ML21278A154

2 to Updated Final Safety Analysis Report, Chapter 5, Appendix 5A, Section 5A.6, Masonry Wall Design

ML21278A154
Person / Time
Site:	Calvert Cliffs
Issue date:	09/07/2021
From:	Exelon Generation Co
To:	Office of Nuclear Reactor Regulation
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References
NEI 99-04
Download: ML21278A154 (1)

Text

CALVERT CLIFFS UFSAR 5A.6-1 Rev. 47 5A.6 MASONRY WALL DESIGN NRC Bulletin 80-11 required licensees to identify plant masonry walls and their intended functions. Licensees were also required to present reevaluation criteria for the masonry walls with analyses to justify those criteria. If modifications were proposed, licensees were to state the methods and schedules for the modifications.

In response to the bulletin, BGE provided the NRC with a description of the status of masonry walls at Calvert Cliffs Nuclear Power Plant. A total of 147 safety-related walls were initially identified. All walls subject to reevaluation were in the Auxiliary Building.

The masonry construction at Calvert Cliffs Units 1 and 2 consists of single-and double-wythe walls of the running bond type whose functions include partition, shielding, blockout, bearing, and filler. Both reinforced and unreinforced walls were built in the plant. Vertical reinforcement was provided by grouting reinforcing bars in vertical cells and "Dur-o-Wall" was used for horizontal reinforcement.

The masonry walls were reevaluated using the following criteria:

a.

The design allowables are based on ACI 531-79.

b.

The working stress design method and the energy balance technique were used in the analysis. Out of 147 safety-related walls, 22 were qualified by the energy balance technique. Based on a subsequent review, four of the 22 walls were reclassified as non-safety-related walls because failure of these walls would not have any impact on safety-related equipment.

c.

Loads and load combinations were consistent with the other parts of this appendix.

d.

Critical damping values of 4% for OBE and 7% for SSE were used for vertically reinforced walls which were assumed to crack under seismic conditions. A damping value of 2% was used for walls that were assumed not to crack.

e.

The typical analytical procedure is summarized below:

1.

Determine wall boundary conditions

2.

Using a one-way beam model and the floor response spectrum, determine the responses of the first three modes and combine them by the square root of the sum of the squares method.

3.

Compare computed stresses with the allowable values in ACI 531-79.

Because arching action had been used to qualify one of the original 147 walls, it was modified to bring it within elastic requirements. All other walls satisfied the reevaluation criteria and no other modifications were proposed.

All but two of the walls were qualified by the elastic criteria (consistent with NRC acceptance criteria) when the existing conservatism in the masonry wall analysis was accounted for. The remaining two walls were also qualified by the elastic criteria using a "plate" analysis approach rather than "beam" analysis approach.

The NRC concluded there is reasonable assurance that all safety-related masonry walls will withstand the specified design load conditions without impairment of either wall integrity or the performance of the required function.