2CAN119805, Forwards Addl Info Re ANO-2 Plant Protection Sys,Per 981014 Meeting with NRC Staff.Util Has Been in Process of Developing Design Change Package to Correct Condition

Forwards Addl Info Re ANO-2 Plant Protection Sys,Per 981014 Meeting with NRC Staff.Util Has Been in Process of Developing Design Change Package to Correct Condition

ML20196B534
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/23/1998
From:	Vandergrift J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN119805, NUDOCS 9812010125
Download: ML20196B534 (6)

Text

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- Entergy Entergy Operations,Inc.

, 8s u ss AmsciMao. AA 72801 Tel 501858-5000 November 23,1998 2CANI19805 U. S. Nuclear Regulatory Commission Document Control Desk Mail Station OPI-17 Washington, DC 20555

Subject:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Additional Information on ANO-2 Plant Protection System Gentlemen:

In letter dated June 30,1998 (2CAN069801), Entergy Operations provided the NRC details regarding an unreviewed safety question involving the Arkansas Nuclear One, Unit 2 (ANO-2) Plant Protection System (PPS). As discussed, Entergy had identified that with a channel of PPS in bypass, a failure of a DC bus (FODCB) could result in an unacceptable plant response. As a result of this condition, controls were promptly established to prevent a PPS channel remaining in bypass for greater than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. These controls have been subsequently refmed to exclude RPS bypasses that are independent of Engineered Safety Features Actuation System (ESFAS). ANO is in the process of developing the modification package that will correct the identified condition. However, even with the proposed modifications to the PPS, the existing failure modes for evaluated equipment in the ANO-2 Safety Analysis Report (SAR) do not accurately reflect the de-energization of either pair of vital instrument buses caused by a FODCB. Therefore, the proposed revision to the ANO-2 SAR had been identified as a USQ and was provided for NRC review and approval.

Entergy met with members of the NRC Staff on October 14, 1998, to discuss the l,

proposed PPS modifications and how the modifications correct the ESFAS response

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portion of PPS. Based on that meeting, additional information was identified which was necessary to clarify the Entergy Operations' June 30,1998, submittal. This information is attached for your review.

ANO-2 has been in the process of developing a design change package to correct the ON condition. Even though the proposed modifications discussed in our June 30, 1998, submittal have not substantially changed, the required design review, and verification and

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9812010125 981123 PDR ADOCK 05000368 P

PDR-

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U.S. NRC Nsvember 23,1998 2CAN119805 Page 2 of 3 implementation of the modification package necessitates extensive further internal resource dedication and outage planning. The proposed modifications to the PPS were previously committed to be installed during the upcoming 2R13 outage, which is scheduled to conunence in January 1999. However, due to near-term demands on common site resources, Entergy Operations has not been able to finalize the design change package in time to support the upcoming outage. Therefore, ANO must modify our commitment to perform the necessary modifications to the following outage (2R14),

which is scheduled to commence in the fall of 2000. This outage will require an extended reactor vessel defuel period for replacing the steam generators. As a result, this outage provides the best opportunity to perform the PPS modifications and to conduct the required integrated circuit testing. ANO has reviewed the operability for the PPS condition and appropriate changes are being made to ensure continued safe unit operation.

Administrative controls will be retained to ensure that a channel of ESFAS is not placed in indefinite bypass until the condition is corrected. This deferral has been discussed with members of the NRC Region IV and the NRR Projects offices.

I Even though the proposed modification is being deferred until the 2R14 outage, Entergy Operations requests that final NRC review and approval of the PPS USQ be completed.

Please contact me ifyou have any questions regarding this matter.

Very truly yours, Qf

.e Ji y D. Vandergdft Director, Nuclear Safety JDV/sab Attachment

1 U.S. NRC November 23,1998

-2CANI19805 Page 3 of 3 Mr. Ellis W. Merschoff cc:

Regional Administrator U. S. Nuclear Regulatory Commission RegionIV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064

. NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 i

Mr. Chris Nolan NRR Project Manager RegionIV/ANO-2 i

. U. S. Nuclear Regulatory Commission NRR Mail Stop 13-H-3 One White Flint North 11555 Rockville Pike Rockville, MD 20852 L

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Attachment to 2CANI19805 Page1ef3 AdditionalInformation Regarding i

ANO-2 Plant Protection System Review of ANO-2 Plant Protection System letter dated June 30,1998, section titled

" Actuation Logic" describes modifications to the Emergency Feedwater Actuation System (EFASI and EFAS2), and the Main Steam Isolation System (MSIS). In the section titled

" Description of Proposed Changes" EOI identifies three physical changes to the Plant Protection System.

i Item-2 Modification Description Since EFASI and EFAS2 are electrically equivalent, only the wiring changes for EFASI red train need be discussed. [ Note red train EFASI and EFAS2 are electrically identical to the green train (cabinet 2C40)]. Attachment 2 of Enclosure 1 of Engineering Report (ER) 97-R-2015-01 summarizes the application of each interposing relay for both trains. Attachment 4 to ER 97-R-2015-01 represents the existing EFAS1 scheme Interposing relays K624A and K724A control the EFW pump discharge valves. Solid state relay (SSR) trip path I (TPI) controls K624A and SSR TP2 controls K724A. For EFAS, the valves cycle based on TP demand

- based on steam generator level and pressure. The proposed modification replaces single TP logic with selective TP logic for each EFW pump discharge valve. (ref.

' ). With reference to Attachments 4 and 5 of ER 97-R-2015-01, note the subgroup (actuation) relays and the lockout functions remain "as is".

The lockout relay and manual reset pushbuttons are relocated in the circuit to prevent locking out interposing relays (K624A and K724A) that are shown wired to the trip bus. Since the interposing relays are required to cycle with TP demand (not locked out), TPl and TP3 are added in series with the actuation relays for trip leg 1/3 prior to the lock out relay circuit. This arrangement provides the desired (TP1 or TP3) logic. Similarly, wiring TP2 and TP4 in series with the actuation relays on trip leg 2/4 provides the (TP2 or TP4) logic. The "and" function required between the two trip legs is provided by the wire installed between the two trip legs prior to the lock out / manual reset in each trip leg. The modified wiring provides the EFW flow logic (TPI or TP3) and (TP2 or TP4). The resulting feed only good generator (FOGG) or stop flow logic is TPI and TP3 or TP2 and TP4.

Each red train EFW pump discharge valve in line to SGI will be controlled by the selective logic generated by EFASI (2C39). Each red train discharge valve in line to SG2 will be controlled by the selective logic generated by EFAS2 (2C39).

Each grees trala EFW pump discharge valve in line to SGI will be controlled by the selective logic generated by EFAS1 (2C40). Each green train discharge valve in line to SG2 will be controlled by the selective logic generated by EFAS2 (2C40).

Attachment to 2CAN119805 Page 2 of 3 The new lockout / manual reset circuit location doesn't provide the sane passive monitoring of the lockout relay contact status. With reference to Figure 4 of ER 97-R-2015-01 for the existing design, interruption of trip path current flow through either pair of four diodes results in an alarm. With the modified circuit, parallel current flow paths consisting of the interposing relay coils and the lockout relay contacts could prevent an alarm. Alarm circuit modifications are functionally represented by the series contacts K624A and K521 A for trip leg 1/3 and K724A and K719A for trip leg 2/4. Final NCP installation will wire the four relay contacts in series with relay (K731A) coil that was an existing spare on the DEFAS subpanel. A single K731 A contact will be wired in the alarm circuit. A second K731A contact will be wired to block DEFAS actuation similar to the existing design that used lock out relay contacts to block DEFAS actuation.

Item - 3 Modific1 tion Description TPs for the MSIS lockout, when tripped, require manual reset at both the ARCS and the PPS cabinet. With reference to Attachment 4 of ER 97-R-2015-01, pushbuttons are provided on the auxiliary relay cabinets for resetting the MSIS subgroup relays. The MSIS wiring changes described below will be performed for both power trains as depicted in Attachment 5 for 2C39 and 2C40. With reference to Attachment 5, the existing MSIS interposing relays, K623A and K723 A, will be rewired to the primary trip bus similar to the subgroup relays. This necessitates relocating the two TPs (SSR TPI and SSR TP2) from the interposing relay circuit to the primary trip leg. Considering MSIS interposing relays have no cycling function, the wiring changes have no impact on the MSIS functionality. This wiring change does preclude single trip path inadvertent actuation of the MSIS output relays (K623A or K723A) that closes the associated EFW pump discharge valves (ref. Attachment 2 of ER 97-R-2015-01). The discharge valve schemes are wired such that an EFAS signal will override the MSIS close signal based on FOGG logic.

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