ML20024D025

Ro:On 830421,following Preliminary Manual Test Insertion (Mti)Test,Actuation Module Lights Came on Due to Module Energizing.Cause Unknown.Operators Stationed to Mitigate Problems or Actuation If Mti Required

ML20024D025
Person / Time
Site:	Millstone
Issue date:	07/15/1983
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO.
To:	Deyoung R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
MP-5244, NUDOCS 8307210342
Download: ML20024D025 (3)

Text

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P O BOX 270

} , HARTFORD. CONNECTICUT 06101 (203) 666-6911 3 L J Mr. Richard C. DeYoung, Director July 15,1983 Office of Inspection and Enforcement U.S. Nuclear Peguhtory Camission MP-5244 Washington, D. C. 20555

Reference:

Facility Operating License No. DPR-65, Docket No. 50-336

Dear Mr. DeYoung:

This letter forwards the Special Report required to be subnitted within ninety days pursuant to Millstone Unit 2 Appendix A Technical Specifica-tions, Section 6.9.2.e and 3.5.2.b, IOCS Actuation.

Plant Conditions Prior to the Event:

On April 21, 1983 at 1340 hours0.0155 days <br />0.372 hours <br />0.00222 weeks <br />5.0987e-4 months <br />, Unit 2 was operating at 67% power, with 2 charging pumps operating and an 80 gallon per minute continuous dilution in progress. Earlier in the day, a dropped CEA caused a reduction of power to less than 70%. Xenon had not yet peaked, therefore it was still adding

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strong negative reactivity. An Instrumentation and Controls (I&C) technician had obtained permission to perform surveillance procedure SP 2403J Panual Test Insertion (MII) surveillance on the Engineered Safeguards Actuation Systan (ESAS).

Event Cescription The I&C technician had satisfactorily ccmpleted the preliminary tests of the MII equipnent and had begun to connect the box to the ESAS cabinets.

lie had connected the ccumon ard Vo leads to the Channel A Containnent Pressure bistable and the cmmon lead to the Channel C Containment Pressure bistable. As the Vo lead was connected, all of the actuation module lights cane on. He imrediately rmoved the lead and all lights went out, without having to push any reset buttons. h Containment Pressure bistable had not energized. At the instant the actuation modules energized, both facility I and II SIAS equipnent energized. The operators innediately

, . observed Pressurizer and Containment pressures and found them to be normal.

h Shift Supervisor verified with the technician that it had been an inadwrtent initiation as a result of the testing. 'Ihe Control Operator (CO) secured the Boric Acid punps and shut the Boric Acid Storage Tank gravity feed valves. The charging pump suction was restored to the Volume Contial Tank (VCT) . The Supervising Control Opstor (SCO) reduced turbine load to match reactor power. h sudden reduction of reactor power fran the boration prior to the turbine load reduction resulted in a slight cmldown (approx. 2 F on Tc) and a resultant RCS pressure drcp of c.pproxi-mately 20 PSI. h CO and SCO 1mnediately began restoration of egaipment to normal operating condition. Operating Provh 2394, Inadvertent IICS Initiation, was obtained and equipnent verified to be restored.

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Analysis of Event:

2 During the performance of OP 2394, it was discovered that all pumps and  ;

fans responded to the SIAS signal, throttle valves were found to be in a throttled position and scnne valves and dampers had not changed position. ,

h initial determination of the event therefore, was that a random ac- j tuation of SIAS Actuntion bbdules had occurred since not all equignent i respcnded. Subsequent investigation revealed that all valves which were =

found not to be in their accident position wem air operated valves and the 3 actuation modules associated with those valves had in fact fired since i other equipnent had gone to their accident position. Motor operated valves  ?

had gone to their accident position. a

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A test was perfonned on certain valves which were known to not hnve j responded to the SIAS signal. When their associated act21ation rnodule f energized, all valves responded and remained in their required position / 1 mode until reset by the operator. Further checking of air operated valves ]

showed that if the valve does not go full travel before the signal is 2 -

t rmoved the valve will return to its original position. Since the SIAS signal was innediately rmoved, all air operated valves were discovered in their original position. This also explains the "as found" position of the 4 ventilation dampers.  !

a A theory which could explain why the actuation occurred is that sten the y test gear was connected to the Containment Pressure bistable, it could have -

loaded or scruehow reduced the 15 volt logic power supply such that the .

actuation roodules associated with Containment Pressure /SIAS signal fired.

As soon as the probe was renoved, the actuation inodules reset since they --

were not " locked-in" through the logic circuitry. h reason for the J

" crowbar circuit" is to short the 24 volt actuation nodule power supply if a voltage dip on the 15 volt logic power supply is sensed. h crcwbar i prevents randcm firing of the actuation modules. In this case the test i prthe was connected downstream of the voltage sensing device, therefore the $

crowbar protection was not available.  ;

i h intention of the MrI is to test the various logic conbinations for 11 actuation module response. This signal is of such a short duration (less

than 2 milliseconds) that equipnent acblation does not occur. In this 5 event, the prebe insertion was sufficient to result in equignent actuation. J R

A couplete check was performed on the MPI test equipnent and no inconsis- 2 tencies or abnonnalities were found. A check of the test circuit diagram E also revealed no reason or means of causing the actuation. It should be $

noted that as a precautionarv measure, the MrI box is always powered through an isolation transformer. 'Ihis should have prevented the d grounding / loading of the 15 volt supply as described above. }

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Consequences of Event:

There were no consequences effecting plant operation as a result of the initiation other than a slight increase in PCS boron concentration (approximately 15 PPM) with its resultant power decrease of 7%. Since letdown flow had not isolated, the heating effect produced by the Pegenera-tive Heat Exchanger was still present, therefore there was no thermal shock to the charging line nozzles or in the reactor coolant systen in general.

Conclusions:

Though the exact cauw of the inadvertent initiation is not known, all equipnent responded as required. In the future, the MPI surveillance will be satisfied whenever possible by the Autcmatic Test Insertion (ATI) device which is in continuous operation and will verjfy proper ESAS operation. If the MrI is required to be performed, operators vill be stationed to mitigate any potential problems or indertent actuation.

Yours truly, NORIHEAST NUCLEAR ENErsTI ANY 6V,'-g at/

E. J. Mroczka Station Superintendent Millstone Nuclear Power Station FJM/JGR:mo cc: Dr. T. E. Murley, Region Administrator, Region I, King of Prussia, PA.19406 Director, Office of Management Information and Preguuu Control, Washington, D. C. 20555 (3)

U. S. Nuclear Regulatory Camission, c/o Document Management Brarch, Washington, D. C. 20555 L _

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