ML20086S426

AO-S2-74-10:on 741129,unsatisfactory Leakage Ovserved While Performing Periodic Test 16.4.Caused by Stress to Four Keyways of Rockshaft Due to Valve Closure.Counterweights Modified & Repositioned on Weight Lever

ML20086S426
Person / Time
Site:	Surry
Issue date:	02/14/1975
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20086S428	List: ML20086S426 ML20086S430
References
AO-S2-74-10, NUDOCS 8403020189
Download: ML20086S426 (7)

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Mr. Norman C. Moseley, Director Serial No. 424 Directorate of Regulatory Operations P0&M/JTB:clw United States Nuclear Regulatory Commission Region II - Suite 818 Docket No. 50-281 230 Peachtree Street, Northwest License No. DPR-37 Atlanta, Georgia 30303

Dear Mr. Moseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereby submits forty (40) copies of Abnormal Occurrence Report No. A0-S2-74-10.

, The substance of this report has been reviewed by the Station Nuclear Safety and Operating Committee and will be placed on the agenda for the next meeting of the System Nuclear Safety and Operating Committee.

Very truly yours s ev ' ' */vu.A C. M , S ling 5

. Vice President-Power Supply and Production Operations Enclosures 40 copies of A0-S2-74-10 cc: Mr. K. R. Coller GP $

8403020189 75C214 PDR ADOCK 05000291 ,

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' ABNORMAL OCCURRENCE REPORT

' -REPORT NO. A0-S2-74-10 CONTAINMENT SPRAY AND RECIRCULATION j SPRAY ISOLATION CHECK VALVES i

JANUARY 9.- 1975 I DOCKET NO. 50-281 LICENSE NO. DPR-37 i

s SURRY POWER STATION j

VIRGINIA ELECTRIC'AND POWER COMPANY j

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1. INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Operating License Number DPR-37, this report describes an abnormal occurrence which occurred on December 30, 1974. The Directorate of Regulatory Operations, Region II, was notified on December 31, 1974.

The occurrence reported herein is classified as an abnormal occurrence pursuant to Technical Specification 1.0.I.6 which states "An abnormal occurrence is defined as: Engineered safeguard system malfunction or other component or system malfunction which rendered or could render the engineered safeguard system incapable of performing its intended safety function."

The occurrence described herein could have resulted in flow blockage of the containment spray and outside recirculation spray lines.

II.

SUMMARY

OF OCCURRENCE On November 29, 1974, with Unit No. I at refueling shutdown, an unsatisfactory leakage was observed while performing Periodic Test 16.4,

" Containment Isolation Valve Leakage." Subsequent investigation led to the discovery of cracked rockshaf ts on recirculation spray check valves 1-RS-11 and 1-RS-17. The cracks were found at the outside keyways of the rockshafts. All similarly designed check valves -in the recirculation spray and containment spray system-on Unit Nos. I and 2 were subsequently inspected.

On December 27, 1974, with Unit Nos. I and 2 at cold shutdown a crack was noted at an outside keyway of the rockshaft for containment spray check valve 2-CS-13. 'During a-final inspection, following replacement a

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of the cracked rockshaft, a small crack was also found in the upper body of the valve. A dye-penetrant test was then performed on the valve body.

The crack was ground out. Following rewelding of the valve, dye-penetrant tests indicated that a longer crack had developed, running from the thicker upper body of the valve to a thinner walled section in the lower body.

The valve was replaced.

Inspection of all similarly designed valves in the containment spray and recirculation spray systems of Unit Nos. I and 2 provided the following results:

1. Cracks were found at all four rockshaft keyways on 1-RS-11 and 2-RS-11.

2. One interior and one exterior rockshaf t keyway was found cracked on 1-RS-17.

3. Rockshafts for 1-CS-13 and 2-RS-17 were found free of cracks following visual inspection and_ dye-penetrant tests.

4. One interior rockshaft keyway was found cracked on 1-CS-24, with both interior keyways cracked on 2-CS-24.

5. One exterior rockshaft keyway _uas cracked on 2-CS-13.

6. The 2-CS-13 valve body was the only one found cracked.

III. ANALYSIS OF OCCURRENCE The containment and recirculation spray check valve discs are held against their seats by counter weights positioned on weight levers, which,'

like the disc arm assemblies, are keyed- to the rockshaf ts. . These positive L.

o O closure check valves are designed to remain seated until two pounds per square inch pressure differential exists across the valve.

The minimum seating torque can be calculated by multiplying the area of the disc times the pressure differential and the length of the disc arm (center of rockshaft to center of disc): Required Seating Torque =

(78.54 in.2 x 2.00 psi x 7.125 in. )/(12 in./f t) = 93.27 f t-lb. The actual seating torque can be found by multiplying the volume of the weight times the density of the material, the number of weights, and the length of the weight lever (center of weights to centerline of rockshaft): Actual Torque = (.218 f3 t x 395.09 lb/ft3 x 4 weights x 25.5 in.)/(12 in./ft) =

732.1 0 ft-lb. Taking into account the angle of the weight lever 732.10 ft-lb. x cos 30 = 634.00 ft-lb. It can be seen that there were actually 6.8 times the torque required to keep the disc seated.

During Periodic Test 17.1, " Containment Spray System," the containment spray pumps are operationally tested monthly by closing the discharge motor operated isolation valves and setting up a recirculation flowpath with the refueling water storage tank. Leakage past the pump discharge valves can be sufficient to cause the containment isolation check valves to cycle open and shut during the required thirty seconds of pump operation ~. As the ch'ck e

4 valve closes, a column of water acts with the counterweights to slam the disc against its seat, concentrating considerable stress at the four keyways of each rockshaft.

i The manufacturer's non-destructive testing of the aforementioned check valves included a visual inspection for cracks or other surface defects. It:

is possible that the cracks in the body of 2-CS-13 was considered to be a l

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o O satisfactory sand inclusion during initial inspection and passed on acceptable.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The initial corrective action was to inspect all containment and recirculation spray check valves for both rockshaf t and body cracks.

Containment spray check valve 2-CS-13 was replaced, as were all cracked rockshafts.

i In order to prevent recurrence the counterweights were modified and repositioned on the weight lever to provide the required seating torque.

Unit No. 2 rockshafts will be inspected again during the first refueling I

shutdown; Unit No. I will be inspected again during the next cold shutdown.

l V. ANALYSIS AND EVALUATION OF SAFETY IMPLICATIONS OF THE OCCURRENCE The containment spray subsystem and the recirculation spray sub-systems work together to reduce containment temperature, return the con-l tainment pressure to subatmospheric, and to remove heat from the containment after a loss-of-coolant accident. Each reactor unit has two 100 per cent capacity containment spray pumps and four 50 per cent capacity recirculation spray pumps. Failure of the two outside recirculation spray check valves, resulting in flow blockage, would not have affected the ability of the full capacity inside recirculation spray system to perform its function.

Failure of _both containment spray check valves, assuming flow blockage, l could have rendered the containment spray system inoperable.

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VI... CONCLUSIONS The licensee concludes that:

1. The cracked rockshafts were the result of high impact loading of the valve discs resulting from excessive torque.

2. The crack in the body of containment spray check vavle 2-CS-13 was caused by a sand inclusion which was apparently acceptable at the time of manufacture.

3. The occurrence described herein did not affect the safe operation of the station.

4. The occurrence described herein did not adversely i affect the health or safety of'the general-public.

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