ML20216C300

Informs That During 451st Meeting of ACRS on 980402,NRC Reviewed Various Chapters of AP600 Ssar & Associated Chapters of Draft Final SER

ML20216C300
Person / Time
Site:	05200003
Issue date:	04/09/1998
From:	Seale R Advisory Committee on Reactor Safeguards
To:	Callan L NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
References
ACRS-R-1750, FACA, NUDOCS 9804140386
Download: ML20216C300 (4)

Text

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o,, UNITED STATES l

! o NUCLEAR REGULATORY COMMISSION PDR fo eJWisORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20666

.****** April 9,1998 Mr. L .losoph Callan Executive Director for Operations U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

SUBJECT:

THE SAFETY ASPECTS OF THE WESTINGHOUSE ELECTRIC COMPANY APPLICATION FOR CERTIFICATION OF THE AP600 PLANT DESIGN -

INTERIM LETTER 2 During the 451st meeting of the Advisory Committee on Reactor Safeguards, April 2-4,1998, we reviewed various chapter:: of the AP600 Standard Safety Analysis Report (SSAR) and associated chapters of the draft Final Safety Evaluation Report (FSER). Our Subcommittee on Advanced Reactor Designs reviewed these chapters on March 31-April 1,1998. During these reviews, we had the benefit of discussions with representatives of the NRC staff and the Westinghouse Electric Company and of the documents referenced.

We reviewed the followmg SSAR and associated draft FSER chapters:

. Chapter 2 - Site Characteristics Chapter 9 - Auxiliary Systems, including Appendix 9A- Fire Protection Analysis Chapter 10 - Steam and Power Conversion System

. Chapter 12 - Radiation Protechon Chapter 13 - Section 13.6, industrial Security

. Chapter 15 - Accident Analyses Based on our review of the above SSAR and associated draft FSER chapters, we offer the following comments and recommendations.

Chanter 2 - Site Characteris+ien in order to meet the 10 CFR 50.34, " Contents of applications; technicalinformation," siting dose criteria, site-specific short term and long-term atmospheric dispersion factors X/ Q should meet the AP600 design acceptance valusa. These acceptance values place limits on the outcomes of site-specific atmospheric dispersion calculations and define bounds on the meteorological characteristics of acceptable sites.

<I The NRC staff should ensure that the calculational methodologies used by the Combined License applicant to derive x/Q not mask the effects of any unique site meteorological pge

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characteristics related to topology, geographical location, directed wind flows during specific times of the day, or any peculiar atmospheric inversion characteristics.

Chm _rd_ar 9 - AuviHarv Svatoms. Inehwiina Anaandix 9A - Fire F M=> Analvsis We have not completed our review of the fire protection system and the fire protection analysis.

We plan to provide our views at a later date.

Chapter 13 - Section 13.6. Industrial Secunty The design simplicity of the AP600 permits a security design that eliminates the need for some of the features described in 10 CFR 73.55, " Requirements for physical protection of licensed activities in nuclear power reactors against radiological sabotage." The number of access portals to the vital areas is reduced to a minimum to accommodate personnel and material flow.

This approach enhances the security design and requires less manpower for responding to attempted intrusions.

Although the proposed security design meets the applicable regulations, it appears to make routine operations and maintenance activities more difficult. Restrictions such as personnel searches will cause delay for personnel when entering areas of the plant containing equipment, which must be surveilled, operated, and maintained. These restrictions could have safety implications, especially during plant upset conditions, emergencies such as fires, and implementation of the station Emergency Plan. ,

We recommend that the staff evaluate the impact of the security design on the safety aspects of the plant. The additional time required to perform personnel searches might well increase the expected response times of the fire brigade and operators attempting to mitigate safety significant events. We expect to review the results of this evaluation.

Chapter 15 - Accident Analyses in assessing the acceptability of the AP600 design in meeting the regulatory dose criteria associated with design-basis accidents (DBAs), Westinghouse has proposed taking credit for natural aerosol removal processes that occur in the containment. These processes include agglomeration, gravitational sedimentation, diffusional plateout, diffusiophoresis, and thermophoresis, in the past, the design-basis source term was considered to account implicitly for these and other natural aerosol removal processes in both the reactor coolant system and in the containment. The new source term released to the containment implicitly accounts for only the effects of aerosol removal processes in the reactor coolant system. Radionuclide deposition in the containment :nust now be calculated explicitly.

The processes of agglomeration, sedimentation, and diffusion are present at all times for all accident sequences and containment designs (and are not significantly dependent on thermal-1 hydraulic conditions). Thus, these specific processes can be accounted for explicitly without specifying the thermal-hydraulic conditions. The processes of diffusiophoresis and thermophoresis, on the other hand, depend on the synchronization of the thermal-hydraulic

1 processes (steam condensation rates and development of thermal gradients across boundary layers) with the associated source-term concentrations in the containment. For current operating plants, the relative timing of source term release and thermal-hydraulic phenomena have been shown to be dependent on both plant design and event sequence. It is not clear  ;

what thermal-hydraulic conditions should be associated with the DBA source term, which is an '

amalgamation of source terms associated with a range of severe accident sequences.

Westinghouse has chosen the thermal-hydraulic conditions of a specific sequence (i.e., a direct vessel injection line break) for use with the DBA source term to take credit for diffusiophoresis and thermophoresis. The DBA concept is intended to ensure that the containment design results in an acceptable risk for all accident sequences. It is not clear that the thermal-hydraulic conditions of the selected sequence is consistent with the desired generality of the source term.

Specifying the thermal-hydraulic conditions associated with a specific sequence for use with the new source term appears to constitute an unprecedented interpretation of the design-basis concept. We recommend that the justification for granting credit for acrose: removal due to ,

diffuslophoresis and thermophoresis be documented. Furthermore, the staff should make it l clear that such credit is not intended to be generic for other plant designs. l Dr. Dana A. Powers did not participate in the Committee's deliberations regarding the DBA source term.

l Sincerely,

/{. f. ~ - -<

l R. L Seale l Chairman i

References:

1. Letter dated February 19,1998, from R. L. Seale, Chairman, ACRS, to L. Joseph Callan, Executive Director for Operations, NRC,

Subject:

Interim Letter on the Safety Aspects of the Westinghouse Electric Company Application for Certification of the  !'

AP600 Plant Design.

2. U.S. Department of Energy report prepared by Westinghouse Electric Corg4;en, "AP600 Standard Safety Analysis Report," updated through Revision 20 dated February 6,1998.

3. Memorandum dated March 9,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of i Advanced Copy of Chapter 12 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft).

i

. -4 -

4. Meinorandum dated March 17,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Chapter 2 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft).

5. Memorandum dated March 17,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Chapter 9 of the AP600 Final Safety Evaluation Re.nort (FSER)

(Predecisional Draft).

6. Memorandum dated March 17,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Chapter 10 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft).

7. Memorandum dated March 17,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Chapter 15 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft). .

8. Memorandum dated March 24,1998, from Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, .?xecutive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Section 9.5.1 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft).

9. Memorandum dated March 23,1998, f,om Jack W. Roe, Office of Nuclear Reactor Regulation, NRC, to John T. Larkins, Executive Director, ACRS,

Subject:

Transmittal of Advanced Copy of Section 13.6 of the AP600 Final Safety Evaluation Report (FSER)

(Predecisional Draft).

10. Westinghouse AP600 Security Design Vulnerability Analysis Report, GS-ASR-002, Revision 2, dated February 3,1998 (Safeguards information).

11. Westinghouse AP600 Security Design Report, GS-ASR-001, Revision 5, dated February 3,1998 (Safeguards Information).