ML20204H745

Safety Evaluation Supporting Amend 202 to License NPF-6

ML20204H745
Person / Time
Site:	Arkansas Nuclear
Issue date:	03/23/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9903290149
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I UNITED STATES j

j NUCLEAR REGULATORY COMMISSION 2

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SAFETY EVALUATION PY THEOFJI.Ri. OF NUCLEAR REACTOR REGULATION RELATED TO AMENCMENT NO.202 TO FACILITY OPERATING LICENSE NO. NPF-6 ENTERGY OPERATIONS. INC.

. ARKANSAS NUCLEAR ONE. UNIT NO. 2 DOCKET NO. 50-338

1.0 INTRODUCTION

By letter dated February 25,1999 (2CAN029913), Entergy Operations, Inc. (the liconsee) submitted a request for changes to the Arkansas Nuclear One, Unit No. 2 (ANO-2) Technical Specifications (TSs). The requested changes would add a footnote to TS Table 3.3-1,

• Reactor Protective Instrumentation," Action 2, to allow plant startup with the functional units associated with the reactor protective system (RPS) Channel "D" ex-core nuclear instrumentation inoperable. This exception is authorized until Mid-Cycle Outage 2P99, which is the next planned entry into Mode 5, " Cold Shutdown," for ANO-2. The functional units included in this footnote are as follows: logarithmic power level-high, linear power level-high, local power density-high (LPD-high), departure from nucleate boiling-low (DNBR-low), and core protection calculators (CPC).

ANO-2 TS 3.3.1.1 states that the minimum reactor protective instrument channels and bypasses as provided in TS Table 3.3-1 shall be operable. TS Table 3.3-1 requires that three of four channels of linear power level-high, LPD-high, DNBR-low, and CPC be operable in Modes 1 and 2. In addition, TS Table 3.3-1 requires that three of four channels of the logarithmic power level-high function be operable in Mode 2, and in Modes 3,4, and 5 when the protective system trip breakers are closed and the control element assembly (CEA) drive system is capable of CEA withdrawal. Action 2 of Table 3.3-1 states "With the number of channels OPERABLE one less than the Total Number of Channels, operation in the applicable MODES may continua provided the inoperable channel is placed in the bypassed or tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. If the inoperable channelis bypassed for greater than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the desirability of maintaining this channelin the bypassed condition shall be reviewed at the next regularly scheduled PSC [ Plant Safety Committee] meeting in accordance with the QA Manual Operations. The channel shall be returned to OPERABLE status prior to startup following the next COLD SHUTDOWN."

ANO-2 TS Limiting Condition for Operation (LCO) 3.0.4 prohibits entry into an operational mode or other specified condition when the conditions of the LCO are not met and the associated action requires a shutdo'un if they are not met within a specified time interval. Entry into an 9903290149 990323 ADOCK0500g8 DR

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2-operational mode or other specified condition may be made in accordance with the action requirement when conformance to them permits continued operation of the facility for an L

unlimited period of time.

On November 3,1998, with ANO-2 operating in Mode 1, the upper detector of the "D" RPS Channel (one of four channels) of ex-core r uclear instrumentation failed to zero during the performance of surveillance testing. This condition rendered the Channel"D" linear power level-high, CPC, LPD--high, and DNBR-low functions ineperable. The channel was maintained in the bypass or trip condition for the remainder of the operating cycle in accordance with TS Table 3.3-1 until the unit was shut down for Refueling Outage 2R13 on January 9,1999.

During Refueling Outage 2R13, the Channel"D" detector assembly was replaced with a spare detector assembly. The replacement detector passed all pre-and post installation electrical tests. On February 22,1999, during startup activities with the unit in Mode 3 and the trip breakers closed, the Control Board Operator identified that the Channel "D* logarithmic power channel was reading approximately one decade higher than the other channeis. Channel *D" we.s placed in bypass in accordance with the TS. Subsequent troubleshooting identified that the middle detector or associated cables fcr the Channel"D" ex-core assembly were faulty.

The channel was left in bypass and was considered inoperable. ANO-2 maintenance personnel were unsuccessfu; in repairing the installed detector, but were able to confirm that the middle chamber was not responding as designei The licensee has stated %t a replacement j

detector assembly is not available due to its unique design and that m., vendor lead time for a j

replacement assembly was greater than 2 months.

l The ANO-2 TSs allow operation with a channel of the RPS in bypass. However, Table 3.3-1, Action 2 requires that the inoperable charinel be returned to operable status prior to startup 4

l from the next cold shutdown. Since Channel "D" was inoperable prior to unit shutdown for i

2R13, the TS requires that it be returned to operable status prior to restart. In addition, TS l

1 LCO 3.0.4 is interpreted to prohibit entry into the applicable operational mode since TS Table 3.3-1, Action 2 has not been satisfied.

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1 The licensee requested that the Nuclear Regulatory Commission (NRC) exercise discretion not i

to enforce compliance with the actions required by TS 3.0.4 and TS Table 3.3-1, Action 2, until j'

an exigent TS amendment could be processed to revise TS Table 3.3-1, Action 2. By letter j

dated February 24,1999 (2CAN029912), the licensee submitted its formal request for a Notice of Enforcement Discretion (NOED) pursuant to the NRC's policy regarding exercise of j

discretion for plants attempting to startup, set out in Section Vll.c of the " General Statement of l

Policy and Procedures for NRC Enforcement Actions"(Erforcement Policy), NUREG-1600. By letter dated February 25,1999, the staff documented the issuance of the NOED for ANO-2.

The NOED had been issued verbally on February 23,1999, after the staff concluded that the licensee's technical basis for the request was satisfactory. By letter dated February 25,1999, the licensee cubmitted a request for an exigent TS amendment to revise TS Table 3.3-1, Action 2. The proposed change would add a footnote to TS Table 3.3-1, Action 2, to allow plant startup with the functional units associated with the RPS Channel"D" ex-core nuclear instrumentation inoperable. This exception is authorized until Mid-Cycle Outage 2P99, which is de next planned entry into Mode 5, " Cold Shutdown," for ANO-2.

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3-l 2.0 'EVALU ATION The ex-core nuclear instrumentation system includes neutron detectors located around the l

reactor core and signal conditioning equipment located in the auxiliary building. Neutron flux is l

. monitored from source levels through full power and signal outputs are provided fc; Nector l

protection and for information display. The ANO-2 ex-core nuclear instrumentation system, as i

described in ANO 2 Safety Analysis Report (SAR) Section 7.2.1.1.2.3, includes four safety channels. Each safety channel utilizes a fission chamber assembly made up of three detectors that permits the measurement of axial power shape during power operations. The safety channels provide neutron flux information from startup neutron flux levels to 200 percent of 4

rated power covering a range of approximately 10 to 200 percent power.

As stated in the licensee's submittal, each detector feeds a linear amplifier which provides input to the RPS CPC trips for LPD-high and DNBR--low. Outputs of the three linear amplifiers (per channel) are also provided to a summer, which averages the signals and provides input to the linear power level-high trip. The center detector also inputs to the logarithmic power circuitry, which inputs to the logarithmic power-high trip.

l The ANO-2 SAR, in Section 7.2, " Reactor Protective System (Reactor Trip System)," describes the function of the RPS Section 7.2.1.1, " System Description," notes that "A 2-out-of-4 coincidence of like trip signals is required to generate a reactor trip signal. These same features include the capability of the RPS to operate, if need be, with up to two channels out of service (ono bypassed and another tripped) and still meet the single failure criteria. The only operating restriction while in this condition (effectively 1-out-of-2 logic) is that no provision is made to bypass another channel for periodic maintenance. The system logic must be restored to at least a 2-out-of-3 condition prior to removing another channel for maintenance."

Even though the RPS has the capability to provide a 2-out of-4 coincidence trip logic, the

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existing design and licensing bases for the ANO-2 RPS supports a 2-out-of-3 coincident trip logic. This basis is described in the Safety Evaluation for ANO 2 License Ammdment No.159 (April 3,1995, TAC No. M87147), which explains the justification used to trar,oon from a 2-out of-4 coincidence trip logic to a 2-out-of-3 coincidence trip logic basis. The original requirement for the RPS trip logic to provide a 2-out-of-4 coincidence feature was based on the concem over common mode failures. The NRC staff was concerned that a single failure may affect more than one channel if adequate separation is not maintained between the channels, i

in support of ANO-2 License Amendment No.159, ANO-2 provided a July 22,1993, submittal that detailed an evaluation performed to demonstrate the physical and electrical separation inherent in the RPS justifying a 2-out-of-3 coincidence trip logic basis. This evaluation considered high energy line break, singic failure combination with prolonged bypass, channel independence, independence of vital buses, and logic matrix circuitry failure due to a vital bus single failure. The NRC staff agreed with the licensee's conclusions and approved License Amendment No.- 159, which adopted a 2-out-of-3 coincidence trip logic design and licensing bases. The TSs were revised as part of License Amendment No.159 to allow for an indefinite

. bypass of a single RPS channel. From a licensing perspective, this change resulted in the classification of the fourth channel as an installed spare. In addition, the Safety Evaluation indicated that TS Table 3.3-1, Actiors ' was added to require PSC review for any channel bypassed for more than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> and to return the bypassed channel to operable status prior to m.

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. startup following the next cold shutdown as a means of ensuring that any inoperable channel would be retumed to service as quickly as possible.

As discussed in the Safety Evaluation for TS License Amendment 159, the CEA ejection accident was the only design basis event affected by ex-core response to an asymmetric power l

distribution. At the time of the Safety Evaluation, a 10 percent measurement uncertainty was included in the analyses of that event to conservatively account for power asymmetry effects on the ex-core detectors for any ejected CEA. Based on its letter dated February 25,1999, the licensee indicated that recent core designs using more aggressive fuel management techniques have required that the power measurement uncertainty be increased in order to

- account for the asymmetric power effects of a CEA ejection with one ex-core detector indefinitely bypassed and an additional detector failed. These power measurement uncertainties are up to 20 percent in some cases. These uncertainties are included in the CEA ejection analyses for Cycle 14. The Cycle 14 analyses showed that no fuel failure would result l

from the SAR Chapter 15 CEA ejection event. This licensee indicated that all other inputs and l

assumptions associated with the initial evaluation remain valid.

Although the ex-core nuclear instrumentation system does provide a safety function at power, bypassing one channel does not prevent fulfillment of its intended safety function as previously discussed. In addition, the licensee supplemented this deterministic basis with a risk-informed evaluation that determined the in.,oact associated with operations of Channel"D" of the RPS in bypass during startup and power cperations until Mid-Cycle Outage 2P99 to be minimal. The l

ANO-2 licensing bafs clearly indicates the system is capable of performing its safety function with one channel of RPS inoperable. The restrictions provided in TS Table 3.3-1, Action 2, are intended to ensure maximum availability and not to specify minimum requirements for safe operation. The NRC staff is satisfied that the licensee made a good faith effort to comply with TS Table 3.3-1, Action 2, when it replaced the Channel"D" ex-core detector assembly during Refueling Outage 2R13.

In its letter dated February 25,1999, the licensee indicated that the RPS Channel "D" ex-core l

Instrumentation will be restored to operable status prior to startup from Mid-Cycle Outage 2P99, which is the next scheduled entry into cold shutdown. In its letter dated February 24,1999, the licensee committed to restore the RPS Channel"D" ex-core instrumentation if ANO-2 enters a mode in which the detector can be replaced without creating undue risk to plant personnel and/or equipment before Mid-Cycle Outage 2P99, provided a new detector is on site.

Based on these considerations, the NRC staff concluded that the licensee's proposal to add a footnote to TS Table 3.3-1, Action 2, to allow startup with the RPS Channel"D" logarithmic power level-high, linear power level--high, LPD-high, DNBR-low, and CPC functional units inoperable until the startup following Mid-Cycle Outage 2P99, is acceptable.

3.0 EXIGENT CIRCUMSTANCE The Commission's regulations, as stmed !n 10 CFR 50.91, contain exceptions for issuance of

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amendments when the usual 30-day public no6ce period cannot be met. One type of special exception is an exigency. An exigency is a case where the staff and licensee need to act promptly and time does not permit the staff to publish a Federal Reaister notice allowing i

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5-30 days for prior public comment. The staff also determines that the amendment involves no significant hazards considerations.

Under such circumstances, the Commission notifies the public in one of two ways: by issuing a Federal Register notice providing an opportunity for hearing and allowing at least 2 weeks for public comments, or by issuing a press release discussing the proposed changes, using the local media. In this case, the Commission used the first approach.

The licensee submitted the request for amendment on February 25,1999. It was noticed 5 the Federal Reaister on March 8,1999 (64 FR 11067), at which time the staff provided an opportunity for hearing and proposed a no significant hazards consideration determination. The public was allowed 14 days after the date of publication of that notice to provide comments. No comments were received.

In its application, the licensee requested that the amendment be processed as an exigent request pursuant to 10 CFR 50.91(a)(6). The exigency was created during startup activities from Refueling Outage 2R13 when ANO-2 identified that the newly replaced RPS Channel"D" ex-core nuclear instrumentation detector assembly was determined to be inoperable. Technical Specification Table 3.3-1, Action 2, requires Channel"D" to be restored to operable status prior to startup since the plant had entered cold shutdown and Channel"D" had been declared inoperable due to a detector failure during the last operating cycle. Therefore, the ANO-2 TSs prohibited continuation with startup activities and planned power operation.

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la order to allow plant startup and continued operation in noncompliance with TS Table 3.31, Action 2, er.forcement discretion was verbally requested by the licensee and granted by the NRC on February 23,1999. The NOED, which was documented in a letter dated l

February 25,1999, granted enforcement discretion from the requirements of TS Table 3.3-1, Action 2, until an exigent TS amendment is processed to revise TS Table 3.3-1, Action 2.

Accordingly, pursuant to 10 CFR 50.91(a)(6), the Commission has determined that the licensee 4

4 used its best efforts to make a timely application and that exigent circumstances exist in that i

the licensee and the Commission must act quickly to prevent an unnecessary interruption of 1

plant operations. Further, the Commission has determined that the exigency could not have been avoided and that the licensee did not create the exigency.

4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION

DETERMINATION The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final i

determination that a license amendment involves no significant hazards considerations if l

operation of the facility in accordance with the amendment would not (1) involve a significant j

increase in the probability or consequences of an accident previously evaluated; or (2) create 2

the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.

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.. As required by 10 CFR 50.91(a), the licensee has provided its analysis of the issue of no significant hazards consideration, which is presented below:

An evaluation of the proposed change has been performed in accordance with 10 CFR 50.91(a)(1) regarding no significant hazards considerations using standards in 10 CFR 50.92(c). A discussion of these standards as they relate to this amendment request follows:

Criterion 1 - Does not involve a significant increase in the probability or consequences of an accident previously evaluated.

Startup and operation with the ANO-2 Reactor Protective System (RPS) linear power level-high and logarithmic power level-high functional units, and the Core Protection Calculator (CPC) local power density-high (LPD-high), and departure from nucleate boiling ratic-low (DNBR-low) functional units in a 2-out-of-3 logic mode has no effect on the probability of any accidents previously evaluated as it has no impact on the causes of initiating events in the plant.

i Startup and operation with these functional units in a 2-out-of-3 logic mode has no effect on the consequences of an event previously evaluated since, with one channel of each functional unit in bypass, the functional units maintain a functional redundancy of one. This ensures protective system actuation in 4

accordance with the assumptions of the accident analysis. The accident analysis has accounted for those events that might have an effect on the functional units due to the geometry of the installed sensors, and demonstrated acceptable results in such a case, assuming a single failure and a channel in bypass.

Therefore, startup and operation with the ANO-2 RPS linear power level-high and logarithmic power level-high functional units, and the CPC LPD-high, and DNBR-low functional units in a 2-out-of 3 logic mode does not involve a significant increase in the probability or consequences of an accident previously evaluated.

Criterion 2 - Does not create the possibility of a new or different kind of accident from any accident previously evaluated.

The only way the proposed change could alter the course of an event would be l

by the ANO-2 RPS linear power level-high and logarithmic power level-high functional units, and the CPC LPD-high, and DNBR-low functional units failing I

to actuate when required. These functional units maintain a functional redundancy of one when operating in a 2-out-of-3 logic mode, thus the functional units will not failin this manner.

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Therefore, startup and operation with the ANO-2 RPS linear power leve!-high j

and logarithmic power level-high functional units, and the CPC LPD-high, and i

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DNBR-low functional units in a 2-out-of-3 logic mode does not create the possibility of a new or different kind of accident from any previously evaluated.

Criterion 3 - Does not involve a significant reduction in the margin of safety.

The ANO-2 technical specification (TS) for RPS linear power level-high and logarithmic power level-high functional units, and the CPC LPD-high, and DNBR-low functional units allows operation through the remainder of the cycle j-with only three channels operable, providing that the desirability of maintaining this configuration is reviewed at the next regularly scheduled Plant Safety Committee (PSC) meeting. The TS requires that the inoperable functional uni:

be retumed to operable status prior to startup following the next Cold Shutdown.

Per the Safety Evaluation Report for TS Amendment 159, which addad these provisions to the TS, the goal of the PSC review and the requirement to retum the system to an operable status prior to startup was to repair the inoperable channel and return it to service as quickly as practical. Review of the design and installation of these functional units has demonstrated that, while starting up or operating in a 2-out-of-3 logic mode, their functional redundancy is one. For any design bases event, with the occurrence of any postulated single failure, the ANO-2 RPS linear power level-high and logarithmic power level-high functional units, and the CPC LPD-high, and DNBR-low functional units will provide the protection assumed in the accident analysis.

Therefore, startup and operation with the ANO-2 PPS linear power level-high i

and logarithmic power level-high functional units, i.nd the CPC LPD-high, and DNBR-low functional units in a 2-out-of-3 logic mode does not involve a significant reduction in the margin of safety.

Based upon the reasoning presented above, Entergy Operations has determined that startup and operation with the ANO-2 RPS linear power level-high and logarithmic power level-high functional units, and the CPC LPD-high, and DNBR-low functional units in a 2-out-of-3 logic mode does not involve a significant hazards consideration.

Based on the above considerations, the staff concludes that the amendment meets the three l

criteria of 10 CFR 50.92(c). Therefore, the staff has made a final determination that the proposed amendment does not involve a significant hazards consideration.

5.0 STATE CONSULTATION

In accordance with the Commission's regulations, the Arkansas State official was notified of the proposed issuance of the amendment. The State official had no comments.

6.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility j

component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has l

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6 8-determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant Meiease in individual or cumulative occupational radiation exposure. The Commission has made a final finding that the amendment involves no significant hazards consideration. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need bo prepared in connection with the issuance of the amendment.

7.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: Chris Nolan Date: March 23, 1999 4

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