ML20214T399
| ML20214T399 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 12/02/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20214T363 | List: |
| References | |
| NUDOCS 8612080576 | |
| Download: ML20214T399 (4) | |
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December 2, 1986 SUPPLEMENTAL SAFETY EVALUATION CARLE SEPARATION LA SALLE COUNTY STATION UNIT 2 DOCKET NO. 50-374
1.0 INTRODUCTION
By letter dated June 13, 1986, Comonwealth Edison (licensee) submitted cable separation analyses for the reactor protection systems to resolve the deficiencies described in Appendix D (trip report) to Supplement No. 7 of the Safety Evaluation Report NUREG-0519, (SSER #7). The concern for cable separation was identified as a license condition.for Unit 2, Item 2.C.(10).
The licensee committed to review the NRR staff trip report (Appendix D) concerning cable separation at la Salle, Unit 2 and Sections 4.1, 4.2, 4.3 and 4.5 of that report. The trip report indicated that the cable instal-lations at the local instrument racks, cable spreading room, control room panels, remote shutdown panel, and automatic depressurization system (ADS) relief valves lack the required independence between different divisions of Reactor Protection System (RPS) subchannels, and thereby, may be challenged via Class IE or associated IE cables from the same division.
2.0 DISCUSSION AND EVALUATION As a result of a site visit on September 28, 1983, various cable separation concerns identified by the NRC staff were examined by the staff at the local instrument racks, cable spreading rocm, control room panels, remote shutdown panel and ADS relief valves. The trip report provided detailed information in support of the findings and positions presented in SSER #7 regarding cable separation in Unit 2.
By letter dated November 15, 1983, the licensee had committed to take appropriate actions to resolve all the identified cable separation deficiencies by modifications, analysis and justification for lesser separation.
In its letter of June 13, 1986, the licensee submitted the RPS cable separation analysis for the deficiencies described in SSER #7.
The following bases were used by the licensee to analyze all cables associated with the RPS systems.
A.
RPS cables of each channel are routed in separate raceways out-side of control panels. The separation of RPS cables from cables associated with safety-related divisions and nonsafety-related 8612080576 861202 PDR ADOCK 05000374 E
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" cables inside the control panels may be less than required by Regulatory Guide (R.G.) 1.75. An analysis was performed to,iustify the lesser
'l separation of RPS cables from other cables inside of control panels.
B.
All cables used to interconnect RPS are the same quality as-those used in Class IE circuits, associated circuits, and nonsafety-related circuits. These types of cable comply with the requirements of IEEE 383-1974 and have been proven to be highly fire retardant by testing.
C.
The cables under these analyses are constrained to control and instrumentation circuits, which by their very nature, are low energy circuits. Control circuits are generally 120 V ac or 125 V de, whereas the insulation rating for these applications is 600 volts.
D.
There are no power cables in contact with the control and instrumentation cables that are in question. Also, there are no
.high energy sources located within control panels that contain RPS cables.
2.1 Reactor Protection System Separation The required independence between RPS subchannels is challenged 'by safety-related or nonsafety-related cables having less than the required separation inside the enclosure. These concerns were identified in Sections 4.1 and 4.3 of the trip report (Appendix D). The following discussions demonstrate that the independence of RPS circuits / channelization inside control panels is adequately maintained for the circuits to perform their safety functions.
1.
One division of the safety-related or nonsafety-related cables is terminated with one division of RPS cables in' side the enclosure.
The physical separation criteria between safety-related for nonsafety-related) cables and RPS cables deviate,from requirements of R.G. 1.75. Therefore, the NRC staff has analyzed the failure secuences which would have to occur to result in potentially damaging effects to the RPS cables'as a result of faults in safety-related or nonsafety-related cables. Any division of RPS cables is independent and separate from its redundant division of RPS cables in the enclosure at its other end; and therefore, it is concluded that the indepen-dence of RPS cables is not degraded below an acceptable level. This analysis is applicable to the enclosures, 2H22-P004, 2H22-P005, 2H22-P006, 2H22-P009, 2H22-P010, 2H22-P015, 2H22-P022, 2H22-PO?S, 2H22-P026, 2H22-P027, 2PA 13J, 2PA 14J, 2H13-P601, 2H13-P603, 2H13-P608, 2.
Single division RPS cables are terminated in their dedicated enclosure (panel), and also there are no safety-related/non-safety-related cables in this panel. This analysis is acceptable and is applicable to the Suppression Pool Temperature Monitoring
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Power Supply Cabinets, 2PLF 5J and 2PLF 6J.
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3.
The redundant RPS cables are teminated in a particular section of the panel with a safety-related cable. This safety-related cable is 125 V de control circuit and is protected by a fuse and a redundant circuit breaker connected in series. Also, a single A2 cable of RPS is rcquired for the backup scram valves which are not redundant to any Al and B1 cable terminated with this panel section. Therefore, j
this analysis is acceptable. This is applicable to Panels, 2H13-P609, 2H13 - P611 (8a), 2H13 - P611 (9a), 2H13 - P611 (9c), 2H13 - P635 (12b),
2H13 - P636 (13b) 4.
Safety-related cables are terminated in a section of the panel with redundant division RPS cables. However, these safety-related cables are alarm circuits which are low energy, and the panel is located in the control room which is considered to be a protected area.
Instru-mentation cables for use in alarm circuits ate rated for 600 volts with insulation tested to a minimuin of 1500 volts with an overall jacket.
The electrical fault current in the alarm circuit cable is not enough to generate thermal energy over a long period of time to cause a failure of an isolation device to adversely affect the RPS cables. Also, the insulation level in the alarm circuit cables assures adequate isolation from voltage transient in the alarm circuit cable from adversely. affect-ing RPS cables. Therefore, this justification of the analysis is accept-able. This analysis is applicable to Panels, 2H13-P611 (8b), 2H13-P611 (9bi, 2H13-P635 (12al, 2H13-P636 (13a).
2.2 Separation of Safety-Related Cables to Nonsafety-Related Cables Section 4.2.(2) of the trip report (Appendix D) identified that safety-related cables and nonsafety-related Cables entering the bottom of the control room panel from the cable spreading room did not meet the minimum separation recuirements. The NRC staff recommended in their trip report 5
that the licensee examine the cable design in the cable spreading room as related to the concern identified in Section 4.2.(2) of the trip report and demonstrate that the effects of lesser separation between i
safety-related cables and nonsafety-related cables is acceptable. The licensee examined and analyzed these concerns identified in the cable spreading room and these concerns were acceptably resolved by analysis and accepted by the staff prior to the trip.
2.3 Automatic Depressurization System (ADS) Relief Valves-Actuation Solenoids Connections The cables supplying power to the redundant solenoids mounted on the ADS valve casing are routed in separate conduits until they reach the proximity of the valves where the cable exits the conduit. From the ends of the conduits to the termination at the ADS valves, the cables are suspended in air. Section 4.5 of the trip report (Appendix D) indicates that the cable installation discussed above is considered to be in violation
4 of the separation criteria documented in'the Final Safety Analysis Report
- (FSAR) which set forth minimum separation requirement between redundant safety-related cables located in hazard zor.es. The staff recommended in the trip report that the safety-related cables in air be either enclosed in a stainless steel flex conduit or wrapped with asbestos zipper tubing.
The licensee by its June 13, 1986, letter committed to wrap all divisional cables associated with the ADS valves with the asbestos zipper tubing.
Therefore, this concern is acceptably resolved by the addition of zipper tubing to all divisional cabling associated with the ADS valves.
3.0 CONCLUSION
The staff has reviewed the licensee's analysis and its justification for redundant RPS circuits' separation criteria which address Section 4.1 and 4.3 of the trip report. Rased on the evaluation discussed above, the panel-hy-panel analysis has demonstrated that the redundant RPS circuits will not be degraded below an acceptable level due to the electrical fault in the safety-related/nonsafety-related cables and is, therefore, acceptable.
The initial cable design for the ADS valves recuired one division cable to be enclosed in zipper tubing and the redundant division cable terminated to the solenoid with no additional barrier as documented in 4
the FSAR. This concern identified in Section 4.5 of the trip report is resolved by the addition of zipper tubing to all divisional cables associated with the ADS valves.
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