ML072850072
| ML072850072 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/24/1992 |
| From: | Dromerick A Office of Nuclear Reactor Regulation |
| To: | J. J. Barton GPU Nuclear Corp |
| SECY RAS | |
| References | |
| 50-219-LR, AmerGen-Intervenor-56, FOIA/PA-2009-0070, RAS 14373 | |
| Download: ML072850072 (6) | |
Text
US. NUCLEAR REGULAyM COMISSM e~afer~~'~
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Citizens Exhibits 56 6ooket No. ,5'i)-0 i-LIKlfficial Exhibit No.
PAS /qS 73 OFF9RED by: Applirý. -___.
April 24, 1992 IV - .I..
Docket No.. 50-219 Dock*llWdi4tft* , ACRS 1i NRC & Local PDRs e Mr. John J. Barton PD 1-4 Plant Vice President and Director SVarga DOCKETED
.GPU Nuclear Corporation JCalvo USNRC Oyster Creek Nuclear Generating Station SNorri s Post Office Box 388 ADromerick October 1, 2007 (10:45am)
Forked River, New Jersey 08731 OGC OFFICE OF SECRETARY CPTan RULEMAKINGS AND
Dear Mr. Barton:
ADJUDICATIONS STAFF
SUBJECT:
-EVALUATION REPORT ON STRUCTURAL INTEGRITY OF THE OYSTER CREEK DRYWELL (TAC .NO. M79166)
The staff has completed the review and evaluation of the stress analyses and stability analyses reports of the corroded drywell with and without the sand bed. Our evaluation report is contained in the enclosure. GPUN used the analyses to justify the removal of the sand from the sand bed region. Even though the staff, with the assistance of consultants-from Brookhaven National Laboratory (BNL), concurred with GPUN's conclusion that the drywell meets the ASME Section III Subsection NE requirements, it is essential that GPUN continue UT thickness measurements at refueling outages and at outages of opportunity for the life of the..plant. The measurements should cover not only areas previously inspected but also accessible areas which have never been inspected so as to confirm that the thickness of the corroded areas are as projected and the corroded areas are localized.
S We request that you respond within 30 days of receipt of this letter indicating your intent to comply with the above requirements as discussed in the Safety Evaluation.
The requirements of this'letter affect fewer than 10 respondents, and therefore, are not subject to Office of Management and Budget review under P.L.96-511.
Sincerely,
/s/
Alexander W. Dromerick, Sr. Project Manager Project Directorate 1-4 9204300078 920424 Division of Reactor Projects - [/11 PDR ADOCK 05000219 Office of Nuclear Reactor Regulation E PDR
Enclosure:
As stated cc w/enclosure: NrIC FILE CENTER COPY See next page OFFICIAL RECORD COPY Document Name: M79166 OFC .... :LA:PI-4 4 :D:P.I-4 ..
NAME :S N 'r's 4~ cc~
ATY 4/.'92 :4/, /92 9.4/,/J92 "e(1p/a'* =,secy- O6; B
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON. 0. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ORYWELL STRUCTURAL INTEGRITY-OYSTER CREEK NUCLEAR GENERATING STATION GPU NUCLEAR CORPORATION DOCKET NO. 50-219 I. INTRODUCTION In 1986 the steel drywell at Oyster Creek Nuclear Generating Station (OCNGS) was found to be extensively corroded in the area of the shell which is in contact with the sand cushion around the bottom of the drywell. Since then GPU-Nuclear Corporation, (GPUN, the licensee of OCNGS),.has instituted a program of periodic inspection of the drywell shell sand cushion area through ultrasonic testing (UT) thickness measurements.. The inspection has been extended to other areas of the drywell and some areas above the sand cushion have been found to be corroded also. From the UT thickness measuremehts, one, can conclude that corrosion of the drywell shell in the sand cushion area is continuing. In an attempt to eliminate corrosion or reduce the corrosion rate, the licensee tried cathodic protection and found it to be of no avail.
An examination of the results of consecutive UT measurements, confirmed that the corrosion is continuing. There is concern that the structural integrity of the drywell cannot be assured. Since the root cause-of the corrosion in the sand cushion area is the presence of water in the sand, the licensee has considered sand removal to be an important element in its program to eliminate the corrosion -threat to the drywell integrity.
In the program, the. licensee first established the analysiscriteria and then.
performed the analyses of the drywell for its structural adequacy with and without the presence of the sand. The licensee performed stress analyses and stability analyses for both with and without the sand cases and concluded the drywelI with or without'the sand to be in compliance with the criteria' established for the reevaluation. It Is to'be noted that the original purpose of the sand cushion is to provide a smooth transition of stresses from the fixed portion to the free standing portion of the steel drywell.
The staff with the assistance of consultants from Brookhaven National Laboratory (BNL) has reviewed and evaluated the information (Refs. 1,2,3,4,5) provided by the licensee.
920424 9204300067 .O5000219 PDR ADOCK E PDR
,i
.1I Re-Analysis Criteria The drywell was originally designed and constructed to the requirements of ASME Section VIII code and applicable code cases, with a contract date of July 1, 1964. The Section VIII Code requirements for nuclear containment vessels at that time were less detailed than at any subsequent date. The evolution of the ASME Section III Code for metal containments and its relation with ASME Section VIII Code were reviewed and evaluated by Teledyne Engineering Services (TES). The'evaluation criteria used are based on ASME Section III Subsection HE Code throuyh the 1977 sumnmer addenda. The reason for the use of the Code of this vintage is that it was used in the Mark I containment program to evaluate the steel torus forhydrodynamic loads and that the current ASME Section III Subsection NE Code is closely related to that version. The following are TES's findings relevant to-Oyster Creek application:
a) The steel material for the drywell is A-212, grade 8, Firebox Quality (Section VIII), but it is redesignated as SA-S56 grade in Section Il1.
b) The relation between the allowable stress (S) in Section VIII and the stress intensity (Smc) in Section III for metal containment is.
L.IS - Smc.
c). Categorization of stresses into general, primary membrane, general bending and local primary membrane stresses and membrane plus bending stresses is adopted as in Subsection NF.
d) The effect of a locally stressed region on the containment shell is considered in accordance with NE-3213.10.
In addition to ASME Section III Subsection NE Code, the licensee has also invoked ASME Section XI IWE Code to demonstrate the adequacy of the Oyster Creek drywell. IWE-3519.3 and IWE-3122.4 state that it is acceptable if either the thickness of the base metal is reduced by no more than 10% of the normal plate thickness or the'reduced thickness can be shown by analysis to satisfy therequirements of the design specification.
The staff has reviewed the licensee's adoption of ASME.Section III Subsection NE and Section XI Subsection IWE in its evaluation of the structural adequacy of the corroded Oyster Creek drywell, and has found it to be generally reasonable and acceptable.
.By adopting the Subsection NE criteria, the licensee has treated the corroded areas as discontinuities per NE-3213.10, which was originally meant for change in thicknesses, supports, and penetrations. These discontinuities are highly localized and should be designed so that their presence will have no effect on the overall behavior of the containment shell. NE-3213.10 defines clearly .the
level of stress Intensity and the extent of.the discontinuity to be considered localized. A stress intensity limit of 1.1 Smc is specified at the boundary of the region within which the membrane stress can be higher than 1..1 Smc.
The region where the stress intensity varies from 1.1 Smc to 1.0 Smc is not defined in the Code because of the fact that it varies with the loading. In view of this, the licensee rationalized that the 1.1 Smc can be applied beyond the region defined by NE-3213.10 for localized discontinuity without any restriction throughout the drywell. The staff disagreed with the. licensee's interpretation of the Code. The staff pointed out that for Oyster Creek.
drywell, stresses due to ihternal pressure should be used as the criterion to establish such a region. The interpretation of Section XI Subsections IWE-3519.3 and IWE-3122.4 can be made only in the same context. It is staff's position that the primary membrane stress limit of 1.1 Smc'not be used indiscriminately throughout the drywell.
In order to use NE-3213.10 to consider the corroded'area as a localized discontinuity, the extent-of the reduction in thickness due to corrosion should be reasonably known. UT thickness measurements are highly localized; however, from the numerous measurements so far made on the Oyster Creek drywell, one can have a general idea of the overall corroded condition of the drywell shell and it is possible to judiciously apply the established re-analysis criteria.
- 2. Re-analyses The re-analyses were made by General Electric Company for the licensee, one reanalysis considered the sand present and the other considered the drywell without the sand. Each re-analysis comprises a stress analysis and stability analysis. Two finite element models, one axisymmetrlc and another a 36' pie slice model were used for the stress analysis. The ANSYS computer program was used to perform the analyses. The axisymmetric model was used to determine the stresses for the seismic and the thermal gradient loads. The pie slice model was used for dead weight and pressure loads. The pie slice model includes the vent pipe and the reinforcing ring, and was also used for buckling analysis. The same models were used for the cases with and without sand, except that in the former, the stiffness of sand in contact with the steel shell was considered. The shell thickness in the sand region was assumed to be 0.7004 for the with-sand case and to be 0.736" for the without-sand case. The 0.70" was, as claimed by the licensee, used for conservatism and the 0.736m is the projected thickness at the start of fuel cycle 14R. The same thicknesses of the shell above the sand region were used for both cases.
For the with-sand case, an analysis of the drywell with the original nominal wall thicknesses was made to check the shell stresses with the allowable values established for the.re-analyses.
The licensee used the same load combinations as specified In Oyster Creek's final design safety analysis report (FDSAR) for the re-analyses. The licensee made a comparison of the load combinations and corresponding allowable stress I
limits using the Standard Review Plan (SRP) section 3.8.2 and concluded they are-comparable.
The results of the re-analyses indicated that the governing thicknesses are in the upper sphere and the cylinder where the calculated primary membrane stresses are respectively 20,360 psi and 19,850 psi vs. the allowable stress value of 19,300 psi. There is basically no difference, in-the calculated stresses at these levels, between the with and without sand cases. This should be expected, because in a steel shell structure the local effect or the edge effect is damped in a very short distance. The. stresses calculated exceed the allowable by 3% to 6%, and such exceedance is actual.ly limited to the corroded area as obtained from UT measurements. However, in order to perform the axisymmetric analysis and analysis of the pie slice model, uniform thicknesses were assumed for'each section of the drywell. Therefore, the calculated over-stresses may represent only stresses at the corroded areas and the stresses for areas beyond the corroded areas are less and would most likely be within the allowable as indicated in results of the analyses for nominal thicknesses. The diagram in Ref. 6 indicated such a condition. It is to be noted that the stresses for the corroded areas were -obtained by multiplying the stresses for nominal thicknesses by the ratios between the corroded and nominal thicknesses.'
The. buckling analyses of the drywell were performed in accordance with ASME Code Case N-284. The analyses were done on. the 36" pie slice model for both with-sand and without-sand cases. Except in the sand cushion area where a shell thickness of 0.7" for the with-sand case and a shell thickness of 0.736" for the without-sand case were used, nominal shell thicknesses were considered for other'sections. The load combinations which are critical to buckling were identified as those involving refueling and post accident conditions. By applying a factor of safety of 2 and 1.67 for the load combinations involving refueling and .the.post-accident conditions respectively, the licensee established for both cases the allowable buckling stres'ses which are obtained after being modified by capacity and plasticity reduction factors. It is found that the without-sand, case for the post-accident condition is most limiting in terms of buckling with a margin of 14%. The staff and its Brookhaven National Laboratory (BNL) consultants concur with the licensee's conclusion that the Oyster Creek drywell has adequate margin against buckling with no sand support for an assumed sandbed region shell thickness of 0.736 inch.
A copy of BNL's technical evaluation report is attached to this safety evaluation. (
Ill. CONCLUS1ON With the assistance of consultants From BNL, the staff has reviewed and evaluated the. responses to the staff's concerns and the detailed re-analyses of the drywell for the with-sand and without-sand.cases. The reanailses by I. the licensee indicated that the corroded drywell meets the requirements for
containment vessels as contained in ASME Section III Subsection NE through summer 1977 addenda. This Code was adopted in the Mark I containment program.
The staff agrees with the licensee's justification of using the above mentioned Code requirements, with one exception, the use of 1.1 Smc throughout the drywell shell in the criteria for stress analyses. It is the staff's position that the primary membrane stress limit of 1.1 Smc not be used indiscriminately throughout the drywell. The staff accepted the licensee's reanalyses on the assumption that the corroded areas are highly localized as indicated by the licensee's UT measurements. The stresses obtained'for. the case of reduced thickness can only be interpreted to represent those in the corroded areas and their adjacent, regions of the drywell shell. In view of these observations, it is essential that the licensee perform UT. thickness measurements at refueling outages and at outages of opportunity for the life of the plant. The measurements should cover not only areas previously inspected but also accessible areas which have never been inspected so as to confirm that the thicknesses of the corroded areas are as projected and the corroded areas are localized. Both of these assumptions are the bases of the
.reanalyses and the staff acceptance of the reanalysis results.
References:
- 1. "An ASME Section VIII Evaluation of the. Oyster Creek Drywell Part I, Stress Analysis" GE Report No. 9-1 DRF #00664 November 1990, prepared for GPUN (with sand).
- 2. "Justification for use of Section ill, Subsection NE, Guidance In Evaluating the Oyster Creek Drywell" TR-7377-1, Teledyne Engineering Services, November 1990 (Appendix A to Reference 1).
- 3. "An ASME Section VIII evaluation of the Oyster Creek Drywell, Part 2, Stability Analysis" GE Report No. 9-2 ORF #00664, Rev. 0, & Rev. I.
November 1990, prepared for GPUN (with sand)..
- 4. "An ASME Section VIII Evaluation of Oyster Creek Drywell for without sand case, Part I, stress analysis" GE Report No. 9-3 DRF #00664, Rev. 0, February 1991. Prepared for GPUI.
- 5. "An ASME Section VIII.Evaluation of Oyster Creek Drywell, for without sand case, Part 2 Stability Analysis" GE Report No. 9-4, DRF #00664 Rev. 0, Rev. -1November 1990, prepared for GPUN.
- 6. Diagram aftached to a letter from J. C. DevineJr. of GPUN to N1RC dated
'January 17, 1992 (C321-92-2020, 5000-92-2094).
Principal Contributor: V.P. Tan Date: April 24, 1992
Attachment:
BNA Technical Evaluation Report