ML20114C377
| ML20114C377 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 01/31/1985 |
| From: | ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY |
| To: | |
| Shared Package | |
| ML13309B505 | List: |
| References | |
| CEN-293(S)-NP, NUDOCS 8501300227 | |
| Download: ML20114C377 (14) | |
Text
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SONGS-2 End of Cycle 1 Shoulder Gap Evaluation f
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'A January,1985
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4 LEGAL NOTICE THIS REPORT WAE PREPARED AS AN ACCOUNT OF WORK SPONSORED BY COMUSTION ENGINEERING, INC. NEITHER COMSUSTION ENGINEERING NOR ANY PERSON ACTING ON ITS SEHALP:
A.
MAKES ANY WARRANTY OR REPRESENTATION, EXPRESS OR llWUED INCLUDING THE WARRANTIES OF PITNESS POR A PARTICULAR PURPOSE OR MERCHANTAStuTY, WITH RESPECT TO THE ACCURACY, COMPLETENESS, OR USEPULNESS OF THE INFORMATION CONTAINED IN THIS REPORT, OR THAT THE USE OF ANY INFORMATION, APPARATUS, METHOO, OR PROCESS Ol8 CLOSED IN THIS REPORT MAY NOT INFRINGE PRIVATELY OWNED RIGHTS;OR B. ASSUMES ANY UABIUTIES WITH RESPECT TO THE USE OF, OR FOR DAMAGES RSSULTING PROM THE USE OF, ANY INFORMATION, APPARATUS, METHOO OR PROCESS DISCLOSED IN THIS REPORT.
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SONGS-2 End of-Cycle 1 Shoulder Gap Evaluation I. Introduction San Onofre Nuclear Generating Station, Unit 2 (SONGS-2) completed Cycle 1 operation on October 21, 1984 During the refueling outage, measurements of the shoulder gaps (distance between the top of the fuel rods and the bottom of the upper end fitting) and fuel assembly guide tube lengths were taken in 23 fuel assemblies.
These measurements were taken as part of the inspection program identified in Reference (1). This report summarizes those inspections and describes the shoulder gap analyses performed that l
justify the fuel assemblies being operated for a second cycle.
l Shoulder gaps change with residence time in the reactor due to differential growth between the fuel rods and the fuel assembly f
L structure (guide tubes). Measurements taken at the first plant using the 16 x 16 fuel design (Arkansas Power and Light's ANO-2 plant, docket 50-368) revealed shoulder gaps less than those predicted. Mechanical modifications, namely, the installation of guide tube shims, were made to selected ANO-2 Batch C fuel c
assemblies to ensure that adequate shoulder gap was available for the third cycle of operation for those assemblies (Reference (2) and (3)). Measurements of shoulder gap changes have now been made at ANO-2 on selected fuel assemblies after Cycles 1, 2 and 3.
These measurements have provided the opportunity to monitor the actual behavior of the 16 x 16 fuel design, and thus permit a more L
accurate evaluation of shoulder gap changes for fuel assemblies being inserted for their second or third cycle.
l The inspection program at $0NGS-2 was designed to provide data for justification of Cycle 2 operation for the SONGS-2 fuel.
II. Shoulder Geo' Criterion and Evaluation (Pre-Shutdown)
The criteria used to evaluate the adequacy of the shoulder gaps at the end of Cycle 2 is as follows:
I At a 95% probability, the worst rod in the assembly will not have shoulder gap closure at the end of Cycle 2.
Theevaluationapproachfor50NGS-2[4)icle2.parallelsthemethod C
used for ANO-2,~ Batch D (Reference
, i.e., end of Cycle 2 shoulder gap predictions were based on the minimum available -
shoulder gap at the beginning of life, a conservatively-high fuel rod growth prediction and a conservatively low guide tube grnwth prediction. These parameters are discussed in more detail below:
I
a.
The minimum available shoulder gap at the beginning of life accounted for component dimensional tolerances, elastic compression of the guide tubes, and differential thermal expansion between the fuel rods and the guide tubes. ' The end result was to ryluce he 1.332 inch nominal initial shoulder gap (cold) to a
. inch minimum shoulder gap (hot).
b.
The conservatively high fuel rgd grqwth prediction was taken from the ANO-2 Batch data as, jinchesofgrowthperunit of -fluence (nyt x 10'gg).
This growth rate represents better than a 95/95 prediction of the ANO-2 Batch C data (Figure 1),
which was the fuel type with the highest observed rates.
c.
The conservatively low guide tube growth prediction utilized the lower 95% value calculated using the methods described in Reference (5).
Figure 2 is a comparison of the predictions of the analytical model to the ANO-2 guide tube growth data for assemblies with similar guide tube materials (cold-worked Zircaloy) as in the 50NGS-2 assemblies.
The figure shows that.;
using the lower 95% prediction is conservative relative to all the measured data.
Implementation of this approach for the $0NGS-2, Cycle 2 fuel assemblies showed that all shoulder gaps were predicted to have clearance at the end of Cycle 2.
Therefore, if shoulder gap and k
guide tube length measurements taken on 50 HGS-2 fuel assemblies support the applicability of the predictive models, the second cycle fuel would be justified for Cycle 2 operation.
III. Shoulder Gap and Guide Tube tenoth Measurements The fuel inspection program which provided the data for the evaluation of Cycle 2 shoulder gap adequacy consisted of shoulder gap and guide tube length measurements on a total of 23 fuel assemblies; 4 Batch 8 and 19 Batch C.
The 23 measured assemblies are shown in their Cycle 1 loading pattern in Figure 3.
Guide tube measurements were made on each of the four outer guide tubes in each assembly. Shoulder gap measurements were made on all peripheral fuel rods on the four faces of each assembly.
The guide tube length change data and the shoulder gap cnange data are shown in Figures 4 and 5, respectively,
!Y. Shoulder Gao Evaluation (Post-Shutdown)
Guide tube length change data for SONGS-2 are shown in Figure 4 Also shown in Figure 4 are the length change credictions (lower 95%, best estimate, and upper 95%) resulting from the method describedinReference(5). The figure shows that the measured data are close to the predicted best estimate, and that the limits of the predicted growths (upper and lower 95%) are conservative relative to all the data.
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..e The shoulder gap change data for SONGS-2 are shown in Figure 5,
=along with the design prediction for gap change that was calculated by the method previously described in Section II.
Although the design prediction represented at least a 95/95 bound of the data, the proximity of the data to the prediction, coupled with the knowledge that the guide tubes are growing in excess of what is assumed in the prediction (lower 95%), indic1ted that some fuel rods may have grown at rates higher than the, jinch/unytassumed in Section II. Therefore, the measurement data was investigated to determine how the calculated fuel rod growth rates at SONGS-2 l
. compared with those from ANO-2.
Since a change in shoulder gap is the difference between the guide tube growth and the fuel rod growth, fuel rod length changes can be inferred from the shoulder gap changes and guide tube length changes.
Fuel rod growth rates can then be detennined by dividing the inferred fuel rod growth by the rod's calculated fast fluence.
This has been done for the SONGS-2 shoulder gap data and the resulting fuel rod growth rates are plotted in Figure 6 along with the growth rate data for ANO-2, Batch C.
i The ANO-2 growth rate data presented in Figure 6 shows that the limiting behavior in the fluence range of two and three cycle expo 3ures is not a function of fluence, but is a constant rate of inch /unyt. The low fluence, one cycle SONGS-2 data, however, shows the limiting ' behavior to be dependent on fluence _and that the rates for the low fluence rods can be in excess of thel jin/unyt i
value. Although the 50NGS-2 data that exhibit very high growth a
rates came from a fluence region for which there is no ANO-2 Batch C data available, Figure 6 shows that the trend of the SONGS-2_ data Lis to approach the ANO-2 data as the SONGS-2 fluences increase.
The ANO-2 data is therefore concluded to represent an extrapolation of the SON 65-2 data at higher.fluences and the design line shown in Figure 6 represents at least a 95/95 bound which can be used to predict fuel rod growth rates. The only modification this makes to the method described in Section II is that now the predictive model for fuel rod growth rate is a function of fluence rather than a i
single value throughout life.
Employing the variable fuel rod growth rate model in the method
- described in Section II results in the revised design prediction shown in Figure 7.
As that figure shows, the revised design prediction is conservative relative to all the measurements and the.
prediction shows clearance at the end of Cycle 2.
Based on these results, it is concluded that all the second cycle assemblies being loaded in SONGS-2 Cycle 2 are acceptable for operation through Cycle 2 with respect to-shoulder gap changes.
V. Conclusions i
1.
The length changes of the cold-worked SONGS-2 guide tubes are close to the best estimate prediction and the limits of the predictions (upper and lower 95%) bound all the data (See-Figure 4).
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2.
The inferred fuel rod growth rates for SONGS-2 show a fluence dependency with the lowest fluence rods showing the highest growth rates, at least in the limits. The two and three cycle ANO-2 Batch C fuel rod growth rates have been shown to be acceptable as an extrapolation of the SONGS-2 data. The result is a fuel rod growth rate model that is a function of fluence (see Figure 6).
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3.
.The revised design prediction with the variable fuel rod growth model has been shown to be conservative relative to the data (See Figure 7).
4.
It is concluded that all fuel assemblies being loaded in Cycle 2 satisfy the shoulder gap criterion for Cycle 2 without requiring increases in their shoulder gap.
VI. References 1.
" San Onofre Nuclear Generating Station Units 2 and 3, Cycle 2 Reload Analysis Report", September, 1984.
2.
J. R. Marshall to Robert A. Clark, Docket No. 50-358, Letter # 2CAN128207, 12/10/82.
3.
J. R. Marshall to Robert A. Clark, Docket No. 50-368, I
Letter # 2CANO.38307, 3/10/82.
4.
CEN-261 (A), " Arkansas Nuclear One, Unit 2 Cycle 4 Shoulder Gap Evaluation", issued November,1983.
5.
CENPD-198-P, "Zircaloy Growth In-Reactor Dimensional Changes in Zircaloy - 4 Fuel Assemblies", December 1975, including Supplement 1, December, 1977, and Supplement 2, November, 1978.
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. FIGURE 2:
Guide Tube i.ength Change Versus Design Predictio'ns for ANO-2 Assenblies with Cold-Worked Guide Tubes
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FIGURE 5.
SONGS-2. Shoulder Gap Change Data and Design Prediction (Constant Fuel Rod Growth Rate)
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SONGS-2 Shoulder Gap Change Data and Rsvis:d Design Prediction (Variable fuel Rod Growth Rate) 2 o
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