ML13317A756
| ML13317A756 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/02/1981 |
| From: | Baskin K Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-03-06, TASK-3-6, TASK-RR NUDOCS 8112040404 | |
| Download: ML13317A756 (3) | |
Text
SOUTHERN CALIFORNIA EDISON P.O. BOX 800 2244 WALNJT GROVE AVENUE ROSEMEAD, CALIF. 91770 December 2, 1981 Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attention:
D.M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing
Subject:
Docket No. 50-206 Seismic Re-evaluation Program San Onofre Nuclear Generating Station,Ufnit 1 Gentlemen:
The purpose of this letter is to supplement our letter of November 23, 1981 regarding the capacity of the Fuel Storage Building. In our previous letter we indicated that the capacity of the Fuel Storage Building above elevation +42 feet, was difficult to estimate on the basis of calculations performed for the assumed modifications, since these modifications would significantly alter the response of the building.
Subsequent to our November 23 letter and as a result of telephone conversations with the NRC staff, we undertook to review recent results of our inelastic analysis of similar masonry walls. This was done to establish an objective basis which would support our conclusion that the Fuel Storage Build ing is capable of withstanding a 2/3g Housner Response Spectrum ground motion without failure of the structural system. The results of this review did provide an objective basis which supports our conclusion regarding the capability of the struc" ture to withstand a 2/3g Housner Response Spectrum ground motion.
These results were presented to the NRC staff in a meeting on December 1, 1981.
In this meeting we described the basis for modifications that have been assumed in the Fuel Storage Building.
8112040404 811202 PDR ADOCK 05000206 P
-2 above elevation +42 feet. The basis for these modifications included (1) limiting stresses above elevation +42 feet to with in the elastic range, (2) providing tornado protection for the pool and (3) providing design margin for the seismic response due to the 2/3g Housner Response Spectrum ground motion. We also reiterated our understanding of the original design basis described in our November 23,11etter.
In order to provide the NRC staff with a full understanding of the work relating to the seismic reevaluation of the Fuel Storage Building, our presentation included a general discussion of the work performed over the past 1 1/2 years in addition to the specific results of our recent review. The following para graphs summarize our December 1 presentation.
The reevaluation of the Fuel Storage Building began in mid 1980.
Concurrent with the initiation of the reevaluation of the Fuel Storage Building, work began to evaluate masonry walls in response to I.E.Bulletin 80-11. The initial review of the existing masonry walls led to the conclusion that inelastic response analysis would be required to establish the capacity of the walls, both at.-grade and at elevation +42 feet.
In order to ensure that the analysis was performed utilizing appropriate -.:
methods and criteria Computech Engineering Services, whose princi pals are recognized authorities in the field of masonry structures, was retained. Initially they were assigned the following task:
- 1. Perform a visual inspection of the masonry walls
- 2. Develope and recommend an analysis technique to be used in the evaluation of masonry walls.
- 3. Recommend acceptance criteria for the evaluation of masonry walls.
As a result of the visual inspection of the masonry walls performed by Computech, it was concluded that the quality of construction was quite good.
In addition, it was recommended that the analysis and acceptance criteria for the walls be based upon an inelastic response analysis. Computech was assigned the additional task of performing this analysis on masonry walls located below elevation +42 feet. These analyses have been recently completed. The results of these analyses have indicated that the governing condition (computed strain in the rebar) is substantially below the allowable limit. Specifically, the analysis of the Ventilation Equipment Building walls resulted in a computed strain ratio varying from.7 times the yield strain to 3.65 times the yield strain. These computed valubs -
are substan tially below the allowable strain ratio limit of 45, which is the limit specified in the reevaluation criteria. This limit of 45 is one half the ASTM specified minimum ultimate strain for grade 40 reinforcing. This result is of particular significance
-3 in relation to the Fuel Storage Building masonry walls above elevation +42 feet because the Ventilation Equipment Building walls have similar span (19 feet versus 21 feet) and are identically reinforced (#7 @ 32 vertical and #5 @ 48 horizontal).
Even taking into account possible increased inputs die to the amplication of the Fuel pool, it is concluded that the margin in the Ventilation Equipment Building walls is sufficient to ensure that a similar evaluation the Fuel Storage Building masonry walls above elevation +42 feet would result in computed stains within the allowable limits of the reevaluation criteria.
In addition, the evaluation of the Ventilation Equipment Building.
indicated that the connection anchorages to the roof diaphragm would be required to be strengthened to increase the design margin to ensure elastic allowable stresses would not be exceeded in the connections.
It is our opinion that this may not be required in the Fuel Storage Building because the walls analyzed in the Ventilation Equipment Building were more heavily loaded with attached conduit, cable trays and ducting.
On this basis it is therefore concluded that the Fuel Storage Building will withstand a 2/3g Housner Response Spectrum ground motion.
In view of our recent review we have concluded that the Fuel Storage Building-walls above elevation +42 feet to ensure elastic response is..not necessary. We-have therefore decided to perform an inelastic analysis similar to the analysis performed for masonry walls located at grade in order to qualify the Fuel Storage Building. The results will be provided by January 31, 1981.
If modifications are required for the Fuel Storage Building or any other safety related structures being reevaluated, we will providela description of the modification and the basis therefore, including whether the modifications are required to restore design margins or to assure structural integrity. If the modifications are required to assure structural integrity, we will provide an evaluation concerning the impact on continued operation.
During the December 1 meeting, we also discussed our review of the NRC staff's evaluation of SEP Topic 111-6, Seismic Design Considerations -
San Onofre Unit 1, dated November 16, 1981. We indicated that based on our review of SEP Topic 111-6 we have con-cluded it is factually correct.
If you have any questions or desire further information, please let me know.
Very truly yours, K. P. Baskin Manager of Nuclear Engineering, Safety, and Licensing KPB/sk.