ML20198S523
| ML20198S523 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/31/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198S509 | List: |
| References | |
| NUDOCS 9901110352 | |
| Download: ML20198S523 (5) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 300eH001
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3 SACETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.196 TO FACILITY OPERATING LICENSE NO. NPF-6 ENTERGY OPERATIONS. INC.
ARKANSAS NUCLEAR ONE. UNIT NO. 2 DOCKET NO. 50-368
1.0 INTRODUCTION
i By letter dated September 17,1998, Entergy Operations, Inc. (the licensee) submitted a request for changes to the Arkansas Nuclear One, Unit 2 (ANO 2), Technical Specificat!ons (TSs). The requested changes would resolve one technical deficiency identified by the licensee and provide clarifying statements in two general areas affecting the ANO-2 TSs. In addition, following discussions with the licensee, the staff has taken this opportunity to make a clarifying change in the use of the term " Rated Thermal Power" when referring to the high logarithmic power level trip setpoint and other power level setpoints in the source and intermediate range.
Although the editorial change clarifying the use of the term " Rated Thermal Power" was not included in the licensee's sPmittal, the staff finds that it is consistent with other editorial changes discussed and, therefore, did not change the initial proposed no significant hazards consideration determination.
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2.0 EVALUATION 2.1 Hiah Loaarithmic Power Level and Core Power Calculator Trio Bvoass Permissives The first change involves the use of the high logarithmic power level and the core power calculator (CPC) trip bypass permissives associated with tne design of the plant protection system (PPS). The PPS encompasses both the reactor protective system (RPS) which generates the signals required to actuate a reactor trip and the engineered safety features actuation system (ESFAS) which generates the signals required to actuate the engineered safety features (ESF) designed to mitigate the consequences of postulated accidents. Operating bypass features are used during routine reactor startup and shutdown evolutions to minimize the potential for unwanted ESF actuations or reactor trips when the specific protection is not required based on plant conditions. These operating bypasses can be manually inserted when the permissive logic is satisfied. The operating bypasses are designed to be removed automatically when plant conditions reach a point where the trip function is necessary. Per FSAR Section 7.2.2.2.2, the high logarithmic power level trip is designed to ensure protection for unplanned criticality from a shutdown condition resulting from a boron dilution or control element assembly (CEA) withdrawal events. This trip must be in effect and the manual bypass automaticaliy removed for power levels at or below 10E-4 percer't power as measured from the ex core neutron flux monitoring system.
9901110352 981231 PDR ADOCK 05000368 P
. This requirement is specified in TS Table 2.2-1, " Reactor Protective Instrumentation Trip Setpoint Limits," note (1) and Table 3.3-1, " Reactor Protective Instrumentation," note (a). The trip bypass permissive is satisfied for power levels above 10E-4 percent power. The CPC generated trips with bypass permissives are the low departure from nuc'eate boiling ratio (DNBR) trip and the high local power density (LPD) trip. Per FSAR Sections 7.2.2.2.3 and 7.2.2.2.4, these trips are provided to ensure that the core does r.ot exceed its design fuel limits during power operations.
These trips must be in effect and the manual bypass automatically removed for power levels at or above 10E-4 percent power as measured from the ex-core neutron flux monitoring system. This requirement is specified in TS Table 2.2-1, note (5) and Table 3.3-1, note (c). Therefore, the high j'
logarithmic power level and the above mentioned CPC generated trips are required to be active at j
10E-4 percent power.
i The design of the PPS at ANO 2 utilizes a single bistable to control the permissives for these trips. The single bistable control of these functions ensures that CPC trip protection is sutomatically enabled any time that a permissive exists to bypass the high logarithmic Nwer level trip. Likewise, the bistable function ensures that high logarithmic power level trip protection is automatically enabled any time a permissive exits to bypass the CPC generated trips. The CPC operating bypass at ANO 2 is currently removed automatically at the setpoint value of the bistable on an increasing signal. The high logarithmic power level trip operating bypass is automatically removed at the reset value of the bistable on a decreasing signal. The reset value of the bistable is below its setpoint value by the deadband characteristic of the bistable. This design makes it physically impossible to comply with both TS notes simultaneously because both functions can not be physically set at 10E-4 percent power. Historically, ANO-2 has established the bistable setpoint at a value that automatically removes the CPC bypass before exceeding 10E-4 percent power during startup. This results in the bypass for the high logarithmic power level trip not being automatically removed until power decreases to the reset value of the bistable which is slightly less than 10E-4 percent power. The proposed change would be to establish a range between 10E-4 and 10E-2 percent power for the automatic removal of the bypass for the high logarithmic l
power level trip and the CPC generated trips in order to permit future TS compliance. The TS requirement will be such that the CPC generated trips will automatically come out of bypass before power exceeds 10E 2 percent power. The CPC generated trips will be allowed to be manually bypassed below 10E-2 percent power. The requirements for the high logarithmic power level trip will continue to be required to automatically come out of bypass before power decreases below 10E-4 percent power and will continue to allow manuel bypassed above 10E-4 percent power. This change effects TS Table 2.2-1, notes (1) and (5); Table 3.3-1, notes (a) and (c);
Bases 2.2.1; and Bases 3/4.3.
The proposed change does not alter the existing requirements for the high logarithmic power level trip. The high logarithmic power level trip is credited in providing protection in the event of an uncontrolled boron dilution incident or an uncontrolled CEA withdrawl from suberitical conditions.
The trip setpoint is 0.75 percent power. The manualinitiation of the high logarithmic power level i
trip operating bypass only occurs during a controlled power increase and thus these trips would j
not be bypassed if the power increase was due to an inadvertent reactivity addition. :n addition, i
since there is only a short period of time between the bypass permissive and the high logarithmic i
power trip, it is assumed in the analysis that this trip remains active and is not bypassed. The i
prcposed change does not impact the analysis assumptions, the trip setpoint, or the range over l
which this trip is required. Since the bypass permissive feature for this trip is linked to the setpoint for automatic removal of the CPC generated trip operating bypasses via the bistable design f
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3-feature, the proposed change may result in the setting of the bypass permissive for the high logarithmic power trip at a higher power level. This condition is conservative in nature and will not prevent the trip from performing its design function.
The proposed change does impact the point at which the operating bypass for the CPC generated trips must be automatically removed. The proposed change would raise the power level for this requirement from 10E-4 percent power to 10E-2 percent power. The CEA bank withdrawl event from hot zero power (HZP) critical conditions was analyzed for ANO-2 with the reactor initially assumed to be critical at a power level of 10E-4 percent power. This value was chosen as the lowest power level for which the high logarithmic power level trip can be manually bypassed maximizing the amount of positive reactivity inserted prior to the initiation of a reactor trip. The analysis demonstrated that the CEA bank continues to withdrawl until the CPC variable overprower trip (VOPT) provides a trip function at 30 percent power. Neither the low DNBR trip or the high LPD trip are credited for this event. Therefore, the change to 10E-2 percent power for the automatic removal of operating bypasses for the CPC generated trips does not impact the existing analysis. Thus, the low DNBR trip and high LPD trip will be automatically enabled with an initial power level allcwing sufficient response time such that these trips can perform their design function for all credited anticipated operation occurrences and accident conditions.
The single bistable control of these functions ensures that CPC generated trip bypass is automatically removed any time that a permissive exists to bypass the high logarithmic power level trip. Likewise, the bistable function ensures that high logarithmic power level trip protection is automatically enabled any time a permissive exits to bypass the CPC generated trips. This design feature provides positive control to ensure that one of the two trip functions is in effect over the entire range of power such that at no point can both the high logarithmic power level trip and the CPC generated trips be simultaneously bypassed. Therefore, the staff finds the proposed change to be acceptable.
2.2 Low Pressurizer Pressure Trio Bvoass Permissive T he second change was a clarification for the wording of the setpoint for the automatic removal of the bypass permissive for the low pressurizer pressure trip. This change affects TS Table 2.2-1,
" Reactor Protective Instrumentation Trip Setpoint Limits," note (2); Table 3.3-1, " Reactor Protective Instrumentation," note (b); Table 3.3 3," Engineered Safety Feature %tuation System Instrumentation," note (a); Table 3.3-4," Engineered Safety Feature Actuation System Instrumentation Trip Values," note (1); and Bases 3/4.3. This clarification was made to promote consistency for the table notes with respect to other changes authorized by this amendment. This changes is editorial in nature and does not impact the limitation of the TSs. Therefore, the staff concludes that the licensee's proposal is acceptable.
2.3 Soecial Test Excer/sns The third change will add TS Table 2.2-1 to the discussion of TS 3.10.3,"Special Test Exceptions
- Reactor Coolant Loops," which allows the suspension of certain requirements during the performance of startup and physics testing. TS Table 3.3-1 is already discussed by TS 3.10.3.
The addition of TS Table 2.2-1 to the discussion of TS 3.10.3 correct : an omission that occurred in the originalissuance of TS 3.10.3. This change does not impose any new requirements nor relax existing restrictions. This change is an editorial clarification intended to eliminate confusion
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' I that could be created by suspending the application of TS Table 3.3-1 without simultaneously including TS Table 2.2-1 during startup and physics testing. Therefore, the staff concludes that the licensee's proposal is acceptable.
2.4 Clarification Reaardina The Definition Of Rate Thermal Power i
in addition, following discussions with the licensee, the staff has taken this opportunity to make a clarifying change in the use cf the term " Rated Thermal Power" when referring to the high logarithmic power level trip setpoint and other power level setpoints in the source and intermediate range. The term " Rated Thermal Power" will be replacea with the term " Power" for these cases. The following areas of the TSs are effected: TS Table 2.2-1," Reactor Protective l
Instrumentation Trip Setpoint Limits," item 1, notes (1) and (5); TS Table 3.3-1, " Reactor Protective Instrumentation," notes (a) and (c); and Bases 2.2.1. Per TS definition 1.3, Rated l
Thermal Power is described as the total reactor core heat transfer rate to the reactor coolant of l
2815 MWt. Thus, rated thermal power is a composite term that describes the combined effect of l
fission power and decay neat as compared to the licensed thermal power for the reactor coolant system. The decay heat component of rated thermal power results in an erroneous application of l
this term to power levels in the source and intermediate range follow initial plant startup. Per i
l FSAR Section 7.2.2.2, the ex-core neutron flux monitoring system which monitors neutron flux l
rather then the combination of neutron flux and decay heat is provided as an input value for the l
high logarithmic power level trip and the CPC generated trips. Therefore, a clarification was
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made to replace " Rated Thermal Power" with " Power" to eliminate the potential for confusion.
l The staff has taken this opportunity to implement this c!arification based on the experience with l
other plants (e.g., San Onofre Nuclear Generating Station, Unit 2 and Waterford Steam Electric Station, Unit 3) which have required this change on an emergency basis. This change is l
considered to be an appropriate clarification. Therefore, the staff concludes that this change is l
acceptable.
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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 comment.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change 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 change surveillance requirements. The Nuclear Regulatory Commission staff has determined that the amendments involve 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 proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding (63 FR 56247). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no i
environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
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5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safciy of the public will not be endangered by operation.
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in the proposed manner, (2) such activities will be conducted in compliance with the Commissio'n's l
. regulations, and (3) the issuance of the amendments will not be inimical to the common defense
- and security or to the health and safety of the public.
Principal Contributor: Chris Nolan Date:
December 31, 1998 l
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