ML20076E140
| ML20076E140 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 07/30/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20076E138 | List: |
| References | |
| NUDOCS 9108150256 | |
| Download: ML20076E140 (6) | |
Text
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' UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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WASHINoTON, D C. 20066
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. SAFETY-EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 79 TO FACILITY OPERATING LICENSE NO. NPF-29 ENTERGY OPERATIONS, INC., ET AL.
GRAND GULF NUCLEAR STATION, UNIT 1 DOCKET NO. 50-416
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1.0 INTRODUCTION
By letter dated June 19, 1989, as: revised May 31 and December 7, 1990, and as supplemented February 7, March-4 and April _10,1991, the licensee (System Energy Resources, Inc., before June-6,-1990, and Entergy Operations, Inc., on or after June 6, 1990), submitted a request for changes to the Grand Gulf
- Nuclear Station,' Unit.1, Technic.1-Specifications (TS).
The requested changes-would change TS 3/4.1.5 " Standby Liquid Control System" and associated Bases by specifying-an acceptable range of sodium pentaborate solution temperature
.(75 - 130 *F), concentration (13.6 - 15.2 weight percent) and volume (4281 -
~ 5088 gallons) for normal operation in lieu of the presently specified range of
-solution temperature (67 - 130 *F), concentration (13.6 - 28.5 weight percent),
. minimum volume (4530-gallons) and minimum weight--(5800 pounds).
An additional
-Action statement would allow the. solution concentration to be as high as 28.5 weight percent for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided the solution temperature is above the saturation temperature as measured each 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
An additional surveillance requirement would be the_ daily determination of-the operability of heat tracing on pump suction piping by determining that power is available to at least one of the two re undant circuits.
- The. proposed changes'resulted from an assessment of the standby liquid control
-system (SLCS) by the-licensee'_in August 1988, which concluded, in part,- that
.the fS:should be changed ~to reduce-the potential for precipitation of sodium pentaborate in.the-solution. -Theimaximum-solution concentration of 28.5 L
percent permitted for. nonnal' operation in the present TS requires a' temperature -
E of 130 *F~to prevent precipitation.
However the SLCS tank heaters and heat-tracing are designed to maintain +,he solution in the tank and suction piping between 85~and.95 *F and the disc arge piping, which is not heat traced, is maintained at the containment temperature between 70 and 80 F.
2.0- EVALUATION L
2.1 Ar.alyses for Proposed Technical Specifications The. function of the.SLCS is to inject. sodium pentabrate solution, a neutron poison, into the reac'.or coolant system to assure a safe shutdown condition during an anticipated transient without scram (ATWS) event.
The ATWS rule as
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. specified in paragraph (c)(4) of 10 CFR 50.62 requires that each boiling water reactor must have a standby liquid control system with a minimum flow capacity and' boron content equivalent in control capacity to 86 gallons per minute (gpm)
M 13 weight percent sodium pentaborate solution.
To be in compliance with the
.s CFR 50.62 requirements, the licensee established the lower bound on solution concentration (13.6 percent), based upon the two pump design flow rate of 82.4 gpm.
The curr_ent TS specifies the minimum weight of sodium pentaborate of 5800 pounds to be maintained in the SLCS and requires the concentration of boron in solution to be within the limits of Figure 3.1.5-1, which defines the required I
concentrations of the sodium pentaborate solution (ranging from 13.6 percent to i
28.5 percent by weight) as a function of temperature (varying from 67 to 130 F).
The existing TS requires the tank heaters and the heat tracing subsystem or the SLCS suction piping _to be operable in order to maintain the higher concen-trations of sodium pentaborate solution above its saturation temperature.
This requirement precludes solution precipitation and thus avoids the potential for flow blockage in the SLCS.
In order to reduce the need to actuate the tank heaters and the heat tracing subsystem, the licensee proposed to operate the plant at lower sodium pentaborate_ concentrations ranging from 13.6 percent to 15.2 percent for normal operations and only allow higher concentrations for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, if necessary, during addition of borax or dilution of the sodium pentaborate solution.
To maintain the required minimum weight of sodium pentaborate of 5800 pounds in the solution, the licensee proposed in Figure 3.1.5-2 to specify the required solution volumes (ranging from 4281 to 5088 gallons) as a function of the solution concentrations (13.6 percent to 15.2 percent).
The upper bound on solution concentration (15.2 percent) is established to assure t'1at its corresponding saturation temperature of 70 *F is below the minimum allowable temperature of 75 F for the solution in the SLCS.
Since the containment ambient temperature is normally auove 75 F, tank heaters and heat tracing on suction piping will not normally need to be actuated.
The licensee established the lower temperature limit of 75 F to provide 5 F margin to the saturation temperature for solution at the maximum allowable concentration (15.2 percent), and the upper temperature limit of 130 F to meet the net pump suction head (NPSH) requirements for two pump operation and provide about 20 F margin to the 150 F temperature rating of the SLCS piping.
The licensee established the required volumes of the solution in proposed Figure 3.1.5-2_to assure that the solution will contain a weight of sodium pentaborate of 5800_ pounds.
This weight was previously approved by the NRC in the existing TS as the quantity of nuclear poison needed for cold shutdown margin during an ATWS event.
The upper bound on the required volumes is limited by the tank volume of 5088 gallons.
In'the proposed TS, a maximum concentration of 28.5 percent of sodium penta-borate could be maintained in the SLCS tank for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The temperature of the solution would have to be 130 F which is 16 F higher than its saturation temperature.
However, during injection, when the solution passes through the 70 F piping linking the SLCS tank and the reactor vessel, it loses heat and its temperature drops below the saturation temperature, causing precipitation of
. sodium pentaborate.
The calculation was made to demonstrate that excessive precipitation would not block the piping and retard or stop the flow of sodium pentaborate to the reactor vessel.
The licensee performed the calculations for steady state and transient condi-tions.
Transient state occurs when the hot solution is introduced into the cold pipes.
During this period most of the heat from the solution is trans-ferred to the pipe wa'Is and raises their temperature.
Only a relatively small amount is transferred to the outside.
During steady state condition, the pipe walls have already reached their equilibrium temperature and heat from the solution is transferred to the outside.
The licensee performed calculations using a computer code.
The method was described in the submittal and a numerical example was given.
The licensee found that during steady state, loss of heat from the solution was so low that its temperature dropped only a fraction of a degree Fahrenheit.
- However, during the transient condition the heat transfer from the solution to the pipe was significant and the temperature of the solution dropped below the satura-tion temperature for sodium pentaborate. The licensee calculated precipitation of 6.993 pounds of sodium pentaborate salt.
This is a very small quantity, representing less than 0.1 percent of the total amount of sodium pentaborate in the tank.
For the minimum specified volume at 28.5 percent the total amount of sodium pentaboratt is much greater than the required 5800 pounds for cold shutdown margin.
Therefore, control of the reactivity by SLCS injection would not be affected.
Such a small precipitation would also be unlikely to cause blockage of the injection piping.
In order to confirm that blockage would not likely occur, the licensee performed a laboratory experiment in which 28.5 percent solution of sodium pentaborate was cooled down from 130 *F to approxi-mately 77 F with continuous stirring.
The resulting precipitation occurred in the form of suspended particles which dissolved when the solution was reheated.
No plating of the precipitated sodium pentaborate was observed.
We have reviewed the licensee's analysis and performed an independent calcula-tion.
We found that both steady state and transient analyses performed by the licensee are conservative.
Our calculations have indicated that in both these cases temperatures of the solution calculated by the licensee were slightly below those determined by us.
The amount of sodium pentaborate precipitated was calculated to be 7.392 pounds, which is close to the licensee's value.
Based on its review of the proposed TS changes and its independent calculation of precipitation during injection of high-concentration sodium pentaborate solution, the staff concluded that the proposed TS assure the capability of the SLCS to inject the required amount of solut*on without excessive precipitation and are, therefore, acceptable.
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.: 2.2 Proposed-Technical Specifications (1)- Required Volume of the Solution - Figure 3.1.5-2, TS 4.1.5.a.1 and 4.1.5.a.2 Figure 3.1.5-2 is added for the required volume of the solution in the SLCS tank as a function of concentration of the sodium pentaborate solution.
The surveillance requirements of volume and temperature limits for TS 4.1.5.a.1 and 4.1.5.a.2 are changed to be consistent with the limits specified in Figure 3.1.5-2.
The staff finds that the proposed changes are consistent with the licensee's analytical results and in compliance with the requirements of the ATWS rule as specified in 10 CFR 50.62 and.
-therefore, concludes the changes are acceptable.
(2) Heat Tracing Operability - TS 4.1.5.a.3 The surveillance requirement of TS 4.1.5.a.3 for heat tracing operability is revised to require the operator not only to confirm the SLCS pump suction pipe temperature to be not less than the saturated temperatures as required -in the current TS, but also to verify the powe. to be available to at least one division of heat tracing circuitry.
Since the added surveillance requirement reduces the probability of flow blockage due to sodium pentaborate precipitation, the staff concludes that the change is acceptable.
(3) Required Minimum Weight of Sodium Pentaborate - TS 4.1.5.b.3 The existing TS 4.1.5.b,3 requires the operator to maintain the minimum weight of codium pentaborate of 5800 pounds to meet the cold shutdown margin requirement.
In the revision, TS 4.1.5.b.3 deletes the minimum required weight of sodium pentaborate and requires the operator to main-tain the concentration of boron in solution to be within the limits of Figure 3.1.5-2.
Since the " normal operation" area of Figure 3.1.5-2 is established to maintain at least 5800 pounds of sodium pentaborate in solution, the change meets-the same cold shutdown margin as in the existing TS.
Therefore, the staff concludes that the change is acceptable. -
(4) Reference of Design Minimum Weight of Sodium Pentaborate to Figure 3.1.5 Bases 3/4.1.5 The revised Bases 3/4.1.5 reflects the TS changes by referring to Figure 3.1.5-2 for the required quantity of sodium pentaborate solution which contains the minimum weight of sodium pentaborate of 5800 pounds.
The changes are consistent with the assumptions used in the analysis to support the TS changes and are, therefore, acceptable.
(5) Action Statement for Sodium Pentaborate Solution Concentration Greater l
than 15.2 percent - TS 3.1.5.a.3 l
The licensee proposed to normally operate the plant at lowered sodium pentaborate concentrations (ranging from 13.6 percent to 15.2 percent) in the SLCS tank.
TS 3.1.5.a.3 is proposed as an additional Action statement l
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. which would allow for temporary variations due to addition of Borax powder, non-uniform mixing and other unidentified causes.
With the sodium pentaborate concentration greater than 15.2 percent, and solutior, volume within the limits of Figure 3.1.5-2, TS 3.1.5.a.3 requires the operator to (1) verify the sodium pentaborate solution temperature to be within the limits of Figure 3.1.5-1 every four hours, and (2) restore the sodium pentaborate solution to within the normal operating limits (13.6 percent to 15.2 percent) of Figure 3.1.5-1 and Figure 3.1.5-2 within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The operator is required to bring the plant to the hot shutdown condition within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> if the Action statements of TS 3.1.5.a.3 discussed above are not met.
Since analyses demonstrated that there would not be exces-sive precipitation which could block the unheated discharge piping, if the solution at the maximum allowable concentration were injected, the staff concludes that the changes are acceptable (see Section 2.1 above).
2.3
SUMMARY
The staff has reviewed the proposed Technical Specification changes and the supporting analyses.
The changes would result in a reduced potential for-precipitation of the sodium pentaborate solution during normal plant operation by limiting concentrations to 15.2 weight percent.
For a limited time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, concentrations up to 28.5 percent if injected, would not result in sufficient precipitation to block the unheated discharge piping.
Since the assumpticas used in the analyses are reasonable and the calculated results demonstrate that the TS changes will meet the requirements of the ATWS rule for the SLCS as specified in 10 CFR 50.62, the staff concludes that the proposed TS changes are acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Mississippi-State official was notified of the proposed issuance of the amendment.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or usE of a 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, i
and that there is no significant increase in individual or cumulative occupa-l tional radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (56 FR 29273).
Accordingly, l
l the amendment meets the eligibility criteria for categorical exclusion set l
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, forth-in 10 CFR 51.22(c)(9),
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmentcl assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is r0asonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such 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 defense and security or to the health and safety of the public.
Principal Contributors:
- 5. Sun, SRXB/NRR K. Parczewski, EMCB/NRR Date: July 30,1991 i
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