ML22035A330

Requests for Confirmation of Information for Exemption to Delete Diverse Auxiliary Feedwater Actuation System Based on Risk-Informed Process for Evaluations

ML22035A330
Person / Time
Site:	Palo Verde
Issue date:	02/10/2022
From:	Siva Lingam Plant Licensing Branch IV
To:	Lacal M Arizona Public Service Co
Lingam S, 301-415-1564
References
EPID L-2022-LLE-0004
Download: ML22035A330 (1)

Text

February 10, 2022 Mrs. Maria L. Lacal Executive Vice President/

Chief Nuclear Officer Mail Station 7605 Arizona Public Service Company P.O. Box 52034 Phoenix, AZ 85072-2034

SUBJECT:

PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 -

REQUESTS FOR CONFIRMATION OF INFORMATION FOR EXEMPTION TO DELETE DIVERSE AUXILIARY FEEDWATER ACTUATION SYSTEM BASED ON RISK-INFORMED PROCESS FOR EVALUATIONS (EPID L-2022-LLE-0004)

Dear Mrs. Lacal:

By letter dated January 14, 2022, Arizona Public Service Company (APS, the licensee) submitted an exemption to delete Diverse Auxiliary Feedwater Actuation System (DAFAS) using the Risk-Informed Process for Evaluations (RIPE) for Palo Verde Nuclear Generating Station, Units 1, 2. and 3 (Palo Verde). Specifically, the proposed change is a request from APS for an exemption under Title 10 of the Code of Federal Regulations (10 CFR) Section 50.12, Specific Exemptions, from certain requirements in 10 CFR 50.62, Requirements for reduction of risk from anticipated transients without scram (ATWS) events for light-water-cooled nuclear power plants, for Palo Verde.

The licensees request is for partial exemption from 10 CFR 50.62(c)(1). The portion of 10 CFR 50.62(c)(1) for which the exemption is requested is shown below in bold.

(c) Requirements. (1) Each pressurized water reactor must have equipment from sensor output to final actuation device, that is diverse from the reactor trip system, to automatically initiate the auxiliary (or emergency) feedwater system and initiate a turbine trip under conditions indicative of an ATWS. This equipment must be designed to perform its function in a reliable manner and be independent (from sensor output to the final actuation device) from the existing reactor trip system.

The requirements for Palo Verde is to provide a Diverse Scram System (DSS), DAFAS, and Diverse Turbine Trip (DTT). The exemption request will remove the requirement for the DAFAS from the Palo Verde licensing basis based on the RIPE. This exemption does not alter the requirements for the DSS or DTT at Palo Verde.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed your application for the subject exemption and accepted it on January 31, 2022. The NRC staffs further review concluded that additional requests for confirmation of information (RCIs) are required for complete evaluation.

M. Lacal Please note that we transmitted the draft RCIs on January 31, 2022, and at the licensees request, held a clarification call on February 10, 2022. Enclosed are the NRC staffs RCIs.

Please provide the responses within 2 weeks from the date of this letter, as mutually agreed during the clarification call. Your timely responses will allow the NRC staff to complete its review on schedule.

If you have any questions, please contact me at (301) 415-1564 or via e-mail at Siva.Lingam@nrc.gov.

Sincerely,

/RA/

Siva P. Lingam, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-528, STN 50-529, and STN 50-530

Enclosure:

Requests for Confirmation of Information cc: Listserv

REQUESTS FOR CONFIRMATION OF INFORMATION REGARDING EXEMPTION TO DELETE DIVERSE AUXILIARY FEEDWATER ACTUATION SYSTEM USING THE RISK-INFORMED PROCESS FOR EVALUATIONS ARIZONA PUBLIC SERVICE COMPANY PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 DOCKET NOS. STN 50-528, STN 50-529, AND STN 50-530 By letter dated January 14, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22014A415), Arizona Public Service Company (APS, the licensee) submitted an exemption to delete the Diverse Auxiliary Feedwater (AFW) Actuation System (DAFAS) using the Risk-Informed Process for Evaluations (RIPE) for Palo Verde Nuclear Generating Station, Units 1, 2. and 3 (Palo Verde, PVNGS). Specifically, the proposed change is a request from APS for an exemption under Title 10 of the Code of Federal Regulations (10 CFR) Section 50.12, Specific exemptions, from certain requirements in 10 CFR 50.62, Requirements for reduction of risk from anticipated transients without scram (ATWS) events for light-water-cooled nuclear power plants, for Palo Verde.

The licensees request is for a partial exemption from 10 CFR 50.62(c)(1). The portion of 10 CFR 50.62(c)(1) for which the exemption is requested is shown below in bold.

(c) Requirements. (1) Each pressurized water reactor must have equipment from sensor output to final actuation device, that is diverse from the reactor trip system, to automatically initiate the auxiliary (or emergency) feedwater system and initiate a turbine trip under conditions indicative of an ATWS. This equipment must be designed to perform its function in a reliable manner and be independent (from sensor output to the final actuation device) from the existing reactor trip system.

The requirements for Palo Verde is to provide a Diverse Scram System (DSS), DAFAS, and Diverse Turbine Trip (DTT). The exemption request will remove the requirement for the DAFAS from the Palo Verde licensing basis based on the RIPE. This exemption does not alter the requirements for the DSS or DTT at Palo Verde.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed your application for the subject exemption and accepted it on January 31, 2022 (ADAMS Accession No. ML22032A031). The NRC staffs further review concluded that the following additional requests for confirmation of information (RCIs) are required for complete evaluation.

RCI-1 Section 4.5, Manual Operator Actuation of Auxiliary Feedwater, of the Enclosure to the APS application dated January 14, 2022, states that core heat removal and reactor coolant system (RCS) heat removal are critical safety functions following the Palo Verde standard post trip actions. The RCS pressure analysis discussed in the exemption indicates that there would be no time limit for operator action. This information could be misleading.

Enclosure

The NRC staff noted that the Integrated Decisionmaking Panel (IDP) package describes a deterministic engineering evaluation (Engineering Work Order No. 21-03084-003). This evaluation provides insight into the beyond design basis case of a loss of normal feedwater flow accident, which occurs coincidently with a trip on supplementary protection system high-high pressurizer pressure, no auxiliary feedwater actuation signal (AFAS) -1, no AFAS-2, and no DAFAS. The results of the IDP analysis show that in the worst-case scenario, approximately 10 minutes are available for the operators to manually actuate auxiliary feedwater before a lack of adequate inventory occurs in the steam generator. Avoiding the lack of adequate inventory in the steam generator by taking this operator action can address the critical safety function of core and RCS heat removal.

Please provide a description of, or the information from, the analysis in Engineering Evaluation 21-03804-003, Deterministic Computer Code Runs to Support RIPE Process, which provides the justification and basis for the need to manually actuate AFW flow to preclude a lack of adequate inventory in the steam generator within 645 seconds as discussed in the IDP held on September 30, 2021, and observed by the NRC staff. This approximate 10-minute time requirement is alluded to in Enclosure Attachment 3 of the licensees application dated January 14, 2022.

RCI-2 In Section 2.2, Implementation of 10 CFR 50.62 Requirements at Palo Verde, and Section 4.4, PVNGS Design Features, of the Enclosure to the APS application dated January 14, 2022, the licensee describes the ATWS implementation and general design respectively of the reactor protection system (RPS) and engineered safety features actuation system (ESFAS) as if the systems are physically separate and independent instrumentation and controls systems.

However, the Palo Verde Updated Final Safety Analysis Report (UFSAR), Revision 21, Section 7.1.1.1, Protection System (ADAMS Accession No. ML21201A262), describes both of these systems as sections of the plant protection system (PPS) and in fact these two subsystems have common inputs as well as extensive physically shared cabinets, instrument racks, and drawers. Please verify whether RPS and ESFAS are physically separate systems or part of the same system. Also describe the physical separation of subcomponents between the PPS-RPS and the PPS-ESFAS.

RCI-3 Section 4.5 of the licensees application dated January 14, 2022, describes (on page 16)

N AFW Pump as Class 1E. However, the Palo Verde UFSAR, Revision 21, Section 10.4.9.2, System Description, describes this pump as neither Class 1E electrical nor seismically qualified. While manual operator actions can be taken to energize the pump motor from the A emergency diesel generator during a loss of power, the connecting circuitry is not Class 1E beyond the 4 kilovolts Class Bus NB01 connection, and the pump motor is normally aligned to a non-class electrical bus. Please provide clarification as to whether the N AFW Pump is Class 1E or Non-Class.

RCI-4 Please verify that the described manual operator actions are formally credited in the exemption license basis, as independent diverse means to actuate auxiliary feedwater upon RPS/AFAS failure, and not resulting in more than a minimum decrease in defense-in-depth and safety

margin with respect to the existing system and operations (Criterion 5 of Step 2 Screening Assessment of the Enclosure Attachment 1 to the APS application dated January 14, 2022).

ML22035A330 *by email OFFICE NRR/DORL/LPL4/PM* NRR/DORL/LPL4/LA* NRR/DRA/APOB/BC*

NAME SLingam PBlechman AZoulis DATE 2/10/2022 2/10/2022 2/10/2022 OFFICE NRR/DORL/LPL4/BC* NRR/DORL/LPL4/PM*

NAME JDixon-Herrity SLingam DATE 2/10/2022 2/10/2022