2CAN018801, Responds to Request for Addl Info Re Application for Amend to License NPF-6.Time from Actuation of Control Room Alarm to Loss of Shutdown Margin for Modes 3,4,5 & 6 Listed.Values Satisfy Acceptance Criteria of SRP

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Responds to Request for Addl Info Re Application for Amend to License NPF-6.Time from Actuation of Control Room Alarm to Loss of Shutdown Margin for Modes 3,4,5 & 6 Listed.Values Satisfy Acceptance Criteria of SRP
ML20149F562
Person / Time
Site: Arkansas Nuclear Entergy icon.png
Issue date: 01/19/1988
From: Howard D
ARKANSAS POWER & LIGHT CO.
To: Calvo J
Office of Nuclear Reactor Regulation
References
2CAN018801, 2CAN18801, NUDOCS 8802170256
Download: ML20149F562 (2)


Text

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ARKANSAS POWER & LIGHT COMPANY January 19, 1988 2CAN018801 U. S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 ATTN: Mr. Jose Calvo, Director Project Directorate IV

SUBJECT:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Additional Information Regarding Technical Specification Change Request for Refueling Water Tank and Safety Injection Tank Boron Concentration Increase

Dear Mr. Calvo:

The Arkansas Power and Light Company (AP&L) recently submitted three Technical Specification Amendment requests for your consideration. One of the requests (2CAN108705) was for an increase in the boron concentration of the refueling water tank and safety injection tank. The submittal presented a reevaluation of tne boron dilution event. During the review of tne amendment request, your staff requested additional information in support of the evaluation. In a telephone conversation with the ANO 1 and 2 Project Manager on January 4, 1988, we agreed to provide additional information on the boron dilution event.

The time from initiation of a boron dilution event to the loss of shutdown I margin was provided in Table 2 of the submittal. The additional information requested was the time from actuation of a control room alarm to the loss of shutdown margin for Modes 3, 4, 5 & 6.

The values presented in fable 2 for Modes 5, with the RCS drained, and 6 (36 and 55 minutes respectively) also represent the time from actuation of an alarm to the loss of shutdown margin. Under these conditions the initiation  !

of the event will coincide with alarms related to the start of the charging pumps. This is consistent with the original analysis for Mode 6 presented in the FSAR for Cycle 1.

ANO-2 procedures for Cycle 7 operation in Modes 3, 4 and 5 (with charging  !

pumps running) will require that either a bank of control rods be withdrawn l to provide trippable reactivity, or a count rate monitor with an alarm on  !

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increasing count rate be in service. In either situation the Control Room Operator would be alerted to a boron dilution event by an alarm. If control rods are withdrawn, boron dilution would result in a high logarithmic power level trip with the associated alarms. The reactor would return to subcriticality by the worth of the inserted rods requiring additional time to the loss of shutdown margin. If the count rate monitor is in service with control rods inserted, an alarm on increasing count rate would alert the operator while the reactor is still substantially subcritical.

The time to loss of shutdown margin from the alarm provided by either of these conditions has been calculated for both Nodes 3, 4, and 5 with a charging pump running. The calculations assume very conservative values for critical boron concentration, inverse boron worth, initial shutdown margin, effective reactor coolant system volume, and trippable rod worth. Based on the conservative assumptions for trippable rod worth, minimum time from alarm to loss of shutdown margin is calculated for the condition of rods withdrawn (i.e, without reliance on the count rate monitors). In this condition the operator would be alerted to a boron dilution event in Modes 3 and 4 with 21 minutes remaining to loss of shutdown margin, and 31 minutes in Mode 5.

These values, along with the corresponding acceptance criteria from Standard Review Plan (SRP) Section 15.4.6, are summarized in the Table below.

Time from alarm to loss SRP 15.4.6 Mode of shutdown margin, min. Acceptance Criteria, min.

3 - Hot Standby 21 15 4 - Hot Shutdown 21 15 5 - Cold Shutdown 31 15 (Charging Pump Running) 5 - Cold Shutdown 36 15 (0 rained) 6 - Refueling 55 30 The values calculated for Modes 3, 4, 5, & 6 satisfy the respective acceptance criteria of the Standard Review Plan.

Very tr y yours, Dan R. Howard Manager, Licensing DRH:1w