ML20209J345
| ML20209J345 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 01/16/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20209J315 | List: |
| References | |
| NUDOCS 8702060289 | |
| Download: ML20209J345 (5) | |
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NUCLEAR REGULATORY COMMISSION UNITED STATES h.
WASHINGTON, D. C. 20555 E
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 13 TO FACILITY OPERATING LICENSE NO. NPF-38 LOUISIANA POWER AND LIGHT COPPANY WATERFORD STEAM ELECTRIC STATION, UNIT 3 DOCKET NO. 50-382
1.0 INTRODUCTION
By applications dated July 15, 1986, Louisiana Power and Light Company (the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License No NPF-38) for the Waterford Steam Electric Station, Unit 3.
The proposed changes would:
(1) revise the axial shape index allowable ranaes; (2) revise the moderator temperature coefficient allowableranae;(3)revisethepart-lengthcontrolelementassemblyinsertion limits; and (4) allow the suspension of the part-length control element assembly insertion limits during certain startup tests.
2.0 DISCUSSION The proposed changes to the technical specifications requested by the licensee are in four areas, as described below.
2.1 Axial Shape Index Allowable Ranges (NPF-38-24)
The proposed change would revise the Axial Shape Index (ASI) allowable ranges given in Technical Specification 3.2.7.
2.2 Moderator Temperature Coefficient Allowable Range (NPF-38-25) l The proposed change would revise the moderator temperature coefficient (MTC) l mostnegativelimitto-3.3x10~} Specification 3.1.1.3byextendingthe allowable range given in Technica delta k/k/ F at all level power and by extending the niost positive limit to +0.5 x 10 g of thennal l
delta k/k/ F at or below 70% thennal power.
2.3 Part-Length Control Element Assembly Insertion Limits (NPF-38-26) 1 i
The proposed change would revise the Part-Length Control Element Assembly (PLCEA) insertion limits in Technical Specification 3.1.3.7 and its associated surveillance requirements.
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. 2.4 PLCEA Insertion Limits Durino Startino Testing (NPF-38-27)
The proposed change would modify Technical Specification 3.10.2 to allow the suspension of the part-length control element assembly insertion limits during certain startup tests.
3.0 EVALUATION The proposed changes to the Technical Specifications requested by the licensee and described in four areas above, are evaluated below.
3.1 Axial Shape Index Allowable Ranges (NPF-38-24)
In order to ensure that the peak linear heat rate and departure from nucleate boiling ratio remain within the safety limits during anticipated operational occurrences and to ensure that the actual value of ASI is maintained within the range of values used in the safety analyses, Technical Specification 3.2.7 requires the ASI to be maintained between -0.23 and +0.50 when the Core Operating Limit Supervisory System (COLSS) is operable and between -0.19 and +0.24 when COLSS is out-of-service and the Core Protection Calculator (CPC) is used for monitoring limiting conditions of operation. The proposed change would revise the ASI allowable band to -0.23 and +0.28 when COLSS is operable and to -0.17 and +0.22 when COLSS is out-of-service.
Because of the higher radial power peaking factors anticipated for Cycle 2 caused by increased fuel enrichments and changes in the fuel reshuffling scheme, additional thermal margin is needes to offset some of the margin losses associated with these higher peaking factors. By narrowing the ASI band, the modeling uncertainties associated with COLSS and CPC calculations are reduced because of the less extreme axial power shapes. This reduction in uncertainties leads to an increase in thermal margin which is sufficient to compensate for the peaking factor margin losses.
Since the proposed changes to the ASI band are in a more restrictive direction and have been properly accounted for in the plant safety analyses using approved calculational methods, the changes are acceptable.
3.2 Moderator Temperature Coefficient Allowable Range (NPF-38-25)
The limitation on MTC specified in Technical Specification 3.1.1.3 is pro-vided to ensure that the MTC assumptions used in the plant safety analyses remain valid throughout the fuel cycle. The MTC varies slowly as a function of core burnup, due principally to the reduction in reactor coolant boron concentration with fuel burnup.
It is most positive at the beginning of cycle and becomes more negative with increasing burnup and decreasing l
boron concentration.
l TheproposedchangewouldlowertgeallowableMTCnegativelimitto-3.3x 10~4 delta k/k/*F from -2.5 x 10~ delta k/k/*F at all levels of thennal power.
This change is required to accomodate the higher fuel burnup at the end of the next fuel cycle as well as anticipated future cycles. A negative
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, MTC has an adverse effect on events which result in cooldown of the reactor coolant system since it results in a positive reactivity addition. Therefore, as part of the Cycle 2 reload analysis, the Waterford 3 FSAR Chapter 15 accident analyses were reviewed to determine if any reanalyses would be required due to the more negative MTC limit. The FSAR cooldown events adversely affected by a negative MTC were the Chemical Volume Control System (CVCS) malfunction (inadvertent boron dilution), steam line break, inadvertent opening of a steam generator atmospheric dump valve, increased main steam flow, and part-length or full-length control element assembly (CEA) drop
-3.3 x 10'gese were all analyzed in the FSAR with a negative MTC of at least events. T delta k/k/*F and, therefore, remain bounding. Of these events, the steam line break and full length CEA drop were reanalyzed for the Cycle 2 reload due to changes in core characteristics and reactor trip assu The reanalyses were performed assumino a negative MTC of -3.3 x 10 gptions.
delta k/k/ F and demonstrate continued compliance to the applicable NRC acceptance criteria in Section 15 of the Standard Review Plan for the Review of Safety Analysis Reports of Nuclear Power Plants (NUREG-0800).
TheproposedchangewillalsoincreasgtheallowableMTCpositiveIfmitator below 70% thermal power to +0.5 x 10~The current positive limit of 0.0 x 10 f F f delta k/k delta k/k/ F.
delta k/k/*F above 70% thermal power is not modified by this change. This change is required to accommodate the higher boron concentration in Cycle 2.
A positive MTC has an adverse effect on those events which involve an increase in moderator temperature since it results in a positive reactivity addition. These'heatup events are caused by a decrease in heat removal by the secondary system, a decrease in reactor coolant flow rate, or reactivity and power distribution anomalies.
In addition, it may also affect the reactivity insertion as a function of moderator density input to the LOCA evaluation. Except for the beginning-of-cycle CEA ejection event initiated from zero power, all other heatup events adversely affecteg by a positive MTC were analyzed in the FSAR assuming a value of +0.5 x 10' delta k/k/ F and, therefore, remain bounding.
In response to the staff's concerns about the CEA ejection event, the licensee stated that the ejected CEA worth for the zero power case in the FSAR analysis was 0.80% delta k/k compared to 0.49% delta k/k for Cycle 2.
This difference more than compensates for any possible additional reactivity added by the change in MTC from the l
Cycle 1 value to the more positive Cycle 2 value below 70% power. The staff l
agrees and concurs that the Cycle 2 CEA ejection results are bounded by those shown in the FSAR. Reanalysis of other events for Cycle 2 which are adversely affected by a positive MTC, such as the single reactor coolant pump sheared shaft, total loss of forced reactor coolant flow, and CEA withdrawal from
+0.5 x 10 j and low power conditions, were perfomed assuming a positive MTC of subcritica delta k/k/*F and demonstrate continued compliance to the applicable NRC acceptance criteria in Section 15 of the Standard Review Plan.
The small break LOCA analysis presented in the FSAR used the same full power MTC value that was used for Cycle 2.
In response to the staff's concern aboutthemorepositiveallowableMTCvalueforCycle2,thelicenseeindjcated that the reactor power must be less than 70% for the MTC to be +0.5 x 10- delta i
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. k/k*F. The small break Loss of Coolant Accident (LOCA) results are more sensitive to initial power (decay heat level) than to the MTC and the short 4
duration power change that a positive value causes before a reactor trip occurs. The reduction of the initial power more than compensates for a more positive MTC.
In addition, the very conservative treatment of the moderator reactivity feedback characteristics assure that the small break LOCA analysis presented in the FSAR is bnunding for Cycle 2.
The staff concurs with the above conclusions and finds, therefore, that the effect of the more positive MTC limit on small break LOCA results is acceptable.
3.3 Part-Lenoth Control Element Assembly Insertion Limits (NPF-38-26) i The PLCEAs are provided to help control the core power distribution, in-cluding the suppression of xenon induced axial power oscillations. Each PLCEA has three distinct axial sections: the lower 50% is Inconel; the next 40% consists of a follower section filled with water; the upper 10%
consists of boron carbide (similar to a full-length CEA).
Technical Specification 3.1.3.7 imposes limits on the allowable position of PLCEAs and on the allowable burnup interval during which the PLCEA may remain within allowable position range during Modes 1 and 2.
The Specification is intended to eliminate the potential for unexpected re-activity additions due to a PLCEA drop, prevent undesirable perturbations on the axial burnup distribution due to PLCEA insertion, and prevent high axial power peaking due to movement of the PLCEAs. When the PLCEAs are withdrawn between 0 and 17 inches, the highly absorbing boron carbide section remains partially within the active core and may create undesir-able perturbations on the axial burnup distribution. Therefore, the PLCEAs are currently limited to O to 17 inches withdrawn for a maximum period of 7 Effective Full Power Days (EFPD) out of any.30 EFPD.
For PLCEAS withdrawn more than 17 inches, the boron carbide section would be above the active core and any withdrawal position is allowed without-restriction.
The proposed change adds Figure 3.1-3 which allows a maximum PLCEA insertion l
.of 25% (112.5 inches withdrawn) during long term steady state operation above 20% power and allows a maximum transient PLCEA insertion of 85% (22.5 inches i
withdrawn) between 20% and 50% power for no longer than 7 EFPD out of any 30 EFPD period or 14 EFPD per calendar year. Since PLCEA insertion below 20%
power has a negligible effect on axial burnup distribution as well as on axial power peaking, any PLCEA insertion below 20% power is allowed. The proposed change, therefore, would impose more restrictive limits on allowable PLCEA l
insertion limits than do the current Technical Specifications above 20% of thermal power.
These more restrictive PLCEA insertion limits make the consequences of anticipated operational occurrences such as a PLCEA drop less severe than previously analyzed when any pre-drop position was allowable. These more restrictive limits also provice additional assurance that adverse axial shapes
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and rapid local power changes which affect radial power peaking factors and l-DNB considerations do not occur as a result of the PLCEAs being positioned in the sanie axial segment of fuel assemblies for an extended period of time.
l l
, l Therefore, since the proposed change imposes more restrictive limits as l
well as surveillance requirements to ensure adherence to these limits, and i
results in improvements in the potential consequences of related anticipated operational occurrences, the staff finds it acceptable.
3.4 PLCEA Insertion Limits During Startup Testing (NPF-38-27)
In order to perform certain startup tests such as the verification of radial peaking factors and the measurement of control element assembly (CEA) worths, it is necessary to insert the PLCEAs beyond the insertion limits specified in Technical Specification 3.1.3.7.
This is similar to the currently allowed suspension of the insertion limits for full-length CEAs during these startup tests for Waterford and other Combustion Engineering (CE) plants.
In addition, the linear heat rate is required to be monitored continuously during these tests, which are relatively short in duration, to assure that the operating safety limits are maintained. Therefore, the staff concludes that this test exception on PLCEA insertion limits is acceptable.
4.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Administrator, Nuclear Energy Division, Department of Environmental Quality, State of Louisiana of the proposed determination of no significant hazards consideration. No comments were received.
5.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes in the installation or use of facility components located within the restricted area. The staff has determined that the amendment involves no significant increase in the amounts 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 proposed findings that the amendment involves no significant hazards consideration, and there has been no public coninent on such findings. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(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 this amencment.
6.0 CONCLUSION
Based upon our evaluation of the proposed changes to the Waterford 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 Conunission'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.
We, therefore, conclude that the proposed changes are acceptable, and are hereby incorporated into the Waterford 3 Technical Specifications.
Dated:
January 16, 1987 l
Principal Contributor:
L. Kopp l
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