ML20090A953
Text
-
it.
.g-yy.
- g. -
g g
g-g -. :-
g-r-y oc
,-3 i
e._.
MAR 9 19 8 }
rg e
a
(
'd Docket Nos. 50-329 & 500330 MEMDRANDUM FOR:
F. Miraglia, Acting Chief. Licensing Branch f3 4//
Division of Licensing U N 7
//g8 L7
-/A FROM:
S. Pawlicki. Branch Chief. Materials Engineering ts e
(
Branch. Division of Engineering l
SlJBJECT: '
MIDLAND VESSEL HOLDDOWN M0DIFICATIONS 4
e Raferences:
1.
Note to Bosnak. Pawlicki. Butler And Schauer frcs F. Miraglia " Review Schedule for Midland Vessel Holddown Modification" dated December 23, 1980.
2.
Teledyne Engineering Services Tec;mical Report TR3887-1 Rev.1 "Investig,3tien of Preservice Failure of Midland FPV Anchor Studs" dated May 15, 1980.
3.
Teledyne Engineering Services Technical Report TR3887-2 Rev.1. "Accepta-l bility for Service of Midland RPV Anchor Studs" dated May 20, 1980.
4.
Teledyne Engineering Services Technical Report TR3887-1. Addendum 1 L_
" Investigation of Preservice Failure of Midland RPV Anchor Studs" dated June 6,1980.
j Plant Name: Midland 1 & 2 Supplier: B&W Docket Numbers: 50-329 and 50-330 I
Licensing Stage: OL Responsible Branch & Project Manager: LBf3. D. Hood Rsviewer:
C. D. Sellers Technical Review Branch Involved: Materials Engineering Branet, j
Description of Task:
Review of Midland Vessel Holddown M,dificaticas l
R2 view Status: Couplete Suninary R2ference l'provided a package of materials for a revised design concept for tha reactor vessel support modification resulting from the preservice failure of holddown studs in the vessel support skirt of Midland Plant. Unit 1. This design concept included defensioning of the studs to rather low preload and incorporating upper latera, supports to restrict most overturning moments in order to permit the very tw stud preload.
I
Contact:
D. Sellers X29493 OO l
-)
j
......h.,....n.1...........
..........}
DATE h
...l...............
m,n -
r &r'-
,. (-.
(. -.
g, y
.j-7 y
y F. Miraglid References 2, 3 and 4 described the meta 11urgiceJ analysis, stress analysis, and fracture mechanics analysis of the failed stuos and presented solutions to the problems.
+
It is the MTEB staff position that the use of the high strength studs in Midland Unit 1 is satisfactory at the reduced preload. Other staff organiza-tions must review and accept the auxiliary upper lateral support structa which permits the use of such low preloads.
The Unit 2 studs were not as grossly under tempered as were those of Unit 'l (although s'ame exceeded the maximum hardness specified) and it was proposed to detension to the originally specified preload and not add the upper lateral supports.
It is the MTEB staff position that a small likelihood of : failure of some of tha Unit 2 studs exists during the life of the plant and that the addition 1
cf the upper lateral supports of this time would preclude a much more difficult modification of the contaminated plant later in its lifetime.
I Discussion Briefly sunnarized, the Midland I vessel holddown problem is as follows:
Three studs (of 96) were found to have failed. These studs hold the reactor i
vessel skirt to the concreta base. It was found that the studs were of higher strength than anticipated and that they had been preloaded to a higher stress i
(92Ksi) than had been anticipated (75Ksi). This unfortunate combination of high strength and high load had caused failure in stress corrosion.. It was proposed that the remaining studs be used after detensioning to a very low (8Ksi)preload. The very low preload could be.used if auxiliary structure were added around the top of the vessel to limit lateral movement.
The reactor vessel holddown studs of Midland 2 were found to be closer to th2 specified hardness levels and if the preload were as specified, the studs i
might perfonn 'n service as desired. The lift required to perform the reduction in: preload should serve as a proof test of sorts which would probably fail any of those bolts which might have developed cracks whilst stressed at the 92Ksi.
This is particularly applicable to those studs which had achieved a higher l
hardness during manufacture. The hardness level of some of the Unit 2 bolts is such that failure in stmss corrosion would probably not occur in pure water er hunid air. However, data am available to indicate possible failure of material of this strength level in salt water. Salt water data might be more applicable for winterpoured concrete. Therefore, failure of a few of the studs in Unit 2 may be anticipated but a further detensioning is not indicated because so few stuis were in the high hardne-1 range.
(A total of 19 exceeded RC 38 of which four were greater than RC 40 and all of them were only RC 41.) liowever, if the upper lateral support fix were incorporated into the Midland 2 plant there would be no possible reason for concern about bolt failures.
No P ** >.............................................................
"'"~>........................................
.m>
.....:..............l p o= = m no,.on==cu o n o nM
^
(:
(~
4-
-y-g.-
g-.
p.
y y-F. Hiraglid '
Conclusions and Recomendations 1.- The detensioned Unit 1 studs will be adequate with the incorporation of the upper lateral support fix and will be at sufficiently low state of stress that no further stress corrosion failures are anticipated.
2.
Although the detensioned bolts of Unit 2 are less likely to exhibit stress corrosion failures, if failures do occur the fix would probably be the
- addition of upper lateral supports. Because these can~be insta11ed
.~
~
much more conveniently prior to start-up, when there will be no radiation exposure problems, we recomend that the lateral supports be added at this time.
i S. Pawlicki. Branch Chief Materials Engineering Branch i
Division of Engineering l
cc:
R. Vollmer D. Eisenhut V. Noonan S. Pawlicki i
W. Hazelton l
D. Hood D. Sellers i
DISTRIBUTION:
CENTRAL FILE i
MTEB READING l
MTEB MIDLAND FILE
_mQ m
,,,icep DSel W pot delton spa l
ME****** 'D
.UE'm B' '""'
' " ' * * * >3l.y.j81..^.........a jla r......
1;........
uny
.............. 1 Ic Pomu sie sioisoinencu ca4o
- C