ML18058A287

LER 92-011-00:on 920212,discovered Inadequate Electrical Isolation of Class 1E Pressurizer Pressure Indicator Cable. Caused by Inadequate Design Control When Equipment Installed in 1980.Mod Controls Re Changes revised.W/920313 Ltr

ML18058A287
Person / Time
Site:	Palisades
Issue date:	03/13/1992
From:	Hillman C, Slade G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-92-011, LER-92-11, NUDOCS 9203230256
Download: ML18058A287 (4)

Text

consumers Power GB Slade General Manager .

l'OWERINli MICHlliAN"S l'ROliRESS Palisades-Nuclear Plant: 27780 Blue Star Memorial Highway, Coven, Ml 49043 Nuclear Regulatory Commission .

Document Control Desk Washington, DC 20555 DOCKET 50-255 - . LICENSE DPR PALISADES PLANT -

LICENSEE EVENT REPORT 92-011; INADEQUATE ELECTRICAL ISOLATION OF CLASS IE PRESSURIZER PRESSURE INDICATOR CABLE Licensee Event Report (LER)92-011 is attached. This event is r~portable to the NRC per IOCFR50.73(a)(2}(ii)(B)* as a condition that is outside the design basjs of the plant.

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DATI 1151 L I I On .February I2, I992, at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />, with the plant in cold shutdown, the Plant staff verified that the Class IE Pressurizer Pressure fostrument Loop (PT-OIOSA) was connected to the non-Class IE primary instrumentation processor and feedwater purity datalogger computers without adequate electrical isolation.

The root cause of this event is attributed to inadequate desfgn control when the equipment modification was engineered and installed, which occurred in late I980.

Corrective action for this event includes a I992 Refueling Outage modification _

_to provide ~lectrical isolatioh in the PT-OIOSA instrument loop to isol~te the signals going to the non-Class .IE primary instrumentation processor and -

feedwater purity datalogger computers and a review of the RG I.97, Category I instrumentation loops to verify adequate electrical isolation.

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.T11rT * - - * - - - - - - - - ...... .-..*111111 EVENT DESCRIPTION On February 12, 1992, at approximately IIOO hours, with the plant in cold shutdown, the Plant staff verified that the Class IE Pressurizer Pressure Instrument Loop (PT-OIOSA) [AB;PT] was;tonnected to the non-Class IE primary instrumentation processor [ID] and feedwater purity ~atalogger computers [IO]

~ithout adequate electrical i~olation; During the week of January 13-I7, 1992, the NRC performed an inspection

, of Palisades compliance with*the requirements of Regulatory Guide (RG) 1.97, "Instrumentation for Light-Water Cooled Nuclear Ppwer Plants to Assess Plant and Environs Conditions During and Fo77owing an Accident." During the course of this inspection, it was identified that one channel of the RG I .97, Type A,*

Category I, variable pressurizer. pressure instrument loop PT-OIOSA may not have been provided with adequate electrical isolation from the non-Class IE primary instrumentation processor and_ feedwater purity d~talogger computers.

This is contrary to the requirements of Table I, Item 2 of RG I.97 which states, " ... redundant or diverse channels should be electrically independent

• and physically separated from each other and from equipment not classified important to safety." On February I2, I992, following the NRC inspection, it was confirmed that the pressurizer pressure loop did not have adequate eledrical. isolation between the Class IE and non-Class IE interface. This conclusion ~as re~ched following a review of electrical sche~atics, electrical ~

wiring diagrams and a walkdown of the electrical scheme in the control room.

This event is reportable to the.NRG per IOCFR50.73(~)(2)(ii)(B) as a condition that is outside the design basis of the plant.

CAUSE OF THE EVENT The root cause of this event is attributed to inadequate design control when the equipment modification was engineered and installed, which occurred in late I980.

This event did not involve the failure of any equipment important to safety.

ANALYSIS OF THE EVENT Two.redundant pressurizer.pressure instrument loops are provided in accordance with the RG I.97 requirements for Category I variables. One loop (PT-OIOSB) meets all of the requirements of RG I.97 for electrical and physical .

I independence. The second loop (PT-OlOSA) is incorrectly wired to the non-.

II Class IE primary instrumentation processor and feedwater purity datalogger

• computers without adequate electrical isolation.

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The two pressurizer pressure instrument loops provide input to the subcoriled margin monitors which are required to be operable when the primary coolant system temperature is above 325°F by Technical Specifications Table 3.17.4, Item 12. As the discrepancy with PT-0105A was determined while the plant was shutdown, there are no immediate operability concerns related to potent.i al failures of this instrument loop.

Several modifications were performed to the PT-0105A pressurizer pressure instrument loops during the early 1980s to bring the instrument loop into compliance with the requirements of the environmental qualificatiori rule and Regulatory Guide 1.97. In latel980, Specification/Field Change 80-126 was performed to replace pressurizer pressure transmitters PT-0105A and PT-01058

~ith en~ironmentally qualified transmitters and relocate the transmitters above the maximum flood level in containment. At the same time, Facility Change 464 was being performed to install the subcooled margin monitors. as required by NUREG-0737. The pressurizer pressure instrument loops provide input to the subcooled margin monitors and thus these instrument l*oops were modified as part of FC-464. Although electrical isolation req~irements were discussed as part of FC-464, and some electrical isolators were installed as*

part of this modification, no electrical isolation was provided to the primary instrumentation processor and feedwater ~atalogger computers. Thi~ failure is attributed ~o the lack of definftion of r~quirements related to electrital isolation which existed in the early 1980s.

CORRECTIVE.ACTION A review of the RG 1.97, Category 1, instrumentation loops will be performed to verify that adequate electrical isolation is provided. This action, which will be fo 11 owed as part of E-PAL-92-005, wi 11 be completed by June 30, _1992.

Additionally, electrical isolation will be provided in the PT-0105A irtstrument.

loop to _isolate the signals going to the .non-Class lE primary inst,runlentation -

processor and feedwater purity datalogger computers. This modification will.

be completed by the end 'of the current refueling outage.

Modification controls in AP 9.03, "Facility Changes," have been extensively revised since the mid 1980s to include additional guidance for identifying design requirements applicable to a design change. The "Design Inp~t Checklist," which is required to be completed for a modification, requires that electrical separation and isolation be.addressed for modifications affecting instrumentation and controls or electrical circuits. These added I controls are considered sufficient to prevent the lack of isolation between Class IE and non-Class lE circuits from occurring in future modifications.

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Therefore, no additional corrective action to prevent recurrence is proposed.

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I INFORMATION

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