ML20085H452
| ML20085H452 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 06/09/1995 |
| From: | Mcintyre B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20085H457 | List: |
| References | |
| DCP-NRC0346, DCP-NRC346, NUDOCS 9506210179 | |
| Download: ML20085H452 (6) | |
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Westinghouse Energy Systems Ba 355 Pmsburgh Pennsylvania 15230-0355 l
Eleetric Corporation DCP/NRC0346 June 9,1995 document Control Desk l
United States Nuclear Regulatory Commission Washington, D.C. 20555-001 ATTENTION:
MR. DENNIS M. CRUTCHFIELD i
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SUBJECT:
DRAFT COMMISSION PAPER ON STAFF POSITIONS ON TECHNICAL l
ISSUES PERTAINING TO THE WESTINGHOUSE AP600 STANDARD PRESSURIZED REACTOR DESIGN
Dear Mr. Crutchfield:
l Westinghouse appreciates the opportunity to comment on the draft policy paper provided in your letter to Mr. Liparuto of May 18,1995. Specific comments on each of the 10 issues is presented in the attachment 1. The Westinghouse formal comments on the proposed changes to 10 CFR Parts 50,52 and 100 are presented in attachment 2.
Please contact me if you have any questions concerning these comments.
A e
Brian A. McIntyre, Manager Advanced Plant Safety and Licensing
/nja Attachments 9506210179 950609 PDR ADOCK 05200003
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L A'ITACHMENT 1
. DRAFT COMMISSION PAPER ON STAFF POSITIONS ON TECHNICAL ISSUES PERTAINING TO i
THE WESTINGHOUSE AP600 STANDARD PRESSURIZED REACTOR DESIGN WESTINGHOUSE COMMENTS I
I.
Leak Before Break Approach The proposed staff position on leak-before-break approves a leakage rate limit of 0.5 gpm for the l
AP600 at the design certification stage, provided that a margin of at least 1.41 is available -
between the maximum combined load calculated for the piping and the load at which crack -
stability is established. The staff believes this margin is necessary to cover as-built pipe routings
- and materials. Discussions with the staff have indicated that the leak-before-break methodology will be a Tier 2* item in the AP600 design control document. This implies that the methodology -
can be changed, with staff approval, by the combined license (COL) applicant at the time of COL application.
Westinghouse does not agree with the draft policy position on leak-before-break that has been prepared by the NRC staff. The draft position requirement to use a factor of 1.41 on loads will likely lead to more plant hardware that may be adverse to overall plant safety.L This may include pipe supports, pipe whio restraints, and jet shields for the primary coolant loop piping, main steam line, main feedwater line and reactor coolant system auxiliary piping four inches and larger in.
diameter located inside containment. Westinghouse requests approval to use the absolute sum of the various loadings in order to provide margin on loads. This approach to margin on loads is.
consistent with General Design Criteria 4, draft Standard Review Plan section 3.63, and NRC approved applications of leak-before-break to operating plants. The Westinghouse margin on loads will result in_ improved safety, plant simplification, and a more economical plant. The design process for AP600 assures that once leak-before-break is demonstrated during the design ceitification stage, it will be met in all subsequent stages of design and constmetion.
The safety benefits that can be realized by successful application of leak-before-break include reduced plant congestion, better access for in-service inspection and maintenance, lower radiation dosages, and lower risk ci udntended resistance to thermal growth. This is achieved by reducing the number of pipe sup;urts, pip whip restraints, and jet shields and simplifying the plant design.
The result is a safer and more economical plant.
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In our discussions with the NRC staff subsequent to issuance of the draft policy paper, we U
understand that they have the following concerns which resulted in their requirement for the.
additional margin on load:
Leak-before-break application is deterministic in nature and would require a higher level of margins.
2.
Application of leak-before-break at 0.5 gpm leak rate allows smaller pipes to be qualified.
Smaller pipes require additional margins..
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l 3.
Only preliminary piping analyses will be available during the design certification review l
of the AP600. The staff would like additional margins at this stage to ensure that the as-built AP600 meets the requirements applied to current plants.
The following paragraphs delineate how the AP600 addresses these staff concerns:
The Westinghouse position on_ leak-before-break includes adequate margins for uncertainties. A margin of 10 on leak rate is uxd to address unce tainties in detecting and calculating the leakage from a through wall crack. The leakage crack length will produce a leak rate that is 10 times the detectable leak rate. Uncertainties in the calculations for crack stability are addressed by applying the absolute sum of the loads to a through wall crack that is twice as long as the leakage crack.
Absolute summation of loads would result in an added conservatism in the range of a factor of 1.1 on the average.
The NRC staff position on leak-before-break adds complexity.to the Westinghouse position by-requiring that crack stability also'be verified when 1.41 times the algebraic sum of the loads is applied to the leakage crack. To meet this criterion, the stresses in the pipe would need to be reduced by using a more complicated pipe layout and support configuration. This required reduction in pipe allowable stress increases with the diameter of the pipe. There are other factors that affect the pipe layout and support configuration, such as plant access, maintenance, inspection,-
and laydown space. The combination of these factors, along with the 1.41 margin on loads in the NRC staff position, will result in more supports on some of the pipe lines and could cause some lines to not qualify for leak-before-break. Pipe whip restraints and jet shields.would then be required for those lines that do not qualify.
The Westinghouse design process for the AP600 assures that leak-before4reak acceptance criteria can be met at all stages of the plant design and construction. The preliminary' pipe stress analysis is completed during design certification. The pipe layout and support configuration are controlled by three dimensional electronic model of the plant. Preliminary vendor data is used for valves and equipment to assure design feasibility. Pipe materials and welding processes are selected. Piping isometric drawings are prepared for input into the pipe stress analysis. The pipe stress analysis i
is performed for the limiting loading conditions and minimum material strenfth properties, and the leak-before-break bounding analysis curves are met.
During the beyond-design-certification engineering stage, the final pipe stress analysis is i
performed. Firm vendor data is used for valves and equipment. Minor changes to the pipe layout and support configuration are controlled by the electronic plant model. Revised isometric drawing are prepared, as required, for input into the pipe stress analysis. The ASME piping Design Specifications are prepared to provide a complete basis for the piping design. Pipe stress analysis is performed in accordance with the Design Specifications to satisfy all ASME Code requirements.
Refinements in the pipe stress analysis methods may be used to meet the leak-before-break j
bounding analysis curves. Support design and stress analysis is performed to confirm the design interface for the pipe stress analysis. The COL applicant will use this final analysis to obtain the combined license. t
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During construction the procurement documents are reviewed to assure conformance with the final pipe stress analysis. New pipe stress analysis is performed for a limited number of lines as required. Construction tolerances are utilized to assure that constmetion closely follows the design. After construction the as-built configuration and materials are reviewed to assure -
conformance with the final pipe stress analysis. ' As-built tolerances for pipe stress analysis are used to reconcile the as-built configuration with the final pipe stress analysis.
The Westinghouse position is that this margin should not be taken from the plant design
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organization so that the full benefit of leak-before-break can be applied to the design stage rather than at the time of each COL application. There is a greater benefit in not designing additional supports than removing them at the COL stage.
in summary, the Westinghouse approach is to use the absolute sum of 'the various loadings in order to provide margin on loads. This approach is consistent 'with General Design Criteria 4, draft Standard Review Plan section 3.6.3, and NRC approved applications of leak-before-break to operating plants.
The Westinghouse approach will result in improved safety, plant -
simplification, and a more economical plant. The design process for AP600 assures that once leak-before-break is demonstrated during the design certification stage it will be met in all subsequent stages of design and construction.
II.
Security Design The staff's understanding of the proposed approach to security for the AP600 is correct.
Westinghouse is updating the AP600 SSAR to reflect this change to the design and is in the -
process of developing a Security Design Report that will be submitted to the staff for review.
III.
Technical Specifications Westinghouse agrees with the staff's assessment of the status and approach to resolution for this issue.
IV.
Initial Test Program Westinghouse agrees with the staff's assessment of the status and approach to resolution for this -
issue. Meetings have been held with the staff to discuss their concerns in this area. ' Westinghouse is developing new abstracts for the initial test program and will submit these to the staff for review.
V.
Passive System Thermal-Hydraulic Performance Reliability' Westinghouse agrees with the staff's assessment of the status and approach to resolution for this issue. A schedule has been developed and submitted to NRC for the efforts associated with resolution of this issue.
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VI.
Regulatory Treatment of Nonsafety Systems The position presented in the paper delineates the key issues associated with resolution of the RTNSS issue. These issues are; post 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> actions, acceptance of the baseline PRA, adverse systems interactions and technical specifications for the RTNSS important systems. Westinghouse agrees that these are the important issues and that the staff and Westinghouse are meeting to pursue resolution.
VII.
Containment Performance Westinghouse agrees with the staff's assessment of the status and approach to resolution for this l
issue using both probabilistic and deterministic criteria.
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l VIII.
External Reactor Vessel Cooling Westinghouse agrees with the staff's assessment of the status and approach to resolution for this issue. Meetings have been held'with the staff concerning the technical aspects of in-vessel-l retention.
I IX.
Passive Hydrogen Control Measures Westinghouse agrees with the staff's assessment of the status and al proach to resolution for this i
issue. Additional information will be provided to the staff on the performance of autocatalytic hydrogen recombiners.
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X.
DBA and Long Term Severe Accident Radiological Consequences l
The first sentence of the third paragraph refers to the higher leakage rates that would exist for the AP600. Tnis is misleading and incorrect. The sentence should be revised to read, "The effect of i
l-higher concentrations of suspended radionuclides for longer periods could lead to...".
l In the fifth paragraph there is the statement that the staff "... will allow flexibility in some i
aspects of DBA dose calculations." This does not specifically identify what the flexibility will be.
In the seventh and eighth paragraphs the NRC refers to Westinghouse's use of the EPRI source term. While Revision 3 of the SSAR reflects the EPRI source term, Westinghouse has presented to the NRC a commitment to change source terms to use the new NRC source term from NUREG-1465 in almost every aspect. The results of this revised analysis will be submitted to the staff in June,1995. The paragraphs present an image of Westinghouse as holding onto an L
approach that the NRC is opposed to and that we have made no progress since submitting the SSAR in 1992. It is recommended that the first three sentences of paragraph seven be deleted since they do not reflect Westinghouse positions that have been presented to the staff. It is also recommended that following be added to the end of the paragraph.
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Westinghouse's proposal for performing the DBA dose ~ calculations agrees' with the NRC approach in most ways.
There are three departures.
- First, i
Westinghouse contends that the duration for the site boundary accident doses should be the first two hours of the accident or, alternatively, the first portion of the accident including the time up to the initiation of the core damage sequence plus the first two hours after onset of core damage. Secondly, Westinghouse -
proposes that core release fractions identified in NUPEG-1465.for low-volatile elements be reduced (reduction factor of five for Sr, Ba, and the cerium group.
and a reduction factor of two for the lanthanide group). Lastly, Westinghouse has.-
suggested that the 25 rem TEDE dose limit identified in the proposed revisions to 10 CFR 100 and 10 CFR 50 be increased.
Paragraph eight should have the first sentence deleted since the referenced EPRI source term is no longer germane to the AP600. 'Ihe table of release fractions that follows paragraph eight.
should also be deleted.
1 The third sentence of paragraph ten should be revised, replacing " Westinghouse propo' es to s
calculate doses.." with "In past practice doses have been calculated...".
Also in the tenth paragraph, reference to a 25 rem TEDE dose limit should be removed. - Its
. presence in this paragraph is not appropriate since it should be addressed as a separate subject (and it is the main subject of the following paragraph). Its use presumes a final acceptance of the -
limit when it is only a proposed limit at this time. Therrfore, the phrasing should be changed from "... the dose to an individual should not be in excess of 25 rem TEDE,,. " to "... the dose to an individual should not be in excess of the defined limits... ".
In paragraph eleven, the use of " proposed" should be revised to " proposes". The current wording implies that the dose limit proposed in 60 FR 10810 - February 28,-1995 has been finalized.
Adopting this position prior to the Commission dispositioning public comments on the proposed changes to 10 CFR 50,52 and 100 is premature.
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