ML20093N128
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i May 28,1980 A
MEMORANDUM FOR:
P. Shewmon, Chairman Midland Subcomittee FROM:
Garry G. Young, Reactor Engineer
SUBJECT:
NRC MEETING WITH CONSUMERS POWER TO DISCUSS. REACTOR VESSEL HOLDDOWN STUD FAILURES AT MIDLAND On May 23, 1980, the NRC Staff met with representatives from Consumers Power Company to discuss the failed reactor vessel anchor studs and pro-posed remedial actions. Mr. Darl Head, NRC Project Manager, conducted the meeting.
DESCRIPTION OF PROBLEM Since the installation of the reactor vessel anchor stud 5:acMiillandill,,
a total of three studs have failed. These studs were analyzed by Teledyne and failure was attributed to stress-cormston cracking with subsequent cleavage failure. The mason for failure is that the Midland-1 studs are significantly more brittle than the average stud material. However, the material did meet the applicable material codes under which they were purchased.
Teledyne representatives stated that the design pm-load of the studs for structural stiffness of the mactor vessel support was 55 Ksi.
B&W recomended a pre-load of 75 Ks1 to allow for stretch of the studs during operation and ibnsumers used 92 Ks1 for added assurance of support stiff-l ness. The combination of 92 Ks1 pre-load, exception' ally brittle stud material, and moisture in the air resulted in stress-corrosion cracking i
for the Midland 1 studs.
l The Teledyne investigation resulted in a mconnendation that the existing Midland-1 studs be restricted to a design pre-load of 6 Ks1 with a short, duration design load of 43 Ksi. The invsstigation of the Midland-2 studu revealed that no restriction needs to be applied to that material other than the original restrictions.
PROPOSED FIXES Since the restriction on stud pre-load sugilested by Teledyne results in unacceptably flexible reactor vessel supports, a new design was proposed by consumers. The existing studs are able to handle the mactor vessel vertical loads but they cannot handle the horizonal design loads. There-fore, Consumers proposed to add upper lateral supports to the reactor vessel. These supports would be located around the head flange of the reactor vessel and would be essentially burpers surrounding the vessel.
The existing neutron shield suDDorts located at the head flance would ha stiffened and shirm$d to act as upper lateral s upports.
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P. Shewmon, Chairman Consumers has analyzed the proposed fix and found that it is actually a stronger support than the previous reactor vessel skirt support design.
Additionally, the new design would not require replacement of the existing broken support studs.
The proposed fix is only ne$essary for Midland-1. However, the Midland-2 design would be modified to add the upper lateral support as a design enhancement.
CONCLUSION Consumers Power Representatives stated that the details for the proposed design will be submitted to the NRC by September 1980. No actual field work on the proposed design will be allowed until NRC approval is received.
The proposed fix was not seriously questioned during the meeting but the NRC Staff stated that a full revfew would be necessary before any type of appmval is given.
Attachment:
Meeting Agenda cc: ACRS Members ACRS Staff ACRS Fellows FILE: MIDLAND-1 o a,ce >..Acas.......
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PROPOSED MEETING AGENDA REACTOR ANCHOR STUDS Friday, May 23, 1980 At 9AM.
PHILLIPS BUILDING - ROOM P-lik 4
BETHESDA, MD Opening Remarks (JWCook/DHood)'- (10 minutes)
I.
II.-
Reactor. Vessel Anchor Studs Description of Hold-down Design and Criteria (TRT) - (20 minutes)
A.
Background of Anchor Bolt Occurrences (HWS) - (10 minutes)
B.
Results of Teledyne Investigations (HWS/WEC) - (90 minutes)
C.
1.
Investigations of first two failed studs 2.
Investigations of the third failed stud 3
Conclusions as to cause of failure 4.
Acceptability of the Unit 2 studs
- 5. ' Allowable stresses for the Unit 1 stude Proposed Unit No 1 RV Support Design Revision (TRT/ME) - (30 minutes)
D.
Investigations and Findings of Other Areas of Plant (HWS) - (20 minutes)
III.
Administrative Aspects of NRC Review (DMBudzik) - (30 minutes)
..IV.
ANTICIPATED ATTDTDEES_
Consumers Power Bechtel _
B&W Teledyne APTECH BDher JGalford WECooper GEgan WRBird DMBudzik MElgaaly CEMahaney WGDobson JWCook JARutgers HWSlager TRThiruvengadam CC: WRBird DMBudzik (30)
JWCook HWSlager TRThiruvengadam 9