ML20150D456
| ML20150D456 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/11/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20150D401 | List: |
| References | |
| NUDOCS 8803240271 | |
| Download: ML20150D456 (4) | |
Text
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-h UNITED STATES 4'
NUCLEAR REGULATORY COMMISSION
,y WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO AMENDMENT NO. 82 TO FACILITY OPERATING LICENSE NO. NPF-6 ARKANSAS POWER AND LIGHT COMPANY ARKANSAS NUCLEAR ONE, UNIT NO. 2 DOCKET NO. 50-368
1.0 INTRODUCTION
By letters dated October 28,1987(2CAN108704and2CAN108705), Arkansas Power and Light Company (AP&L r the licensee) requested amendments to the Technical Specifications (TSs) appended to Facility Operating License No.
NPF-6 for Arkansas Nuclear One, Unit 2 (ANO-2). The proposed amendments would change the boron concentration in certain tanks.
Specifically the licensee requested approval to increase the refueling water concentration (from between 1731 ppm and 2250 ppm to between 2500 and 3,000 ppm, and the corresponding concentrations in the refueling water tank (RWT and the safety injection tanks (SITS). Concurrently, the licensee requested approval to decrea the boron concentration in the Boric t.cid Makeup Tank (BAMT) from between 5 wt% and 12 wt% to between 2.5 wt% and 3.5 wt%.
Supplemental information en the boron dilution event was provided with licensee letter of January 19, 1988 (2CAN013801).
2.0 EVALUATION 2.1 Increased Boron Concentration in RWT and SIT The licensee has evaluated the impact of increasing the minimum refueling water boron concentration and the baron concentration in the RWT and the SIT on the Safety Analysis Report (SAR) Chapter 15 l
events as well as on long tenn horic acid buildup cala1ations and post-LC0A containment pH values reported in SAR Chapter 6.
In particular, the effect of an increase in RWT and SIT boron concentration on the boron dilution event was evaluated since this event could be the one most adversely affected by the increase. The effects on the steam line break and steam generator tube rupture events were also evaluated.
The results of the boron dilution event reanalyses verified that the calculated time from an alarm to the loss of shutdown margin for a boron dilution event initiated from Modes 3, 4, 5. or 6 satisfy the respective acceptance criteria of SRP 15.4.6.
Since a boron dilution esent during power operation (Modes 1 and 2) would cause the reactor to be rapidly shutdown by the reactor protection system, e803240271 BPO311 A00CK 050 Q B DR
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a Mode 1 and 2 reanalysis was not performed. The staff concludes that the results of any postulated boron dilution event occurring with the proposed increase in RWT and SIT boron concentration are acceptable.
Since the stean line break event is partially mitigated by the addition of borated water from the high pressure safety injection pumps and the SIT to the reactor coolant systen, the proposed increased boron concentration will enhance the mitigation of the reactivity increase portion of thir. event. Therefore, since the proposed boron concentration increase would essentially increase the margin of safety for the steam line break event, the staff finds the proposed changes acceptable with respect to postulated steam line break events.
For the steam generator tube rupture event, the high pressure injection pumps inject borated water from the RWT into the reactor ccolant system. Because the reactor will be scrammed, the increase in RWT and SIT boron concentration increases the shutdown nargin and, therefore, makes the proposed changes acceptable with respect to a postulatad steam generator tube rupture event.
2.2 Reduced Boron Cor. centration in the BAMT i
The licensee has evaluated the impact of reducina the BAMT boron concentration on the ability to maintain reouired shutdown margin; during a cooldown withcut letdown, the long term boric acid buildup, ard the post-LOCA containment pH value. Safety Analysis Report (SAR) Chapter 15 transients and accidents were not reevaluated since addition of borated water from the BAMTs to the reactor coolant system for reactivity control were not credited in any of these events.
The original cooldown without letdown analysis assumed that all the boron necessary to achieve the required shutdown margin during the cooldown was provided by the BAMT during the initial steges of the event. The reanalysis also credits the baron contributiot 7f the refueling water tank (RWT) thereby allowing the total boron inventory of the BAMTs to be reduced.
Since the new analysis includes a detailed evaluation of shutdown margin requirements, which are satisfied throughout the event, the staff finds the crediting of both the BAVT and the RWT berated water sources acceptable.
Since the proposed revision would allow the boren concentration in the BAMTs to be as low as 2.5 weight percent, the ninimum BAMT volume of approximately 13,150 gallons required by TS Figure 3.1-1 as a function of BAMT and RWT concentration would not be met with only one BAMT. Therefore, the proposed revision would provide an option for combining the contents of both BAMTs at low concentrations. When both BAMTs are required, two independent flow
paths from each tank must be operable. This has been incorporated into the proposed Technical Specifications and the staff finds this acceptable.
Chemical analyses have shown that a 3.5 weight percent solution of boric acid will not precipitate at solution tempertures above 50*F.
Since the revised minimum flow path temperture would be 55*F, the staff considers the 5'F nargin over the maximum precipitation temperature to be sufficient to pennit the proposed elimination of heat tracing operability requirements.
2,3 Combined Effect of all changes in the Boron Concentratiert The effect of the preposed changes on the long term boric acid buildup calculations previously reported in thapter 6 of the SAR have been evaluated by the licensee. Since the change involves decreasing the boren concentration in the BAMT, the potential for boric acid precipitation during lorg tern ECCS operation will be likewise reduced. However, the increase the boron concentration in the RWT and the SIT essentially offsets the BAMT inventory reduction with respect to post LOCA reactor ccclant system boron concentration. Consequently there is no change in the potential for boric acid precipitation and no inpact en the time requirenent for initiation of the core flush flow.
The effects of the proposed changes on the post LOCA containment pH value calculations reported in SAR Chapter 6 have also been evaluated by the licensee. The result of a decrease in the BAMT boron concentration and an increase in the RWT and SIT boron concentratier. is a slight reduction in the calculated spray and sump pH values. The maximum spray pH of 11.0 remains bounding while the minimum equilibrium surp value of 8.9 decreases to 8.8.
Since the original decontamination factors for icdine remain valid with tha reduced pH value, the change has no significant impact on iodine removal capabilities. Also, since the solution is still basic, there is no significant inpact on containment corrosion cheracteristics.
3.0 SIF. MARY Based on the above evaluation, the staff concludes that the proposed changes in the refueling water boron concentration and the corresponding concentration changes in the RWT, SIT and the PAMTs are acceptable.
Further, the elimination of heat tracing operability requirements associated with the change in the BAMT boron concentration is also acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
The NRC staff has censidered the environmental impact of the proposed changes to the TS. An "Environmental Assessrent and Finding of No Significant Impact was published in the Federal Register on March 7, 1988 (53 FR 7268).
5.0 CONCLUSION
The staff has concluded, based er the considerations disc.ussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be et langered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commissien's regulations, and the issuance of the amendment will rot be inimical to the common defense and security or to the health and safety of the public.
Date: March 11,1988 Principal Contributors:
L. Kopp
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