BECO-LTR-96-094, Discusses power-flow Stability Tech Specs Re Installation of BWROG Enhanced Option 1A

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Discusses power-flow Stability Tech Specs Re Installation of BWROG Enhanced Option 1A
ML20134K427
Person / Time
Site: Pilgrim
Issue date: 11/07/1996
From: Boulette E
BOSTON EDISON CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20134K430 List:
References
BECO-LTR-96-094, BECO-LTR-96-94, NUDOCS 9611190105
Download: ML20134K427 (4)
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. Pdgrim Nuclear Power Staten Rocky Hill Road .

Plymouth, Massachusetts 02360 '

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E. L Mue, MD '

Senior Vice President-Nuclear. November 7' 1996 '

BECo Ltr. #96-094 U.S. Nuclear Regulatory Commission -

Attn: Document Control Desk l

' Washington, D.C. 20555 -  !

Docket No. 50-293 License No. DPR-35 Subiect: Power-Flow Stability Technical Specifications Related to Pilarim's Installation of BWROG Enhanced Option 1A BACKGROUND Boiling water reactor (BWR) cores are susceptible to coupled neutronic/ thermal-hydraulic reactor instabilities in certain portions of the core power / flow operating domain. General Design Criterion  !

(GDC) 12 requires that established fuel thermal limits not be violated.as a result of such instabilities. Compliance with GDC 12 can be achieved by preventing the instabilities. The Boiling -

Water Reactor Owners' Group (BWROG) developed stability long-term solution Enhanced Option

.lA to provide a methodology for prevention of reactor instabilities. - Pilgrim participated in the BWROG Enhanced Option 1A effort and plans to begin imp!ementing it during Refueling Outage (RFO) #11.

The Enhanced Option IA Stability Solution uses hardware modifications to the flow-biased APRM rod-block and neutron flux scram logic cards to enforce the restriction of plant operation in regions susceptible to core thermal-hydraulic instability. The scram function is set down at low reactor flows to exclude entry into an " exclusion region" that includes the high core power, low core flow operating region now restricted by plant procedures. The rod block function is set down to create the " restricted region," a buffer zone between the " exclusion region" and an outer zone known as the " monitored region." An additional LPRM fed monitor provides a waming of decreasing margin

! to stable core operation. l Enhanced-Option 1A also includes " defense-in-depth" features to provide diverse protection, removing reliance on a single system or methodology. These features include the monitored region and the Period Based Detection System.  !

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CONCLUSION CONCERNING PROPOSED STANDARD TECHNICAL SPECIFICATIONS  ;

We have reviewed the BWROG proposed standard technical specifications (STS) for Enhanced 1 Option 1A vis-A-vis Pilgrim's Technical Specifications and have concluded our current technical specifications and administrative controls address this modification with minimal changes being required. We have attached a comparison matrix to this letter and have discussed the basis for our conclusion below.

BASES for CONCLUSION l -e STS PROPOSED 3.2.5 Fraction of Core Boilina Boundarv (FCBB) l The purpose of the LCO is to establish limits on the boiling boundary to ensure that the core will remain stable during normal reactor operations in the restricted region of the power-flow map

, defined in the Core Operating Limits Report (COLR). PNPS design permits normal plant I

evolutions without requiring intentional entry into the restricted region of the power flow map; j therefore, Pilgrim's planned modification does not include implementation of the Fraction of Core

Boiling Boundary (FCBB). In addition, Pilgrim is already proscribed from exceeding the limiting
values for power / flow relationship as specified in the COLR (i.e., operating in the restricted l region) by Technical Specification 3.11.D. This specification, along with supporting Off-Normal ,

l Condition procedures, requires exiting this region by returning to the allowed operating domain as - l l defined in the cycle-specific Power / Flow Operating Map (COLR "igure 3.4 -1).-

COLR Figure 3.4-1 and the Off-Normal Condition procedures will be revised in accordance with NEDO 32339, Supplement 5, as appropriate.

. STS PROPOSED SR 3.2.5.1 - FCBS STS (SR) 3.2.5.1 requires verifying FCBB 51.0 once/24 hours and once within 15 minutes l following an unexpected transient.

l l Since Pilgrim is not implementing FCBB and because we prohibit operation in the restricted region, SR 3.2.5.1 has no application at Pilgrim.

Pilgrim's Technical Specification 4.11.D requires " daily" (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) determination of compliance with power / flow relationships specified in the COLR ensuring that Pilgrim is not inadvertently operating in the restricted region; if operdion is in the restricted region, corrective actions (i.e.,

' exiting the region or shutting down) are imposed. in addition, Pilgrim's Off-Normal Condition procedures for loss of feedwater heating and recirculation system problems require assessing operating conditions by plotting power vs. flow on the power / flow map and taking action as appropriate.

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. STS PROPOSED 3.3.1.1 Surveillance Reauirements l The proposed changes to the surveillance requirements for the "APRM Flow Biased Simulated Thermal Power - High" (Function 2.b of Table 3.3.1.1) would :

l l 1. Replace SR 3.3.1.1.3, for adjusting the channel to conform to a calibrated flow l signal every 7 days, with SR 3.3.1.18 requiring adjusting the flow control trip

! reference card to conform to reactor flow once within 7 days after reaching equilibrium conditions following a refueling outage; and

2. Exempt the digital components of the flow control trip reference cards from the 184 day CHANNEL CALIBRATION requirements.

Current Pilgrim Technical Specification Table 4.1.2 (calibration frequencies) surveillance requirements for the APRM flow bias scram function specifies a calibration of the flow bias signal every 3 months. Note 1 to Table 4.1.2 clarifies this as, " Adjust the flow bias trip reference, as necessary, to conform to a calibrated flow signal." Since Pilgrim's implementation of Enhanced l Option 1 A will modify the existing APRM flow biased circuit cards with digital flow control trip i reference cards, the surveillance requirements will be revised for the new circuitry as part of Pilgrim's adoption of STS in 1998.

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. STS PROPOSED 3.3.1.3 Period Based Detection System (PBDS)

The purpose of the LCO for PBDS is to provide the operator with indication (alarms) that conditions consistent with a significant degradation in the stability performance of the reactor core has occurred while operating in the restricted or monitored region. Pilgrim will operate in the monitored region during normal and transient conditions; however, Pilgrim will only enter the restricted region as a result of unexpected transients. PBDS is defined as a " defense-in-depth" feature in NEDO 32339, and as a " defense-in-depth" feature, we believe PBDS is not within the l purview of Technical Specifications as established by the criteria set down in 10 CFR 50.36. l Pilgrim will incorporate the implementation of PBDS into the FSAR and plant procedures in accordance with the requirements of Enhanced Option 1A.

. STS PROPOSED 3.4.1 Recirculatina Loops Operatina This LCO requires two recirculating loops with matched flows to be operating while in Modes 1 and 2 (Run and Startup) and provides the requirements for single loop operation, if the requirements are not met, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> are allowed to restore applicability. Piigrim's License Condition E prohibits power operation with single recirculation loop operation greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Recirculation system balance and other requirements for two loop operation are contained

in Pilgrim Technical Specifications 3/4.6.E and F. Because single loop operation is limited to only l 24 hrs, the proposed requirements do not apply.

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SUMMARY

l Pilgrim will be installing equipment to address power-flow instabilities. We have reviewed the proposed STS against Pilgrim's Technical Specifications and conclude Pilgrim's Technical Specifications require changes only to the surveillances for the APRM Flow Biased Scram  ;

function and the COLR to address the issues for instability. To further enhance safe operation, the guidance / requirements of NEDO-32339 will be incorporated into the FSAR and procedures, J as appropriate.

l Should you require further information on Pilgrim's implementation of Enhanced Option 1 A, please contact P. M. Kahler at (508) 830-7939. -

E. T. Boulette, PhD

Enclosure:

Technical Specification Comparison Matrix PMK/dmc/optionia cc: Mr. Alan B. Wang, Project Manager Project Directorate I-1 Office of Nuclear Reactor Regulation ,

Mail Stop: 1482 I U. S. Nuclear Regulatory Commission l 1 White Flint North  !

11555 Rockville Pike Rockville, MD 20852 Regional Administrator, Region i U.S. Nuclear Regulatory Commission 475 Allendale Road i King of Prussia, PA 19406 i Senior Resident Inspector Pilgrim Nuclear Power Station l

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