ML20141F392
| ML20141F392 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/27/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20141F391 | List: |
| References | |
| TAC-59883, TAC-59884, NUDOCS 8604230009 | |
| Download: ML20141F392 (10) | |
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8 UNITED STATES i
7, NUCLEAR REGULATORY COMMISSION g
WASHINGTON, D. C. 20555 g me p
....+
SAFETY EVALUATION AMENDMENT N0.43 TO NPF-10 AMENDMENT N0. 32 TO NPF-15 SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 & 3 DOCKET NOS.60-361 AND 50-362
1.0 INTRODUCTION
Southern California Edison Company (SCE), on behalf of itself and the other licensees, San Diego Gas and Electric Company, The City of Riverside, California, and The City of Anaheim, California, has submitted several applications for license amendments for San Onofra Nuclear Generating Station, Units 2 and 3.
One such request, Proposed Change PCN-200, is evaluated herein. This change was submitted by letter dated October 9, 1985 and would revise the technical specifications relating to boric acid concentration and flow paths. Specifically, PCN-200 will make the following changes, which are appliable to Cycle 3 of both Units 2 and 3:
(1) reduce the boric acid concentration and volume requirements for the boric acid makeup (BAMU) tanks; (2) remove the requirement for heat tracing associated with the BAMU tanks; (3) remove the surveillance requirement for verification of a minimum
. charging flow rate from the BAMU tank flow paths.
(4) increase the upper. limit on boron concentration from 2300 to 2500 ppm for the refueling water storage tanks and safety injection tanks.
N$E Also, the licensee submitted a change applicable only to Unit 3, C gga which would reduce the lower limit on safety injection tank (SIT) ycle 2, og boron
$a concentration from 1720 to 1420 ppm.
Y The NRC staff has reviewed the proposed changes to the technical specifica-8k tions and the related supporting documents, and has prepared the following Qt evaluation of proposed change PCN-200.
h 2.0 EVALUATION OF CALCULATIONAL METHOD
$a.a The function of the boric acid makeup (BAMU) system is to provide an adequate volume of borated water to be injected into the reactor coolant system (RCS) to assure safe plant co d shutdown from normal operation or anticipated operational occurrences. The system also provides an emergency core cooling function by injecting the borated water into the RCS via the charging pumps to assure adequate core cooling during accident conditions.
The
existing technical specification requirements on boric acid concentration and water volume in the BAMU tanks were based upon an analysis which showed that the plant can achieve a cooldown to cold shutdown without letdown flow.
The required baration was achieved by injecting borated water into the RCS while simultaneously filling the pressurizer. To maintain the required shutdown margin specified in the technical specifications, the baron concentration typically would increase to 800 ppm prior to initiating cooldown. Since the available space in the pressurizer is limitad, it is necessary to maintain a high concentration of boren solution in
.ie BAMU tanks. With the baron concentration allowed by the existing ter nical
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specifications, heat tracing is required to prevent boron from precipitating at low temperatures. The surveillance requirement associated with this requires a minimum charging flow of 40 gpm to be available from the BAMU tanks in order to detect and avoid flow blockage due to boron precipitation.
In order to increase operating flexibility, the proposed change would reduce the boric acid concentration in the BAMU tanks. The boron concentration is reduced to a low level so that precipitation will not occur at ambient temperatures. The proposed change would also eliminate heat tracing and surveillance requirements for minimum charging flow.
The proposed changes are based on a cooldown method which allows boration of the RCS without letdown flow concurrently with plant cooldown.- While the pressurizer water level is maintained unchanged, the boration will be achieved by using the charging pumps to inject borated water into the RCS concurrently with cooldown as part of normal inventory makeup to compensate for coolant contraction.
To support the proposed change to the technical snecifications, the licensee submitted, at the staff's request, a report (Reference 2) for review and approval. The method documented in Reference 2 consists of two distinct series of calculations of the required and available boron concentration in the RCS to maintain a safe shutdown margin.
Both are applied throughout plant cooldown.
2.1 Evaluation of Analysis for Required Baron Concentration The analysis is based on the shutdown requirements of Branch Technical Position RSB 5.1 (SRP Section 5.4.7).
Specifically, the shutdown margin requirements are consistent with that specified in Technical Specifications 3.1.1.1 and 3.1.1.2 for Operating Modes 1 through 4, and 5 through 6, respectively. The ROCS and DIT computer codes (Reference 4) were used to calculate the baron concentration required in the RCS for the shutdown margins required by the technical specifications.
In the analysis, the analytical and measurement uncertainties were included to ensure that the upper bounding boron requirements were determined. The uncertainties include 9% in scram worth, 10% in moderator temperature feedback, 15%
in Doppler reactivity feedback, 50 ppm in baron measurement uncertainty, and time constant of 26 hours3.009259e-4 days <br />0.00722 hours <br />4.298942e-5 weeks <br />9.893e-6 months <br /> for xenon decay to maximize the xenon poison effect.
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4 We have reviewed the analysis for required boron concentration and found the analysis acceptable since (1) the NRC approved codes ROCS and DIT (Reference 4) were used for th'e analysis, (2) the appropriate uncertainties for the important core parameters were included to obtain the maximum i
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required boron concentration and (3) the required boron concentrations provide shutdown margins that are consistent with the technical specification l
values.
2.2 Evaluation of Analysis for Available Baron Concentration i
The calculational method is based on a steady state mass balance for boron in the entire RCS.
It is assumed that the borated water added to the RCS is equal to the fluid volume contraction due to the cooldown while the pressurizer water level is maintained constant. To simplify the analysis, instantaneous and complete mixing of the RCS fluid and makeup fluid added to the RCS through the loop charging nozzle was assumed.
In response to i
cur questions regarding the mixing model used in the analysis, the i
licensee performed an additional analysis (R ferences 2, 5) to assess the effect of boron mixing delay on the available boron concentration. The t
analysis assumed a slug fluid model with delay time of 30 minutes for the boron added and the results_, with inclusion of the uncertainties for the 2
core conditions, showed that the proposed boron concentration and volume of the BAMU tanks are sufficient to provide borated water to the RCS to meet the required shutdown margin as discussed in Section 2.1, above.
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In the analysis, various core conditions were considered by the licensee to maximize the boron concentration requirements. The limiting core conditions identified and used in the analyses were: (1) end-of-c conditions with initial RCS concentrations at zero ppm boron, (2)ycle the core with the most reactive control rod stuck fully out, (3) plant power at 100% with 100% equilibrium xenon prior to initiation of plant shutdown and (4) a relatively slow plant.cooldown rate of 12.5 F/hr.
i We have reviewed the analysis, including the delay effect and find the analysis acceptable since (1) the use of a delay time of 30 minutes is consistent with the results of tests which were performed in the same plant during natural circulation conditions (Reference 3), and (2) a slug fluid model of boron transport is conservative to maximize the delay effect. We have clso reviewed the above core conditions used in the
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analysis and we agree with the licensee that use of these conditions is conservative with respect to maximizing the boron requirements since items (1) and (2) above minimize the existing boron worth in the core, and items (3) and (4) above maximize the xenon poison effect.
In addition, the use of a cooldown rate of 12.5"F/hr is consistent with the plant test procedures used during the boron mixing test under natural circulation conditions for SONGS as described in Reference 3.
In response to a request by the staff, the licensee also submitted an analytical result 4
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3 boron concentration requirement for the case with the maximum cooldown rate allowed by the technical specifications (75'F/hr) is bounded by the case with the slow cooldown rate of 12.5 F/hr. We, therefore, conclude that the assumptions used for the analysis are conservative in that they maximize the boron concentration requirements and are therefore acceptable.
In summary, we find that an approved method was used to calculate the required boron concentration, and that the results are consistent with the shutdown margins required by the technical specifications. We also find that conservative core conditions were used and that the analytical results with inclusion of fluid mixing delay demonstrate that the proposed boron concentration and volume of the BAMU tanks is adequate to maintain safe shutdown margin consistent with the technical specification requirements.
Therefore, we conclude that the calculational method and the analytical results included in Reference 2 are acceptable for use as a basis for justification of the proposed technical specification changes for SONGS Units 2 and 3.
2.3 ' Transient and Accident Evaluation The licensee performed an evaluation to assess the impact on transient and accident behavior of the proposed reduction in boron concentration of the SIT and BAMU tanks.
The licensee has stated that the borated water injected from the BAMU tank was not taken into account in the steamline break accident.(SLB) analyses but the boron concentration in BAMU tanks of 1720 ppm was included in the loss-of-coolant-accident (LOCA) analysis. Also, the licensee stated that since the revised boron concentration in the BAMU tanks is higher than 1720 ppm, the licensee concluded that the reduction in boron concentration for the BAMU tanks would not effect the analytical results in the FSAR for the SLB and LOCA accidents.
The licensee has also evaluated the impact of the reduced boron concentra-tion in the SIT on the results of the steam line break and LOCA analyses.
For the SLB events, two limiting events were identified:
(1) hot full power with a loss of AC power and (2) zero power with a loss of AC power.
For both cases, the licensee stated that the return-to-power peaks without or before initiation of the SIT.
In addition, the licensee reviewed the non-limiting cases (SLBs with AC power available) and confirmed that the SIT was not required to prevent return-to-power.
For the LOCA analysis, the licensee indic;ted that the analytical results showed that the SIT boron solution with a lower limit of 1420 ppm is sufficient to provide an adequate shutdown margin (1%) for the Unit 3 Cycle 2 core during LOCA conditions.
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i We have reviewed the licensee's submittal and find that the proposed technical specifcation changes regarding reduced boron concentration in the SIT and BAMU tanks are acceptable, because they will not result in a significant reduction in safety margin.
By letter da.ted March 4, 1986, (Reference 6) the licensee committed to provide confirmatory analyses to support the conclusions presented to the staff regarding the effect of reduced boron concentration in the SIT on the transient analysis.
Based on this comitment, and our review of the information provided to date, we conclude that the transient and accident analyses are acceptable.
3.0 EVALUATION OF TECHNICAL SPECIFICATION CHANGES The specific technical specification changes proposed in PCN-200 and the reasons for their acceptability are as follows:
Technical Specification 3/4.1.2.1 The proposed changes to this technical specification would eliminate the heat tracing of the boric acid makeup (BAMU) system and the associated surveillance requirements related to a minimum charging flow rate.
The purpose of heat tracing of the BAMU system is to maintain the temperature of the fluid in the BAMU tanks high enough to prevent the boric acid from precipitating. The proposed changes to T.S. 3/4.1.2.8 would reduce the allowed concentration in the BAMU tanks to a maximum of 3.5 weight percent boric acid, which will not precipitate at fluid temperature higher than 50 F.
Table 9.4.4 of the FSAR indicates that the design temperature range for the BAMU tanks is 50-104 F which is sufficiently high to prevent boron from precipitating in the BAMU system. With respect to removing the surveillance requirement on the boration path, the main purpcse of this requirement is to ensure that precipitation has not caused flow blockage. The proposed ct,ange ir, boron concentration will preclude precipitation. Also, there are other technical specificetions associated with the inservice inspection (ISI) program that will verify the operability of the pumps and valves in this system.
The proposed changes are, therefore, acceptable.
Technical Specification 3/4.1.2.2 Currently, this technical specification requires two out of the following three flow paths for boron injection into the RCS:
(1) a BAMU tank
gravity feed path and associated heat tracir.g (2) a BAMU tank path via a boric acid makeup pump and associated heat tracing, or (3) the gravity feed path from the refueling Water tank via a charging pump.
The technical specifications also require heat tracing to be operable and verification at least once per 18 months to ensure that the flow path from the BAMU tanks are capable of delivering a flow of at least 40 gpm to the RCS.
The proposed change would add a new item, in addition to the current requirements, which requires both existing flow paths (through the gravity feed valve and BAMU pumps) from any credited BAMU tanks to be operable.
The existing technical specifications require only one flow path to be operable. The change constitutes an additional restriction, and is therefore acceptable. Also the changes to remove the surveillance require-ments related to the heat tracing and the associated flow rate verification are acceptable for the reasons stated above.
Technical Specification 3.1.2.6 This technical specification requires that operable BAMU puups be capable of being powered from an operable emergency power source. Since the same requirement is specified in Technical Specification 3/4.8.1.1, Electrical Power System (AC Sources), the proposed change to delete this requirement is editorial and is therefore acceptable.
Technical Specification 3/4.1.2.7 (for Operating Modes 5 and 6)
The existing technical specification requires that either (1) one BAMU tank and the associated heat tracing be operable with the tank's content in accordance with Figure 3.1-1, or (2) the Refueling Water Storage Tank (RWST) be operable and a minimum borated water volume of 9970 gallons with a minimum boron concentration of 1720 ppm. The technical specification also requires verification of the BAMU tank solution temperature. The proposed change would require a minimum bcron content in accordance with revised Figure 3.1-1 for a BAMU tank, or a minimum required volume of 5150 gallons to be maintained in a RWST with a minimum boron concentration of 1720 ppm.
The changes are consistent with the analytical results discussed in Section 2.2, above (the analysis is applicable to the cooldown by using either the BAMU or RWST tanks for Modes 5 and 6.) and therefore are acceptable. The deletion of the temperature requirement for the BAMU tank solution is acceptable since the boric acid content in BAMU tanks has been reduced to 3.5 weight percent which will not precipitate at the ambient temperature around the BAMU tanks.
Figure 3.1-1 (for Operating Modes 1 to 4)
This figure spe'ifies the minimum required BAMU water volume and temperature as a function of stored boric acid concentration for the various plant
operating modes. The revised figure specifies the minimum required water volume (contained in one or both BANU tanks) as a function of boric acid concentration for a given boron concentration in the RWST.
The range of boron concentration in the BAMU tank has been reduced from 8.5-12 weight percent boric acid to 2.25-3.5 weight percent.
The proposed changes are consistent with the analytical results (as discussed above for plant conditions in Operating Modes 1 to 4, will maintain the required safe shutdown margin, and are therefore acceptable.
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Technical Specification 3.1.2.8 (Operating Modes 1 to 4)
This technical specification requires that at least one BAMU tank and its associated heat tracing be operable with the contents of boric acid in the tank to be in accordance with Figure 3.1-1.
Figure 3.1-1 requires a minimum volume of boric acid of 5450 gallons at a concentration of 8.5 weight percent to be maintained in the BAMU tank. The technical specifica-tion also requires that the RWST be operable, containing a minimum of 362,000 gallons borated water with the boric acid concentration between 1720 and 2300 ppm.
The prcposed changes would reduce the range of the boric acid concentration as specified in the revised Figure 3.1.1.
Also, the concentration of the borated water in the RWST would be changed to range between 1720 and 2500 ppm while the boric acid volume is maintained unchanged. The surveillance requirement to verify the BAMU tank solutfor. temperature would be deleted.
We conclude that the revised Figure 3.1.1 is acceptable since the analytical r
results discussed in Section 2 above support the changes.
The change of upper limit from 2300 to 2500 ppm for baron concentration in the RWST is acceptable since boric acid at a concentration of 2500 ppm will not precipitate at temperatures higher than 32 F.
Based on this we conclude that the change will not result in boron precipitation in the RWST nor in the Reactor Coolant System after a LOCA.
The deletion of the surveillance requirement on the BAMU solution temperature is acceptable since the concentration of the BAMU solution is low and precipitation will be avoided at ambient temperature.
Technical Specifications 3.5.1 and 3.5.4 These changes would increase the upper limit on boron concentration for the RWST and the SIT from 2300 ppm to 2500 ppm.
These changes are acceptable because boric acid at a concentration of 2500 ppm will nct precipitate at temperatures higher than 32 F and thus will not precipitate in the core following a LOCA.
The change would also reduce the lower limit on boric acid concentration in the SIT from 1720 ppm to 1420 ppm for the Unit 3 Cycle 2 core. The change is consistent with the evaluation results discussed in Section 2.3, above and is acceptable.
i Technical Specification 3/4.1.2 Bases This technical specification defines (1) the required components for the boron injection system which ensures that negative reactivity is available during each mode of operation and (2) the boric acid concentration and volume requirements for the BAMU tanks.
The proposed change would delete the requirement for heat tracing of the BAMU tank and reduce the boric acid concentration and volume requirement in accordance with the proposed Figure 3.1-1.
We have reviewed the proposed changes and find (1) that they are consistent with the assumptions used for the analysis and (2) that the analytical results discussed in Section 2, above demonstrate that the required shutdown margin is available. On this basis we conclude that the changes are acceptable.
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4.0
SUMMARY
OF STAFF EVALUATION We have reviewed the proposed changes (PCN-200) to the SONGS 2 and 3 technical specifications.
The changes involve a reduction in boric acid concentration and volume requirements for the BAMU tanks, deletion of the requirements for heat tracing in the BAMU system and verification of a k
minimum flow rate from the BAMU flow paths. We have also reviewed the
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associated request to reduce the minimum required boron concentration frem 1720 ppm to 1420 ppm for the SIT for the Unit 3 Cycle 2 core. As is discussed above in detail, we find that the proposed changes are acceptable because they meet the applicable General Design Criteria and the applicable sections of the Standard Review Plan.
5.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Chief of the Radiological Health Branch, State Department of Health Services, State of California, of the proposed j
determinations of no significant hazards consideration. No commer.ts were l
received.
6.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes in the installation or use of facility components located within the restricted area.
The staff has determined that the amendments involve no significant increase in the amounts of any effluents that may be released offsite and that there is no significant increase in individual or cummulative occupation radiation exposure. The Commission has previously issued proposed findings that the amendments involve no significant hazards consideration, and there has been no public comment on such findings. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR Sec. 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environ-mental assessment need to be prepared in connection with the issuance of these amendments.
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7.0 CONCLUSION
Based upon our evaluation of the proposed changes to the San Onofre Units 2 and 3 Technical Specifications, we have concluded that:
there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and such activities will 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. We, therefore, conclude that the proposed changes are acceptable, and are hereby incorporated into the San Onofre 2 and 3 Technical Specifications.
Dated:
March 27, 1986 1
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8.0 References 1.
Letter dated October 9, 1985, with attachments, from M. Medford (SCE) to G. Knighton (NRC).
2.
Letter dated February 11, 1986 from M. Medford (SCE) to G. Knighton (NRC) transmitting CEN-316 (S), " Boric Acid Makeup Tank Concentration Reduction Effort, Technical Bases and Operational Analysis (January 1986)."
3.
Letter dated July 2, 1984 from K. P. Baskin (SCE) to G. Knighton (NRC) enclosing CEN-259, "An Evaluation of the Natural Circulation Cooldown Test Performed at the San Onofre Nuclear Generating Station,"
Combustion Engineering, January 1984.
4.
CENPD-266-P-A, "The ROCS and DIT Coinputer Codes for Nuclear Design,"
Combustion Engineering, April 1983.
5.
Letter dated February 19, 1986 from Medford (SCE) to G. Knighton (NRC) transmitting the responses to NRC review questions on PCN-200.
6.
Letter dated March 4, 1986 from Medford (SCE) to G. Knighton (NRC) trasmitting information inadvertently omitted from the February 11, 1986 letter.
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