ML20028E043
| ML20028E043 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/14/1983 |
| From: | John Marshall ARKANSAS POWER & LIGHT CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| 2CAN018313, 2CAN18313, NUDOCS 8301200292 | |
| Download: ML20028E043 (4) | |
Text
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^RKANSAS POWER & LIGHT COMPANY POST (;FFICE BOX 551 LITTLE ROCK. ARKANSAS 72203 (501) 371-4000 January 14, 1983 2CAN018313 Director of Nuclear Reactor Regulation ATTN: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 PPS Information Submittal -
Long Term Program Gentlemen:
Our letter to you dated January 8,1983,(2CAN018307) committed to provide you four items of information regarding our completed and upcoming reviews of the Plant Protection System (PPS). The following fulfills that commitment.
Item 1. Submit the results of a review of the PPS including an identification of any single design point that could cause a simultaneous actuation of Engineered Safety Feature Systems similar to the December 17, 1982, event an San Onofre Unit 3.
Response: The design philosophy of the PPS matrix / trip path logic has been established for many years. This system philosophy (as reviewed and approved by NRC) is presented in Sections 7.2 and 7.3 of the FSAR.
The NRC licensing approval of this philosophy was received after resolution of numerous NRC questions concerning single failure criteria, independence of vital buses, etc.
Realizing that the matrix / trip path logic philosophy has been physically proven through years of operation, our first priority was to review the PPS concentrating on the actual implementation of the design philosophy (i.e. detailed wiring). Therefore, an engineering review of each power supply, fuse, connector, circuit card and relay within each j ,
channel of the system. As the event at 50NGS-3 caused full ESF system plO Of actuation of all four channels, it was determined that circuitry contained in only a single channel could not be suspect.
8301200292 830114 p DR ADOCK 05000368 MEMBER MIDDLE SOUTH UTILITIES SYSTEM
Mr. Robert Clark January 14, 1983 Our efforts were, therefore, focused on the areas within the design where circuits / wiring crossed the channel boundary (i.e. power distribution, matrix and trip path logic). The results of this engineering evaluation re/ealed that disconnection (or loss of continuity) of connectors AJ3109 (in PPS-A) and DJ3109 (in PPS-D) could result in a full ESF actuation and reactor trip similar to the SONGS-3 event. This design implementation error during the initial vendor fabrication of the PPS cabinets was discussed with you in our letter dated December 28,1982,(2CAN128219) our LER 50-368/82-052/0IT-0,and during our meeting in your Bethesda offices on January 10, 1983.
The engineering evaluation did not reveal any other single points within any of the four PPS cabinets that could result in a full ESF actuation and/or reactor trip. Further, it confirmed that after the modification of the wiring through connectors AJ3109/AJ3110 and DJ3109/DJ3110, no single failure, degradation, or disconnection of a given component could cause a complete ESF actuation and/or reactor trip. The validity of existing FSAR analyses presented in Sections 7.2 and 7.3 was therefore confirmed.
This engineering evaluation was confirmed by a physical verification effort (as discussed with your staff on January 12,1983). This effort involved disconnection of connectors, removal of fuses, deenergization of power supplies, etc. This was accomplished one item at a time with observation of the results. The PPS was then restored and the next interface / power supply taken out of service with observation of the results. The effort was conducted on all four PPS cabinets.
We believe the engineering analyses supported by our physical verification effort prove conclusively that no single points within the AN0-2 PPS can, in themselves, result in a full ESF actuation and/or reactor trip and thus the design basis of the PPS is intact and proven.
Item 2: Submit a schedule for modification of all items identified in Item 1 above.
Response: As discussed with you and your staff in our meeting with you on January 10, 1983, we were in the design process of modifications to connectors AJ3109 and DJ3109 to correct the identified wiring error.
This was accomplished by exchanging sixteen circuits between connectors AJ3109/DJ3109 and AJ3110/DJ3110. The modification was completed on January 12, 1983. Post implementation testing verified that loss of continuity through any one of the four connectors would not result in a full ESF actuation and/or reactor trip.
AP&L therefore considers our activities in response to Items 1 and 2 of our January 8,1983,(2CAN018307) letter to be complete.
Item 3: Submit an outline of a long term integral evaluation of the PPS and Recirculation Actuation Signal (RAS) initiation and system response.
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Mr. Robert Clark January 14, 1983 Response: We have outlined and are preparing to implement a more long term and integrated evaluation of the PPS and ESFAS. This program is outlined below.
Step 1: Review the functional requirements of the ESFAS to assure conformance to the original design basis.
Step 2: Eveluate the consequences of spurious actuation of various combinations of ESFAS. Possible combinations will be evaluated regardless of identification of a mechanism for their oCCurrance.
Step 3: Identify any equipment failures that could possibly result from Step 2. Further evaluation will then be conducted to determine if such failures could be detrimental to mitigating a design basis event or result in a complete loss of a system safety function.
Step 4: Verify that current FSAR analyses bound the potential plant transients resulting from the spurious actuation of the various ESFAS combinations from Step 2.
Step 5: Identify possible system modifcations that have a potential to mitigate any undesirable consequences of a postualted combination of spurious actuations as identified in Step 3.
Step 6: Evaluatate the possible modifications from Step 5 and select those that increase system reliabilty and are consistent with the current AN0-2 design basis.
Step 7: Develop implementation schedules for modifications chosen from Step 6.
Concerns have already been identified with a spurious and simultaneous actuation of SIAS and RAS. We have completed modifications to the High Pressure Safety Injection mini recirculation valves to alleviate the immediate concerns with possible damage to these pumps following a simultaneous SIAS and RAS. We will, however, be conducting a further evaluation of this ESFAS combination. Possible modifications might include separation of RAS from the PPS, manual actuation of RAS, etc.
. Item 4: Submit the best schedule available for the completion of Item 3 above.
Response: Currently, our best schedule indicates that these seven items can be completed by March 30, 1983. We must point out, however, that until the results of Step 2 are available, we will not know the complete scope and magnitude of the effort required to accomplish the remaining steps. Thus, some uncertainty is involved in our schedule.
This schedule appears to us to be reasonable and appropriate. The verification of the PPS provides assurance we are not susceptable to a single failure which could result in a full ESF
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Mr. Robert Clark January 14, 1983 actuation. Modifications completed on January 10, 1983, (as discussed in our letter dated January 5,1983,(2CAN918304) to the High Pressure Safety Injection (HPSI) mini-recirculation valves have alleviated the concerns of equipment damage following a simultaneous actuation of SIAS and RAS.
As stated to you previously, we consider this entire issue to be serious and strongly desire to support and undertake the programs and actions necessary to assure the continued safe operation of ANO-2. We believe this position has been demonstrated by the prompt implementation of administrative controls (the day after we learned of the SONGS-3 event), our modifications to the HPSI mini recirculation valves, our expidited modifications to the connector wiring, our PPS verification effort, and the scope and intent of the above program. We do not take the complexity and importance of the above program lightly and therefore it should be conducted in a timely yet meticulous manner. The importance of thoroughness cannot be overstressed to provide assurance that problem areas are correctly identified and addressed without the creation of new problems. We believe our above schedule is appropriate to assure both.
Very truly yours, John R. Marshall Manager, Licensing JRM/JTE/dir l
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