ML19254D954
| ML19254D954 | |
| Person / Time | |
|---|---|
| Issue date: | 10/18/1979 |
| From: | Rubenstein L Office of Nuclear Reactor Regulation |
| To: | Taylor J BABCOCK & WILCOX CO. |
| References | |
| NUDOCS 7910300359 | |
| Download: ML19254D954 (6) | |
Text
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,C, UNITED STATES yy fj NUCLEAR REGULATORY COMMISSION 4 4.', ?, A c
wAsWNGTON, D. C. 20555
'I$$G OCT 18 lCN Mr. James H. Taylor Manager, Licensing Babcock & Wilcox Company Nuclear Power Generation P. O. Box 1260 Lynchburg, Virginia 24505
Dear Mr. Taylor:
SUBJECT:
EVALUATION OF INTERIM PROCEDURE FOR CALCULATING DNER REDUCTI0f1S DUE TO ROD B0W We have completed our evaluation of your report entitled " Determination of the Fuel Rod Bow DNB Penalty" (Reference 2).
We have @termined that the proposed method described in this report, as modified by the information provided in References 4 and 5, is acceptable for use in licensing calcula-tions. A summary of our evaluation is enclosed.
If our criteria or regulations change, such that our conclusions concerning this report are invalidated, we will notify you and provide you with an opportunity to revise and, if you desire, rest.bmit this report for our review.
In your letter of March 27,1979 (Reference 4), you requested that Appendix A, "The Analysis of the Bowed and Unbowed CHF Test Date," be withheld from public disclosure pursuant to 10 CFR 2.790.
In support of th1: request, you submitted an affidavit with your letter of March 27, 1979, which contained statements as to the reasons for withholding this information from public disclosure.
We have reviewed your application a.id material based on the requirements and criteria of 10 CFR 2.790 and have determined that the above-mentioned document sought to be withheld contains trade secrets or confidential or privileged commercial or financial information.
We also have found at this time that the right of the public to be fully apprised as to the bases for and effects of the proposed. licensing action does not outweigh the demonstrated concern for protection of your competitive position.
Accordingly, we have determined that the information should be withheld from public disclosure.
We therefore approve your request for withholding pursuant to 10 CFR 2.790 and are withholding Appendix A from public inspection as proprietary.
Withholding from public inspection shall not affect the right, if any, of persons properly and directly concerned to inspect the documents.
If the need arises, we may send copies of this information to our consultants working in this area.
We will, of course, assure that the consultants have signed the appropriate agreements for handling proprietary data.
1229 164 79,0300357 C.
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l',r. Janes H. Taylor -
If -he basis for withholding this information from publi: inspec-ion should char.ge in the future such that the information could then be made available for public inspection, you should promptly notify the NR:.
Sincerely, y
.O N hJf L
'GC QT,
L. S. Ru enstein, Acting Chief Light Water Reactors Eranch No. 4 Division of Project Management
Enclosure:
As stated cc:
Mr. Robert B. Borsum Babcock & Wilcox Company 7735 Old Georgetown Road Bethesda, Maryland 20014 l 2 b' I
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References 1
Letter from D. B. Vassallo, USi!RC, to J. H. Taylor, E&W, June 12, 1978.
2.
Letter from J. H. Taylor, B&W, to D. B. Vassallo, US"RC, Dccember 12,1978.
3.
Letter from S. A. Varga, USf;RC, to J. H. Taylor, B&W, March 12, 1978.
4 Letter from J. H. Taylor, B&W, to S. A. Varga, L5!!RC, t' arch 27, 1979.
5.
Letter from. J. H. Taylor, B&W, to S. A. Varga, USI'RC, June 22, 1979.
IJ29 166 O
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-E"C LC S U D.E The reduction of fuel rod spacing due to fuel rod bowing has been shcwn ex;erimentally to result in a reduction in the departure from.ucleate boiling ratio (DNBR). The magnitude of this reduction in CN3R is a function of the closure of the gap between adjacent fuel rods.
Eabcock & Wilcox perfor ed a series of experiments in which the spacing was reduced to 55';
of the ncminal. The conclusion drawn from these experiments by E&W was that at this spacing, no reduction in DNBR occurs.
This conclusion was used by S&W in a suggested staff procedure adooted by E5W for calculating the reduction in the DNBR safety linit for a reactor core.
B&W presented their analysis in Reference 2.
We reviewed this procedure and the accompanying data (as presented in References 2 and 4).
It was our conclusion from this review that upon statistically testing the hypothesis that there was a DNBR reduction at 555 closure, the hypothesis could r-t be rejected at a 955 confidence level; that is, there appeared to Ls a reduction in DNBR at 555 gap closure.
After discussions with B&W, S&W proposed a statistical procedure to account for the fact that there was a non-zero probability of a DNSR reduction at 555 gap closure.
This procedure is described in 2,eferenc. ;. The procedure is illustrated in Figure 1.
Rather than drawing a line f"am the DNBR reduc-tion resulting from 100% closure to a zero reduction in LNPR at 55'; (the dotted line in Figure 1), a finite reduction in DNBR is calculated at 555 gap closure based on the difference between the means of the data from the bowed bundle (C10) and the similar unbowed bundle (C9).
Including this effect, as can be seen by the solid line in Figure 1, results in the DNBR reduction being predicted to become non-z tro at a gap closure of less tN o 5 5 *;.
This analysis does not take into account the variation of all the critical heat flux data submitted by B&W in Reference 4, it only compares Clir' data from bundle C9 (unbowed) with CHF data from bundle C10 (bowed).
Thus, the analysis is not as conservative as it could have been, but it is our judgement that the B&W procedure is sufficiently conservative for li-censing calcu.lations.
Applying the B&W proce6e results in a reduction in DNER at a bur.dle average burnuo of 33,000 Mwd /F'U (a typical end-of-life burnus) of 2.55.
31W Jid r-: dis:uss generic nargins which may be available to offset this :NER reduc-ti:n.
'le, therefore, expect that any Targins available to cf' set this C..ER re:uction will be acdre sed on each reload e. 5it:al, i' :esirec.
1227 167
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It should alsb be noted th't the CHF data presented by S&W in Reference 4 was used only to estabiish a threshold for an anount of fuel rod bowinc at which there would be a CNER reduction. To accomplish this, only the variation of the data was required, the critical heat flux values were not used. The data are presently being reviewe'd by the staff and the use in the context of fuel rod bowing does not imply accectance by us of the data or the resulting SWC correlation for other applications.
Co ncl usic;,
The procecere suggested by Babcock & Wilcox in Reference 2 and codified in Reference 5 for calculating the reduction in DNER due te fuel rod cowing is acceptable for licensing calculations. Acceptance of this procedure does not imply acceptance of the CHF data or the BWC correlati:n f:r other applica-tions. This is stiP. under review by the staff.
Any margins used to offset the reduction in DNBR due to fuel rod bowing should be discussed in the individual reload or OL applications.
122'l i 68
IGURE 1 f
flew B&W CURVE FOR REDUCTI0fl Ill DilBR DUE TO FUEL R0D B0WiflG flu innin Reduction
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IN DflBR Reduction Assuming E
DilBR Reduction Including
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fio Uncertainty in Point Uncertainty in Point of of Zero DilBR Reduction
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Zero DflBR Reduction
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__ g Y
~2 k;
}
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Decrease in DflBR due to N
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tincertainty in Point of N
Zero DflBR Reduction
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cy 0
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q 100 GAP CLOSURE (%)
DUE TO FUEL R0D B0WIrlG