ML19319E203
| ML19319E203 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/18/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19319E194 | List: |
| References | |
| NUDOCS 8003310716 | |
| Download: ML19319E203 (4) | |
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ABNORMAL OCCURREf!CE REPORT p<
l@~ 7 DOCKET NO. 50-312-74-3 I.
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a Reporting Date:
Septenber 18,1974
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Occurrence'Date:
September 10,1974 Time:
0558 Facility:
Rancho Seco Nuclear Generating Station Unit No. 1 Clay Station, California
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Identification of Occurrence:
P.eactor Coolant System overpressure during heatup Condition Prior to Occurrence:
The plant was at refueling shutdown completing final testing prior to i..itial criticality.
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Description of Occurrence:
On the morning of September 10, 1974, the reactor coolant system temperature was being increased within the limits of the heatup curve N
established in the Technical Specifications. The system was stabilized
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at 355'F and 1700 psig to insert cocked rods and remove all the shutdown bypass keys-from the reactor protection instrucentation as required by the operating procedure. After removing this shutdown bypass inhibits, the reactor system was in the process of increasing pressure by energizing the pressurizer heaters. The. pressure was increased to 1950 psig which is above the lcw pressure trip of 1900 psig and all the reactor protection channels were reset. Concurrent with this heatup, a routine inspection of plant equipment was being conducted. As an cperator was walking through the "D" inverter room, he heard a " snapping" sound coming frcm the internals of the S10 inverter cabinet. The operator informed the Shift Supervisor of the situation and he also inspected the inverter. The plant was not being effected by the inverter problem and since an electrical technician was expected to report to work within an hour, the Supervisor decided to have the technician work on the system.
-When the technician arrived at 0500, he. opened the cabinet and observed an inductor heat sink ground screw lug loose and it was sparking to the grounding bar. To prevent electrical trans'ients and further degrada-tion of the' inductor lug, he advised that the SlD inverter be de-energized _
and he would start repair of the unit immediately. At 0537 with the electrical technician ready, SID was secured.
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n f3 The reactor operated smoothly until 0549 when the high rt. actor coolant pressure alarm sounded. This indicates at least 2255 psig reactor coolant pre.ssure and the operttor inspected his indicators. The wide range pressure recorder indicator was reading 1950 psig; the narrow range pressure recorder indicator ("B" loop pres:ure) was at 1950 psig, and the narrow range pre 5sure indicator ("A" loop pressure) was at 2400 psig and rising sharply. The operator decided that the latter reading was correct and he stopped the high pressure makeup pump. The pressure quickly decreased and at 2l00 psig the operator energized the pressurizer heaters to assure that the "A" loop pressure was responding correctly and that there was still a steam bubble in the pressurizer. Shortly after the heaters were energized, the pressure started to increase and he was confident that the "A" loop pressure indicator was responding to true reactor coolant conditions and that a steam bubble was still in the pressurizer. The reactor coolant pressure was decreased to 1900 psig by natural decay and then reduced to 1600 psig by request of the Plant Superintendent to centralize the loci point within the limits of the heatup curve until a complete analysis of
.the situation could be made.
Corrective Action Taken or Which Should be Taken:
An analysis of the pressure transient by the on-site Mechanical
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Engineer determined that the reactor coolant system did not sustain any adverse effect because:
O 1.
The reactor coolant system terrperature was above 100*F.
2.
The pressurization occurred under isothemal conditions.
3 The system design pressure of 2500 psig was not exceeded.
4 These pressure / temperature conditions are permitted by the Technical Specifications for leak testing per Section3.1.2.2(a).
In addition to the internal analysis, an external review of the Pressure-Time transient was conducted at Babcock & Wilcox Company in Lynchburg, Virginia. They concluded that the pressure spike had no harmful consequences on the reactor coolant system.
Desianation of Accarent Cause:
Design Analysis of Occurrence:
One of the systems that the S1D inverter supplies is the reactor non-nuclear instrumentation "X" power. This bus feeds numerous signal converters, transmitters, indicators, controllers, recorders and selector stations. The specific modules on this bus which relate directly to the pressurization of the reactor coolant system are:
l.
Seal Injection Flow Transmitter. and Valve Controller.
When the SlD inverter was secured the seal injection b) valve went to 50" open which is the neutral (zero signal) 3 j
control position.
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2._ Makeup' Flow Controller. When the 51D inverter was secured, the makeup flow control valve vent to 50%
open which is-the neutral (zero signal) control s
position.
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3.
Letdown Flow Transmitter. When the 510 inverter was secured, the letdown flow valve went to 50% open which is the-neutral (zero signal) control position.
- 4..: Reactor.. Coolant Pressure flarrow Range Recorder B Loop.
When the S10 inverter was secured the recorder drive stopped and the. indicator _ stopped at the pressure indicated.
5._. Reactor Coolant Pressure Wide Range Recorder B Loop.
When the S10 inverter was secured the recorder drive stopped and the indicator stopped at the pressure
' indicated.
6.
Pressure Level Recorder. When the 51D inverter was secured, the recorder drive stopped at the level indication then current..
..The response of Items 1 and 2 above amounted to a greater cuantity of water injection into the reactor coolant system than was being removed by Item 3.
The increased inventory accumulated in the pressurizer with a l
resultant reactor coolant increase.
l The pressure indicator / recorders (Items 4 and 5) were indicating I
a non-transient condition during the pressum increase. The pressurizer l
level recorder (Item 5) was also indicating a non-transiene condition during the level and pressum increase. Only the alarm function and the
. indicator / recorder on "A" loop were operational and indicating the transient condition. The operator had had difficulty in making the loop "A" recorder
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properly ink its recorder trace prior to the occurrence. Although the mcorder did properly indicate: pressure throughout the event, the short
.l period over which the pressure-transient occurred made the visual display less apparent particularly when the two other pressure recorders were indicating an apparent stable condition. The operator stopped the pressure increase at 2400 psig which is 350 psig above the allowable pressure at 355*F during'heatup.. The pressurization occurred over a period of approximately 22 minutes and _the depressurization to 1900 psig was over a period of one hour and 30 minutes. The temperature during transient did not change from the' ini tial. 355*F.: As described under " Corrective Action Taken," a thorough analysis:of. the transient revealed no adverse effects to the reactor coolant
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system.-
EquipmentiI.O.:
The.SlD inverter is manufactured by Static Products of Garland, Texas, Model fio. SP-DC120-611-250-60.' The inductor which had a. loose screw on thr 1
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. Action'Requircd to Prevent a Reoccurrence:
1.
Operating-personnel have been' issued a more detailed explan tion of what indication will be lost upon de-energiz'ng:."X" power.=
.'2.' ~ A design change has been initiated to provide dual power supplies to "X" power.by means of rapid automatic -
' switching.
3.. Until material and installation of Iten 2 above can' be accomplished, a manual switch has been installed to-provide for manual' switching of "X" AC power to an alternate power supply-(lighting) when required. The "X" DC power has been split into two separate auctioneered power supplies either.of which can carry the entire "X" load.
1 Failure Data:
None 4
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