ML19326D511

Interim Deficiency Rept Re Reactor Containment Bldg Fire. Caused by Hot Welding Slag Dropping on Insul-Tarps. Tarps Will No Longer Be Used to Retain Heat in Concrete Curing & Addl Fire Protection Will Be Provided.Diagrams Encl

ML19326D511
Person / Time
Site:	Midland
Issue date:	12/20/1974
From:	Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
References
NUDOCS 8006170917
Download: ML19326D511 (7)

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.o 1 di General Offices: 212 West MICNgan Avenue, Jackson, Micnigan 49201 December 20, 1974 MIDLAND PLANI Reactor Containment Building Fire Dockets No 50-329 and 50-330 Dr. Donald F. Knuth, Director -

Directorate of Regulatory Operations US Atomic Energy Commission IHIS DOCUMENT CONTAINS Washington, DC 20545 P0OR QUAUTY PAGES

Dear Dr. Knuth:

At approx 1=ately 1:30 PM on November 21, 1974, a fire occurred in the Unit No 2 Reactor Containment Building at the Midland Nuclear Plant site. 'Ihe fire started when some hot velding slag from a liner plate welding activity dropped on some "Insul-Tarps" which were hung next to the liner plate on the inside of the containment building.

These "Insul-Tarps" had been used as thez=al insulation to keep the curing concrete in the containment vall from getting too cold. When attempts to extinguish the fire with portable extinguishers failed, Bechtel personnel cut the wire ropes supporting the "Insul-Tarps" allowing them to drop to the floor of the containment building where the tarps continued to burn. The Midland City Fire Department was called, responded and extinguished the fire at 2:46 PM. Figure 1 shows the locations of the fire.

Upon examination of the containment building after the fire, damage was as follows:

1. Bulges in the liner plate.

2. Possible metallurgical damnge to the liner blade steel.

3 Possible heat damage to the containment wall concrete.

4. Smoke and soot damage to the liner plate coating.

5 Possible heat damage to the horizontal steel reinforcing bar at the containment floor.

In view of the extent of damage (both potential and observed),

J. L. Corley, the Consumers Power Midland Pro. ject Quality Assurance Superintendent, telephoned Mr. T. E. Vandel, the Region III Principal

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Dr. Donald F. Knuth 2 Midland Plant December 20, 1974 Inspector assigned to the Midland Project, at 4:20 PA on November 21, 1974. Messrs. Corley and Vandel agreed that, since the damage (if it had remained uncorrected) could have adversely affected the safety of cperations of the nuclear power plant and the damage could involve extensive evaluation and repair to establish the adequacy of the components to fulfill their safety function, this incident would be treated as reportable under the requirements of 10CFR50:55(e). Since all evaluations are not complete at this time and, therefore, full corrective action has not been determined, this letter represents an interim report as required by 10CFR50:55(e).

However, some corrective action has been taken and some evaluations have been made as described below:

Prevention of Future Similar Fires

a. "Insul-Tarps" will no longer be used to retain heat during curing of concrete. In the future, heat will be retained inside containment by the use of a covering over the top of the containment building.

b. Additional fire protection will be provided in both contain-ment buildings. This protection will consist of a temporary 2-1/2-inchfirelinewithnecessaryhosesandfittingscom-patible for use by either the Midland Fire Department or the site Fire Brigade. This temporary protection will remain in place until the permanent plant fire protection system is installed,

c. Bechtel welding and cutting procedures have been modified to require workmen to check the work area for fire ha::ards prior to beginning work.

Irregardless of the above, certain fire precautions had been taken prior to this incident.

a. "Insul-Tarps" were supposed to have been fire resistant.

b. Boilermakers were assigned fire watch duties to detect and extinguish such fires.

In relation to the five types of damage discussed above, some evaluations have begun but the analysis of safety implications is not complete and the need for repair has not been determined. The status of the evaluations is as follows:

1. Bulges in the Liner Plate To date, no bulges have been found at the elevation where the fire started. However, bulging was found in the wall liner plate immediately above the knuckle plate where the burning "Insul-Tarps" fell.

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Dr. Donald F. Knuth 3 Midland Plant -

December 20, 1974 The location and size of the bulging are shown in the attached sketches (Figures 2 and 3). It should be noted that the location of the bulges indicates that the liner plate did not pull loose from the welded stiffeners, in that all bulging was between stiffeners. The effect of these bulges on the safety related function of the liner plate is currently being evaluated.

2. Possible Metallurgical Damage to the Liner Plate Steel In order to evaluate possible metallurgical damage to the liner plate itself, a 4-inch square sample of the plate was removed frem the center of one of the larger bulges.

Portions of the sample will be Rockwell and micro hardness tested and also metallographically examined. This evaluation l is not co=plete at this time.

3 Possible Heat Damage to the Containment Wall Concrete In order to determine the extent (if any) of damage to the concrete in the containment wall, concrete in the area where the 4-inch square of liner plate was removed has been examined.

This examination included both a visual examination of the surface as well as testing the concrete with a Swiss Hamner.

(For correlation purposes, the exterior face of the contain-ment was Swiss Hammer tested in the same vicinity). To date, no deleterious effect on the concrete has been detected but the evaluation has not been completed.

4. Smoke and Soot Tamage to the Liner Plate Coating l Prior to the fire, most, if not all, of the liner plate had been prime-coated and some of it had been finish-coated. -

As a result of the fire, the coating was contaminated by (a) extensive to moderate smoke and soot damage, (b) melted plastic weather protection which is now adhering to the 1 coating and (c) grease and other contaminates which have l been splattered over the coating surface. As of this time, l it appears that the coating will have to be repaired but  !

the full evaluation is not completed.  !

5 Possible Heat Damage to the Horizontal Steel Reinforcing Bar at the Jontair ent Floor 1

Ynen the "Insul-Tarps" were dropped to the containment floor, they landed on the horizontal No. 6 steel reinforcing bar shown in Figure 1. In order to determine if this reinforcing bar was damaged, tensile tests are being made on samples of the reinforcing bar. Here again, the full evaluation is not completed.

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Dr. Donald F. Knuth 4

' Midland Plant December 20, 1974 Since none of the evaluations of damage are complete and repair require:nents have not yet been determined, the evaluations of the safety implications of the damage and the methods of repair selected will be addressed in subsequent reports. At this time, it appears possible that a final report can be provided by January 21, 1975 If, at that time, insufficient information is available, another interim report will be provided.

Yours very truly,

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