ML19289A047
| ML19289A047 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 06/28/1978 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | Mattson R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19289A046 | List: |
| References | |
| NUDOCS 7901030033 | |
| Download: ML19289A047 (3) | |
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MEM0Ple'DUM FOR:
R. J. Mattson, Director Division of Systems Safety FROM:
Victor Stello, Jr., Director Division of Operating Reactors
SUBJECT:
OPERATitiG EXPERIEtlCE l'.EMORAtlDUM ti0.13 PIPE SUPPORT BASE PLATE PROBLEM PROBLElj Recently during inservice inspections at Millstone Unit 1, structural f ailures of rigid pipe supports for class 2 safety equipment were observed.
These inspections, recently implemented at Millstone, were conducted in accordance with Section XI of the ASME Code, s -
as endorsed by regulation,10 CFR 50.55 a(g), in February 1976.
Several base-plate anchor bolts of pipe supports in the Core Spray
/ and the Low Pressure Coolant Injection Systems at Millstone were not properly embedded; cnd, iri some c6ses the anchor bolts were completely pulled out and no supncrting function was provided.
Deficiency reports, in accordance with 10 CFR S0.55(e), filed by Long Island Lighting Company, on Shoreham Unit 1, indicate that design of base plates with drilled anchor bolts using rigid plate assumptions has resulted in underestimation of loads on some anchor bol ts,
inspection of anchor bolt installations at Shoreham has shown over fif ty percent of the bolt installations were deficient.
Supports for both piping systems and electrical raceways have been reported as deficient at Shoreham.
PRESUMED CAUSE It is currently believed that two interacting factors contribute to the failure of the supports.
First, the desigri assumption that the base plates perform structurally as rigid instead of flexible members may provide low estimates of imposed loads on the supports.
l Secondly, incorrect anchor bolt embedment may also contribute j
to insufficient support.
The attached memorandum from V. tioonan to B. Grimes, dated
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June 2, 1978, provides additional information.
790103 Ocry3
2 SAFETY SIGft!F]CAliCE Depending on equipment layout, improperly designed or installed anchor supports could:
l.
result in less of_ support function in some cases; and, 2.
result in high stressing of piping systems during a seismic event or during a significant flow transient.
, REPAIR Millstone with assistance from Teledyne Engineering has completed design modifications and repaits.
These changes include increased base plate thickness and larger anchor bolts for failed supports; Shoreham in conjunction with Stone and h'ebster is evaluating both i
piping and electrical type supports.
The review is scheduled to be completed by December,1978.
DDR ACTION The Engineering Branch will review the design procedures used on i
/ operating plants to determine anchor bolt loads, ti,e techniques used to determine load ratings for anchor bolts, and the installation procedures.
This review will be done through an A/E vendor inspection audit in conjunction with IE.
These A/E audits will be started during early l
July, 1978.
He anticipate that criteria will be developed for design and installation of base plate-anchor bolt assemblies, and those operating plants requiring corrective action will be identified.
I Additionally EB staff will further assess the occurrence and corrective actions taken at Millstone,
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i RECOP.P.Ef!DATIONS We recommend that this problem be addressed on all CP and OL reviews.
At this time it appears that considerations should be given to the analytical methods used to.. determine whether or not base plates behave as flexible or rigid members. This in turn may effect the anchor bolt size and embedmont to properly cope with loads imposed on the supports.
4
3-It may be appropriate to require that applicants provide for review their:
1.
Inethods for determining base plate thickness and anchor bolt loads; 2.
criteria for anchor bolt installation; and, 3.
criteria for load rating techniques for anchor bolts, including cyclic loads, i
Ue s' hall coordinate our meetings, discussions and evaluations of this issue with your staff.
Supplenental information will be provided.
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Victor Stello, Jr., Director Division of Operating Reactors l
l PRlf,'CIPAL DDR PERS0ill1EL Reviewer:
J. Fair
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Enclosure:
/ iomorandum dated 6/2/78 l
cc:
w/ enclosure E. G. Case S. Hanauer R. S. Boyd i
H. R. Denton F. Schroeder i
DSS AD's DDR AD's DDR BC's DDR SL's J. Fair u f. flichols W. Rutherford J. Sniczek i
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