ML20209B706
| ML20209B706 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/14/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20209B692 | List: |
| References | |
| NUDOCS 8704280500 | |
| Download: ML20209B706 (4) | |
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'o UNITED STATES 8
NUCLEAR REGULATORY COMMISSION
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c WASHINGTON, D. C. 20555 y
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SAFFTY EVALUATION RY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N05, 93 AND 78 TO FACILITiOPERATINGLICENSENOS.NPF-4ANDNPF-7_
i' VIRGINIA ELECTRIC AND POWER COMPANY OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWER STATION, UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339 i
i INTRODUCTION i
By letter dated December 22, 1986, the Virginia Electric and Power Company (the licensee) requested a change to the Technical Specifications (TS) for the 1
North Anna Power Station, Units Nos. I and 2 (NA-1821. The proposed change would amend the NA-1&2 TS by increasino the boron concentration in the j
refueling water storage tank (RWST), the casing cooling tank (CCT) and the i
safety injection accumulators. The recuested change to the NA-1A2 TS is j
required since design changes such as the recently approved core power uprate and the transition to an eighteen-month fuel cycle have reduced the available shutdown margin at current boron concentrations. The proposed change would increase the boron concentration in the RWST and CCT from the current NA-1&?
TS limit of 2000-2100 parts per million (ppm) to 2300-2400 ppm. Also, the safety injection accumulator boron concentration would be increased from 1900-2100 ppm to 2200-2400 ppm.
DISCUSSION NA-1&2 Emergency Core Cooling System (ECCS1 boration is provided by the RWST, l
CCT and accumulators. The boron from these cources provides negative reactivity to ensure core shutdown for the Loss of Coolant Accidents (LOCA) i and other accidents. The NA-182 TS currently require that the RWST boron j
concentration be maintained between 2000 and 2100 pom, while the accumulator boron concentration must be maintained between 1900 and 2100 ppm. By raising the allowed boron concentration limits by 300 ppm, high eneroy core reloads l
would maintain the necessary shutdown requirements. An increase in the boron concentration affects several areas. The licensee has addressed these areas by evaluatino the impact of the increased boron concentration on the following:
accidents affected by core boration, post-LOCA boron precipitation, post accident sumo pH and equipment cualification, non-LOCA accident analyses, RWST solubility limits and plant chemistry.
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Loss of coolant accidents (LOCA) require core boration. The licensee has
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analyzed the effects of increased boron concentration on both large break and small break LOCAs. The licensee characterized the laroe break LOCA by two phases, ECCS operation and long term cooling. Peak clad temperature occurs during the first phase of the accident, and therefore, peak clad temperatui:-
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is not dependent on the boron concentration in the accumulators or RWST. Voic j
formation rather than core boration initially shuts down the reactor followino i
a large break. For these reasons the docketed accident analysis presently in place for NA-182 remains valid. The results of the licensee's analysis of the I
increased boron concentration indicates that the reactor will remain shutdown during the reflood and long term cooling phase even with no control rods t
inserted into the core. The small break LOCA model assumes the insertion of control rods in the calculation of core shutdown. Consequently, the boron i
concentration reautred to achieve the level of negative reactivity necessary to assure shutdown for the small break LOCA is significantly lower than the concentration required to assure shutdown for a laroe break LOCA. The j
increase in boron concentration provides additiona1' conservatism for.the small l
break LOCA. The licensee has not specifically reanalyzed the effects for increased RWST, CCT and accumulator boren concentration citino the above 3
i reasoning for the continued validity of previous analysis. Therefore, raising the limits for allowable boron concentration in the RWST, CCT and accumulators j
- u will provide additional margin for maintaining the core suberitical.
One effect of boration during a LOCA is the progressive increase over time of
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the boron concentration in the core. This occurs because the water vaporizes out of the break and leaves behind the boron it originally contained. If the concentration exceeds a critical value, boric acid can crystallire in the core and precipitate out of solution. The concern is that the precipitation of boric acid crystals could block core cooling.
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To preclude the possibility of boron precipitation, the concentration should not exceed 23.53 weight percent, which is the boric acid solubility limit less l
a 4 weight percent margin. The increased boron concentration in the RWST, CCT i
and accumulators will require a shorter hot leg / cold leg recirculation l
switchover time than that which was calculated in the original NA-1A2 analysis.
j The licensee has analyzed this situation and detemined that boron l
precipitation can be prevented if the operator alternates between hot leg and cold leg recirculation every 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> as opposed to the current limit of 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. This will require a change to the North Anna Nuclear Plant Emergency Procedures. This change will be implemented concurrently with any increase in boron concentration.
i The licensee perfomed an evaluation to determine the impact that the increase in boron concentration would havt on sump pH and how this would affect the environmental qualification of safety-related electrical equipment inside i
containment. The results' demonstrate that the pH varied only slightly and that the range is maintained within the range of NA-1&2 TS Basis 3/4.5.5.
i Consequently there is no impact on environmental qualification from the proposed change.
in addition, the effect on stress corrosion cracking and iodine evolution are negligible because the pH remains within the Standard i
Review Plan (SRP) limits.
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i 3-Each of the NA-182 Chapter 15 transients specified in the Updated Final Safety i
Analysis Report (UFSAR) were evaluated for the effects of the increased boron concentration. Only the non-LOCA boron dilution transient was found to have a more potentially severe result due to increased boron concentration. The other non-LOCA transients either were not impacted or were made less severe from the proposed increase in boron concentration. For the boron dilution transient, the presently, specified NA-182 TS 3.1.1.3.2 precludes the possibility of an unplanned baron dilution by specifying that the primary j
grade water flow control valve be locked closed durina operations in Modes 3, 4, 5 and 6 except during planned boron dilution or makeup activities. The current SRP acceptance criteria for the boron dilution transient are met through this presently specified NA-182 TS 3.1.1.3.2.
Only the boron dilution transient during refueling and startup was detemined to be more sevem at the j
proposed boron concentration. The dilution transient during refueling is most limiting since the primary coolant volume is smallest at that time. An analysis for the proposed boron concentration during refueling and based on j
the maximum flow rate available shows that the operator would have 37 minutes j
to take corrective action in the' event of excessive dilution during planned activities. The 37 minutes available for operator action is only very slightly less than the 39 minutes operator action time specified in the NA-182 l
Final Safety Analysis Report (FSAR) in Section 15.2.4 for an uncontrolled boron dilution transient. Thus the operator would have sufficient time to i
teminate the boron dilution event before shutdown margin is lost and the consequences are not significantly increased by the proposed boron i
concentration.
l The boron solubility limit at 32*F is 3850 ppm. An increase in the boron I
concentration to 2400 ppm will not cause crystallization of the RWST i
contents. Margin in excess of TS limits is maintained despite the increase in l
concentration.
f EVALUATION:
Regarding the aporoach of solubility limits caused by the increased boron concentrations, the staff has verified that sufficient margin exists to i
preclude boron " freeze-up" of the tanks and piping. The licensee has l
demonstrated satisfactory assessment of the effects of increased boron j
concentration on large and small break LOCAs, post LOCA boron precipitation in i
the reactor vessel, equipment oualification, non-LOCA accidents RWST and CCT solubility limits, and overall plant chemistry. Therefore, based on the above, 1
the licensee's request to increase the specified boron concentration in the i
j RWST and CCT from 2000-2100 ppe to 2100-2400 ppm is acceptable.
In addition, l
based on the above, the request to increase the boron concentration in the accumulators from 1900-2100 ppm to 2200-2400 ppm is also acceptable.
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ENVIRONV, ENTAL CONSIDEPATION These amendments involve a change in the installation or use of a facilitv l
component located within the restricted area as defined in 10 CFR Part 2n.
The staff has determined that the amendments involve no significant increase in the amounts, and no significant chance 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 sionificant hazards consideration and there has been no public comment on such findina.
Accordingly, these amendments meet the eligibility criteria for cateaorical exclusion set forth in 10 CFR 651.22(cl(91 Pursuant to 10 CFR 451.22(bl, no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendments.
j CONCLUSION l
We have concluded, based on the considerations disc.5 sed above, that (11 there i
is reasonable assurance that the health and safety of the public will not be endancered by operation in tne proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance o
of the amendrents will not be inimical to the comnon defense and security or to the health and safety of the public.
Date: April 14, 1957 Princical Contributors:
i R. Aarsh L. Engle i
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