ML19350D369

Significant Const Deficiency Rept,Originally Reported on 810305,re 810304 Discovery of Deformations on Inner Surface of Drywell Shell.Caused by Local Overpressurization During Concrete Placement.Concrete Removed

ML19350D369
Person / Time
Site:	05000355
Issue date:	04/06/1981
From:	Martin E Public Service Enterprise Group
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8104150331
Download: ML19350D369 (3)

Text

Thomas J. Martin Public Service Electric and Gas Company 80 Park Place Newark, NJ. 07101 201/430 4316 Vece President Engineering and Constructs April 6, 1981 ca e g

Mr. Boyce H. Grier, Director U. S. Nuclear Regulatory Commission b .

8-Office of Inspection and Enforcement 2 C-l Region 1 ~MQ AP82 h- b 631 Park Avenue  %=%en 'our King of Prussia, Pennsylvania 19406

)

Dear Mr. Grier:

SIGNIFICANT CONSTRUCTION DEFICIENCY NO. 2 UNIT (50-355)

HOPE CP.EEK GENERATING STATION On March 5,1981, a verbal report was made to Region 1, Of fice of Inspection and Enforcement representative, Mr. E.

Greenman, advising of a potential significant construction deficiency. The following information is submitted as required by 10CFR50.55 (e):

1. Description of the Deficiency:

Upon completion of concrete placement under the Unit #2 drywell on March 4, 1981, two (2) deformations were dis-covered on the inner surface of the drywell shell. The shell in this area is 7/8" carbon steel plate without exterior stiffeners. The d9 formations consist of bulges approximately seven (7) inches high (a t peak) and in excess of four (4) feet in diameter.

These deformations of the drywell plate were apparently caused by local overpressurization during the concrete placement. External pressure necessary to create an inward bulge at this location is estimated at 25 to 30 psi.

Twenty-four (24) " weep holes", each 3/4" in radius,were cut in the top of the drywell skirt to demonstrate

" fill" of the area under the drywell and to provide venting of the area. Flow of concrete and venting was l constantly monitored during the pour. Construction and l Engineering representatives had orally concurred that i these reasonable and prudent actions would prevent pres-sure ouildup. However, use of this approach in lieu of l

meeting a seven (7) psi limitation stated on the con-l struction drawing was not documented.

gd I gije 8104150h

Mr. Boyce H. Grier .

4/6/81 Our Architect / Engineer postulates that the overpressur-ization occurred due to one of, or a combination of, the

- following:

a. Confinement of fresh concrete within discharge flow zone, due to bridging of aggregate, or because of setting of the previously placed concrete surround-ing the zone of discharge, or because of both.

b. Coratriction of concrete flow as it approached the final venting points due to bridging or blockage of aggregate.

c. A pressure " spike" in the concrete pump discharge during final placement stage when the pump was switched on and off repeatedly to reduce flow rate.

d. Partially due to static pressure from the vertical column of concrete in the pump line.

2. Analysis of Safety Implications:

An analysis of safety implications will be conducted following completion of the evaluations identified below under " Corrective Action. " As these evaluations are not complete, we cannot determine when this analysis will be completed. However, we will keep your of fice advised of the status of this analysis and will report the results upon conclusion.

3. Corrective Action

a. The concrete has been removed from under the de-formed plate and portions of the deformed drywell shell have been removed for access.

b. The following evaluations will be performed:

1) Survey the entire Unit #2 drywell and identify the limits of the deformations. Also, check for any other deformations over the entire concrete placement area.

2) Examine the following welds by MT in the area of the deformations:

I a) Drywell shell to inner skirt.

1 I

e

o .

Mr. Boyce H. Grier 4/6/81 b) Gussets on the outer surf ace of the inner skirt at the drywell shell.

c) Drywell shell to outer skirt.

3) Review test data and observe performance of the cement used in the concrete placed under the drywell.

c. Define the limits of potentially damaged drywell shell plate. Remove and replace this material.

4. Action taken to prevent recurrence:

Replacement of concrete in the excavated zone will be reviewed and planned based on lessons learned from original placement.

A detailed plan for this activity will be developed and reviewed with the cognizant personnel prior to concrete placement. Implementation will be closely monitored by both Bechtel and PSE&G site QA organizations.

Detailed reports of the investigations and corrective actions will be available on site for review by the NRC. We will continue to keep the representatives of your office, who are monitoring this situation on site, fully appraised of our progress in correcting this problem.

Very truly yours, (JalG2iAL SIG.t.u

' ElMARTi CC: / Office of Inspection and Enforcement Division of Peactor Construction Inspection Washington, D.C.