ML20135H380
| ML20135H380 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/09/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20135H379 | List: |
| References | |
| NUDOCS 8509230158 | |
| Download: ML20135H380 (4) | |
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UNITED STATES
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g NUCLEAR REGULATORY COMMISSION E
WASHINGTON, D. C. 20555 2
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I SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 68 AND 54 TO 1
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FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY j
OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWER STATION, UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339 4
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Introduction:==
By letter dated March 11,1985 (Serial No.85-086), the Virginia Electric and Power Company (the licensee) proposed a change to the Technical Specifications (TS) for the North Anna Power Station, Units No. I and No. 2 (NA-1&2).
2 Specifically, the proposed changes would revise the NA-1&2 TS by reducing the
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minimum boron concentration in the Boron Injection Tank and in the boric acid l
system from the presently specified range of 11.5% to 13.0% (by weight) to a proposed range of 7.4% to 9.0% (by weight).
Discussion:
The Boron Injection Tank (BIT) is incorporated into the NA Safety Injection (SI) system to mitigate the consequences of Postulated Steam Line Break (SLB) events by purging highly concentrated boric acid solution into the Reactor Coolant System (RCS). The purpose of the boric acid system is to provide an l
inventory of concentrated boric acid for (1) chemical shim reactivity control.
(2) providing makeup to the reactor coolant system, refueling water storage 3
tank, spent fuel pit and refueling cavity as necessary, and (3) recirculation of boric acid through the BIT via the boric acid transfer pumps. The system i
is shared between NA-182.
The licensee has submitted a request for TS changes including reduction of t
l the boric acid concentration in the BIT and concentrated boric acid system.
The boric acid concentration would be reduced from a range of 11.5% - 13.0%
(by weight) to a range of 7.4% - 9.0% (by weight). The minimum specified boron acid tank (BAT) temperature would be reduced from 145 degrees Fahrenheit (*F) to 115*F. The licensee's proposed TS changes include l
increasing the minimum allowable BAT inventory associated with each unit from l
4,200 gallons to 6,000 gallons. This would preserve the capability for cold shutdown at any time in core life, with the most reactive control rod assembly withdrawn from the core.
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l The licensee stated that the requested reduction in required boric acid concentration for the BIT and the boric acid system will improve heat tracing system performance by reducing the temperature that must be maintained to i
prevent boron precipitation and by reducing system heat losses. Fewer heat tracing failures, fewer line blockages, and less leakage due to boron precipitation and corrosion will increase the system's reliability and reduce future radiation exposures for station personnel. Also, this change will reduce the time required to dilute the RCS following an inadvertent actuation of the safety injection.
This will reduce the amount of letdown which must j
be processed by the boron recovery and waste handling systems.
The existing NA accident analysis events, presented in the Updated Final i
Safety Analysis Report (UFSAR), were evaluated for potential impact from the i
proposed reduction of boron concentration in the BIT and BAT. The events reanalyzed with the proposed reduction in boron concentration included spurious operation of the Safety Injection System (SIS) at power, the main steam line break event, and accidental depressurization of the main steam system.
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The evaluation of the inadvertent operation of the SIS at power event
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incorporated the assumptions in the existiing UFSAR analysis along with the l
revised boron concentration of the BIT.
It was determined that lowering the j
boron concentration in the BIT affects the timirg for this transient and reduces the rate of reactivity change. Limits to the primary system pressure l
and minimum Departure from Nucleate Boiling Ratio (DNBR) were not challenged by this event. The results are found acceptable.
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The proposed reduction in boron concentration for the BIT does impact the results for the main steam line break events. Each steam line has an isolation valve and a nonreturn check valve downstream. These valves prevent
. blowdown of more than one steam generator for any break location even if one valve fails to close. The break flow decreases with decreasing steam generator pressure. The energy extracted from the RCS leads to a reduction of both the primary coolant temperature and pressure. The feedback from the l
negative moderator coefficient results in an increase in reactivity and l
decrease in shutdown margin. The analysis assumed the most reactive rod cluster control assembly to be stuck in its fully withdrawn position. As a result of the stuck rod cluster and asymetric coolant temperature across the reactor vessel, the power peaking factors are abnormally high. The core is ultimately shut down by the boric acid delivered by the SIS.
The core heat flux and reactor coolant system temperature and pressure resulting from the steam line break (SLB) were calculated with the RETRAN i
computer code. The methodology employed is further described in the l
licensee's letter dated March 11, 1985. SLB analyses were performed for four transients. The analyses indicate return to criticality for all four l
transients, with the highest peak heat flux at 23.7% achieved for a large SLB l
initiated at zero power with offsite power available.
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3-For the four transients analyzed, the Westinghouse W-3 correlation was used in conjunction with the licensee's version of the COBRA core thermal hydraulics code to determine the margin to DNB. The W-3 correlation is I
generally considered valid between pressures of 1000 to 2300 pounds per i
squareinchgauge(psig). The resulting RCS pressure in one transient did drop to 910 psig. Although the staff has not approved the use of the W-3
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correlation below pressures of 1000 psig, the calculated DNBRs were appreciably higher than the W-3 1.30 limit, and the staff believes that there is sufficient conservatism in the NA steam line break calculations to assure that DNB will not occur. Thus, no consequential clad perforation is l
expected. As such, the requirements of Standard Review Plan (SRP) 15.1.5 are met. An evaluation for accidental depressurization of the main steam system, as would occur during a spurious opening, with failure to close, of the largest of any single steam dump, relief, or safety valve, was also performed for the proposed boron concentration reduction. As for the SLB event, the l
energy extracted from the RCS causes a reduction of primary system coolant temperature and pressure.
In the presence of a negative moderator 4
temperature coefficient, the cooldown results in a reduction of core shutdown margin. This analysis was performed to demonstrate that, assuming a stuck l
rod cluster control assembly and a single failure in the engineered safety features, the fuel will remain intact (the minimum DNBR remains above 1.30).
The COBRA and RETRAN codes were used for these analyses and the methodology is further described in the licensee's letter dated March 11, 1985.
Evaluation:
1 The staff has reviewed and finds acceptable VEPCO's submittal for reducing the boron concentration in both the boron injection tank (BIT) and the boric acidtank(BAT)from 11.5%-13.0%(byweight)to7.4%-9.0%(byweight).
The analyses do show that the reduction of the boron concentration in the boron injection tank and the boric acid tanks result in a slight increase in the accident consequences (i.e., a small return-to-power for the accidental depressurization of the main steam system). However, the results of these i
analyses show that all of the acceptance criteria for these types of transients are met as shown in Chapter 15 of the NA-182 UFSAR and the SRP.
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I Also we find the reduction in the BAT temperature from 145'F to 115'F to be acceptable since the system modification will improve heat tracing system performance which must be maintained to prevent boron precipitation.
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addition, we find acceptable the increase in the minimum BAT inventory from J
4,200 gallons to 6,000 gallons in order that the capability for cold shutdown l
at any time in core life will be preserved.
The analytical methodology used in evaluating the consequences from postulated i
steam line breaks is undergoing staff review. Our review at this time l
indicates reasonable assurance that the conclusions based on the licensee's submittal will not be appreciably altered by completion of this review.
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! Therefore, based on our review of the applicant's analysis, we find the proposed systems modifications and TS changes to be acceptable.
Environmental Consideration These amendments involve a change in the installation or use of a facility i
component located within the restricted area as defined in 10 CFR Part 20.
The staff has determined that the amendments involve 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 increase in individual or cumulative occupational radiation exposure. The Commission has previously published a proposed finding that these amendments involve no significant hazards consideration and there has been no public i
comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 551.22(c)(9).
Pursuant to 10 CFR 551.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendments.
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Conclusion:==
i We have concluded, based on the considerations discussed above, that (1) there l
1s reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will i
j be conducted in compliance with the Commission's regulations, and the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
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Date: September 9, 1985 i
Principal Contributors:
K. Goetz
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A. Guttman h
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