ML20235G356
| ML20235G356 | |
| Person / Time | |
|---|---|
| Issue date: | 08/19/1986 |
| From: | Ross D NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Sniezek J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| NUDOCS 8707140219 | |
| Download: ML20235G356 (6) | |
Text
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UNITED STATES
's NUCLEAR REGULATORY COMMISSION D-
-l WASHINGTON D. C. 20555 g,, #
1 b AUG g MEMORANDUM FOR:
James H. Sniezek, Director Regional Operations and Generic Requirements Staff FROM:
Denwood F. Ross, Acting Director Office of Nuclear Regulatory ResearcF s
SUBJECT:
RESPONSE TO CRGR COMMENTS CONCERNIhG REVISION OF THE ECCS RULE CONTAINED IN APPENDIX X AND SECMON 50.46 0F 10 CFR PAP,T 50" (CRGR MEETING NO. 91, 7/23/df )
This memorandum responds to CRGR's request of July 23, 1956 that the Office of Research address three items pertaining to the proposed rule presented in the Commission Paper " Revision of the ECCS Rule contained in Appendix K and Section 50.46 of 10 CFR Part 50." This response has been coordir ned with NRR. In addition, telephone conservation have been held with 05:.
The items addressed are as follows:
1.
Concerning the elimination of the Dougall-Rohsenow correlation as an acceptable feature of Appendix K:
Why is it appropriate to allow plants to contirue operation if we are a.
stating that the correlation is non-conservatism e over certain regions?
b.
What will happen to plants using the Dougall-E:hsenow correlation if we indicate that it is non-conservative and de:ete it from Appendix K?
2.
Are the reporting requirements of the proposed rule appropriate?
a.
Should every error be reported?
b.
Does the staff really want to impose a 60-day -esponse requirement on itself?
3.
The Director of the Office of Research must determie.e whether the proposed rule would result in any decrease in plant safety ara result in substan-tial cost savings for the industry.
With respect to the first item, RES and NRR staff have ret to consider four options related to the elimination of the Dougall-Rohser x correlation as an acceptable Appendix K feature.
These options (Enclosure A) have been enclosed for CRGR discussion.
Practical considerations led to a;*eement on the second option which pennits existing Evaluation Models (EMS) tc be " grandfathered" and removes the Dougall-Rohsenow correlation as a generally acceptable Appendix K feat 7e.
It is our judgement that current ECCS EMS are sufficiently conserva-tive en the whole to permit continued use of the Dougal'-Rchsenow correlation in existing EMS.
For future modifications to EMS, including error corrections,
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8707140219 060019 PDR REVGP NRCCHCR CORRESPONDENCE PDR o
e the impact of continued acceptability of the Dougall-Rohsenow correlation based on the overall conservatism of the evaluation model will be considered..If a new evaluation model is submitted, such as an EMS modified because of errors or model revisions, or a new computer code, the applicabii$ty of the Dougall-Rohsenow correlation would have to be addressed. This approach permits
. phase out of the inappropriate use of this correlation Aile minimizing the impact to the licensee.
For the present however, this estion would leave an inconsistency in the rule.
Section I.C.5a of Appendix r to Part 50 states that' post-CHF heat transfer correlations shall be compared tc data and that such comparisons "shall demonstrate that the correlation predicts values of heat transfer coefficient equal.to or less than the mean value of the applicable experimental heat transfer data throughout the range of parameters for which the correlation is to be used."' By allowing existing EMS to be grandfathered, there is a high probability. that EMS using the Dougall-Fchsenow correlation do not meet the criteria of Section I.C.5.a.
Enclosure B shows that the Dougall-Rohsenow significantly overpredicts heat transfer over a wide region.
Because of this, RES would be more comfortable if an estimate of the degree of non-conservatism were obtained for each of the EMS whict use the Dougall-Rohsenow correlation. However, the cost of such analses would be large, and we agree that we know reasonably well that currently approved EMS are sufficiently conservative.
With respect to the second item identified by CRGR, bott RES and NRR believe that the proposed reporting requirements are an improvement over the existing rule implementation whfch require the licensee to immediately re) ort and correct all errors, even though they may be very minor. Althougl NRR wants to be informed immediately of all errors, they would like to allow flexibility in how quickly these errors are to be corrected. This is consistent with the wording of the proposed rule. On the other hand, RES believes that all errors should be noted and submitted'to the agency on a regular basis.
Immediate reporting of minor errors (less than 50 F effect on calculated peak cladding temperature and not exceeding 50.46b criteria) would no: be a requirement. A comparison of the current rule reporting requirements t those of the proposed rule (including possible RES options) is provided in En:1osure C.
With respect to CRGR's item 2(b), the sixty day response requirement on NRC staff pertains soley to NRC approval of the licensee's schedule subsequent to its submittal and is therefore not excessively burdensone.
Lastly, based on my review of the proposed rule and its regulatory analysis, it is my determination that the proposed rule would not result in any decrease in plant safety because the conservative safety limits of section 50.46(b) would l
not be reduced.
However, the CRGR should be aware of tre fact that the use of realistic calculational methods, as permitted under the proposed rule, may allow licensees to operate their plants closer to the limits of 50.46(b) than their current operational practice. Although this may r.ot be considered a decrease in plant safety, it does represent a reductior in the margin intro-duced by the currently acceptable, yet overly conservative, calculational methods. On balance, using more realism should produce some safety benefits, albeit nonquantifiable.
c I have also determined that the proposed rule would result in substantial cost savings for the industry. On the average it is estimated that a plant able to upgrade total power by 5% as a result of the proposed ruie, would experience l
lifetime energy replacement cost savings having a present value of between $70 to $100 million dollars.
It is expected that most Westinghouse plants could benefit from the rule revision.
It is estimated that 3-4 staff years will be required tc review the generically based realistic evaluation models that might be submitted by vendors.
Future staff resources will be adequate for this purpose.
If you require any additional information prior to our next meeting concerning this issue, please contact Mr. Jose N. Reyes on 443-7890.
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'wmud Denwood F. Ross, Acting Director Office of Nuclear Regulatory Research
Enclosures:
A. NRR Dougall-Rohsenow Options B. Comparison of Dougall-Rohsenow to Experimental Data.
C. Comparison of Current and Proposed Rule Reporting Requirements.
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e ENCLOSURE A NRR OPTIONS PERTAINING TO USE OF THE DOUGALL-ROHSENOW CORRELATION OPTION 1 Retain the Dougall-P.ohsenow as a generally acceptable correlation in Section I.C.5 of Appendix K.
OPTION 2
" Grandfather" existing Evaluation Models. Delete the use of the Dougall-Rohsenow correlation in Section I.C.5 of Appendix K.
For future modifications to existing evaluation models including error corrections consid-er the impact of continued acceptability of the Dougall-Rohsenow correlation based upon the overall conservatism of the model.
If a new evaluation model were submitted, such as a new computer code, the applicability of the Dougall-Rohsenow correlation would have to be addressed.
OPTION 3 Grandfather existing evaluation models.
Delete the use of Dougall-Rohsenow as a generally acceptable correlation in Appendix K.
For future evaluation models require licensees to demonstrate the acceptability of post-CHF correlation.
OPTION 4 Remove Dougall-Rohsenow from existing and future evaluation models.
Use of Dougall-Rohsenow would have to be justified for every evaluation model.
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