ML19242C990

Responds to IE Bulletin 79-02.Analytical & Experimental Generic Program Used for Baseplate Analysis. Reviewed All Seismic Category I Pipe Supports & Found Expansion Anchor Bolts Are Shell Type

ML19242C990
Person / Time
Site:	Prairie Island
Issue date:	07/06/1979
From:	Wachter L NORTHERN STATES POWER CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
NUDOCS 7908140319
Download: ML19242C990 (3)

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'MM NSP a NORTHERN STATFS POWER COMPANY MIN N E A Po u s. MIN N E G OTA 55401 July 6, 1979 Mr James G Keppler Director - Region III Office of Inspection and Enforcement United States Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Mr Keppler:

PRA1RIE ISLAND NUCLFAR GENEPATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Response to NRC IE Bulletin No. 79-02 Since the receipt of NRC IE Bulletin No. 79-02, Prairie Island Nuclear Generating Plant, Units 1 and 2, has made a continuous effort to comply.

This ef f ort began with our becoming a member of the Generic Program being conducted at Teledyne Engineering Services (TES) in Waltham, Massachusetts.

The Generic Program at TES consists of basically two tasks; analytical and experimental. The analytical task is the development of a pre and post processor for the ANSYS computer program f or the analysis of baseplates.

This program has b sen verified analytically and experimentally and is presently being ustd f or baseplate analysis in our Plant Specific Program, also being performet by TES.

The experimental task in the Generic Program will specifically address item 4a of the bulletin. A test ratrix is presently being set up to perf orm shear-tension interaction tests and low /high cycle fatigue tests. It is our understanding that this test dsta from the Generic Program will be available on July 15, 1979 and a report issued on July 23, 1979.

Our Plant Specific Program began by reviewing all Seismic Category I pipe supports and separating out those that use concrete expansion anchor bolts.

It was found that all expansion anchor bolts used in both Unit 1 end 2 are the shell type.

Next,all applicable drawings were reviewed and categorized by our analysts using simple conservative strength of materials techniques with a criteria of Pu/10 for bolt design load. Any expansion anchor bolts which exceeded this criteria were flagged for more detailed analysis. Also during this categorizing if any anchor bolts were determined to have a f actor of saf ety less than 5 an immediate redesign was implemented and the modiff ation initiated at the site. Some 1.25% of the total number of baseplates (15 of 1199) total from both Units I and 2 fell into this less than a safety factor of 5 category. q,,

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NORTHERN STATES POWER COMPANY Mr James G Keppler

- July 6, 1979 Proceeding concurrently with the analysis was the field verification phase of the program. This phace involved randomly inspecting pipe supports used in each of the Seismic Category I systems. Measurements were made to verify that the support in the plant was the support described on the as built drawings, Patameters such as baseplate dimensions and the dimensions of the attached structure were obtained using conventional tape measures, etc. Baseplate thickness and bolt overall length were obtained using ultrasonic thickness meters. Bolt size and thread engagement were calculated from obtained dimensions. All supports found to vary f rom the drawings were immediately evaluated using the Pu/10 criteria and if found deficient were immediately flagged for analysis and/or redesign.

At this writing, the field verification phase of the program has verified a total of 227 basuplates, randomly selected among the Seismic Category I systees, some 19% of the total applicable supports. Approximately 15% of the verified supports had variations and of these approximately 1% required immediate redesign and repair. Types of variations were short thread engagement based on a 1 X the bolt diameter (ID) as a minimum, center to center bolt spacing, and baseplate thickness varying by more than one . size.

Supports inside containment will be verified during the next outage for both Units 1 and 2, March and January,1980, respectively.

The next phase of the program in response to Bulletin No. 79-02 is the field testing of a representable sample of the bolt population to a bolt tension load of ?u/5 (bolt ultimate capacity divided by a f actor of saf ety of 5).

At this writing a total of 352 enchor bolts used in 169 bastplates have been direct pull tested (tensile test). There was no shell/ joint slippage during any of the tests. The choice of which shell to pull was random throughout the plant , but care was taken to select from each system. Both clean areas and contaminated areas were covered. Supports that use concrete expansion anchor bolts inside containment will be randomly pull tested during the next refueling outage.

During the tensile testing everything possible was done to gather accurate results including removal of some restraints to ensure that the baseplate was not touching the top of the shell. Also all equipment used had the necessary calibration to provide the proper accuracy.

Based on this investigation we plan to continue verification of our base-plates that use concrete expansion anchors.

Concurrent with thia verification we will complete the stress analysic of those baseplates categorized as flexible using the Pu/10 criteria. Some 320 baseplates require detail analyais. Of this total, 20% have been completed and these results show at least a factor of safety of 5 on design. load versus bolt ultimate capacity.

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NORTHERN MTATES POWER COMPANY Mr James G Keppler ., July 6, 1979 The schedule for completion of the above work is 16 to 18 weeks for those outside containment.

We believe that an adequate level of confidence in Prairie Island expansion-type anchorage installation has been established, and we have therefore terminated the tensila-testing phase of the program.

Very truly yours, LJ .achter Vice President - Power Production and System Operation LJU/ak cc: Mr G Charnoff NRC Office of Inspection and Enforcement Washington, DC

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