CY-97-044, Forwards Comments on SECY-97-044, Policy & Key Technical Issues Pertaining to Westinghouse AP600 Standard Pressurized Reactor Design

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Forwards Comments on SECY-97-044, Policy & Key Technical Issues Pertaining to Westinghouse AP600 Standard Pressurized Reactor Design
ML20136H291
Person / Time
Site: 05200003
Issue date: 03/13/1997
From: Mcintyre B
WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To: Hoyle J
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), NRC OFFICE OF THE SECRETARY (SECY)
References
DCP-NRC0771, DCP-NRC771, FACA, SECY-97-044-C, SECY-97-44-C, NUDOCS 9703190107
Download: ML20136H291 (7)
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DCP/NRC0771 1

Westinghouse Energy Systems Rockvdle Nuclear bcensing Center

' Nudear and Advanced remogy Owe Electric Corporatlan One Montiose Metro 11921 Rockville Pike Suite 450 Pockvdle Marytand 20852 Docket STN-52003

, Document Control Desk March 13,1997 United States Nuclear Regulatory Commission Washington, D.C. 20555-001 ATTENTION: MR. JOHN H0YLE

SUBJECT:

WESTINGHOUSE COMMENTS ON " POLICY AND KEY TECHNICAL ISSUES PERTAINING TO THE WESTINGHOUSE AP600 STANDARD PRESSURIZED l REACTOR DESIGN", SECY-97-044

Dear Mr. Hoyle:

Westinghouse appreciates the opportunity, as the designer of the AP600 advanced passive nuclear power plant, to provide our perspective on SECY-97-044, Policy and Key Technical Issues Pertaining to the Westinghouse AP600 Standard Pressurized Reactor Design.

The AP600 represents a substantial improvement in the mitigation of severe accidents and offsite releases by including many safety and nonsafety-related features which would be considered severe i I

accident mitigation design alternatives (SAMDAs) in conventional and evolutionary designs. These systems provide reliable mitigation capability and reduction in the uncertainties associated with severe accident phenomena, in SECY-91-229, " Severe Accident Mitigation Design Alternatives for Certided Standard Designs",

the NRC staff recommended that SAMDAs be addressed for certi0ed designs in a single rulemaking process that would address both the 10 CFR 50.34 (t) and National Environmental Protection Act (NEPA) considerations in the 10 CFR Part 52 design certincation rulemaking. SECY-91-229 further recommended that applicants for design certification assess SAMDAs and the applicable decision rationale as to why they will or will not benefit the safety of their designs. The Commission approved the staff recommendations in a memorandum dated October 25,1991.

The Commission has therefore approved the use of the considerations of the National Environmental Protection Act as the regulatory requirement for determining if appropriate severe accident mitigation features are present in a 10 CFR 52 design certi0 cation rulemaking. This was the standard used by the staff in their review of the two recently approved evolutionary plants. The AP600 has also b evaluated against these considerations. The result of that evaluation was that no further severe accident mitigation design features, beyond those considerable features already built into the design, are appropriate.

0586BAM.WPF/ March 13,1997 I

9703190107 970313

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E Since the AP600 meets existing regulatory prevention and mitigation criteria and provides simplified plant safety, a requirement for addnional systems is neither justified or warranted. Our detailed comments on the issue of Prevention and Mitigation of Severe Accidents are enclosed in attachment 1.

L' Please contact me if you have any questions concerning these comments.

\ 6xfrA Brian A. McIntyre, Manager Advanced Plant Safety and Licensing Chairman Jackson Commissioner Rogers b Commissioner Dieus Commissioner Diaz Commissioner McGaffigan L. J. Callan - FDO

5. Collins - NRR P. Seale - ACRS

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Attachment E

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0586BAM.WPF/ March 13. [997

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s ATTACHMENT 1 POLICY AND KEY TECHNICAL ISSUES PERTAINING TO

.THE WESTINGHOUSE AP600 STANDARD PRESSURIZED REACTOR DESIGN WESTINGHOUSE COMMENTS In SECY-96-128, " Policy and Key Technical Issues Pertaining to the Westinghouse AP600 Standard Pressurized Reactor Design", the staff recognized that the AP600 design embodies significant improvements in the prevention of severe accidents but believed that improvements in severe accident prevention did not support the level of accident mitigation features in the design. '.e staff believed this was particularly the care relative to the removal of airborne activity in the contaihnent since the AP600 includes neither a containment spray system nor post-accident tiltration capabidty, but relies on sedimentation and deposition processes to reduce airborne activity concentrations. The staff proposed that an additional single-train, active, nonsafety related system be added to the AP600 design to augment the tission product removal capability of the design to " address the uncertainties associated with the passive natural tission product removal mechanisms for design basis analysis and for balance between prevention and mitigation of severe accidents."

The staff requirements memorandum of January 15,1997 did not approve this position "not because it may be inappropriate, but because the basic design and performance requirements have not been specified and the requested additional system (s) do not appear to be consistent with a passive design" The Commission further stated that the "tission product removal coefficients for analyzing the consequences of design basis accidents should be based on technical merits and should not be linked to the availability of one or more non-safety systems."

The' Commission, however, indicated a willingness to reconsider the matter "if the staff can be more specific in terms of what additional system (s) are contemplated , including the design and performance requirements."

In SECY-97-044. " Policy and Key Technical Issues Pertaining to the Westinghouse AP600 Standard Pressurized Reactor Design" the staff provided a description of an active, single train, nonsafety-related containment spray system that they believe will provide "an appropriate balance between prevention and mitigation of severe accidents" in the AP600.

Westinghouse maintains that additional systems are not required and that the current design characteristics provide that balance the staff seeks to meet the severe accident safety goals.

The AP600 provides superior capability to both prevent and to mitigate severe accidents. The AP600 provides a robust containment design that meets design basis requirements for preventing the release of radioactive material into the environment. The passive containment cooling system (PCS) assures heat removal and also contribrtes to the removal of airborne activity from the containment atmo:ahere. In addition, the AP600 provides nonsafety related equipment (including containment fan cooler.;) that is available to mitigate severe accidents.

0556BAM.WPF4 lar.h 13.1997 I i

l l Probabilistic safety assessments indicate that the AP600 core damage frequency is orders of magnitude less than conventional plant designs. The AP600 containment provides a reliable barrier against th*

release of radiation to the environment and a significant reduction in nuclear plant risk is achieved. l Unlike conventional plant designs, the AP600 design precludes the recirculation of contaminated reactor coolant outside containment inherent in the use of a containment spray system.

The AP600 containment represents a substantial improvement in the mitigation of severe accidents and offsite releases. The design includes many safety and nonsafety-related features which would be considered severe accident mitigation design alternatives (SAMDAs) in conventional and evolutionary designs. These systems provide reliable mitigation capability with reduction in the uncertainties associated with severe accident phenomena. The severe accident analyses in the PRA credit the safety-related and nonsafety-related systems with severe accident phenomena prevention, mitigation, and offsite dose reduction.

Examples of how the AP600 systems mitigate severe accident phc 'ena include:

I Containment Bypass Mitigation

The ADS is a multi-redundant and diverse system with control from both the protection and safety monitoring system and the diverse actuation system.

  • Low leakage containment 1
  • Online leakage monit'or ensures penetrations that are expected to be normally closed are closed.
  • ADS mitigates high pressure and temperature induced tube ruptures

Containment isolation Failure Mitigation

  • Reduced number of penetrations
  • Penetrations are into the auxiliary building where any radionuelide leakage can settle rather than being released to the atmosphere

+ Open penetrations connected to the reactor coolant system or containment are fail closed

  • Use of smaller valves with higher reliability and lower leakage
  • Large dry containment with high' design pressure
  • Containment isolation controlled by both the safety-related protection and safety monitoring system (PMS) and the nonsafety-related diverse actuation system (DAS) 0586 bah!.wPF/htarsh 13. 1997 2

.- - -._.- _ ~ . - _ . . . . - . . . . - . . . - - - . - . - - . _ - -. -

, t Severe Accident Phenomena Mitigation i

  • Passive containment cooling is a fail safe system for decay heat and fission
product removal.

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  • Hydrogen control in a large dry containment via redundant safety related passive autocatalytic recombiners (PARS) for slow release and using igniters fer fast release
  • ADS mitigates high pressure core damage accidents
  • Reactor vessel flooding to prevent vessel failure and debris relocation to the containment. No bottom penetrations'on reactor vessel.

t

! The AP600 design includes nonsafety-related containment fan coolers that can be used to mix the containment atmosphere and remove heat from the containment. The heat removal process also l *

< causes the deposition of aerosols onto the cooling coils. The fan coolers provide an aerosol removal capability which is independent of the process of aerosol deposition onto the containment shell during

[ passive containment cooling system operation. No credit is taken for these fan coolers in the AP600 accident analysis calculations, but they would be part of an accident management strategy, i

l In SECY-97-044, the staff is proposing the addition of further active nonsafety-related systems <

(containment spray) for the AP600 to enhance aerosol removal from the containment atmosphere, mix

< the containment atmosphere or affect a short term containment pressure reduction during or following ,

j a severe accident.- The justitication for this proposed addition is based upon historical perspectives - ,

operating plants have spray -- and to address uncertainties associated with passive natural fission I

product removal mechanisms. The staff has not provided any quantitiable measure of, or criteria for,

  • the balance between prevention and mitigation they are seeking.

One required measure of severe accident mitigation level is provided by the National Environmental  ;

Protection Act (NEPA), which requires an evaluation of severe accident mit
gation design  !
alternatives (SAMDA) as a part of siting a facility that can release radiation into the environment. In SECY-91-229, " Severe Accident Mitigation Design Alternatives for Certitled Standard Designs", the NRC staff recommends that SAMDAs be addressed for certified designs in a single rulemaking
j. process that would address both the 10 CFR 50.34 (f) and NEPA considerations in the 10 CFR Part i

52 design certitication rulemaking. SECY 91-229 further recommends that applicants for design

eertification assess SAMDAs and the applicable decision rationale as to why they will or will not bei . fit the safety of their designs. The Commission approved the staff recommendations in a memorandum dated October 25,1991. j Appendix IB of the AP600 SSAR provides an evaluation of Severe Accident Mitigation Design i Alternatives (SAMDA) for the Westinghouse AP600 design. This evaluation is performed to evaluate whether or not the safety benetit of the SAMDA outweighs the costs of incorporating the SAMDA in the plant, and is conducted in accordance with applicable regulatory requirements as identified below.

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j i 096BAM.WPF/ Mar 6h 13.1997 3 l

4 l 2 i l

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The National Environmental Policy Act (NEPA), Section 102.(C)(iii) requires, in part, that

. .all agencies of the Federal Government shall ... (C) include in every recommendation or i report on proposals for legislation and other major Federal actions significantly affecting the

quality of the human environment, a detailed statement by the responsible official on . (iii)
alternatives to the proposed action.

1 l 10 CFR 52.47(a)(ii) requires an applicant for design certification to demonstrate i

1

. compliance with any technically relevant portions of the Three Mile Island requirements 4

set forth in 10 CFR 50.34(t) ...

A relevant requirement of 10 CFR 50.34(t) contained in subparagraph (1)(i) requires the performance of

a plant / site specific probabilistic risk assessment, the aim of which is to seek such

{ improvements in the reliability of core and containment heat removal systems as are significant and practical and do not impact excessively on the plant ..

4 An evaluation of candidate moditications to the AP600 design was conducted to evaluate the potential

! for such modifications to provide significant and practical improvements in the radiological risk 4

profile of the AP600 design. This eva'uation included a nonsafety-related containment spray system i that utilized the tire protection pumps as a motive force. The cost of this system was conservatively

, biased on the low side and it was estimated that the spray worked perfectly in that it completely 1 eliminated the risk from all severe accidcnt sequences it was designed to address. This approach maximized the potential benefits associated with each SAMDA.

, In the ease of the containment spray, if it was assumed the system worked beyond expectations and i completely eliminated the risk from all severe accident sequences except containment bypass, which l containment spray does not mitigate, the total averted risk would be 6.9 x 10r2 man-rem per year. As

discussed in Appendix IB of the SSAR, to be consistent with NRC regulatory analysis guidelines, a i value of $1000 per offsitg. man-rem averted was used to convert man-rem per year to dollars per year.

This value is intended to be the surrogate for all offsite consequences including property damage and 7 is referred to as the annual levelized benelit. For the containment spray system, the capital. benefit was $44, compared to the conservatively low capital cost to build such a system of $415,000. It was

. thur judged that a containment spray system was not cost beneticial.

The results of the AP600 SAMDA evaluation show that despite the significant conservatism employed  !

in the evaluation. none of the SAMDAs evaluated provide risk reductions which are cost beneticial.

The results also show that even a conceptual " ideal SAMDA", one which reduces the total plant radiological risk to zero, would not be cost effective. This is due primarily to the already low risk ,

protile of the AP600 design, which is approximately two orders of magnitude below existing plants.

I Where the topic of balance between prevention and mitigation was discussed in the June 15, 1990  ;

staff requirements memorandum for SECY-89102, " Implementation of the Safety Goals", the .j Commissio, directed the staff not to create new de facto large release guidelines or to use industry j design objectives as the basis to establish new requirements. j OM6BAM.WPF/ March 13.1997 4

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i i With respect to the nonsafety-related system described by the staff in SECY-97-044, a system "on the

. . order of a few thousand gallons per minute", is well beyond the capability of the AP600 diesel-driven -

2 tire protection pump. The need to pump the water up inside the containment against a containment

backpressure significantly reduces the flow available for spray. The fire protection pump component data from Table 9.5.1-2 of the SSAR indicates a rated tiow of 2000 gpm at a head of 265 feet. This

! pump is located at an elevation of 100 feet in the auxiliary building, some distance from the containment. The top of the AP600 containment is approximately 256 feet and the containment

, design pressure is 45 psig (104 feet of water). A conceptual containment spray system using the tire j protection pump was discussed with the staff in late 1995. Due to the elevation changes and lengths l

of piping runs required, that system as contigured was capable of delivering a flow of approximately 330 gpm to the elevation of the polar erane rail (232 feet). There was limited benetit from this design to remove tission products and little or no benetit to reduce containment pressure.

in summary, the Commission has approved the use of the considerations of the National
Environmental Protection Act as the regulatory requirement for determining if appropriate severe
accident mitigation features are present in a 10 CFR 52 design certification rulemaking. The AP600
has been evaluated against these considerations. The result of that evaluation was that no further l severe accident mitigation design features, beyond those considerable features already built into the
design are appropriate.
Westinghouse Recommendation'  !

1 Since the AP600 meets existing regulatory prevention and mitigation criteria and provides simplified plant safety, a requirement for additional systems as proposed by the staff in SECY-97-044 is neither i justitled or warranted.

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