ML17222A724
| ML17222A724 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/13/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17222A723 | List: |
| References | |
| NUDOCS 8903220470 | |
| Download: ML17222A724 (13) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 40 TO FACILITY OPERATING LICENSE NO. NPF-16 FLORIDA POWER
ST.
LUCIE PLANT UNIT NO.
2 DOCKET NO. 50-389
1.0 INTRODUCTION
By letter dated September 1, 1988, the Florida Power and Light Company (FP&L, the licensee) requested Technical Specifications changes for the St. Lucie Plant, Unit No. 2.
The proposed changes would revise the requirements of the boric acid makeup system such that the boric acid concentration would be lowered, the water volume would be increased, and heat tracing of the circuits would no longer be required.
In addition, the licensee reevaluated the post-LOCA containment sump chemistry to determine the effect of boric acid concentration reduction.
The licensee also submitted Combustion Engineering report number CEN-365(L) entitled "Boric Acid Concentration Reduction Effort, Technical Bases and Operational Analysis," to serve as the technical basis for the proposed changes.
2.0 DISCUSSION The proposed changes would modify the requirements for the boric acid makeup (BAMU) system, which is"used to provide an adequate volume of borated water in the reactor coolant system (RCS) to assure that the shutdown margin is met in all modes of reactor operation.
The boron contained in the BAMU system is not taken credit for in reactivity control during transients and accidents.
- Thus, the plant's accident analysis basis is not changed as a result of the proposed changes to the requirements of the BAMU system.
Presently, the minimum required boric acid concentration in water is 8 percent.
This requires the IIIinimum water temperature to be approximately 105'F.
In
- practice, the boric acid concentration has operational range, i.e.,
8 to 12 weight per cent in this case.
Twelve weight percent boric acid concentration requires a water temperature of approximately 135'F.
If the minimum water temperature is not maintained for a given boric acid concentration, the boron in the boric acid will precipitate out of solution and solidify at the bottom of tanks and piping.
If the boron starts to precipitate, the BAMU system cannot be called upon to meet shutdown margin requirements.
Thus, the water temperature in the BAMU system is continually being maintained by electrical means called heat tracing.
The boric acid concentration can be lowered to an extent that heat tracing is not necessary, but other compensatory measures would also have to be ta ken.
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The li'censee proposed to delete the heat tracing requirement for the BANU system.
In order to do so, the licensee proposed to decrease the required boric acid concentration and increase the required borated water volume to offset the reduced concentration.
The range of boric acid concentration is proposed to be reduced from 8.0 to 12.0 weight percent to 2.5 to 3.5 weight percent.
This reduction in boric acid concentration will prevent boron precipitation at ambient temperatures in the auxiliary building after the heat tracing is removed.
For example, the minimum water temperature necessary to keep the boron in solu-tion is only 50'F.
The range of borated water volume in a boric acid makeup tank is proposed to be changed from the approximate range of 6140 - 6520 gallons to the range of 5350 - 8650 gallons for Nodes 1 through 4, and at least 3550 gallons (assumes 2.5 weight percent concentration) for Nodes 5 and 6.. The following Technical Specifications would be changed to effect the above described changes:
TS 3/4.1.2.1, Boration Systems
- Flow Paths - Shutdown; TS 3/4.1.2.2, Boration System - Flow Paths - Operation; TS 3.4.1.2.7, Borated Water Sources - Shutdown; and TS 3/4 1.2.8, Borated Water Sources - Operating.
- 3. 0 EVALUATION The proposed changes to the requirements for the BANU system, the associated Technical Specifications
- changes, and the calculated results associated with the Combustion Engineering report are evaluated below.
3.1 ~Bd C
The methodology and analytical results to support the request for the Technical Specifications changes are documented in Combustion Engineering report number CEN-365(L), and include two distinct series of calculations for the required and available boron concentration in the RCS to maintain a safe shutdown margin.
Both are employed at each time of interest in the plant cooldown conditions.
3.1.1 Evaluation of Anal sis for Re uired Boron Concentration According to the licensee, the analysis for the required boron concentration is based on the shutdown requirements of Branch Technical Position 5.1, entitled "Design Requirements for the Residual Heat Removal System" (SRP Section 5.4.7).
Specifically, the shutdown margin requirements are consistent with those spec-ified in Technical Specifications 3.1.1.1 and 3.1.1.2 for operating Nodes 1
through 4, and 5 through 6, respectively.
Reasonable core physics parameters were used to calculate the boron concentration required to be present 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 bound boron requirements were predicted.
The uncertainties include
-13% in scram worth,
+10'in moderator temperature
- feedback,
~15% in Doppler reactivity feedback, and the 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.
The staff has reviewed the licensee's analysis for required boron concentration and finds the analysis acceptable.
3.1.2 Evaluation of Anal sis for Available Boron Concentration The licensee specified that the calculational method to determine the available boron concentration 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.
In the analysis (CEN-365(L)), various core conditions were considered to minimize the available boron reactivity effect.
.The limiting core conditions identified and used in the analysis were (1)
'nd-of-cycle conditions with initial RCS concentrations at zero ppm boron, (2)
'he core with the most reactive control rod fully stuck out, (3) plant power at 100% with 100% equilibrium xenon prior to initiation of plant shutdown, (4) a
":low plant cooldown rate of 12.5'F/hr.,
(5) end-of-cycle moderator cooldown
- effects, and (6) end-of-cycle boron reactivity worths.
These assumptions are conservative with respect to minimizing the boron reactivity effects since assumptions (1) and (2) minimize the existing boron within the core and avai lable scram worth assumptions (3) and (4) maximize the xenon poison effect, and assumption I5) maximizes the horatian requirements due to moderator cooldown effects.
End-of-cycle (EOC) inverse boron worth (IBM) data were used in combination with EOC reactivity insertion rates normalized to the most negative Technical Specification Moderator Temperature Coefficient (NTC) limit,,since it was known that this yields results that are more limiting than the combination of actual MTC and actual IBM valves at all periods through the fuel cycle prior to EOC.
The use of a cooldown rate of 12.5'F/hr.
is consistent with the plant test procedures for the boron mixing test performed during a natural circulation test at another Combustion Engineering plant.
Included in CEN-365(L) is an analysis that demonstrates that the boration requirements for the fastest cooldown rate of 100'F/hr.,
as allowed by the Technical Specifications, is bounded by the case when the cooldown rate was limited to 12.5'F/hr.
The report (CEN-365(L)) uses a conservative method to calculate the required boron concentration necessary tomaintain the shutdown margin required by Technical Specifications 3.1.1.1 and 3.1.1.2 during a safe shutdown scenario.
A conservative RCS makeup scenario was used to demonstrate that the proposed boron concentration and volume requirements for the BAHU tanks will maintain the safe shutdown margins required by the Technical Specifications.
The staff agrees with the above licensee
- analysis, showing that the available boron meets the required boron concentration requirements, and finds it acceptable.
4 3.2 Transient and Accidents The licensee addressed off-normal operations as follows.
As stated in Section 2.6 of CEN-365(L), credit is not taken for boron addition to 'the RCS from the boric acid makeup tanks 'for the purpose of reactivity control in the accidents analyzed in Chapter 15 of the plant's Final Safety Analysis Report.
The response of an
- operator, therefore, to such events as steam line break, overcooling, boron dilution, etc., will not be affected by a reduction in boric acid makeup tank (BANT) concentration.
In particular, the action statements associated with Technical Specification 3.1.1.2 require that boration be commenced at greater than 40 gallons per minute using a solution of at least 1720 ppm boron in the
~ event that shutdown margin is lost.
Such statements are conservatively based
'pon the refueling water tank concentration and are therefore independent of the amount of boron in the BANTs. It should be noted that even after reducing the boron concentration in the BANTs, the minimum boron concentration in these tanks is higher than 1720 ppm.
Similar to the Technical Specifications action steps in the event of a loss of shutdown margin, the operator guidance in Combustion Engineering's Emergency Procedure Guidelines (EPBs),
CEN-152, Rev. 2, are also independent of specific boron concentration within the boric acid makeup tanks.
Specifically, the acceptance criteria developed for the reactivity control section of the Functional Recovery Guidelines of CEN-152 are based upon a boron addition rate from the chemical and volume control system of 40 gallons per minute without reference to a particular boration concentration.
Therefore, the reduction in boron conce'ntration within the BANTs has no impact on, and does not change, the gui-dance contained in the EPGs.
The staff agrees with the above licensee analysis and finds it acceptable.
3.3 Evaluation of the Im act on Containment Sum H and Affected E ui ment The lice'nsee reevaluated the post LOCA long-term containment sump inventory calculation to reflect the new operating parameters as a result of the reduction in boric acid concentration in the BANTs.
Two scenarios were considered.
The first would result in a maximum post-LOCA containment sump boric acid concentration and the second would result in a minimum boric acid concentration.
Both scenarios were also analyzed for a loss of offsite power where only one emergency train was available'uring the LOCA (assume one emergency diesel generator fails to start).
With this information, the licensee was able to calculate the pH value for each case.
The results of the calculation established that the post-LOCA long-term contain-ment sump and spray chemistry shall have new bounding values for boric acid concentration and pH:
Naximum Ninimum Boric Acid Concentration pH 2225 ppm boron 8.00 0
ppm boron 7.00 The licensee performed an analysis to determine if the new boric acid concen-tration and pH ranges affected equipment Environmental gualification during a
LGCA.
The result of the analysis showed that the equipment in the containment is qualified for the new bounding valves of the boric acid concentrations and pH values.
The licensee also performed an evaluation to determine the effect of the new pH range on mechanical systems and components due to corrosion.
By maintaining the pH of the long-term containment sump and spray system at between 7.0 and 8.0, the evolution of iodine and the effect of chloride and caustic stress are minimized.
3.4 Technical S ecification Chan es The Technical Specifications changes and the reasons for their acceptability are provided below.
Technical S ecification 3/4.1.2.1 Boration S stems Flow Paths - Shutdown The proposed changes to the Technical Specifications eliminate the requirements for heat tracing of the BAMU system.
The design purpose of heat tracing of the BAMU system is to maintain the temperature of fluid in the BAMU tanks and the boration flowpaths high enough to prevent the boric acid from precipitating.
The proposed changes to TS 3/4.1.2.7 and TS 3/4.1.2.8 (explained later) reduce the concentration in the BAMU tanks to a maximum concentration of 3.5 weight percent boric acid, which will not precipitate at a borated water temperature higher than 55'F.
Chemical analyses have shown that a 3.5 weight percent solution of boric acid will remain dissolved (i.e., will not precipitate or "plate out") at solution temperatures above 50'F.
The proposed changes also include a
surveillance requirement to ensure that the borated water source is operable by verifying that the temperature in the BNU is above 55'F whenever. the auxiliary building temperature is below 55'F.
The 55'F requirement provides a 5'F margin, since the boron will remain in solution down to 50'F.
Consistent with the new surveillance requirement
- above, the old surveillance requirement to verify the flow path temperature above the temperature limit line on Figure 3.1-1 has been deleted.
The licensee specified that the auxiliary bui lding temperature will be monitored at the Boric Acid Makeup Station.
Therefore, the Technical Specification changes are acceptable.
Technical S ecification 3/4.1.2.2 Flow Paths - 0 eratin Currently, the Technical Specifications require two out of the following three flow paths for boron injection into the RCS:
(1) a BAMU tank gravity feed path and associated heat tracing, (2) a BAMU tank path via a boric acid makeup pump and associated heat tracing, or (3) flow path from the refueling water tank.
The proposed change requires a flow path from any credited source of water (refueling water storage tank and/or BAMU tank (or tanks)) to be operable.
These changes are consistent with the assumptions used in CEN-365(L).
The proposed changes to the Technical Specifications eliminate the requirement for heat tracing of the BAMU system.
As in Technical Specification 3/4.1.2.1, deletion of the requirement to heat trace the BAMU system is consistent with the ability of the boric acid to remain in solution at temperatures above 50'F.
The proposed changes include a surveillance requirement to assure that the borated water source is operable by verifying that the temperature in the BANU is above 55'F whenever the auxiliary building temperature is below 55'F.
As in Technical Specification 3/4.1.2.1, the old surveillance requirement for temperaure verification of the flow path from the BAMTs has been deleted.
The Technical Specification changes are therefore acceptable.
Technical S ecification 3/4.1.2.6 Boric Acid Makeu Pum s - 0 eratin Currently, this Technical Specification references Specification 3.1.2.2a, Flow Path.- Operating.
Due to the additional items which have been proposed to Specification 3.1.2.2 for the subject proposed amendment, reference to Specifi-cation 3.1.2.2a is no longer applicable.
Therefore, reference to Specification 3.1.2.2a has been changed to reference Specification 3.1.2.2.
Technical S ecification 3/4.1.2.7 Borated Water Sources - Shutdown The existing Technical Specification requires that one of the two BANU tanks and its associated heat tracing be operable with the tank containing 8 weight percent boron and a minimum content of 4,150 gallons.
The proposed changes will delete the heat tracing operability requirement, lower the boric acid concentration to a range of 2.5 to 3.5 weight percent, change the minimum BANT content to 3,550 gallons (assumes a minimum of 2.5 weight percent boric acid concentration),
and modify the surveillance requirement to verify that the BAMU tank temperature is above 55'F whenever the auxi liary bui lding temperature is below 55'F.
As in Technical Specification 3/4.1.2.1, the old surveillance requirement to verify the temperature of the flow path from the boric acid makeup tanks has been deleted.
These changes are consistent with the analysis presented in CEt)-365(L), which demonstrates adequate boration capability at the lower boric acid concentrations and. the ability for boric acid to remain in solution at these concentrations at temperatures above 50'F.
Therefore, the Technical Specification changes are acceptable.
Fi ure 3.1-1 (for 0 eratin Nodes 1 throu h 4)
The existing figure specifies the minimum required BANU water volume and temperature as a function of stored boric acid concentration for the various plant operating modes.
The existing figure is applicable to either of the two BANU tanks, each having a maximum capacity of 9,975 gallons.
The revised figure specifies the minimum required water volume (contained in one or both BANU tanks) as a function of boric acid concentration in the BANU tank.
This curve was generated in report CEN-365(L) for a minimum refueling water tank boron concentration of 1720 ppm boron.
This curve conservatively bounds BAMU tank minimum required water volumes for conditions when the refueling water tank boron concentration is greater than 1720 ppm (a Technical Specification requirement).
The range of boron concentration in the BAMU tank has been reduced from 8.0 to 12.0 weight percent boric acid to 2.5 to 3.5 weight percent.
The
Il
upper range of the required borated water volume has been increased from 6,520 gallons (8 weight percent) to 8,650 gallons (2.5 weight percent).
The lower range of the required borated water volume has been decreased from 6,140 gallons (12 weight percent) to 5,350 gallons (3.5 weight percent).
The revised Figure 3.1-1 is consistent. with the analytical results of CEN-365(L) for plant condi-tions at Operating Nodes 1 through 4 to maintain the required safe shutdown margin.
The temperature versus BAMT concentration curve has been removed from the Technical Specifications since it is no longer required. 'he revised figure is acceptable.
Technical S
ec ificati on 3.1.2.8 Borated Water - 0 eratin The current 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 consistent with the existing Figure 3.1-1.
The existing Figure 3.1-1 specifies the volume of boric acid of 6,520 gallons at a minimum concentration of 8.0 weight percent to be maintained in the BANU tank.
The proposed changes provide a
new range of boric acid concentration of 2.5 to 3.5 weight percent for one or both of the BAMU tanks.
The revised volumes of Figure 3.1-1 lower the minimum water volume to 5,350 gallons.
Deletion of the requirement to heat trace the BAMU system is consistent with the ability to maintain 2.5 to 3.5 weight percent boric acid in solution at temperatures above 50'F.
The revised surveillance requirements delete verifying the BAMU tank temperature unless the auxiliary building temperature is below 55'F.
For conser-vatism this verification of temperature is done more frequently (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> versus 7 days and the old surveillance requirement has been deleted Since the borated water source can be made up of one BAMU tank (1A or 1B) per the proposed Technical Specifications, and considering that one tank has a
maximum capacity of 9,975 gallons, a minimum concentration of boric acid needs to be specified.
The minimum weight percent boric acid is specified as 3.2 weight percent under these conditions.
The proposed Technical Specification changes are acceptable.
Technical S ecification 3/4.5.1 Safet In'ection Tanks The existing Technical Specification requires each reactor coolant system Safety Injection Tank (SIT) to contain a borated water volume of 1,540 cubic feet maximum in Nodes 3 and 4 when the pressurizer is less than 1750 psia'.
The maximum SIT volumes specified are not consistent with the maximum volume requirement (1556 cubic feet) for the SIT's in Modes 1,
2 and 3 when the, pressurizer pressure is above 1750 psia. 'Technical Specification 3/4.5 has been revised to correct the inconsistency.
Bases - 3/4.1.2 Boration S stems The Technical Specifications define the required components for the boron injection system, which ensures that negative reactivity is available during each mode of operation, and define the boric acid concentration and volume requirements for the BAMU tank and refueling water tank (RWT).
Since heat tracing will no longer be required, the deletion of the heat tracing
- system, as part of the boron injection system components, has been deleted from the bases statements.
This change is acceptable.
The permissible range of boric acid concentration and associated water volumes needs to be changed in the bases statements.
The bases statement for Nodes 1
through 4 now reads, "This range is bounded by 5,350 gallons of 3.5 weight percent (6119 ppm boron) from the BAHT and 16,000 gallons of 1720 ppm borated water from the RWT to 8,'650 gallons of 2.5 weight percent (4371 ppm boron) boric acid from BAHT and 12,000 gallons of 1720 ppm borated water from the RWT."
The Combustion Engineering report, Table 2-34, page 2-67, specified 4,842.2 gallons of 3.5 weight percent boric acid and 8,118.1 gallons of 2.5 weight percent boric acid for Nodes 1 through 4.
The relationship between these values and the Technical Specification values is explained on page 2-21 of the Combustion Engineering report.
Each value was rounded up to the nearest 50 gallons and 500 gallons was added to provide conservatism.
For example, 8,118.1 gallons was rounded to 8,150 gallons, and adding an additional 500 gallons yields 8,650 gallons.
Therefore, the proposed changes are acceptable.
The bases statement for Nodes 5 and 6 specifies 3,500 gallons of 2.5 to 3.5 weight percent boric acid solution.
The 3,550 gallon calculation in the Combustion Engineering report assumed 2.5 weight percent boric acid solution.
- Thus, any concentration greater than 2.5 weight percent, up to and including 3.5 weight percent, is conservative.
In addition, the 3,550 gallon value is made up of the following components.
The Cori&Jstion Engineering report on page 2-11 specifies that 3,049.0 gallons of 2.5 weight percent boric acid solution is the required value per analysis.
An additional 500 gallons was added to this figure for conservatism.
Finally, the 3,549.0 gallon number was rounded up to the nearest 50 gallon value of 3,550 gallons.
Therefore, the proposed changes are acceptable.
Bases
- 3/4.5 Emer enc Core Coolin S stem - 3/4.5.4 Refuelin Mater Tank The pH values for the solution recirculated within the containment after a
LOCA were incorrectly specified as between 7.0 and 11.0.
The correct pH is between 7.0 and 8.0.
The bases have been revised to delineate the correct pH range.'ases
- 3/4.6 Containment S stems - 3/4 6.2.2 Iodine Removal S stem The pH values for the solution recirculated within the containment after a
LOCA were incorrectly specified as between,7.0 and 11.0.
The correct pH is between 7.0 and 8.0.
The bases have been revised to delineate the correct pH range.
1 I
3.5
SUMMARY
The staff has reviewed the proposed changes to the St. Lucie Plant, Unit No.
2 Technical Specifications involving reduction in boric acid concentration and volume requirements for the BAMU system, and deletion of the requirement for heat tracing in the BAMU system.
The staff concludes that the proposed changes are acceptable since the changes of boric acid requirements for the BAMU system do not reduce shutdown margin below the required values specified in Technical Specifications 3.1.1.1 and.3.1.1.2.
Because the concentration of boric acid in the BAMU system has been reduced to a value which will not cause precipitation at ambient temperatures for the BAMU system, heat tracing in the BAMU system is not required.
The proposed. Technical Specifications are acceptable since they are consistent with the proposed changes to requirements for the BAMU system and are supported by the analytical results.
ENVIRONMENTAL CONSIDERATION This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change to a survei llance requirement.
The 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 published a proposed finding-that the amendment involves no 'significant hazards consideration and there has been no public comment on such finding.
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 551.22(c)(9).
Pursuant to 10 CFR 51.22(b),
no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
CONCLUSION We have concluded, based on the considerations discussed above, that (1) there is reasunable assurance that the:health and safety of the public will not be endangered by operation in the proposed
- manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the'amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date:
March 13, 1989 Princi al Contributors:
J. Norris S.
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