ML20003C403
| ML20003C403 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 02/06/1974 |
| From: | JERSEY CENTRAL POWER & LIGHT CO. |
| To: | |
| References | |
| AO-50-219-74-9, NUDOCS 8103030641 | |
| Download: ML20003C403 (3) | |
Text
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,v OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence Report No. 50-219/74/9 mm 6
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Report Date:
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February 6, 1974 l'i.,
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k January 31, 1974 Identification of Occurrence:
Violation of the Technical Specifications, paragraph 2.3.7, low pressure main steam line pressure switches (RE23A and D) were found to trip at pressures less than the specified value (850 psig plus 10 psig for head correction). This event is considered to be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15A.
Conditions Prior to Occurrence:
The plant was operating at steady state power.
The major plant parameters at the time of the event were as follows:
Power - Core, 1902.9 MWt Flow - Recire., S7.9x10{g)
Elec.,'669 MWe lbm/hr 6
' Feed., 7.2x10 lbm/hr Stack Gas - 23,230 pCi/sec Description of Occurrence:
On Thursday, January 31,1974, at 1320, while performing routine surveil-lance testing on the four main steam line low pressure switches, it was discovered that RE23A and RE23D tripped at 858 psig and 856 psig, respec-tively. This was 2 psig and 4 psig below the set point of 860 psig.
Although the Technical Specifications call for a main steam line low pressure set point of 850 psig, the set point for the switches is 860 psig to account for the difference in head between the switches and the main steam line.
As, found switch settings were:
Test #1 Test #2 RE23A 860 psig 858 psig 1'1'~J 4 RE238-860.psig 860 psig RE23C 863 psig 862 psig 856 psig 856 psig RE230 f/03030GW
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Abnormal Occurrence No. 50-219/74/9 Page 2 Repeatability of the sensors was checked by observing two consecutive trip points.
The pressure switches were then recalibrated and checked to actuate as follows:
Test #1 Test #2 RE23A 861 psig 861 psig RE23D 862 psig 861 psig Apparent Cause of Occurrence:
Design and unusual service conditions are factors contributing to the cause of this event. Sensor set point drift is a recognized problem and work is in progress to formulate a final solution. The steps proposed to achieve this end were delineated in Abnormal Occurrence Report No. 50-219/74/1.
Analysis of Occurrence:
As indicated in the bases of the Technical Specification, "The low pressure isolation of the main steam lines at 850 psig was provided to give pro-tection against. fast reactor depressurization and the resultant rapid cool-down of the vessel. Advantage was taken of the scram feature which occurs when the main steam isolation valves are closed to provide for reactor shutdown so that high power operation at low reactor pressure does not occur, thus providing protection for the fuel cladding integrity safety limit."
The adverse consequences of reactor isolation occurring at reactor pressure approximately 4 psi below the specified minimum value of 860 psig is limited to those effects attendant to a greater than normal reactor cool-down rate. The fuel cladding integrity safety limit only comes into effect for power operation greater than 354 MWt with less that 10% recirculation flow. Therefore, the consequences of a 4 psi lower than normal reactor isolation and scram set point has no threatening effect whatsoever on the fuel cladding integrity.
The effects of a too rapid cooldown due to the lower isolation pressure are inconsequential since there is 'less than 1*F difference between the saturation temperature for 860 psig and 856 psig.
The adverse safety effect of RE23A and RE23D actuating at the as found pressures is in the loss 'of system redundancy. The other two sensors, RE23B and C, would have functioned normally.
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Abnormal Occurrence No. 50-219/74/9 Page 3 Corrective Action:
Continuing corrective actions being taken at this time are as follows:
1.
Investigation is being conducted into the basis for the steam line low pressure setting of 850 psig.
Development of a Technical Specification change to lower the set point will follow if results of transient analyses indicate this possibility.
2.
Vendor recommendations to possibly reduce or eliminate the sensor set point change problem will be evaluated as soon as they are available.
3.
A request has been initiated for engineering assistance to determine the cause of drift in these and other pressure sensors of concern, and to recommend corrective solutions.
Failure Data:
Manufacturer data pertinent to these switches are as follows:
Meletron Corp. (subsidiary of Barksdale)
Los Angeles, California Pressure Actuated Switch Model 372 Catalog #372-6SS49A-293 Range 20-1400 psig Proof Psi,1750 G Previous Abnormal Occurrence Reports involving these switches are:
1.
Letter to Mr. A. Giambusso from Mr. D. A. Ross dated
' December 24, 1973.
2.
. Abnormal Occurrence Report No. 50-219/74/1