ML20062J331

Application for Amend to License DPR-35 Proposing Changes to Remove Low Condenser Vacuum Scram in Order to Reduce Spurious Scrams,Unnecessary Plant Transients & Turbine First Stage Pressure Setpoint

ML20062J331
Person / Time
Site:	Pilgrim
Issue date:	10/19/1993
From:	Boulette E BOSTON EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20062J334	List: BECO-93-132, Proposed Tech Specs Removing Low Condenser Vacuum Scram in Order to Reduce Spurious Scrams,Unnecessary Plant Transients & Turbine First Stage Pressure Setpoint ML20062J331
References
BECO-93-132, NUDOCS 9311040013
Download: ML20062J331 (5)

Text

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BOSTON EDISON Pilgrim Nuclear Power Station 10CFR50.90 4 Rocky Hill Road Plymouth, Massachusetts 02360 t

BECo 93 132  :

E. T. Boulette, PhD ' October 19, 1993 >

senior Vee President-Nuclear U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 License DPR-35 Docket 50-293 PROPOSED TECHNICAL SPECIFICATION CHANGE TO THE TURBINE FIRST STAGE PRESSURE BYPASS PARAMETER AND REMOVAL OF THE LOW CONDENSER VACUUM SCRAM Boston Edison Company (BECO) hereby proposes the attached modification to Appendix A of Operating License No. DPR-35 in accordance with 10CFR50.90.

This proposed change removes the Low Condenser Vacuum Scram (LCVS) to reduce the potential of .;purious scrams and unnecessary plant transients. The LCVS -

is physically being removed from Pilgrim.

The second proposed change reduces the turbine first stage pressure setpoint.

at which it is permissible to bypass the Turbine Control Valve fast Closure and the Turbine Stop Valve Closure trip (scram) signals. This charige is made in response to infomation provided by General Electric Nuclear Services Information letter (SIL) No. 423 dated May 31, 1985. The new allowable limit

[ was developed using methodology consistent with Regulatory Guide 1.105.

The Technical Specifications Bases for section 3.1 are revised to. reflect both proposed changes.

The requested changes are described in Attachment A. The revised Technical Specification pages are provided in Attachment B. Attachment C provides the existing pages marked-up to show the proposed changes.

CRwHr _

E. T. Boulette  ;

C monwealth of Massachusetts)

ounty of Plymouth )

Then personally appeared before me, E. T. Boulette, who being duly sworn, did state that he is Senior Vice President - Nuclear of Bnston Edison Company and that he is duly authorized to execute and file the submittal contained herein in the name and on behalf of Boston Edison Company and that the statements in said submittal are true to the best of his knowledge and belief.

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,0 .S. Nuclear Regulatory Commission-Page 2 Attachments; (A) Description of Proposed Change (B) Amended Technical Specification Pages (C) Marked-up Pages from current Technical Specifications 1 signed original and 37 copies cc: Mr. R. Eaton, Project Manager Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation Mail Stop: 14D1 U. S. Nuclear. Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockville, MD 20852 U. S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 e

Senior NRC Resident inspector l Pilgrim Nuclear Power Station .

Mr. Robert M. Hallisey, Director {

Radiation Control Program i

%ssachusetts Department of Public Health  !

South Street j

< v2.ca Plain, MA 02130 l

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Attachment A to BEco Letter No.93-132 Prooosed' Chance Changes are proposed to remove reference to the Low Condenser Vacuum Scram (LCVS) from PNPS Technica1' Specifications (TS), reflecting the physical removal of this i

scram from Pilgrim. The removal will occur in concert with NRC approval of this ~1 proposed change.

j Changes are also prcposed to Note 4 to Table 3.1.1, " Reactor Protection System 1 (SCRAM) Instrumentation Requirement", and associated Bases. Note 4 currently ahe j bypassing the lurbine Control Valve (TCV) Fast Closure scram signal, and the Turbine i Stop Valve (TSV) Closure scram signal when the turbine first-stage pressure is less 'l than 305 pounds per square inch gauge (psig). We propose changing the 305 psig to i 112 psig based on information received from General Electric, our Nuclear Steam l Supply System (NSSS) manufacturer by Service Information Letter-(SIL) No. 423. The i 112 psig value was developed using the methodology provided in Regulatory Guide -

1.105.  !

Reason for Change A review of the LCVS indicates it is an anticipatory scram and not part of the PNPS.  !

design basis used in the accident or transient analysis. It is therefore not  !

required to ensure the safe operation of PNPS. Deleting this anticipatory scram i from Technical Specifications potentially adds to plant availability and safety l because it eliminates the possibility of a spurious scram caused by LCVS. ':

The proposed reduction of the maximum allowed high-pressure turbine section first-stage bowl pressure scram bypass allowable limit from 305 psig to 112 psig ensures-Pilgrim's Reactor Protection System (RPS) maintains the correct thermal margin. The proposed change reduces the likelihood of a challenge to the pressure relief system.

The proposed change also corrects' a nonconservative datum in response to SIL No.

423. The more conservative datum has already been incorporated into Pilgrim's procedures.

Safety Evaluation and Determination of No Sionificant Hazards Considerations The Code of Federal Regulations'(10CFR50.91) requires licensees requesting an amendment to provide an analysis, using the standards in 10CFR50.92, that determines whether a significant hazards consideration exists. The following_ analysis is provided in accordance with 10CFR50.91 and 10CFR50.92 for'the proposed amendment removing the LCVS from Technical' Specifications and for reducing the scram bypass datum for the turbine first stage from'305 psig to 112 psig.

1. The Operation of Pilgrim Station in accordance with the proposed amendment will nnt involve a significant increase in the probability or consequences of an accident previously evaluated.

REMOVAL OF LOW VACUUM SCRAM The LCVS is not required to ensure the safe operation of Pilgrim Station. The LCVS is provided to anticipate the reactor scram associated with the turbine-trip caused by low condenser vacuum, (

Reference:

"PNPS Final Safety Analysis Report," Section 7.2.3.8) and is not relied upon in the plant transient analysis. PNPS FSAR, Section R.2.1.2 explains that an instantaneous loss of vacuum-is the most: severe ~ vacuum transient and is equivalent to a turbine trip -

without bypass. Slow vacuum transients allow for some bypass steam; flow (the 1 of 3 e

bypass shuts at 7 inches of vacuum) and thus results in less severe transients. In addition, the "PNPS Reload Analysis" (NEDE-24011-P-A-4-US, Standard Application for Reactor Fuel) does not take credit for LCVS.

PNPS FSAR, "Section 14.4" includes low vacuum transients adar turbine trip without b; pass. Since this turbine trip scram will remain, and since the LCVS is intended to anticipate the turbine trip scram as well as not being a distinct element of the accident analysis, instrumentation associated with the LCVS will be removed from Pilgrim and the scram will no longer exist. Removal of the LCVS from Technical Specifications and from Pilgrim will not result in a signifiant increase in the probaDiiity or consequences of an accident previously evaluated but will reduce the possibility of spurious scrams.

REVISION OF TURBINE FIRST STAGE PRESSURE SCRAM SETPOINT The scram signal generated by closure of the TSVs or fast closure of the TCVs preserve sufficient thermal margin for pressurization transients at high core thermal powers. At core thermal powers below 45% of rated, the severity of pressurization transients is reduced such that these scram signals are no longer required; the reactor high-pressure and high-flux scram setpoints provide protection for the reactor as described in PNPS FSAR Section 7.2.

These scram signals are bypassed in the interest of improved plant availability when thermal margin considerations permit.

The Pilgrim Reactor Protection System (RPS) uses the high-pressure turbine section first-stage bowl pressure rather than core thermal power to determine when the scram signals generated by closure of the TSVs or fast closure of the TCVs can be bypassed. Turbine bowl pressure is proportional to core thermal power and is also related to the balance-of-plant (BOP) configuration.

Therefore, the maximum bowl pressure above which the scram signals cannot be bypassed must correspond to 45% of rated core thermal power for the most limiting balance-of-plant configuration.

A reduction in the degree of feedwater heating results in a decreased turbine bowl pressure for a particular core thermal power. Hence, the limiting balance-of-plant configuration for this evaluation assumes all feedwater heaters are out-of-service. In addition to the degree of feedwater heating, the bowl pressure is also affected by the amount of turbine bypass flow.

Bypassing flow around the turbine further reduces the bowl pressure for a particular core thermal power and feedwater heater configuration. However, General Electric analysis, "EAS-53-0587, Rev.1", shows the limiting balance-of-plant configuration does not need to consider opened turbine bypass valves, because, with these valves opened, the consequences of design-basis transients are acceptable without scram signals being generated upon closure of the TSV's or f ast closure of the TCV's, even at core thermal powers greater than 45% of rated.

Based on the above considerations and to provide added conservatism to minimize the possibility of lifting the SRV's after a furbine Trip at low power, the maximum turbine first stage bowl pressure permitting scram signal bypass is determined to be 112 psig. Changing the currently allowed maximum of 305 psig to 112 psig brings the specified datum into conformance with Pilgrim's design and, thereby, does not result in a significant increase in the probability or consequences of an accident previously evaluated.

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.The operation of Pilgrim Station in accordance with the proposed amendment will not create the possibility of a new or different kind of accident from any accident previously evaluated.

LCVS is not part of the Pilgrim Station design basis. Its removal from technical specifications does not, therefore, present any new or different challenges to the integrity or responses of systems designed to prevent or mitigate an accident. Hence. the remnval of ICVS from technical specifications and from Pilgrim will not create the possibility of a.new or different kind of accident from any accident previously evaluated because its removal does not degrade existing systems and because its function is enveloped by the turbine trip scram that remains in technical specifications.

The proposed change to the allowable maximum pressure setpoint results from a recalculation of maximum allowable scram bypass pressure that ensures Pilgrim is operated within the boundaries established to prevent or mitigate the effects of certain accident sequences described in the FSAR.

Hence, the propved change supports the existing Pilgrim analysis and does not create the possioility of a new or different kind of accident from any accident previously evaluated.

3. The operation of Pilgrim Station in accordance with the proposed amendment.

will not' involve a significant reduction in a margin of safety.

Removal of LCVS will not increase the probability of occurrence or the consequences of a loss-of-vacuum transient because the low vacuum turbine trip.

scram provides sufficient protection to prevent plant' damage and offsite consequences. The turbine trip is also a more direct variable for reactor protection. Therefore, LCVS is not a distinct element of Pilgrim's accident analysis and its removal does not impact Pilgrim's safety margin. Hence,.

removal of LCVS from technical specifications will not involve a significant reduction in the margin of safety.

The proposed amendment also ma .itains the margin of safety as defined by Pilgrim's safety analysis by changing the existing maximum allowable turbine first stage pressure permitting scram bypass from 305 psig to the more conservative 112 psig. The change is proposed because information supplied by Pilgrim's NSSS supplier required recalculation of this setpoint to support the margin of safety under condi' Lions and considerations discussed in the above item #1, Therefore, the proposed amendment does not involve a significant reduction in the margin of safety.

This proposed change has been reviewed and recommended for approval by the.

Operations Review Committee and reviewed by the Nuclear Safety Review and Audit Committee.

Schedule of Chanae This change will become effective 30 days following BEco's receipt of the Commission's approval.

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