ML19329B865

RO NP-32-77-12:on 770805,thermal Structural Analysis Indicated 30 Discharges Limit on Six Inch Pressurizer Safety Valve Lines Vs Design Criteria of 288.Caused by Incompatible Loop Seal Lifetime Cycles.Limitations Imposed

ML19329B865
Person / Time
Site:	Davis Besse
Issue date:	08/19/1977
From:	Domeck C, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B819	List: ML19329B818 ML19329B865
References
NUDOCS 8002060872
Download: ML19329B865 (3)

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ggi Thermal / structural analysis indicates 30 discharges limit oni 6" pressurig ies . -- m gp]l zer safety valve...l..i_n_e.s versus design criteria of 288. Analyhis imposes -

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__s TOLEDO EDISON COMPANY DAVIS-BCSSE UNIT ONE MUCLEAR POWER STATION g SUPPLEMENTAL INFOP.MATION FOR LER UP-32-77-12 DATE OF EVENT: August 5, 1977

[ FACILITY: Davis-Besse Unit 1 i IDENTIFICATION OF GCCURRENCE: Thermal / structural analysis of the 6" pressuriter safety valve lines has indicated that an anchor ring close to an elbow (loop seal) is the most critical point. With 410 F maintained by heat tracing, a lifetime i limit of 30 discharges is imposed on these valves compared to a B&W design criteria of 288. Similarly, thermal / structural analysis of the 3" pressurizer power relief valve loop seal piping indicates a limit of 500 valve discharges for a loop seal temperature of 5600F. The B&W design criteria is 8800 lifetime valve actuations. Reportable per Technical Specification 6.9.1.81.

Conditions Prior to Occurrence: The plant was in Mode 3, with Power (MWT) = 0 and Load (MWE) = 0.

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Designscion of Occurrence: During Hot Functional Testing, the 3" pressurizer power relief valve was opened and severe movement of the discharge piping was observed. Analysis of the problem indicated that maintaining 6000F on the loop g seal portion of the 3" line (upstream of valve) would permit the water to flash to steam upon valve discharge. This would considerably limit the discharge pipe movement. Supports were also added to the 8" co= mon discharge line. Testing dur-ing Hot Functional Testing did bring this discharge pipe =ovement into acceptable limits. The design oijective for the permanent electric heater installation was to obtain a temperature of 6000 F on the 3" power relief valve line and 5500F on the 6" safety valve lines.

Test- have indicated that the 3" line temperature can be maintained with one of the two redundant heater strings energized. However, on the two 6" lines, we were able to obtain approximately 4250F with both strings of heaters in operation. Additional heaters and insulation have been installed. Further testing has indicated that the' 6" lines are now being maintained at approximately 4250F, with further increases in temperature to 5000F with all heaters operating.

Designation of Apparent Cause of Occurrence: Analysis of the loop seals indicated ,

a lifetime of 30 cycles for the 6" safety valve lines compared to a design cri-teria of 288. Similarly, analysis imposes a 500 cycle lifetime for the 3" power i relief valve piping versus a design criteria of 8800 valve actuations. Analysis I resulted from not being able to attain the designed loco seal temperature.

t Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. Valve discharges to date are well below the lifetime cycles.

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! TOLEDC EDISON COMPANY I DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENTAL INFORMATION FOR LER NP-32-77-12 PACE 2 i

Corrective Action: Valve discharge limits noted above have been imposed upon the facility. Further analysis may result in elbow anchor design changes. A Periodic Test, PT 5164.03 " Pressurizer Relief Valve Heat Trace Test", will monitor daily the discharge piping temperature and the electromatic relief i vill be made inoperabit if the line is not at the required temperature.

Actuations will be logged in the Trip and Transient Log Book by the Control j Room Operator.

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Failure Data: No previous similar events have occurred. F i

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