ML19241C196
| ML19241C196 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/11/1979 |
| From: | Lundvall A BALTIMORE GAS & ELECTRIC CO. |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NUDOCS 7907300124 | |
| Download: ML19241C196 (4) | |
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BALTI M O RE GAS AN D E LECTRIC CO M PANY GAS AN D ELECTRIC DUILDING B ALTI M O R E, M A RY L A N D 212O3 s
ARTH U R [. luN DVALL,JR
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June 11, 1979 sum.
Mr. Boyce H. Grier, Director Region I, Office of Inspection and Enforce =ent U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406
Subject:
Calvert Cliffs Nuclear Power Plant Units hos. 1 & 2, Docket Nos. 50-317 & 50-318 IE Bulletin No. 79-02 Concrete Ernansion Anchor Bolts
Dear Mr. Grier:
In recent discussions with me=bers of your staff and the Regulatory Staff (ONER), it has been pointed out that both offices are vitally interested in receiving some preliminary information on our investication of hsnrer support plates and anchor bolts which is being conducted pursuant to the subject IE Bulletin. We also learned that there is a concern within NRC that the scope of the findings of our investication has not been communicated effectively to appropriate NRC personnel.
In light of the above, we are submitting this letter to apprise you of the status of our hanger inspection program and to discuss other areas of interest such as:
1.
A description of the program; 2.
Contributing factors to the co=nunications concerning this Bulletin; 3.
Our intentions for the re-start of Unit No. 1; 4.
Our justification for continued operation of Unit No. 2.
INSPECTION STATUS Upon receipt of IE Bulletin No. 79-02 on March 12, 1979 ve made arrangements with our Architect-Encineer and our plant personr.el to develop an inspection pro 7 ram.
Inspections and tests were started just prior to the planned shutdcvn for refueling en April 21, 1979 Since that tir. ve have determined that the number of expansion anchor deficiencies disccvercd on Unit No. 1 is concirtent with or somewhat lower than the nunber which was predicted by the Bulletin based on the Shoreham facility.
Specifically, ve are conducting an inspection and test progran on all of the large pipe hangers contained in all of tne Ceismic Class I systems in Unit No. 1 and those ec= ton to both Units. We vill conduct a similar
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program on Unit No. 2 during our Fall 1979 refueling outage.
To date, we have identified approximately 950 hangers supported by expansion anchors (each hanger has one or more support plates, each of which in turn has four or more anchor bolts).
Of these 950, we have tested approximately 850 and have determined that about 125 are totally satisfactory. The remainder require further analysis. This "further analysis" may be indicated for any of several reasons including inaccessibility of the hanger plates (mostly due to high radiation levels) or any of the bolts for inspection, unsatisfactory test results on one or more bolts upon inspection, hangers not fully in accordance with existing drawings, etc.
By far the greatest number of unsatis factory field tests are associated with a specific type of expansion anchor, Phillips shell-type fasteners (Red Heads). About half of the Unit No. 1 fasteners are this type. Of the remainder, about two-thirds are Wej-its and one third are Hilti Kvik-Bolts. The latter have the best inspection results (only about 10 percent unsatisfactory).
So far, of the hangers referred to our Architect-Engineer for further analysis, about two-thirds have required some sort of physical modifications.
This is not expected to be representative of the final totals since ve have requested that anchors with a greater likelihood of needing repairs be analyzed first.
Subsequent analyses are expected to result in a substantially lover overall repair rate (about h0 percent).
Of the 950 hangers identified,163 are inside of containment.
12h of these vere designated for further analysis, and 99 have been so analysed with a repair figure of 50 (32 of which are already repaired). We have assigned the highest priority to the testing and repair of all hangers inside of contain-ment so that it can be closed out.
Meanwhile, we are continuing analysis /
repair on the remaining hangers.
DESCRIPTION OF THE PROGRAM The testing prorram for Seismic Class I hangers consists of applying a specified torque to the anchor bolts in the support plates, verifying clearance for shell-types and ultrasonic testing for imbedment of vedge-types.
The resultant axial force applied is about equal to 25 percent of the design ultimate strength of the anchor bolt and anchor installation.
In most cases the desien load expected to be seen by the installation is much less than the test force.
In no case is the design load greater than the test force.
The use of a torque test is conservative in that a straight-pull test is expected to result in less failures since the concrete anchors are designed to withstand axial and shear forces but not so be tvisted in the concrete. Additionally, if a pull test vere applied to an entire support plate rather than individual bolts, there vould be less failures due to the synergistic effect of all of the bolts acting tocether to anchor the plate.
A further conservatism is the fact that the design Joads on hangers do not take into account the inherent flexibility of the entire system but, rathe[(('
treat the hangers as rigid supports.
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If any hanger is not able to be properly tested for any reason or if the hanger does not pass the test, it is analyzed by our Architect-Engineer to determine if it is required for system support, if the number of bolts is more than necessary (thus allowing for some failures), if additionel bolts can be inserted, if the plate can be enlarged or relocated to provide adequate support, etc.
This analysis results in a repair order which is then implemented by the field forces.
This entire program is being closely monitored by our Quality Assurance personnel.
COMTUNICATIONG Although our inspection thus far of the hanger supports for Unit No.1 and ccmmon systems had identified a large number of potentially deficient anchor bolt installations, we had not yet submitted a formal vritten report on the subject. Our basis for this was as follows:
1.
IE Bulletin 79-02 required an inspection to be conducted and doc"nented by J 21y 6,1979 It was further specified that our response shoulu include a schedule for repairs. We have chosen to proceed with.dentification and repair as soon as possible and to submit a summary response by the specified date.
In so doing, ve feel ve are treating the matter expeditiously and responsibly.
2.
With the great number of NRC personnel continually on-site, we felt that they vere aware of the f act that ve vere carrying out an inspection an t repair program for hanger supports. We now appreciate the fait that the sheer volume of work being conducted during a refueling outage may severely hamper an inspector's ability to keep abreast of 111 the rept frs and modifications being made.
This aspect has been further complicated by the current concern with treating the symptoms of the Three Mile Island incident.
3.
IE Bulletin 79-02 actually predicted a potential failare rate of about 50 percent.
Our projected repair rate, as discussed above, vill probably be somewhat below that figure.
Hence, the test resulta did not appear to be out of line with what NRC vas expecting.
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Unit No. 1 has been shutdown for refueling during this inspection /
repair process.
UNIT NO. 1 RE-START It is our intention to complete all repairs to expansion anchors inside of containment and to complete all necessary repairs outside of containment prior to starting un.
We fael that there vill be come number of hangers outside of containment which vill still need repair but whose repair prior to start-up is net required for system safety. We vill proceed with these repairs expeditiously throughout the start-up program.
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k-UNIT NO. 2 OPERATION I
IE Bulletin 79-02 states that it is not necessary to shut down a plant for purposes of performing the required inspections. We have conducted a program to identify all of the hangers involved on Unit No. 2.
The total number is around 990. Of these, over 800 use the Hilti anchors, which have experienced the lowest failure rate on Unit No. 1.
In further support of Unit No. 2 operation is our belief that the deferred construction schedule of Unit No. 2 provided substentially more time for proper instal-lation of hangers.
Consequently, it is believed that the actual repair rate on Unit No. 2 vill be lover and vill not constitute a significant safety problem especially since the upcoming refuleing outage is scheduled for October 1979 We intend to address this subject in our July 6, 1979 response to the Bulletin.
Very truly yours,
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J. A. Biddison, Esquire G. F. Trowbridge, Fsquire Messrs. E. L. Conner, Jr. - NRC J. W. Brothers - Eechtel Office of Inspection & Enforcement U. S. Nuclear Regulatory Consission Division of Reactor Construction Inspection Washington, D. C.
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