download: ML20079Q642 (5)

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b VERMONT YANKEE NUCLEAR POWER CORPORATION Proposed Change No. Ils

. ) RD 5, Box 169, Ferry Road, Brattleboro, VT 05301 ,,,ty yo.

y ENGINEERING OFFICE 1671 WORCESTER ROAD FRAMINGHAM. MASSACHUSETTS 01701

. TELEPHONE 617-612-8100 2.C.15.1 January 23, 1984 FVY 84-5 United States Nuclear Regulatory Commission Washington, DC 20555 ,

Attention: Office of Nuclear 'ReSctor Regulation Mr. Darrell G. Eisenhut, Director Division of Licensing Ref erences: (a) License No. DPR-28 (Docket No. 50-271)

(b) General Electric Company, Safety Evaluation of MSIV Low Turbine Inlet Pressure Isolation Setpoint Change for Vermont Yankee Nuclear Power Station, NEDO-22243, Revision 1, dated May, 1983 (c) Letter, VYNPC to USNRC, FVY 81-80, dated May 15, 1981 Subject : Proposed Technical Specification Change to the Main Steam Line Low Pressure Isolation Setpoint

Dear Sir:

Pursuant to Section 50.59 of the Commission's Rules and Regulations, Vermont Yankee hereby proposes the following changes to Appendix A of the Operating License.

PROPOSED CHANGE The change includes revisions to Pages 7,15, 41, and 64 to reflect a change in the main steam line low pressure isolation setpoint when the reactor is in the run mode, from 850 to 800 psig. The change also revises Pages 3, 14a, and 15a to reflect a change in the minimum pressure required for operation in the run mode, froni 850 to 800 psig.

REASON FOR CHANGE As part of the Primary Containment and Reactor Vessel Isolation Control System, Vermont Yankee is equipped with a low pressure isolation function.

Currently, when the main steam line pressure drops below 850 psi while the gl )

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! United States Nuclear Regulatory Commission January 23, 1984 Attention: Mr. Darrell G. Eisenhut Page 2 reactor is in the run mode, Group 1 isolation valves are tripped closed.

Decreasing the low pressure isolation setpoint from 850 psig to 800 psig will L reduce the probabil.ity of an inadvertent reactor isolation and scram due to spurious steam line pressure transients. In addition, this change reduces the probability of challenges to the Primary Containment Isolation System and subsequent challenges to safety-relief valves which may occur as a result of ,

anticipated operational transients. This is consistent with our proposed resolution of NUREG-0737, Item II.K.3.16. " Reduction in the Challenges and Failures of Relief Valves", as discussed in Reference (c).

'In the current Vermont Yankee Technical Specifications, the minimum

-pressure for operation in the run mode and the MSIV low pressure isolation l setpoint are the same. This prevents operation in the run mode below the run mode minimum pressure, since an automatic isolation and subsequent scram will j occur when the. MSIV low pressure isolation setpoint is reached. This automatic enforcement of the pressure requirement for the run mode is desirable both f rom a plant operations and human factor viewpoint. Therefore, the run mode minimum pressure is reduced to 800 psig to. preserve the current relationship between run mode and MSIV isolation setpoint minimum pressures.

Changing the run mode minimum pressure from 850 psig to 800 psig has no adverse effects on plant safcty.

BASIS FOR CHANGE Reference (b) presents the results of an analysis performed to justify i reducing the low pressure isolation setpoint. ,

. As stated on Pages 15 and 64 of the Vermont Yankee Technical Specifications, the purpose of the main steam line low pressure isolation is to prevent excessive vessel depressurization and cooldown in the event of a

, pressure regulator malfunction. The following statement on Page 64 of the Technical Specifications has been removed as part of the proposed change:

"With the trip set at 850 psig, inventory loss is limited so that fuel is not uncovered and peak clad temperatures are much less than 12950F; thus, there is no release of fission products other than those in the reactor water."

This statement implies that the low pressure isolation setpoint is required to satisfy the safety design bases of the Primary Containment and Reector Vessel Isolation Control System for a main steam line break accident.

However, Section 7.3.4.7 of the Vermont Yankee FSAR states that the low pressure isolation is not required to satisfy any of the safety design bases

of this system. As stated in Section 14.6.5.1.1 of the FSAR, the automatic L isolation signal is assumed to be generated on high differential pressure.

across the main steam line flow restrictors (i.e., high main steam line flow) l

(- and not on low main steam line pressure, for the design basis main steam line

break accident.

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United States Nuclear Regulatory Commission January 23, 1984 Attention: Mr. Darrell G. Eisenhut Page 3

. SAFETY' CONSIDERATIONS:

In order to; determine the safety implications of reducing the low pressure isolation setpoint, an analysis was performed [ Reference (b)] to

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simulate the p1 ant response to a Pressure Regulator Failure (open) Transient assuming a 750 psig setpoint. The assumed 750 psig setpoint conservatively bounds the proposed 800 psig setpoint. The calculated maximum change in the

!_ vessel steam done saturation temperature was used to calculate a vessel component peak thermal stress and fatigue usage factor. Reference (b) concludes that lowering the low pressure isolation setpoint from 850 psig to

.750 psig will have a negligible effect on the reactor vessel's lifetime fatigue usage.

The impact on radiological releases has also been considered. . For the

' design basis main steam line break outside containment, the calculated radiological release will not change since the MSIV isolation is assumed to-occur on high steam line flow rate, not low main steam line pressure. Breaks that are too small to be detected by the high flow sensors are. assumed to be detected either by temperatur asors in the steam tunnel or area radiation monitors in'the Turbine Building. Thus, the calculated radiological releases

-wil1~not be affected by. reducing the low pressure isolation setpoint.

Decreasing the setpoint also does .not affect MCPR operating limits. The results for a Pressure Regulator Failure Transient using 750 psig and 850 psig setpoints are identical up until the time at which'the 850 psig setpoint is reached. LBy that time the reactor has scrammed and the power is so low that any subsequent differences between the two cases will not affect the calculated MCPR limit.

The proposed 800 psig low pressure isolation setpoint and run mode minimum pressure are higher than the 800 psia (785 psig) upper limit for application of the 25% of.rnted thermal power safety limit (Technical

. Specification 1.1.B) . Thus, the revised setpoint still offers scram protection such that high power / low pressure operation cannot occur. With the proposed setpoint, a reactor isolation and subsequent scram will occur when

, main steam line. pressure drops below 800 psig, and will prevent violation of the -25% of rated thermal power safety limit.

'The present analysis [ Reference (b)] is considered applicable to future fuel cycles since the Pressure Regulator Failure (open) Transient is not an I MCPR limiting transient, and since the reactor response to this event is insensitive to the cycle-dependent core nuclear characteristics.

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m United States Nuclear Regulatory Commission January 23, 1984 Attention: Mr. Darrell G.. Eisenhut Page 4 4

,An evaluation of this . change has been made, and it has been concluded that the change does not involve an unreviewed safety question as defined in 10CFR50.29(a)(2). The probability of accidents previously evaluated is not increased, 'the possibility of a different type of accident is not created, nor are the margins of safety as defined in the.Sasis of the Technical Specifications .raduc' ed by. this proposed change.

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'.This. change has been reviewed by the' Vermont Yankee Nuclear Safety Audit and ~ Review Committee.

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SIGNIFICANT HAZARDS. CONSIDERATION

.The Commission'has provided guidance concerning the application of standards for determining.whether a significant hazards consideration exists by providing certain examples (48FR14870). One of these examples (vi) of actions whier involve no significant hazards consideration is a change which either may result in some increase in the probability or consequences of a previously analyzed -accident, or may in some way reduce a margin of safety, but where the results of the change are clearly within all acceptable criteria with respect to- the system design or component specified in the Standard

.' Review Plan.

As discussed above, the main steam line low pressure isolation setpoint trip function is provided primarily to provide protection against a pressure a, regulator malfunctio'n which could cause the control and/or bypass valves to 1

open, resulting in s~ rapid depressurization and cooldown of the reactor vessel. The 800 psig trip ~setpoint limits the depressurization such that no excessive vessel thermal stress occurs as a result of a pressure regulator 2

, malfunction. This cetpoint was selected far enough below normal main steam line pressures 'to avoid spurious primary containment isolations consistent with our proposed resolution to NUREG-0737, Item.II.K.3.16, Reduction in the Challenges and Failures of Relief Valves.

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For these reasons, we have concluded that although this change lowers the

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' main steam line low pressure isolation setpoint, the new setpoint is clearly within all acceptable criteria with respect to the intended trip function.

Thus, this change has been deemed not to involve a significant hazards consideration as defined in 10CFR50.92(c)..

t FEE DETERMINATION g 'This proposed change ' requires an approval that involves a single safety issue and is deemed not to involve a significant hazards consideration. For these reasons, Vermont Yankee Nuclear Power Corporation proposes this change as a Class III' Amendment. A payment of $4,000 is enclosed.

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United States Nuclear Regulatory Commission January 23., 1984 Attention: Mr. Darrell G. Eisenhut ~ Page 5 SCHEDULE OF CHANGE i

This change to Vermont Yankee Technical Specification will be implemented as soon as practical following receipt of your approval.

We trust that the information provided is sufficient to allow for your review and for the subsequent issuance of a license amendment. Howeve r, should you have any questions, please contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION Ydu L. H. Heider Vice President LHH/cs COMMONWEALTH OF MASSACHUSETTS)

)ss MIDDLESEX CX)UNTY )

Then personally appeared before me, L. H. Heider, who, being duly sworn, did state that he is a Vice President of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to execute 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 the best of his knowledge and belief.

J(/B. Sinclair Notary Public '

My Commission Expires June 1, 1984

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