ML072770514

Oyster Creek September 2007 Evidentiary Hearing - Applicant Exhibit 22, Gpu Calculation No. C-1302-187-5300-005 (05 Calc.) Statistical Analysis of Drywell Thickness Data Thru 12-31-88

ML072770514
Person / Time
Site:	Oyster Creek
Issue date:	02/02/1989
From:	Johari Moore GPU Nuclear Corp
To:	NRC/SECY
SECY RAS
References
50-219-LR, AmerGen-Applicant-22, RAS 14229 C-1302-187-5300-005, Rev 00
Download: ML072770514 (4)

Text

U.S, NUCLEAR AEGULA1t3RY COMMIUON infttmMowhof AMiWAA\QN=VCO) AQ OD0"N 0.9).Vq1g-LM._Off IralExhibitd N.

. APPLICANTS EXH. 22 08/22/00 09:45:22 OFFERED by"piýat NRq St4ff nsee Intervenor________

Other_______

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1.0 PROBLEM STATEMENT 1.1 Background The design of the carbon steel drywell includes a sand bed which is located around the outside circumference between elevations DOCKETED 81-11-1/4" and 12'-3". Leakage was observed from the sand bed USNRC drains during the 1980, 1983 and 1986 refueling outages indicating October 1,2007 (10:45pm) that water had intruded into the annular region between the drywell shell and the concrete shield wall.

OFFICE OF SECRETARY RULEMAKINGS AND The drywell shell was inspected in 1986 during the 1OR outage to ADJUDICATIONS STAFF determine if corrosion was occurring. The inspection methods, results and conclusions are documented in Ref. 3.1, 3.2, and 3.3.

As a result of these inspections it was concluded that a long term monitoring program would be established. This program includes repetitive Ultrasonic Thickness (UT).measurements in the sand bed region at a nominal elevation of 11'-3" in bays IIA, 11C, 17D, 19A, 19B, and 19C.

• ('.._da The continued presence of water in the sand bed raised concerns of potential corrosion at higher elevations. Therefore, UT measurements were taken at the 51' and 87' elevations in November 1987 during the 1IR outage. As a result. of these inspections, repetitive measurements in Bay 5 at elevation 51' and in Bays 9, 13 and 15 at the 87' elevation were added to the long term monitoring program to confirm that corrosion is not occurring at these higher elevations.

A cathodic protection system is being installed in selected regions of the sand bed during the 12R outage to minimize corrosion of the drywell. The long term monitoring program was also expanded during the 12R outage to include measurements in the sand bed region of Bays 1D, 3D, 5D, 7D, 9A, 13A, 13C, 13D, 15A, 15D and 17A which are not covered by the cathodic protection system. It also includes measurements in the sand bed region between Bays 17 and 19 which is covered by the cathodic protection system, but does not have a reference electrode to monitor its effectiveness in this region.

Some measurements in the long term monitoring program are to be taken at each outage of opportunity, while others are taken during each refueling outage. The functional requirements-for these inspections are documented in Ref. 3.4. The primary purpose of the UT measurements in the sand bed region is to determine the corrosion rate and monitor it over time. When the cathodic protection system is installed and operating, these data will be used to monitor its effectiveness. The purpose of the measurements at other locations is to confirm that corrosion is not occurring in those regions.

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08/22/00 09:45:22 Caic. No. C-1302-1B7-5300-005 Rev. No. 0 Page t.of 1.2 Purpose The purpose of this calculation is to:

(1) Statistically analyze the thickness measurements for Bays 1IA, 1IC, 17D, 19A, 19B and 19C in the sand bed region to determine the mean thickness and corrosion rate.

(2) Statistically analyze the thickness measurements for Bay 5 at elevation 51' and Bays 9, 13 and 15 at elevation 87' to determine the mean thickness corrosion rate.

(3) To the extent possible, statistically analyze the limited data for the 6" x.6" grids in the sand bed region of Bays 9D, 13A, 15D and 17A to calculate the mean thickness and determine if there is ongoing corrosion.

(4) To the extent possible, statistically analyze the limited data for the 6" x I" horizontal strips in the sand bed region of Bays ID, 3D, 5D, 7D, 9A, 13C and 15A to calculate the mean thickness and determine if there is ongoing corrosion.

Statistically compare the thickness data from December 1986 and December 1988 for the trench in Bay 17D to calculate the mean thickness at various elevations in the trench and

..determine if there is ongoing corrosion.

(5) Statistically analyze the thickness data from December 1988 for the Frame Cutout between Bays 17 and 19 to calculate the mean thickness.

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08/22/00 09:45:22 Calc, No. C-1302-IB7-5300-005 Rev. No. 0 Page . of I.'

2.0

SUMMARY

OF RESULTS Bay Area Location Corrosion Rate** Mean Thickness***

2.1 6"x6" Grids in Sand Bed Region at Original Locations 11A Sand Bed Not significant 908.6 +5.0 mils aic Sand Bed Indeterminablb 916.6 +10.4 mils 17D Sand Bed -27.6 +6.1 mpy 864.8 +6.8 mils 19A Sand Bed -23.7 +4.3 mpy 837.9 +4.8 mils 19B Sand Bed -29.2 +0.5 mpy 856.5 +0.5 mils 19C. Sand Bed -25.9 +4.1 mpy 860.9 +4.0 mils 2.2 6"x6" Grids in Sand Bed Reqion at New Locations 9D Sand Bed Indeterminable* 1021.4 +9.7.mils 13A Sand Bed Not significant* 905.3 +-10.1 mils 15D Sand Bed Possible* 1056.0 +9.1 mils 17A Sand Bed Indeterminable* 957.4 +9.2 mils 2.3 6"x6" Grids at Upper Elevations 5 5v' Blev. -4.3 +0.03 mpy 750.0 +0.02 mils 9 87' Elev. Not significant 620.3 +1.0 mils

. 13 15 87' 87' Elev.

Elev.

Not significant Not significant 635.6 634.8

+0.7 mils

+0.7 mils 2.4 Multiple 6"x6" Grids in Trench 17D Trench Not significant* 981.2 +6.7 mils 17/19 Frame Cutout Indeterminable* 981.7 +4.4 mils 2.5 6" Strips in Sand Bed Region ID Sand Bed Indeterminable* 1114.7 +30.6 mils 3D Sand Bed Not significant* 1177.7 +5.6 mils 51 Sand Bed Not significant* 1174.0 +2.2 mils 7D Sand Bed Possible* 1135.1 +4.9 mils 9A Sand Bed Indeterminable* 1154.6 +-4.8 mils 13C Sand Bed Not significant* 1147.4 +3.7 mils 13D Sand Bed Not significant* 962.1 +22.3 mils 15A Sand Bed Not significant* 1120.0 +12.6 mils 2.6 Evaluation of Individual Measurements Below 800 Mile One data point in Bay 19A and one data point in Bay 5 Elev. 51' fell outside the 99% confidence interval and thus are statistically different from the mean thickness.

• Based on limited data. See text for interpretation.

• • Mean corrosion rate in mile per year + standard error of the mean

• • • Current mean thickness in mils + standard error of the mean OCLROO020136

08/22/00 09:45:22 Calc. No. C-1302-187-5300-005 Rev. No. 0 Page 4 of /?t

3.0 REFERENCES

3.1 GPUN Safety Evaluation SE-000243-002, Rev. D, "Drywell Steel Shell Plate Thickness Reduction at the Base Sand Cushion Entrenchment Region" 3.2 GPUN TDR 854, Rev. 0, "Drywell Corrosion Assessment" 3.3 GPUN TDR 851, Rev. 0, "Assessment of Oyster Creek Drywell Shell" 3.4 GPUN installation Specification IS-328227-004, Rev. 3, "]'unctional Requirements for Drywell Containment Vessel Thickness Examination" 3.5 Applied Regression Analysis, 2nd.Edition, N.R. Draper & H. Smith, John Wiley & Sons, 1981 3.6 Statistical Concepts and Methods G.K..Bhattacharyya & R.A. Johnson, John Wiley & sons, 1977 OCLROO020137