ML19294C267
| ML19294C267 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 03/03/1980 |
| From: | Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML19294C268 | List: |
| References | |
| HOWE-51-80, NUDOCS 8003070395 | |
| Download: ML19294C267 (6) | |
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{Q gl Stephen H. Howell Senior Vice PresLient General Offices: 1945 West Parnell Road, Jackson. Michigan 49201 * (517) 788 4 453 March 3, 1980 Hove-51-80 Mr J G Keppler, Regicnal Director Office of Inspection and Enforcement US Nuclear Regulatcry Con =issicn Region III 799 Roosevelt Road Glen Ellyn, IL 60137 MIDLAND NUCLEAR PLANT UNIT NO 1, DOCKET NO 50-329 UNIT NO 2, DOCKET No 50-330 UNIT No 1, REACTCR VESSEL BROKEN ANCHOR EOLT
References:
Letter, S H McVell to J G Keppler; Midland Nuclear Plant; Unit No 1, Decket No 50-329; Unit No 2, Decket no 50-330; Unit No 1 Reactor Ve::sel Broken Ancher Bolt; s
- 1) Ecve-311-79; dated Dece=ber ik, 1979
- 2) Howe-267-79; dated October 12, 1979
'Jhis letter, as were the referenced letters, is an interi: 50.55(e) re;crt cencerning broken enchor bolts in the Unit 1 reacter vessel support skirt flange. The enc 1csure to this letter prcvides a status of the actions being taken to resolve this conditien.
Another report, either interin or final, vill be sent on er before May 1, 1980.
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Enclosure:
Broken Reactor Vessel Anchor Bolt in Unit 1 Status Report, MCAR-37, Interin Repcrt #1, dated February 20, 1980.
CC: Director of Office of Inspecticn & Enforcement Att Mr Victer Stello, USNRC (15)
$0/f tor, Office of Management b
Infon::atica & Prcgram Centrc1, USNRC (1)
/
8003070 39
Enclosure to Hove-51-80 Bechtel Assoc. tes ProfessionalCorporation i,a
SUBJECT:
MCAR 37-(issued 12/28/79)
Broken Reactor Vessel Anchor Stud in Unit !
II:T.ERIM RIPORT 1-DATE:
February 20, 1980 PROJBCT:
Consumtrs Power Company Hidland Plant Units 1 & 2 Bechtel Job 7220 Discrepancy The discrepancies discussed in this report are the failed reactor vessel anchor studs in Unit 1.
Status Reports 1 and 2'*o'n the first failed stud are contained as
. attach =ent to this report.
Ba ck ground The anchor studs in question are 2-1/2 inches in nc=inal diaceter and 7 feet 4 inches long, embedded vertically in the reinforced concrete reactor vessel pedestal (Figure 1).
There is a total of 96 studs per reactor vessel as shown in Figure 2.
The studs extend approximately 15 inches out of the concrete to bolt the reactor vessel skirt flange All the studs were purchased to a to the foundation structure.
The modified version of ASTM A 354-66, Crade BD standards by Bechtel.
modification was a vaiver of the maxicum dia=eter allowed in the 1966 Each stud was preloaded to an initial version for Grade BD bolts.
nominal stress of 75 ksi in the shank region (A = 4.9 squarc inches effective except where the shank diameter was reduced to the equivalent Design thread area) before relaxation losses are taken into account.
the prestress force should have been co=puted calculations indicate that on the basis of effective tensile area (A - 4.0 square inches)., Th4 result was a higher than planned preload (92 ksi versus 75 ksi), but-the resultant stresses remained well under the design allowable stress of the mater'ial.which is 105 ksi.
The anchor studs were purchased from Mississippi Valley Structural Steel All material for the Unit 1 failed _ studs (HVSS) of St. Louis, Missouri.
was supplied from Bethlehem Steel, fabricated by Southern Bolt and Louisiana, and heat treated by Fastener (SB&F) of Shreveport, J.W. Rex of Lansdale, Pennsylvania.
These studs were received on site by Bechtel in early 1976, embedded in April 1977 by Bechtel, and tensioned in late July 1979 by Babcock &
Wilcox Construction Company (B&W CC), subcontractor to Bechtel, as part of its responsibility for installation of the nuclear steam supply 14, 1979.
The failure of the first stud was discovered on Septemb~er 20, 1979, system.
Failure of the second and third studs was reported on December The locations of these studs are and February 5,1980, respectively.
it is presently believed shown in Figure 2.
Based on an ultrasonic test, t
Bechtel Associates Professional Corporation 1
MCAR 37 Interim Report 1 Page 2 the third stud failed in the lower portion of the shank or in the lower threaded area. This stud will not be recoved until the Unit I studs are detensioned.
Investigative Action Records pertinent to the purchase of the reactor vessel anchor studs have Unresolved been reviewed by Eechtel and Consucers Power Co pany.
questions from this review were sent to the vendor for clarification and a meeting subsequently took place on February 14, 1980, in Shreveport, Review of records Louisiana ydth MVSS, SB&F, Bechtel, CPCo, and the NRC.
f or other structures on the Midland project utilizing high-strength, low-alloy steel bolting caterial is currently underway pending deter =ination of the root cause of the failures.
Bechtel has contracted with Teledyne Engineering Services of Waltha=,
This investi-Massachusetts to conduct a failure rechaniss investigation.
gation has, to date, included laboratory testing of the broken portions of the two failed studs and field hardness testing of all re=aining reactor first vessel enchor studs.
The report from this investigation is attached.
The tensioning procedure prepared by E&W CC has been reviewed by Bechtel and
- level, no inconsistency, other than the previously mentioned prestress has been identified.
Preventive Action the studs were Preliminary analysis of the test data indicates that All the anchor rendered susceptible to failure by excessive hardness.
dtuds for the Unit 1 reactor vessel Vill be detensioned to prevent any The further breakage of studs, taking due care for personnel safety.
pretension of the studs in Unit 2 will be lowered to the intended design value of 75 ksi on the effective tensile stress area of 4.0 square inches.
The actual tension in the studs will be deter =ined by lift-off force during detensioning.
Corrective Action Possible corrective action is currently being evaluated.
Safety Implications _
This deficiency, if uncorrected, could adversely affect the safety of operations of the Midland plant at any ti=e throughout the expected life of the plant.
Bechtel Associates Professional Corporation 11 CAR 37 Interim Report 1 Page 3 Reportability This condition was reported by CPCo to the NRC under 10 CFR 50.55(e) on September 14, 1979.
b.d b/ Ak Submitted by:
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4 Approved b,.
[I h d,n h @ crts Concurrence by: [
EH/bjm Attachments: Status Reports 1 and 2(*)
"CPCO NOTE:
The informaticn in these repcrts was ir cluded in the interim 50 55(e) reporto provided by letters Ecve-267-79 and Hove-311-79 Therefore, they have not been included in thic intex im 50 55(e) report.
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