ML19305B723
| ML19305B723 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/06/1980 |
| From: | Albert Lee Office of Nuclear Reactor Regulation |
| To: | Lester Tripp NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NUDOCS 8003200139 | |
| Download: ML19305B723 (4) | |
Text
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@@@2 @$$b yap 0 0 1933 MEMORANDUS' FOR:
Lcwell Tripp, Section Chief. Engineering Support Section No.1 Reactor Construction and Engineering Support Branch, Region I FROM:
Arnold Lee, Section C, Engineering Branch Division of Operating Reactors Office of Nuclear Reactor Regulation
SUBJECT:
IE INVESTIGATION OF ALLEGATION ON MILLSTONE 1 ISOLATION CONDENSER plPING AND SUPPORTS
References:
1.
Memo from E. L. Jordan to R. L. Tedesco, dated Jan. 28, 1980 2.
Task Interface Agreement, Task No. 80-8, dated Feb. 13, 1980 The subject investigation was conducted on two separate trips, namely, Feb. 6 to Feb 8 for the first trip, and Feb. 20 to Feb. 22 for the second trip. The results of the investigation are summarized as follows which indicate that the allegations were not substantiated:
First Trip (includes plant site visit on 2/7/80) 1.
The original EBASCO analysis of isolation condenser supply line was i fly reviewed, with no apparent overstress observed.
2.
The latest supply line analysis by Northeast Utility Company (N",Ce; reviewed.
This analysis was perfomed in compliance with the r equit of IE Bulletin 79-14. The ger.eral analysis method was found a::eptable.
Furthermore, the stresses along the pipe were found to be within the des criteria of B31.1, 1967, under themal loaf is well as the corraination of dead weight, pressure and SSE loading.
3.
For concrete expansion anchor bolts at support X-10A the safe:y fac.
of 4 and 2 respectively, for SSE plus nomal loads and pipe rupturc load plus normal loads, which were required for interim operation, were prese'ited by NUSCO and later on verified by Teledyne Engineering Service daring the second trip of investigation. The calculation by which this result was obtained utilized a linear shear / tension interaction relationship.
4.
One superseded computer analysis for supply line was presented for review.
This particular analysis represented the official NUSCO docunents prior to the above 79-14 analysis in June or July of 1979. We raised the question concerning the adequacy of the spring hangers based on the rasulted support loadings. This question was not resolved until the second trip. The remaining analysis showed the pipe stress to be within allovable.
5.
One computer run identified as ICONS 2 was reviewed. This run was designed to find the high stress points under water hamer incident, to facilitate inservice inspection. To achieve this, two simultaneous loadings of 50,000 lbs. and 25,000 lbs. were applied at two support locations where water hammer loadings were expected to act. For conservatisms, the support stiffnesses in the directions of applied loads were not accounted for. The rationale of tile analysis approach was found acceptable.
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Teledyne is developing a more realistic pipe rupture load and a water These loadings are to be incorporated into 6.
hamner transient load.
Teledyae's final isolation condenser pipe analysis.
on 2/7/80 enhanced general confidence on NUSCO's The plant site visitas built ecnfiguration of isolation condenser pipe system and 7.
as modeled in the 79-14 analysis.
During the plant visit, it was noticed that the rod hanger in 8.
replaced with new one.
The anchor bolts on two support locations in the supply line were pulled They had off by 1/8 to 3/16 inches during the above water hammer incident.
9.
been retorqued to specified values with no failure observed.
Concrete around the perimeters of the baseplates fastened to the wall 10.
found to be damaged near the surface.
With these performed by Teledyne showed deep embedments of 18 to site, we feel that the original anchorage integrity at the Second Trip (includes meeting et Teleayne Engineering Service on 2/21/80)
Questions were raised concerning the correctness of the valve weigh n ts used in the 79-14 analysis.
It was confirmed after NUSCO presented 1.
that support the use of this valve weight.
NUSCO used ASME basic material allowable stresses of s and S, respective e
h at cold and hot temperature for the material concerned, instead of v" 2.
the more conservative B31.1 allowables.
It was found, however, that difference was quite insignificant.
j Computer run for the return line had been presented to Mr. Suresh Chaudha Mr. Chaudhary has 3.
for his review before my second trip of investigation.
then indicated that no overstress was found.
Concerning the possibility of the spring hangers (originally designed by chart method, etc.) being undersized, NUSCO stated that based on the super-4.
seded run and the 79-14 analysis the hangers had been loaded in theirIt is not working ranges, although probably on the border line.In fact, NUSCO st item, according to NUSCO.
Nevertheless, prevails among the major portion of the plant spring hange settings, and make replacement if found desired.
In :ne reevaluation of the restraint X-10A, Teledyne noted that the origina 5.
EBA!CO rupture load had indicated high load at ceiling.
at ce.iling became the limiting case, therefore the modification included
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installation of twc large wide frange kickers, at both above and underneath the floor, which transmit the support loads through the flor.r slab and back to the drywell wall. As a part of this load transmitting mechanism, bearing plates were welded to the base plate to take the in-plane force of the concrete floor. Also, through-bolts were used to hold together the baseplates on top and bottom of the floor slab.
To verify that the restraint X-10A as modified and the floor slab as it is reinforced will be sufficient to take the design loads, Teledyne divided tne analysis into two steps.
Firstly, the contribution of the floor slab to the entire restraint was limited to its in-plane resistance.
The safety factors at anchor bolts were found to exceed 4 and 2, respectively, for the load combinations associated with SSE and pipe rupture.
Secondly, a finite element mesh of the slab was modeled and connected with the restraint.
For the loadings considered, the maximum induced bending moment, in the floor slab, of 23,000in-lb/in.
was found to be much less than the corresponding ultimate moment capacity of 54,000 in-lb/in., in accordance with ACI 349.
In addition, the safety factors at anchor bolts exceed 2 for EBASCO rupture loads. Teldyne therefore concluded that with the modification as it is, the integrity of the restraint X-10A is preserved and is qualified for interim operation.
6.
Again, Teledyne is currently developing a more realistic rupture load as compared to the original EBASCO rupture load.
Since the rupture load was regarded as design load during construction, IE Bulletin 79-02 requires a safety factor of at least 4 for the anchor bolts under the rupture load plus nonnal loads.
Teledyne and NUSCO are committed to satisfy this sa4ty factor for long term operation of the plant.
7.
Because there is no pipe whip restraint designed along the isolation er line specifically to take the rupture load, it is understood that the i.
nt X-10A will take both the SSE load and the rupture load when both occur simultaneously.
For long term operation, we therefore also requested that t
NUSCO examine the adequacy of X-10A against the combination of SSE and %e new rupture load being developed, with the consideration of a safety
.or of at least 4.
NUSCO have expressed potential difficulty in meeting inis requirement and indicated that a later meeting at Bethesda with the hRC 1
staff would be planned to resolve this matter.
8.
Teledyne discussed their approach of deriving the water harmier transient load.
We recommended that factors such as water temperature differer.tial in the vessel and the amount of water slag should be realistically and con-servatively accounted for in the derivation of the load. The integrity of the entire isolation condenser piping system, including the once pulled-loose anchor bolts will be reassessed when the transient becomes available.
1 9.
Teledyne and NUSCO are to assure the NRC of the sufficient design margin of the drywell wall capacity due to the added loads transmitted through the modified restraint X-10A.
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