ML19329B580

RO NP-32-77-08:on 770717,decay Heat Stop Check Valve Leaked When Core Flood Isolation Valve Opened,Allowing Water from Core Flood Tank to Reverse Flow Into Decay Heat Piping. Caused by Component Failure.Rcs Depressurized & Cooled Down

ML19329B580
Person / Time
Site:	Davis Besse
Issue date:	07/28/1977
From:	Batch S, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B509	List: ML19329B507 ML19329B580
References
NUDOCS 8002050715
Download: ML19329B580 (5)

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• g3 Decay Heat Stop Check Valve (DH77) leaked when*the Core Flook I' solation _J 7 89 I

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> Valve was opened allowing water from the Core Flood Tank to reverse flow ]

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DAVIS-LE9SE UNIT ONE NUCLEAR POWER STATION

. SUPPLEMENTAL INFORMATION FOR LER NP-32-77-8

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DATE OF EVENT: July 17, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Failure of Decay Heat Stop Check Valve DH77 to prevent reverse flow.

Conditions Prior to Occurrence: Just prior to the occurrence, the plant was being heated up in Mode 3, with Load (MWE) = 0 and Power (MWT) = 0. Reactor Coolant System (RCS) pressure was approximately 784 PSIC and RCS cold leg temperature was 351 F.

Description of Occurrence: At 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> on July 17, 1977, Operations person-nel were performing Surveillance Test ST 5050.03, " Core Flood System Valve Inter-lock Test, Phase II". This Surveillance Test verifies the automatic opening of the Core Flood Tank Isolation Valves, CF13 and CFLA, at 800 1 30 PSIG Reactor Coolant System (RCS) pressure. At 784 PSIG, Core Flood Isolation Valve CF1B stroked open as intended. As the valve stroked open, the alarms " Core Floed Tank 1 Pressure Low" and " Core Flood Tank Level Low" were received. At the same time, the operators also found that the Decay Heat Pump 1-2 Mini =um Cool-gsg down Flow Indicator FI4908 was indicating a flow and that the Containment Normal j Sump and Reactor Coolant Drain rank levels were increasing. The operators then

, - determined chat DH77, Decay Heat Train 1 Stop Check Vaive was leaking by and allowing a revarse flow.

To rectify the situation, an attempt was made to close the Core Flood Tank 1 Isolation Valve, CF13. As intended, the interlock against closing this valve prevented closing it. Reactor Coolant System pressure was then reduced by pressurizer spray and CF13 was closed at 0627 hours0.00726 days <br />0.174 hours <br />0.00104 weeks <br />2.385735e-4 months <br />.

Before the incident, Core Flood Tank 1-1 level was 13.1 f eet. After CFl3 was closed Core Flood Tank 1-1 was at a level of 10.8 feet and 415 PSIG. This indi-

' cates a total of 1150 gallons of water was discharged to the Decay Heat System.

As the Core Flood Tank discharged to the Decay Heat System, the Decay Heat System Relief Valves PSV 4849, PSV 1529, PSV 1550, PSV 1508 and PSV 1509 lifted and pro-vided overpressure protection as designed to the Decay Heat System. PSV 4849, the Decay Heat System Suction Line from the RCS, relieved to the Containment nor-mal sump. The PSV 4849 setpoint is 320 PSIG. As per the Normal Sump Flow Indi-cator, 166 gallons of water were pumped from the Containment nor=al sump. The remainder of the water was discharged to the Reactor Coolant Drain Tank by PSV 1529, "pecay He,at, Pump 1-1 Discharge to,the ,RCS";_PSV,1550, " Decay _ Heat Pump,1-2 Discharge to the RCS"; PSV 1508, " Decay Heat Pump 1-1 Emergency Sump Suction Relief Valve" and PCV 1509, " Decay Heat Pump 1-2 Emergency Sump Suction Relief Valve". On the Reactcr Coolant Drain Tank, the Reactor Coolant Drain Tank Vent Line Drain Valve, RC 160, was being used as a vent path. The Reactor Coolant V'

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TCLEDO EDISON COMPANY

, /'N CAVIS-BESSE UNIT ONE NUCLEAR POWER STATION '

(a) SUPPLEMENTAL INFORMATION FOR LER NP-32-77-8 PAGE 2 Drain Tank level before the incident was 43 inches. One Reactor Coolant Drain Tank Pump was in service. Of the approximately 984 gallons that were discharged to the Reactor Cool;at Drain Tank, approximately 110 gallons overflowed the tank.

The bulk of the water was pumped to the Clean Waste Receiver Tanks.

At 0700 hours0.0081 days <br />0.194 hours <br />0.00116 weeks <br />2.6635e-4 months <br />, the Operations Engineer was notified. Reactor Coolant System pressure was being maintained at 700 PSlG and RCS temperature was 350 0F.

At 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />, Decay Hea: Is.lation Valve DHlB was closed to perform a leak check on DH77. A Deviation Report was written with respect to entry into an Action Statement of Technical Specification 3.5.2 which requires two independent ECCS subsystems to be operable in Mode 3. After it was verified that DH77 was leak-ing through, DH77 and DH1B were opened to return the Decay Heat System to opera-ble status. The plant was then out of the Action Statement 3.5.2.a of Technical <

Specifications at 1126 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.28443e-4 months <br /> on July 17.

Similarly, at 1145 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.356725e-4 months <br />, DH1A, Decay Heat Isolation Valve for Decay Heat Loop 2 was closed to check DH76 for leakage. DH76 did not leak. Again, a Deviation Report was written for entry into an Action Statement of Technical Specification 3.5.2. At 1310 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.98455e-4 months <br />, DH76 and DHlA were opened and Decay Heat Loop 2 was de-clared operable.

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As a r?sult of the incident, two relief valves, PSV 1529 and PSV 1550 were damaged.

In an attempt to isolate the leakage from the two relief valves, which have a common discharge isolation valve, AC 89, the isolation valve RC 89 was closed.

It also leaked by.

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To make repairs to DH77 and the other components damaged, depressurization and cooldown of the Reactor Coolant System to 250 PSIG and approximately 205 F was  ;

commenced. At 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br /> on July 17, 1977, the plant re-entered Mode 4. To j further facilitate repair of the two relief valves, PSV 1529 and PSV 1550, the RCS was cooled down further. The plant entered Mode 5 at 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> on July 20.

1 The maximum Reactor Coolsnt System Pressure during the incident was 790 PCIG. I Since 800 PSIG was not exceeded, the Core Flood Tanks were not yet " required" to be operable as per Technical Specification 3.5.1. However, Core Flood Tank 1-2 was not affected by the incident and was in an operable status. The Decay Heat System also renained available for Low Pressure Injection.

I Designation of Apparent Cause of Occurrence: Failure of the valve DH77 was )

strictly a component failure. The valve f ailed to perform its design function of preventing the Core Flood Tank from discharging to the Decay Heat / Low Pressure Injection System.

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TOLEDO EDISON CO.sANY n D' AVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENIAL INFORMATION FOR LER NP-32-77-8 -

PAGE 3

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Failure of the two relief valves to reseat after lifting was due to seat damage.

The disc retaining ring' was also found to be broken on one valve and missing on the other valve.

As a result of the incident, the calibration of Flow Transmitter FT 4908, FT 4909 and FT DH2B was checked. Flow Transmitters FT 4909 and FT DH2B were found to have distorted bellows which were replaced and the transmitters recalibrated.

Flow Transmitter FT 4908 was not damaged but was slightly out of calibration and was recalibrated and returned to service. The damaged bellows were possi-bly the result of the reverse direction flow past the two transmitters during the incident.

The leaking valve RC 89 that failed to isolate the two leaking relief valves, 78" 1529 and PSV 1550, was probably due to improper assembly of the valve. No apparent damage was found to RC 89.

Analysis of Occurrence: During the incident, a reverse direction flow existed in the Decay Heat Pump 1-1 discharge piping to th,e RCS. A reverse flow also existed in the suction piping of Decay Faat Pump 1-1. The setpoints of the five ta8ief valves that lifted are as follows:

~'s PSV 4849 320 PSIG s ) PSV 1529 450 PSIG PSV 1550 450 PSIG PSV 1508 75 PSIG PSV 1509 75 PSIG All GCB c' ass piping on the discharge side of the Decay Heat Pumps was hydro-statically tested at 645 PSIG. All GCB class piping on the suction side of the Decay Heat Pumps was hydrostatically tested at 430 PSIG. The HCB class piping on the suction of the Decay Heat Pumps was hydrostatically tested at 106 PSIG.

The relief valves listed above did lift to provide overpressure protection to the Decay Heat System and no physical damage to the system other than listed above was sustained. Therefore, no danger to the health and safety of the public or station personnel did occur.

Corrective Action: Initially, the Reactor Coolant System was depressurized and cooled down to 235 PSIG and 205 F so that repairs could be made to the DH77 valve. This was completed at 0850 hours0.00984 days <br />0.236 hours <br />0.00141 weeks <br />3.23425e-4 months <br /> on July 18, 1977. The RCS was cooled down further so that repairs could be made to PSV 1529 and PSV 1550. Mode 5 was entered at 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> on July 20, ic77.

The two relief valves were relapped and the disk retaining rings were replaced.

The valves were bench tested ,and returned to service at 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> on July 21, 1977. PSV 1529 was returned to service at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> on July 21, 1977.

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s g TOLEDO EDISON COMPANY y DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION

[Q SUPPLEMENTAL INFORMATION FOR LER NP-32-77-8 PAGE 4 The valve RC 89 was disassembled. Although no damage was noted, the diaphragm was replaced and the valve was reassembled.

• The flow transmitter FTDH2B was repaired by replacing the diaphragm and recali-brating the transmitter. FTDH2B was declared operable at 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br /> on July 20, 1977 Flow transmitter FT 4909 was repaired by replacing the capsule assembly and force motor assembly and then recalibrating. FT 4909 was returned to ser-vice at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on July 20, 1977.

Repairs were made to DH77 under the direction of a representative of Velan Engineering Company. DH77 is a 10" stop check valve whose disc has an upper l and lower guiding surface ano also the body guide surfaces. Repairs included l

=mcoching these guiding surfaces, removing 0.002" from 0.D. of the lower guide surface and relapping the valve. Another repair involved relieving or increas-l ing the internal diameter or stem bore of the disc in the area where the stem of the valve meets the disc when the valve is being used as a stop valve. Re-I pair of DH77 was completed at approximately 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> on July 23, 1977. On July 23, 1977, from 1510 to 1832 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.97076e-4 months <br /> Decay Heat Valve DH77 was leak checked.

Decay Heat Valve DH77 passed the leak test and the plant heacup was continued.

To prevent further recurrence fo this incident, steps have been added to PP 1102.02, Station Startup Procedure, to perform a leak check on both DH76 and g

Nw-DH7't prior to performing ST 5050.03 while the plant is being heated up. This ~

char _ge was made by Temporary Modification T-2034.

Failure Data: No previous similar events have occurred.

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