ML19337D759
| ML19337D759 | |
| Person / Time | |
|---|---|
| Issue date: | 08/22/1991 |
| From: | Newberry S Office of Nuclear Reactor Regulation |
| To: | Berlinger C Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9109040300 | |
| Download: ML19337D759 (6) | |
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August 22, 1991 MEMORANDUM FOR: Carl Berlinger, Chief Generic Communications Branch Division of Operational Events Assessment FROM:
Scott Newberry, Chief Instrumentation and Control Systems Branch Division of Systems Technology
SUBJECT:
CLOSEOUT OF PART 21 NOTIFICATION #91 065 In acccedanct 4ith the enclosure, the Instrumentation and Contr i Systems Branch have completed action on ti.a Part 21 Notification. The original of the tracking sheet has been submitted. No further action is anticipated.
Original signed by:
Scott Nevberry, Chief Instrumentation and Control Systems Branch Division of Systems Technology
Enclosure:
OGCB 10 P:rt 21 Tracking Sheet #91-065
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JUN 24 '91 17:08 FROM WEC WP2 PAGE.002 i
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4 Westingflouse Energy Systems Q
Electric Corporation June 24, 1991 NS-NRC-91-3603 Document Control Desk US Nuclear Regulatory Commission Washington, DC 20555 Attention:
Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation t
Dear Dr. Murley:
t The following information is provided pursuant to the requirements of 10 CFR Part 21 to report the potential for the existence of a subs hntial safety 3
hazard as communicated by Ms. P. A. Loftus of Westinghouse t:,
Mr. C. E. Rossi of the Nuclear Regulatory Commission by telephone on June 20, 1991. This issue concerns the non-safety related Auxiliary Relay Racks (ARRs) at the Diablo Canyon Nuclear Power Plant which were supplie' y Westinghouse incorporating a safety related interlock for the safety ir.e
'on and containment spray systems.
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BACKGROUND Westinghouse included in the non-safety related ARRs at both units of the Diablo Canyon nuclear power plant relays whose contacts provided a l
safety-related function. This was identified during March / April 1991 while providing technical support to Pacific Gas & Electric (PGLE) on a separate issue.
The reason for the safety function being located in the ARRs at Diablo l
Canyon is believed to have been due to a lack of a sufficient number of i
l position switches on the RHR suction isolation valves.
Therefore, relays were L
added by Westinghouse to the ARRs for enntact multiplication by placing the relay coils in series with the valve limit switches.
The relays ir. question l
provided interlocks to permit high head safety injection and containment spray recirculation following a postulated loss of coolant accident.
l Pacific Gas & Electric (PG&E) verbally infermed Westinghouse that the l
safety-related function under discussion ha.* already been relocated to the safeguards cabinets as part of a previous plant modificatinn.
NS NRC 71 s6Cs fd24/91 d
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EVALUATION The ARRs have historically contained various non-safety related functions. The i
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ARRs are not sei:mically qualified and are not required to receive safety related power. The ARRs were previously known as the Miscellaneous Relay Racks (MRRs), consequently, safety-related functions may also be housed in the MRRs e
in older plants.
Even though the ARRs have not been provided as safety-related equipment, they were traditionally given train designations (i.e., Train A red Train B). The ARRs are of a design similar to the safeguards racks because many of the control functions performed in the ARRs are ir;.srtant to plant operation, even if not safety functions. Some plants may have provided isolated, safety-related power to the ARRs to further enhance the reliability of I
functions performed in them. Though other specific cases of Westinghouse having located safety-related functions in the ARRs have not been identified, it is possible that other instances such as the one at Diablo Canyon may exist.
In addition, Westinghouse is unable to evaluate the potential for i
modifications initiated by others after the original equipment was supplied to have added other safety functions.
j Westinghouse was advised by two utilities other than PG&E that external ARR circuit wiring was routed with safety-related wiring, although, safety-related actuations were not performed in the ARRs at these plants.
In order to satisfy qualification and separation requirements, the ARRs and AR relays were seismically quali'ied for structural integrity at these plants and isolation tests were performed on the AR relays.
SAFETY IMPACT for the system configuration as supplied for the Diablo Canyon plant, a seismic event of sufficient magnitude may have prevented the ability of the system to initiate the recirculation phase of high head safety injection and containment spray in the event of a Loss of Coolant Accident.
4 Generally, the location of safety-related functions in the ARRs and MRRs, tithout pioper isolation and qualification, could potentially affect the ability of the equipment to perfo.m required safety-related functions.
The reliability of safety functions incorrectly located in the ARRs and MRRs may bc high despite the fact that they were not explicitly designed or seismically qualifiet s safety related equipment.
- 1. Although the ARRs and MRRs are not seismically qualified, their basic def.ign is similar to other cabinets that are qualified. The ARRs at two different plants were seismically qualified for s*ructural integrity and isolation tests were performed on the AR relays.
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- 2. For safety-related functions that may be located in the ARRs or MRRs, t
it is likely that they reside in the separate train designated ARR and MRR cabinets. Hence, redundancy with respect to cabinets and components is likely to exist. Redundancy with respect to power
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supplies may also exist.
- 3. Manual local actions may be possible in response to postulated safety system failures which could be associated with this issue.
l RECOMMENDED CORRECTIVE ACTION
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Since Diablo Canyon was originally supplied (since corrected) with ARRs which housed a safety-related component and external ARR wiring was routed with safety-related circuits at other plants, all customers which have Westinghouse l
ARRs and MRRs will be infomed of this issue.
The potential for safety functions to be performed in the ARRs or MRRs, or the association of ARR/MRR. external Wiring with safety-related, train oriented
.l wiring should be identified by each utility.
If either condition is identified,- utilities will be advised to review the plant licensing basis to determine the acceptability of the condition.
If either condition is i
identified and found to be inconsistent with the licensing basis, either of two alternatives may be considered.
- 1. For safety functions performed in the ARRs or MRRs, evaluata the feasibility of relocating the safety-related components to a seismically
. qualified, safety related system. Electrical separation criteria for these safety-related components should be met consistent with the plant specific licensing basis comitments.
i If the ARR/MRR external wiring is found to be associated with safety-related, train oriented wiring, evaluate the feasibility of i
relocating the ARR/MRR external wiring to a routing which is not train oriented and safety-related. Alternatively, any ARR/MRR external wiring associated with safety-related, train oriented wiring can be provided with suitable isolation devices so that an electrical upset in the ARRs/MRRs i-will not be propagated to safety-related systems.
- 2. If safety functions are performed in the ARRs or MRRs, or ARR/MRR axternal
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wiring is found to be associated with safety-related, train oriented l
wiring, ad the above recommendations are impractical or uadesirable, then the folbwing steps are recomended.
I Perform a seismic evaluation of the ARRs or MRRs consistent with a.
the plant licensing basis. Take any necessary actions indicated by the evaluation to upgrade the status of the ARRs or MRRs to a seismic classification consistent with other safety-related j
j equipment.
c NS Mac-91 3603 6/24/91 i
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JUta 24 91 17:10 FROM WEC UP2 PAGE.005 t
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Ensure that Class-1E power is provided to the ARRs or MRRs.
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Verify that cable routing criteria for safety-related systems are met consistent with the plant licensing basis, d.
Verify that electrical isolation criteria are met for any interfaces between the ARRs or MRRs and interfacing systems which 1
are not safety-related.
If you have any questions regarding this matter, please contact i
Mr. P. J. Morris of my staff at (412) 374-5761, or myself.
t Sincerely, C
S. R. Tritch, Manager Naclear Safety Department l
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