ML20010F769
| ML20010F769 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 08/28/1981 |
| From: | Rhode G NIAGARA MOHAWK POWER CORP. |
| To: | Brunner E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8109110306 | |
| Download: ML20010F769 (3) | |
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M Y NIAGARA nUMOHAWK NIAGARA MOHAWK POWER CORPORATION /300 ERIE BOULEVARD WEST, SYRACUSE N Y.13202/ TELEPHONE (315) 474-1511 August 28, 1981 fc s\\.
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Office of Inspection and Enforcement (f.
9; Region I Attention: fir. E.J. Brunner, Acting Director f
GEE JO b8/A r I
'g' 4 Division of Resident and Project Inspection i
%=h J U.S. Nuclear Regulatory Connission
.h 631 Park,1 venue 7'
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King of Prussia, PA 19406
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Dear Mr. Brunner:
Re: Nine Mile Point Unit 2 Docket No. 50-410 Enclosed is the final report in acccrdance with 10CFR50.55(e) for voids in concrete found adjacent to the primary containment equipnent hatches. These voids becane apparent when the forms were recoved following the concrete This condition was originally reported to Mr. R. Feil of ycur staff as pour.
a potential deficiency on July 24, 1981.
Very truly yours, NIAGARA M0 HAWK P0 LIER CORPORATION 6Ao L Ox Gerald K. Rhode Vice President Systen Project Management PEF:bd l
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Enc 1osure cc: Director of Inspection and Enforcement U.S. Iluclear Regulatory Comission Washington, D.C.
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s NIAGARA H0 HAWK POWER CORPORATION NINE MILE POINT UNIT 2 DOCKET NO. 50-410 FINAL REPORT TO POTENTIALLY REPORTABLE 10CFR 50.55(e) DEFICIENCY REGARDING C0hCRETE VOIDS AROUND PRIMARY CONTAINMENT E0VIPMENT HATCHES 1
Description of the Deficiency _
After renoval of the forns following a concrete placenent of the primary contalnnent wall between elevations 272 and 289 feet, exposed rebars were 4
found on the outside surface in the region of the equipment hatch openings at j '
azinuths 135* and 31S*.
A further investigation using a sounding technique was performed to deternine if the potential for voids also existed on the primary containment liner side of the wall. The investigation has determined a number of regions of suspect concrete-to-liner contact.
l It is believed this condition resulted from incomplete' consolidation of the concrete due to improper vibrat.on.
In this instance steps in the placement 4
of concrete, which could have prevented voids in this very congested area, were not utilized. This was an isolated case and there are no other sinflar placenents.
Analysis o. ~ ety Inpiications r
Outside Hall Surface
- Although there are established proceduras for reworking voids in concrete after fora renoval, the question of safety inplications, had the voids and exposed bar gone undetected, was considered. A review of the design calculations was conducted and it has been determined that, considering contervative estinates of corrosion under reactor building atmospheric ex/osure, the nunher 18 rebar would lose about 20% of its strength over the life of the plant.
In accordance with our review, the containment structural integrity would remain adequate though design nargins would be reduced.
Inside Wall Surface (Liner Side) 3 l
The regions of questionanle concrete to liner contcct has been investigated.
The review of the design calculctions has indicated that the total stresses in the liner, including additional bending stress 'in questionable areas, will, based on preliminary analysis, reaain within allowable design limits.
It has been deternined that the larger voids found on the outside wall do not exist on the liner side of the wall. Therefore, should the snaller potential voids on the inside wall exist, they would not adversely affect the intended function of the liner.
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Corrective Action The voids discovered on the outside wall of the primary containnent will be repaired by renoving all honeycorhed concrete and filling the voids with i
grout. This repair work relating to this condition is docunentri in a procedure developed and approved by the engineers and is availab~le for review on site. On the liner side no repair is anticipated; however, a detailed verification of design calculations still nust be completed. This verification will be completed by December 15, 1981.
If repair is later deternined to be required, your office will be so notified.
In order to mininize the occurrence of similar problens in the future, a training progran for the craftsmen for concrete placement was conducted at the i
site on July 8,1981.
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