ML20126L824

Suppl to Safety Evaluation Supporting Response to IE Bulletin 80-11 Re Reevaluation of 22 Masonry Walls,Utilizing Methods Other than Energy Balance Technique

ML20126L824
Person / Time
Site:	Calvert Cliffs
Issue date:	07/18/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20126L823	List: ML20126L821 ML20126L824
References
IEB-80-11, NUDOCS 8508010073
Download: ML20126L824 (3)

Text

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SUPPLEMENT TO SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION BALTIM0RE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT UNIT NOS. 1 AND 2 DOCKET NOS. 50-317 AND 50-318 MASONRY WALL DESIGN, IE BULLETIN 80-11 In a Safety Evaluation (SE) dated November 21, 1984, the NRC staff concluded that, except for 22 walls (out of a total of 147) qualified by the licensee via the use of the energy balance technique to resist the out-of-plane seismic forces. Items 2(b) and 3 of IE Bulletin 80-11 have been fully implemented at the Calvert Cliffs facility for the remaining walls. The Safety Evaluation also included a staff position on the energy-balance technique and stated that the impler.entation of this position was required to render the above walls acceptable to the staff.

The licensee met with the staff on April 5, 1985, to discuss its proposed approach to respond to the staff position. The proposed arproach was to reexamine the original seismic analysis of the auxiliary butiding which contains the masonry walls in question and the analysis of the masonry walls themselves to identify existing excessive conservatism above and beyond the current staff acceptance criteria in the area of the seismic analysis. The intent was, then, to account for these excessive conservatisms in the wall analysis and qualify the walls on the basis of linear elastic methodology consistent with the staff acceptance criteria. Based on the information

,. presented at the meeting, the staff found this approach to be acceptable.

By a letter dated June 12, 1985, the licensee has now provided the details and results of its evaluation using the above approach. Based on the recent review of the masonry walls, four of the walls have been reclassified as non-safety related walls. The cause for the reclassification is that the failure af these walls will not have any impact on the safety related equipment.

To qualify the remaining 18 walls using the above discussed approach, the licensee has identified several areas of conservatisms in the original analysis. These areas can be divided into two main categories: (1) which affects the seismic analysis of the auxiliary building; and (2) which affects the analysis of the masonry walls. These areas are as follows:

Seismic Analysis of the Auxiliary Building

• Input Time History - the original time history used in the analysis of the auxiliary building exhibit substantial exceedances over the design spectrum in the range of 1 to 10 Hz.

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I - 2-i Radiation Damping - The original seismic analysis of structures neglected radiation damping in the soil-structure interaction analysis.

• Embedment Effects - The original seismic analysis also neglected embedment effects in the soil-structure interaction analysis.

i Masonry Wall Analysis i

Response Spectra Modification: The response spectra used in the

! masonry wall analysis were modified such that peak acceleration l

level was imposed at all frequencies below the peak frequency.

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• Moment Combination and Beam vs. Plate Analysis - The external l moment and maximum reismic inertial moment are combined in the masonry walls analysis as an absolute sum regardless of their location on the wall. . Additionally, the walls have been analyzed as vertical strip rather than plate mechanism.

• As-Built Strength of Walls - The certified material test reports indicate that the average yield strength of #5 reinforcing bar used in the auxiliary building construction is 50.4 ksi as opposed to the specified strength of 40.0 ksi.

j From the list of above areas, the licensee selected only those areas for j which a " generic" lower bound level of conservatism can be easily and clearly identified. For other items, a w:"-by-wall reanalysis would be necessary to

qualify the amount of conservatism. The " generic" items quantified included the following areas

t Radiation Damping Use of an Improved Time History j

Actual Versus Minimum Specified Material Strengths 4

i The use of radiation damping, within the guidelines established by the NRC

? Senior Review Team (Guidelines for SEP Soil-Structure Interaction, NRC letter j dated December 15,1980,LS05-80-12-035) provided a peak response that was

approxinately 40 percent of that obtained from the original analysis. In i addition, employing a time history that more nearly meets the design spectra i'

requirements resulted in an additional conservatism. In general, a 25 percent reduction in response occurred in the frequency range of interest due

to the time history effect. Combining the effects of both the improved time i history and radiation damping (with no other changes to the seismic

analysis) and allowing some conservatism for variations ir. response between i

floor levels and directions of response, the licensee reduced the stress j level to 40 percent of the original analysis results. Based on actual mill

! test data which indicates that the yield strength of the reinforcing steel is at least 115 percent of the minimum specified, the licensee also increased i the wall capacity proportionally.

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J Based on the above qualification of the existing conservatism in the masonry wall analysis, the licensee has determined that all but two of the walls can be qualified on the basis of the elastic criteria (consistent with the staff acceptance criteria) when this conservatism is accounted for. The remaining two walls can also be qualified on the basis of the elastic criteria when a

" plate" analysis approach is used rather than "bearr ' analysis approach.

Based on the review of the above information and discussions with the licensee in the April 5,1985 meeting, the staff concludes that Items 2(b) and 3 have been fully implemented at Calvert Cliffs and that there is reasonable assurance that all safety-related masonry walls at the Calvert w

Cliffs facility impairment of (a)ill withstand wall integritythe specified or (b) design load the performance conditions of the required without function.

Principal Contributor:

N. Chokshi, DE Date: July 18, 1985

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