ML20059M705
| ML20059M705 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/08/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059M703 | List: |
| References | |
| NUDOCS 9311190255 | |
| Download: ML20059M705 (5) | |
Text
__
j3 s arc oq)\\
- 1 UNITED STATES j
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 20555-0001
%... + +./
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO,152 TO FACILITY OPERATING LICENSE NO. NPF-6 t
ENTERGY OPERATIONS. INC..
ARKANSAS NUCLEAR ONE. UNIT NO. 2 DOCKET NO. 50-368
1.0 INTRODUCTION
By letter dated May 7, 1993, Entergy Operations, Inc. (the licensee),
submitted a request for changes to the Arkansas Nuclear One, Unit No. 2 (AN0-2) Technical Specifications (TSs). The requested changes wou'd revise TS Section 3/4.5, " Emergency Core Cooling Systems."
The licensee proposed the following specific changes to TS 3/4.5.1:
(1) reduce the specified minimum safety injection tank (SIT) baron concentration from 2500 parts per million (ppm) to 2200 ppm; (2) revise the related Actions to allow one SIT to be inoperable due to boron concentration alone for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and to allow one SIT to be inoperable for any other reason for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />; (3) revise a surveillance requirement to specify sampling of the affected SIT within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> of a 5% indicated tank level increase that is not the result of addition from the refueling water tank (RWT); (4) revise a surveillance requirement reference to the reactor coolant system pressure from 700 psig to 700 psia; and (5) revise the associated Bases to reflect these changes.
2.0 EVALUATION 2.1 Backaround The functions of the four SITS are to supply water to the reactor vessel during the blowdown phase of a loss-of-coolant accident (LOCA), to provide inventory to help accomplish the refill phase that follows, and to provide reactor coolant system (RCS) makeup for certain small-break LOCAs.
The SITS are pressure vessels partially filled with borated water and pressurized with nitrogen gas. The SITS are passive components, since no operator or control action is required for them to perform their function.
Internal tank pressure is sufficient to discharge the contents to the RCS, if RCS pressure decreases below the SIT pressure.
Each SIT is piped into one RCS cold leg via the injection lines used by the high-pressure safety injection (HPSI) and low-pressure safety injection (LPSI) 9311190255 931108 PDR ADOCK 05000368 P
e.
i systems.
Each SIT is isolated from the RCS by a motor-operated isolation valve and two check valves in series. The motor-operated isolation valves are normally open, with power removed from the valve motor to prevent inadvertent closure prior to or during an accident. Additionally, the isolation valves are interlocked with the pressurizer pressure instrumentation channels to ensure that the valves will automatically open as RCS pressure increases above SIT pressure and to prevent inadvertent closure prior to an accident. The valves also receive a safety injection actuation signal (SIAS) to open. -These features ensure that the SITS will be available for injection without reliance on operator action.
The SIT gas and water volumes, gas pressure, and outlet pipe size are selected to allow three of the four SITS to recover the core before significant clad melting or zirconium water reaction can occur following a LOCA. The need to ensure that three SITS are adequate for this function is consistent with the assumption that the entire contents of one SIT will be lost via the break during the blowdown phase of a LOCA.
2.2 Discussion of Proposed Chances 2.2.I Minimum SIT Boron Concentraticn The minimum boron concentration requirement is based on beginning-of-life reactivity values and is selected to ensure that the reactor will remain subcritical during the reflood stage cf a large-break LOCA. During a large-break LOCA, all control element assemblies (CEAs) are assumed not to insert into the core, and the initial reactor shutdown is accomplished by void formation during blowdown.
Sufficient boron concentration must be maintained in the SITS to prevent a return to criticality during reflood.
The accident analysis for ANO-2 uses a minimum SIT boron concentration of -
2000 ppm. The current minimum SIT boron concentration of 2500 ppm was selected as an operator convenience in that both the SIT and RWT minimum concentrations were specified at the same value. The licensee has proposed to reduce the SIT minimum boron concentration requirement to 2200 ppm.
Specifying a value of 2200 ppm will allow the plant operators to quickly adjust SIT boron concentration to a higher value by addition from the RWT in the event that the SIT boron concentration is diluted by inleakage.
j Operation with the proposed minimum SIT boron concentration will maintain a margin to the concentration used in the accident analysis, ensuring subcriticality during reflood. Therefore, the staff finds the proposed revision acceptable.
~
2.2.2 Action Requirements i
i If one SIT is inoperable due to boron concentration being outside the specified limits, the licensee has proposed a 72-hour completion time to return it to within the limits.
In this condition, the ability to maintain l
l
subtriticality (if the boron concentration is too low), or the minimum boron precipitation time (if the boron concentration is too high), may be reduced.
The effect on core subtriticality during reflood due to a reduction in boron concentration in one SIT to below the minimum value is minor. The dominant reactivity contributor during this phase is void formation in the core and control element assembly insertion.
Long-term reactivity control does rely on baron concentration in the core; however, post-accident boron concentration in the core is dominated by the RWT inventory added by the safety injection pumps.
In addition, the volume of the SIT is still available for injection. Since the baron requirements are based on the average boron concentration of the l
total volume of three SITS, the consequences of a reduction in boron l
concentration in one SIT to below the minimum value are less severe than they would be if a SIT were not available for injection.
Boiling of the emergency core cooling system (ECCS) water in the core during and subsequent to reflood concentrates the boron in the saturated liquid that remains in the core.
Continued concentration could result in boron i
precipitation, which could adversely affect the ability to provide long-term core cooling. Boron concentration in excess of the maximum allowed value in one SIT could reduce the time at which this precipitation would begin; however, as stated above, boron concentration in the core is dominated by the RWT inventory. Therefore, the effect on boron precipitation time would be minimal.
j Based upon the minimal effect on core subcriticality or boron precipitation i
expected due to boron concentration in one SIT being outside the TS limits, the staff concludes that a 72-hour completion time for returning the boron i
concentration to within TS limits is acceptable.
i If one SIT is inoperable for a reason other than baron concentration, the licensee has proposed a 1-hour completion time for returning the SIT to OPERABLE status.
In this condition, the required contents of three SITS cannot be assumed to reach the core during a LOCA due to the unavailability of the inoperable SIT and the assumption that the contents of one SIT are lost via the break. Due to the severity of the consequences should a LOCA occur under these conditions, a 1-hour completion time to open the isolation valve, remove power to the valve, or restore the proper water volume.or nitrogen cover gas pressure ensures that prompt action will be taken to return the i
inoperable accumulator to OPERABLE status. The completion time minimizes the i
exposure of the plant to a LOCA in these conditions. This is acceptable to i
the staff.
2.2.3 Sampling Requirements
)
The licensee proposed two changes to Surveillance Requirement (SR) 4.5.1.b, which stipulates the requirements regarding verification of SIT boron i
l I
concentration. The licensee requested that samples be required after an indicated level increase of 25% in lieu of the present requirement that such samples be conducted after a volume increase of 11%. The licensee also requested that such samples not be required if the source of the level increase is the RWT.
The licensee provided a calculation to demonstrate the effect on SIT boron concentration of an increase in indicated tank level of 5% containing no boron. The calculation, which assumed that the SIT started at the minimum allowed volume and the revised minimum specified boron concentration, demonstrated that after a 5% increase in indicated level containing no boron, the final boron concentration of the SIT would remain above the safety analysis value of 2000 ppm. A similar calculation showed that a potential dilutiori from the minimum allowed volume to the maximum allowed volume (an increase of approximately 7.8% of indicated tank level) would still result in a boron concentration slightly above the value assumed in the accident analysis.
Based on the determination that a 5% level increase would not challenge the boron concentration value assumed in the safety analysis, the staff finds the proposed change from 1% of tank volume to 5% of indicated tank level to be acceptable. The use of tank level in the specification in lieu of volume is consistent with the instrumentation available to the operators.
The licensee stated that it is not necessary to verify boron concentration if the added water is from the RWT, because the water contained in the RWT is eithin the SIT boron concentration requirements. This is consistent with the recommendations contained in NUREG-1366,." Improvements to Technical Specifications Surveillance Requirements," and is considered acceptable to the staff.
2.2.4 Applicability at 700 psia versus SR at 700 psig The licensee proposed a change to SR 4.5.2.d.1 regarding verification of automatic operation of the SIT isolation valve.
The existing specification contains a discrepancy between the Applicability of the TS and the SR.
The TS is specified as being applicable in Modes 1, 2 and 3 (when RCS pressure I
is >700 psia).
SR 4.5.2.d.1 requires verification that the SIT isolation valves autom ticrily open when RCS pressure exceeds 700 psig. This SR does nat ensure that na applicability requirement of >700 psia (which corresponds to approximately C 5 psig) is met. The licensee proposed to revise the SR value from 700 psig to 700 psia to be consistent with the TS applicability statement and the tvcilable pressurizer pressure instrumentation, which reads out in psia. This chcnge will ensure that the SITS are available when required by the TS applicability statement and is, therefore, acceptable to the staff.
l
I l 2.2.5 Bases Changes The staff finds that the proposed bases changes clarify the intent of the significant changes discussed above and are, therefore, acceptable.
3.0 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.
4.0 ENVIRONMENTAL CONSIDERATION
1 The amendment changes a requirement with respect to installation or use of a j
facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has 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 increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a pro-posed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (58 FR t
34075). Accordingly, the amendment meets the eligibility criteria for categorical exclu; ion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no enviranmental impact statement or environmental assessment need be i
prepared in connection with the issuance of the amendment.
l
5.0 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 1
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 I
defense and security or to the health and safety of the public.
Principal Contributor:
R. Schaaf Date: November 8, 1993
~!
.