ML17222A657
| ML17222A657 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 01/12/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17222A656 | List: |
| References | |
| NUDOCS 8901190379 | |
| Download: ML17222A657 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO PROPOSED C-E METHODOLOGY FOR ADJUSTED REFERENCE TEMPERATURE CALCULATIONS FLORIDA POWER AND LIGHT COMPANY ET AL.
ST.
LUCIE PLANT UNIT NO.
2 DOCKET NO. 50-389
- 1. 0 INTRODUCTION On November 27, 1987 (supplemented by letters dated May 4 and 20, 1988) Florida Power and Light Company (FPL) applied for approval of certain changes in the pressure-temperature (P-T) limits in the Technical Specifications for St.
Lucie Unit 2.
Included in the submittal was Attachment 5, "Methodology For Adjusted Reference Temperature Calculations,"
prepared by Combustion Engineering in support of the application for St.
Lucie Unit 2 and for a later submittal expected for St.
Lucie Unit 1.
This Safety Evaluation (SE) contains a review of the "C-E Methodology" as it was applied to the St.
Lucie Units and also provides some guidelines for implementation of the last paragraph in Section
- 2. 1 of Regulatory Guide 1.99, Revision 2.
It states:
For plants having surveillance data that are credible in all respects except that the material does not represent the critical material in the
- vessel, the calculative procedures in this guide should be used to obtain mean values of shift, bRT T.
In calculating the margin, the value of o<
may be reduced from the vNues given in the last paragraph of Regulatory Position
- 1. 1 by an amount to be decided on a case-by-case
- basis, depending on where the measured values fall relative to the mean calculated for the surveillance materials.
Implementation of this paragraph is one of two issues raised by the C-E Methodology.
The other issue concerns the calculation of attenuation of neutron fluence through the reactor vessel wall.
The procedure used by C-E differs from that given in Revision 2 as discussed below.
2.0 DISCUSSION OF THE ATTENUATION ISSUE Equation 3, the formula for attenuation of fluence through the vessel wall, was put in Revision 2 to facilitate the consideration of changes in neutron energy spectrum with location in the wall.
Public comments on Revision 2 and earlier comments on the PTS rule from specialists in the mechanism of radiation embrittlement convinced the staff that this was "better science."
It is, of course, the conservative approach.
390ii90379 390li2 PDR ADDCK 05000389 P
The C-E Methodology does not use the Revision 2 attenuation formula; instead, it uses values of fluence, n/cm~ (E>lMeV), from their neutron transport calcu-lations.
Thus, they do not account for changes in the neutron energy spectrum.
No justification is given other than to say that the final result -- the proposed P-T limits -- "are sufficiently conservative with respect to the guidelines" of Revision 2.
In reviewing proposed P-T limit submittals, the NRC staff normally does not insist on a particular calculational procedure -- they simply test the proposed limits against limits calculated using the procedures given in NRC regulatory documents.
However, the licensee, FPL, asked for a review of,the C-E Methodology.
Therefore, we conclude that its treatment of fluence attenuation is not acceptable, because it does not consider the effects of changes in the neutron energy spectrum.
Revision 2 does permit licensees to use displacements per atom calculations made as part of the fluence analysis for the vessel as an alter-native to using Equation 3 from Revision 2.
- 3. 0 DISCUSSION OF THE MARGIN ISSUE -" ST.
LUCIE UNIT 2 As quoted in the Introduction of this SE, Revision 2 provides for consideration of a reduction in the margin on b,RT if there are credible surveillance data from the plant in question.
The C-E 8$ hodology takes advantage of this provision and reduces the quantity, vb, in Equation 4 by half.
The justification provided for St.
Lucie Unit 2 in Figure 3 is a curve labeled "RTND Shift" for the controlling
- material, P/ate M-605-2, and a plotted point for the measured value -- 35~F shift at 1.6 X 10 n/cm~ -- for the surveillance material reported for Capsule W-83.
The plotted point falls slightly below the curve.
However, the copper and nickel contents for the surveillance material are slightly lower than for the controlling material.
When the plotted point is moved upward to correct for the ratio of chemistry factors for the two materials (92/74), it falls slightly above the curve for the controlling material.
The C-E Methodology also plots surveillance data from six other plants that had plate materials with similar copper and nickel contents.
When corrected for the difference in chemistry factors, these data fall somewhat above the "RTn~ Shift" curve with one exception.
Howeve~, the use of data from other plahP4 is irrelevant to the question this plot is supposed to address:
- namely, what do the surveillance data from the reactor in question, St.
Lucie Unit 2, tell us about the radiation environment in that reactor -- is it typical of conditions in the reactors from which the surveillance data base comes?
- 4. 0 DISCUSSION OF THE MARGIN ISSUE -- ST.
LUCIE UNIT 1 For St.
Lucie Unit 1, the controlling material is axial weld 3-203, but the surveillance weld matches the circumferential weld 9-203.
Their compositions are different:
0.23K Cu and 0. 11K Ni for the surveillance weld, 0.30K Cu and 0.64 Ni for the controlling weld.
The C-E Methodology did not compare the measured shift from surveillance to the mean value calculated using Revision 2.
- Instead, Figure 5 shows data from another plant (Beaver Valley) that had the St.
Lucie Unit 1 controlling material in its surveillance program.
As discussed above, this comparison is irrelevant to the question.
5.0 IMPLEMENTATION OF THE REVISION 2 PROVISION ON MARGIN -- ST.
LUCIE UNITS 1 AND 2 The last paragraph of Section
- 2. 1 begins:
"For plants having surveillance data that are credible in all respects except that the material does not represent the critical material in the vessel..."
Omitted from the C-E Methodology is any discussion of the credibility of the surveillance data for St.
Lucie Units 1 and 2.
In Revision 2, Section B, there are five criteria for "credibility":
1.
Materials in the capsules should be those judged most likely to be controlling with regard to radiation embrittlement according to the recommendations of this guide.
2.
Scatter in the plots of Charpy energy versus temperature for the irradiated and unirradiated conditions should be small enough to permit the determination of the 30-foot-pound temperature and the upper-shelf energy unambiguously.
3.
When there are two or more sets of surveillance data from one reactor, the scatter of b,RT values about a best-fit line drawn as described in Regulatory Posit%
- 2. 1 normally should be less than 28'F for welds and 17~F for base metal.
Even if the fluence range is large (two or more orders of magnitude),
the scatter should not exceed twice those values.
Even if the data fail this criterion for use in shift calculations, they may be credible for determining decrease in upper-shelf energy if the upper shel f can be clear ly determined, following the definition given in ASTM E 185-82 (Ref.l).
4.
The irradiation temperature of the Charpy specimens in the capsule should match vessel wall temperature at the cladding/base metal interface within 225XF.
5 ~
The surveillance data for the correlation monitor material in the capsule should fall within the scatter band of the data base for that material.
Although Criterion 1 is excepted for this discussion, the close similarity of the surveillance plate chemistry to the controlling plate chemistry for St.
Lucie Unit 2 is an argument in favor of its use in considering a reduced margin.
Conversely for St.
Lucie Unit 1, the dissimilarity of the surveillance and controlling welds is an argument against consideration of those surveillance data.
Criterion 2 requires a review of the plots of Charpy energy versus temperature, given for Capsule W-83 from St.
Lucie Unit 2.
Scatter is fairly large, and the measured shift being only 35~F, its credibility is low.
For Capsule W-97 from St.
Lucie Unit 1, scatter is not a problem.
Criterion 3 requires two or more surveillance results.
Having only one weakens the argument for St.
Lucie Units 1 and 2 with regard to Criterion 3, of course, but it also weakens the argument generally.
Criterion 4 is not pertinent to this discussion.
Criterion 5 cannot be applied, because there were no correlation monitor materials in these capsules.
- 6. 0 GENERAL In order to make use of the provision given in the last paragraph of Section
- 2. 1 of Revision 2 permitting consideration of reduced margin if the plant has credible surveillance
- data, the following guidelines should be met:
l.
At least two surveillance results should be available.
2.
Surveillance material should be similar to the controlling material.
3.
Measured shift should be large enough and scatter in the Charpy curves should be low enough to permit determination of the shift unambiguously.
When these guidelines are met, the comparison of measured shifts from the surveillance program for the plait in guestion with calculated shifts (mean values) using Revision 2 is more meaningful
~
CONCLUSION The C-E Methodology for Adjusted Reference Temperature Calculations is deficient in two respects:
1.
The calculations of fluence and RT T at the 1/4t and especially at the 3/4t locations in the vessel wall I not account for the effect of changes in neutron energy spectrum with depth in the wall.
2.
Inadequate justification was offered for reducing the margin on ARTNDT based on having plant surveillance data that were credible in all
- respects, except the controlling material was not represented in the capsule.
The C-E Methodology did not discuss how well the surveillance results (a single capsule for each plant) met the criteria for credibility, and it did not compare the surveillance data with the predictions of Regulatory Guide 1.99, Revision 2 for the copper and nickel contents of the surveillance material.
- Instead, the C-E Methodology reported surveillance data from other reactors, which was not relevant to this issue.
This submittal is the first attempt to use the Revision 2 paragraph on margin reduction.
This SE presents some guidelines for its use in future submittals.
With regard to the review of P-T limits for St.
Lucie Unit 2, an SE has already been sent to the licensee, dated June 14, 1988 approving the limits for only 6 EFPY.
Dated:
January 12, 1989 Princi al Contributor P.
Randall
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