ML090140287

E-mail from Ellegood to M. Chawla Et Al. Palisades SFP Racks with Attachment: Report on Resolution of Outstanding Concerns on Spent Fuel Pit Rack Localized Swelling Palisades Nuclear Plant

ML090140287
Person / Time
Site:	Palisades
Issue date:	07/16/2008
From:	John Ellegood NRC/RGN-III
To:	Mahesh Chawla, Jack Giessner, Lerch R, Christine Lipa, Thomas Taylor, Ross Telson, Frank Tran, Kent Wood NRC/RGN-III
References
FOIA/PA-2009-0026
Download: ML090140287 (16)

Text

,-John Giessner From: John Ellegood.,

Sent: 'Wi-dnesday,July 16, 2008 8:56 AM,;

To: 'Mahesh Cliawla-; Ross Telson; Christine Lipa; John Giessner; Ross Telson; Christine Lipa; Robert Lerch; Frank.Tran; Thomas Taylor; Kent Wood

Subject:

• REiP-aliades-, FP-racks--

Attachments: nus-assess-doc-,-sf &cl.-pd f I have attached the earlier analysis done by Entergy to determine the effects of absorber loss on Keff. In addition, I attached the results from the first panel of the first cell. Data has been collected from 4 or 5 more panels but the data has not been analyzed. Based on the shape of the curves, the licensee believes those panels will fail as well.

From: Mahesh Chawla Sent: Wednesday, July 16, 2008 9:23 AM To: Ross Telson; Christine Lipa; John Giessner; John Ellegood; Ross Telson; Christine Lipa; Robert Lerch; Frank Tran; Thomas Taylor

Subject:

FW: Palisades SFP racks FYI From: Lambros Lois Sent: Wednesday, July 16, 2008 8:48 AM To: Mahesh Chawla Cc: Gregory Cranston; Kent Wood

Subject:

RE: Palisades SFP racks Mahesh:

Kent Wood of SRXB is in charge of SFPs and he has this project. I'm forwarding this to Kent.

Lambros Lois.

From: Mahesh Chawla Sent: Wednesday, July 16, 2008 8:30 AM To: Lambros Lois Cc: John Giessner; John Ellegood; Ross Telson; Christine Lipa; Robert Lerch; Frank Tran; Thomas Taylor

Subject:

FW: Palisades SFP racks Lambros, Let me know if you need more information or discussion on this issue. Thanks From: John Ellegood Sent: Wednesday, July 16, 2008 7:25 AM To: Ross Telson; Christine Lipa; Mahesh Chawla Cc: John Giessner; Robert: Lerch; Frank Tran; Thomas Taylor

Subject:

Palisades SFP racks The licensee has some preliminary results from the BADGER testing of the SFP racks. The first panel did not meet the density requirements. The data from the next four panels is in analysis but the preliminary evil indicates they will not pass.

The licensee has an analysis that shows Keff is less than .95 with no credit for the racks provided SFP boron is above 2054. It is at 2732.

I'll keep you posted.

Mac- do you who we spoke with on the SFP swelling rack issue?

John Ellegood 2

Report on Resolution of Outstanding Concerns on Spent Fuel Pit Rack Localized Swelling Palisades Nuclear Plant SUBJECT This report addresses concerns raised by the NRC on the reliability of the Palisades Spent Fuel Pit (SFP) Region I storage racks to maintain fuel in a subcritical condition in accordance with the original rack design as identified in Technical Specification (TS)

Section 4.3.1, and in consideration of the effects of potential neutron absorber localized degradation.

SUMMARY

OF CONCLUSIONS Based on a review of Palisades reports and observations made to date, and as corroborated by rack surveillance evidence elsewhere in the industry, reasonable assurance exists to support the position that the neutron absorber has not degraded in the Region I racks. Furthermore, an internal Entergy assessment provides reasonable assurance that, even if the neutron absorber were to be completely degraded, the 1R19 boron concentration in the SFP cooling water would more than compensate for any possible loss of reactivity holddown.

BACKGROUND Fuel assembly binding in Region I of the Palisades SFP has been observed since 1991 (Reference 1). This binding has been attributed to localized swelling of the Region I SFP racks due to gas buildup within the rack structure. In 1995, Palisades performed a re-evaluation (Reference 2) to update and more fully document the analyses associated with the localized rack swelling. As of this writing there are ten (10) fuel assemblies that cannot be extracted from the Region I racks due to localized swelling.

Since the affected assemblies are generally in isolated rack locations, with only two in adjacent.cells, it is possible to access these cells for testing or venting of the buildup gas, once the surrounding fuel assemblies have been removed. The SFP is completely filled at the present time. Therefore, repair activities are not possible until completion of the next dry cask storage program at Palisades, currently scheduled for spring 2008.

An additional concern regarding future repair work is the caution associated with cutting or grinding in the vicinity of a trapped pocket of hydrogen gas, even under water.

Entergy is reviewing possible approaches to rack maintenance and repair that should minimize risk of inadvertent combustion, but, again, this emphasizes the position that adjacent cells must be empty in order to take action to vent the trapped gas.

Page 1 of 5

The NRC has voiced concern that the affected Palisades rack cells may be experiencing degradation of neutron holddown, due to potential leakage or slumping of the boron carbide (B4C) neutron absorber within the swollen rack areas. As described in the sections that follow, Entergy has reviewed the engineering bases for the racks and performed a criticality assessment to 'determine the potential impact of absorber degradation.

REVIEW OF RACK ENGINEERING BASES An extensive evaluation was completed by Palisades in support of the Condition Report evaluated in Reference 2. This included input from the B4C manufacturer, the Carborundum Company. Some of the general conclusions of the report are:

• There was visible evidence of an unidentified black material leaching through the vent holes. This could represent a small loss of B4C material. However, because the vent holes are near the tops of the cells and the amount of observed material is small, the impact of any B4C material loss is expected to be very slight.

• The Carborundum Co has reviewed the data (as reported in Reference 3) and concluded that the black material is very likely a boron compound but notes that boron leachability over time is relatively low, although there is no test data to document leaching over a 10-15 year time span.

• There are no vent holes at the base of the racks. Thus, a slow discharge of degraded B4C material, with its inherent loss of reactivity holddown, is not considered a credible scenario.

In addition, interviews with Engineering personnel confirm that the actual locations of the vent holes are below the tie plate, but slightly above the active core height.

Therefore, if the all the interior B4C above the vent were to leak through the holes, there would be an insignificant amount of reactivity holddown degradation in the active fuel region.

Because Palisades does not have rack material surveillance coupons, Palisades has requested supporting information from the Kewaunee plant, which uses a similar B4C rack design and Which has an active surveillance plan. Kewaunee responded (Reference

4) by stating that other than some possible B4C dust leakage and some observed chipping (most likely due to the effects of handling), there was no visible degradation of the B4C material. However, as Kewaunee does not test for brittleness, they were unable to confirm that B4C would not degrade under long-term temperature and radiation exposure. Therefore, it reasonable and conservative to assume at least some degree of B4C degradation over time.

As noted above, there are no vent holes at the rack base to permit egress of degraded B4C. As the majority of the racks remain in their original configuration, we can conclude that, except for the swollen racks, the B4C remains in place. For the swollen Page 2 of 5

rack locations, it is conceivable to consider a B4C "slumping" effect, in which the degraded neutron absorber, now in powdered form, sinks to a lower level inside the racks, as would a liquid. Realistically, the maximum amount of slumping would reduce the absorber height to no lower than approximately 80% of its original position.

However, because slumping to that degree could remove neutron absorber function in the very top of the affected rack locations, Entergy has elected to perform a criticality assessment, considering the potential for B4C loss and crediting SFP boron concentration to compensate.

CRITICALITY ASSESSMENT In order to provide assurance that k-effective was remaining within the limits of design basis assumptions, Entergy has completed a criticality assessment, with SFP boron concentration credited for reactivity holddown in lieu of B4C. Although the criticality analysis of record (AOR) takes no credit for SFP boron in the Region I rack area, the assessment provides assurance that a k-effective below 0.95 will be maintained until such time as rack repairs may be performed.

The criticality analysis was prepared using the existing model of the Palisades Region I racks from the AOR (Reference 5). Note well: The MONK computer code, used previously for the criticality analysis, is no longer available. Therefore, the racks were modeled using the CASMO series of modeling codes (Reference 6), which are compatible with the rack model used by MONK. CASMO-4 was used for the calculated criticality values, with an independent check on CASMO-3 for each Eigenvalue.

However, Entergy is not licensed to use CASMO for design basis calculations: therefore, the results that follow must be considered as an assessment, suitable for operability determination, rather than a formal calculation.

Assumptions associated with the criticality assessment are as follows:

• The model assumes the entire Region 1 is filled with new fuel enriched to 4.95 w/o U-235, as noted in Technical Specification 4.3.1 (Reference 7);

The model takes no credit for B4C reactivity holddown. In other words, it assumes complete degradation of all neutron absorber and its replacement in the gap by B4C off-gas. This is an extremely conservative position, but is retained as it (1) provides a more straightforward model and (2) bounds the current conditions; Because the U-235 enrichment is a nominal one, several cases were repeated for an actual enrichment of 5.00 w/o, which is the nominal value of 4.95 w/o U-235 plus a manufacturing uncertainty of 0.05 w/o;.

• In order to establish the most conservative conditions, an additional case was run with the gap filled with water instead of gas.

Page 3 of 5

The code was run for a variety of SFP boron concentrations. The most significant of these are 1720 ppm, which is the minimum SFP boron concentration required by the Palisades Technical Specification 3.7.15 (Reference 8) and 2550 ppm, which is the 1R19 refueling boron concentration. 2550 ppm is also a procedural minimum (Reference 9) for normal operation in Modes 1-4, required to ensure core subcriticality after a design basis seismic event. For normal operation in Modes 5 and 6, a procedural minimum SFP boron concentration of 1800 ppm is specified.

With these considerations in mind, the results of the criticality assessment are as follows Results are in units of k-inf, which is criticality in infinite array, and bounds (i.e. is always greater than) k-effective:

1. The k-inf for Region 1, crediting a 1720 ppm boron concentration in the SFP, is below 0.98.

2. The k-inf for Region 1, crediting an 1800 ppm boron concentration in the SFP, is below 0.98.

3. The k-inf for Region 1, crediting a 2550 ppm boron concentration in the SFP, is below 0.92.

4. The SFP boron concentration corresponding to a k-inf of 0.95 is approximately 2054 ppm.

5. These conclusions remain valid if the gas within the rack is replaced by unborated water.

6. Increasing enrichment from 4.95 w/o to 5.00 w/o U-235 results in a slight increase in k-inf, across a range of 0.0015 to 0.0027.

Therefore, based on the engineering review and criticality assessments described above, it is reasonable to conclude that B4C degradation, in the Region 1 affected areas, is likely to be very slight. However, any degree of degradation, up to and including complete loss of neutron absorber, is not expected to result in an increase of k-effective above 0.95 while the SFP boron concentration remains at or above the procedural minimum of 2550 ppm. /

Written by:

Reviewed by:

Page 4 of 5

REFERENCES

1. Palisades Deviation Report D-PAL-91-015H

2. Palisades Condition Report C-PAL-95-0343

3. Consumers Power Co Memorandum SEL94*008, Lucier to Krueger, "NUS Spent Fuel Pool Rack Boron Carbide Neutron Absorber Information," 6/13/94

4. E-Mail from Jeffery Ladewig (Kewaunee) to G. T. Wiggins (Palisades) 9/19/07

5. Palisades Calculation EA-SFP-97-02, "Region I Fuel Pool Criticality Calculations," 3/27/00

6. Computer codes CASMO-4 and CASMO-3

7. Palisades Technical Specification 4.3

8. Palisades Technical Specification 3.7.15

9. Palisades Procedures COP-27, COP-27-Basis, SOP-27, SFPO-3, DWC-11 D, DWC-11 D-Basis, PCSO-5, GOP-2

,1 Page 5 of 5

Pallisades Initial Data Analysis m Qualitative Analysis The following analysis shows the comparison of the calibration scan data with the first scan for the Pallisades neutron absorber test. Preliminary analysis shows that, for the first panel scanned, we must reject the hypothesis that this panel meets the minimum certified areal density value with 95% certainty.

For the individual elevation count rates, the uncertainty is Calculated as +/-

• t where oa- Counts and t Count Time. This bounds the count rate with 95% certainty based upon the counts having a poisson distribution.

Count Time uncertainty is less than 10-6 sec and, as such, is neglected.

The following plot shows the calibration scan count rates as a function of elevation for all 4 detectors.

CalScanl Count Rate, cps 60 1 i 50 40 30:&-

10 Elevation, in.

5 10 15

2 PallisadesAnalysis.nb 2 Palilsades Analysis.nb This plot can be compared with the first panel scanned, "Q6 South".

Q6SS2 Count Rate, cps Elevation, in 20 40 60 80 100 120 140 Both scans appear to have similar count rates in the absorber panel region. However, upon further examination, it can be shown that panel "Q6 South" may show a lower areal density (higher count rate) than the calibration cell which is manufactured at the minimum certified areal density value.

Pallisades Ahalysis.nb3 3 The following plot shows the calibration scan (in blue) for detector-2 overlaid upon the scan of panel Q6 South (in red) for the same detector. To exceed the minimum certified areal density value, we would expect that the average maximum count rate (minimum areal density) in the test panel should be less than the average minimum count rate (maximum areal density) in the calibration cell. For regions around 90" elevation, this is clearly not the case.

CalScanl 30 . . .

25 "

• 0.

20 0

0 15-15 20 40 60 80 100 120 Elevation, in

4 PallisadesAnalysis.nb m Statistical Analysis A more quantitative analysis can be performed by examining the average minimum and average maximum count rates for the calibration cell and test cell respectively.

SCalibration Cell Selecting data from the panel region of the calibration cell (between 3" and 10" elevation) shows the average minimum count rate and the associated standard deviation.

The following data shows the raw scan data for detector 2. Uncertainty is calculated as specified previously.

Data is in the format "{Elevation, Count Rate, Count Rate Uncertainty}'"

3.451 19.3667 1.13627 3.946 20.65 1.17331 4.442 20.5167 1.16952 4.956 19.9667 1.15374 5.451 20.1833 1.15998 5.947 19.4167 1.13774 6.443 20.2333 1.16142 6.938 20.85 1.17898 7.452 20.05 1.15614 7.948 19.1 1.12842 8.443 19.9167 1.15229 8.939 20.9833 1.18275 9.453 19.6833 1.14552 9.948 19.9667 1.15374 The average minimum count rate for detector-2 in the calibration cell scan is calculated from the above data.

Average Minimum Count Rate:

1 n

- Z (CountRatei - CountRateUncertaintyi) =

ni=1 18.9067 At a minimum, we would expect that a test panel count rate should not go above this value to be assured of conformance with the minimum certified areal density. Note that this does not take into account the standard deviation associated with the above calculation (shown below).

Minimum Count Rate Standard Deviation:

j 2 ((CountRatei - CountRat eUncertainty1 ) -AverageMinimumCountRate) n i.1 2

0.543706

- PallisadesAnalysis.nb 5 Test Panel "Q6 South" Selecting data from the panel region of the "Q62S" test cell (between 3' and 120" elevation) shows the average maximum count rate and the associated standard deviation.

The following data shows the raw scan data for detector 2. Uncertainty 'is calculated as specified previously.

Data is in the format "{Elevation, Count Rate, Count Rate Uncertainty}"

3.946 18.5778 1.28505 5.947 18. 1.26491 7.948 17.8 1.25786 9.948 17. 1.22927 11.949 18.9111 1.29653 13.95 18.7778 1.29195 15.95 17.9333 1.26257 17.951 19.1556 1.30488 19.952 19.1333 1.30412 21.952 19.6667 1.32218 23.953 18.3778 1.27812 25.954 18.3333 1.27657 27..954 17.7111 1.25472 29.955 19.6889 1.32292 31.956 18.4222 1.27966 33.938 18.5333 1.28351 35.939 18.1556 1.27036 37.939 18.9556 1.29805 39.94 18.5333 1.28351 41.941 19.0667 1.30185 43.941 18.9778 1.29881 45.942 18.1-333 1.26959 47.943 18.2 1.27192 49.943 19.2667 1.30866 51.944 19. 1.29957 53.945 18.2667 1.27425 55.945 18.8444 1.29424 57.946 19.2667 1.30866 59.947 18.2667 1.27425 61.947 19.6222 1.32068 63.948 20.5778 1.35246 65.949 19.2222 1.30715 67.949 19.4889 1.31619 69.95 19.5111 1.31694 71.951 18.9778 1.29881 73.951 18.8222 1.29348 75.952 20.7333 1.35756 77.953 20.1778 1.33925 79.953 20.0222 1.33407 81.954 20.9556 1.36481 83.955 22.2 1.40475 85.955 20.2667 1.34219

6 PallisadesAnalysis.nb 87.938 20.4889 1.34953 89.938 21. 1.36626 91.939 22.4 1.41107 93.94 20.7778 1.35901 95.94 20.6 1.35319 97.941 20.2444 1.34146 99.942 21.3333 1.37706 101.942 20.7778 1.35901 103.943 20.9333 1.36409 105.944 21.0444 1.36771 107.944 19.3333 1.31092 109.945 20.2667 1.34219 111.946 20.3111 1.34366 113.946 19.2222 1.30715 115.947 18.6667 1.28812 117.948 20.7333 1.35756 119.948 19.5111 1.31694 The average maximum count rate for detector-2 in the test cell scan is calculated from the above data.

Average Maximum Count Rate:

1n

- Z (CountRatei + CountRateUncertaintyi) =

n i=1 20.7578 This value exceeds the average minimum count rate associated with the calibration cell as established above.

Thus, we must reject the hypothesis that the test panel exceeds the areal density of the calibration panel which is at the minimum certified areal density.

For reference, the standard deviaiton of the maximum test cell count rate is calculated below.

Maximum Count Rate Standard Deviation:

n 2

• ((CountRatei + CountRateUncertainty) - AverageMaximumCountRate)

Z =

n i=1 1.11177

Pa/lisades Analysis. nb7 7 m Reference Material m Calibration Cell Data Palisades 2008 07/14/08,M. Harris,,

0,18,36,60 7/14/2008,10:55 AM,,

0.000,1749.000,2329.000,2355.000,1884.000 0.441,1689.000,2173.000,221-1.000,1748.000 0.954,1295.000,1711.000,1769.000,1461.000 1.450,1131.000,1379.000,1450.000,1257.000 1.946,981.000,1297.000,1385.000,1144.000 2.441,987.000,1155.000,1234.000,1110.000 2.955,996.000,1220.000,1306.000,1093.000 3.451,970.000,1162.000,1285.000,1055.000 3.946,1023.000,1239.000,1236.000,1083.000 4.442,945.000,1231.000,1328.000,1074.000 4.956,916.000,1198.000,1343.000,1070.000 5.451,1014.000,1211.000,1309.000,1154.000 5 .947,1029.000,1165.000,1329.000,1 126.000 6.443,984.000,1214.000,1236.000,1138.000 6.938,998.000,1251.000,127 1.000,11 28.000 7.452,1041.000,1203.000,1281.000,1113.000 7.948,952.000,1146.000,1265.000,1113.000 8.443,981.000,1195.000,1337.000,1108.000 8.939,1015.000,1259.000,1303.000,1115.000 9.453,966.000,1181.000,1265.000,1112.000 9.948,1017.000,1198.000,1254.000,1116.000 10.444,993.000,1212.000,1340.000,1 145.000 10.939,1083.000,1267.000,1369.000,1112.000 11.453,1111.000,1353.000,1430.000,1272.000 11.949,1346.000,1745.000,1766.000,1527.000 12.445,1701.000,2122.000,2171.000,1867.000 12.940,2126.000,2660.000,2741.000,2000.000 13.454,2487.000,3284.000,3230.000,2488.000 13.950,2761.000,3665.000,3508.000,2640.000 14.445,2808 .000,3698.000,3720.000,2623.000 14.941,2890.000,3824.000,3742.000,2649.000 15.455,2795.000,3722.000,3780.000,2752.000 15.950,2773.000,3668.000,3795.000,2619.000 16.446,2742.000,3731.000,3718.000,2632.000 16.941,2864.000,3743.000,3670.000,278 1.000 17.455,2900.000,3766.000,3910.000,2633.000 17.951,2879.000,3783.000,3772.000,2838.000

a 8Palfisades Analysis.nb Panel "Q6 South" Data Palisades 2008 07/14/08,M. Harris,,

0,144,72,45 7/14/2008,2:00 PM,,

0.000,650.000,795.000,831.000,683.000 1.946,645.000,828.000,905.000,742.000 3.946,605.000,836.000,908.000,744.000 5.947,667.000,810.000,930.000,706.000 7.948,636.000,801.000,915.000,747.000 9.948,596.000,765.000,956.000,698.000 11.949,606.000,851.000,955.000,682.000 13.950,652.000,845.000,963.000,724.000 15.950,613.000,807.000,956.000,730.000 17.951,619.000,862.000,878.000,75 1.000 19.952,603.000,861.000,883.000,675.000 21.952,646.000,885.000,918.000,719.000 23.953,610.000,827.000,950.000,709.000 25.954,642.000,825.000,875.000,685.000 27.954,617.000,797.000,904.000,711.000 29..955,635.000,886.000,939.000,683.000 31.956,659.000,829.000,984.000,715.000 33.938,639.000,834.000,914.000,716.000 35.939,628.000,817.000,928.000,738.000 37.939,631.000,853.000,943.000,718.000 39.940,633.000,834.000,904.000,722.000 41.941,686.000,858.000,947.000,754.000 43.941,673.000,854.000,960.000,70 1.000 45.942,688.000,816.000,935 .000,773.000 47.943,655.000,819.000,918.000,701.000 49.943,649.000,867.000,895.000,732.000 51.944,649.000,855.000,958.000,740.000 53.945,71 5.000,822.000,978 .000,759.000 55.945,681.000,848.000,916.000,737.000 57.946,696.000,867.000,1009.000,715.000, 59.947,674.000,822.000,964.000,709.000 61.947,698.000,883.000,972.000,734.000 63.948,725.000,926.000,941.000,693.000 65.949,720.000,865.000,942.000,779.000 67.949,720.000,877.000,1003.000,759.000 69.950,696.000,878.000,998.000,711.000 71.951,671 .000,854.000,888..000,717.000 73.951,705.000,847.000,938.000,656.000 75.952,722.000,933.000,1025.000,720.000 77.953,725.000,908.000,992.000,726.000 79.953,714.000,901.000,969.000,75 1.000

PallisadesAnalysis.nb 9 81.954,777.000,943.000,980.000,801.000 83.955,769.000,999.000,994.000,745.000 85.955,767.000,912.000,941.000,744.000 87.938,718.000,922.000,966.000,738.000 89.938,756.000,945.000,1057.000,757.000 91.939,761.000,1008.000,1028.000,738.000 93.940,772.000,935.000,988.000,769.000 95.940,718.000,927.000,1042.000,757.000 97.941,741.000,91 1.000,995.000,745.000 99.942,761.000,960.000,1025.000,716.000 101.942,784.000,935.000,964.000,684.000 103.943,775.000,942.000,993.000,717.000 105.944,792.000,947.000,958.000,729.000 107.944,700.000,870.000,956.000,695.000 109.945,757.000,912.000,916.000,675.000 111.946,737.000,914.000,918.000,740.000 113.946,739.000,865.000,991.000,706.000 115.947,730.000,840.000,911.000,671.000 117.948,722.000,933.000,940.000,696.000 119.948,716.000,878.000,932.000,696.000 121.949,728.000,878.000,911.000,683.000 123.950,737.000,916.000,949.000,633.000 125.950,673.000,897.000,959.000,677.000 127.951,732.000,890.000,904.000,707.000 129.952,831.000,1014.000,1154.000,842.000 131.952,1882.000,2414.000,2405.000,1889.000 133.953,2118.000,2690.000,2843.000,2145.000 135.954,1768.000,2313.000,2469.000,1909.000 137.954,1804.000,2320.000,2401.000,1840.000 139.955,1997.000,2636.000,2677.000,2031.000 141.956,1613.000,2108.000,2194.000,1604.000 143.938,983.000,1168.000,1257.000,958.000