ML20212K963
| ML20212K963 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 10/01/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212K958 | List: |
| References | |
| NUDOCS 9910070115 | |
| Download: ML20212K963 (6) | |
Text
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ye UNITED STATES l
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 20066-0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION Egl_ATED TO AMENDMENT NO.144 TO FACILITY OPERATING LICENSE NO. NPF-2 l
AND AMENDMENT NO.
135 TO FACILITY OPERATING LICENSE NO. NPF-8 SOUTHERN NUCLEAR OPERATING COMPANY. INC.. ET AL.
JOSEPH M. FARLEY NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-348 AND 50-364
1.0 INTRODUCTION
Southern Nuclear Operating Company's (SNC's) letter of November 6,1998, requested changes to the Joseph M. Farley Nuclear Plant, Units 1 and 2, Technical Specifications (TS).
The requested changes would revise nuclear instrumentation system (NIS) surveillance requirements. When operating above 15 percent rated thermal power (RTP), the current Farley TS require SNC to adjust the NIS power range (PR) channels when the absolute difference
( ) between the NIS PR indicated power and the secondary side calorimetric-calculated power is > 2 percent RTP. Complying with this TS requirement might result in a nonconservative channel calibration during reduced power operations. The proposed TS changes require SNC to adjust the NIS PR channels only when calorimetric-calculated power is greater than the PR indicated power by more than + 2 percerit RTP. SNC stated that the proposed TS changes will l
prevent unnecessary adjustments of the NIS PR channels and reduce operational challenges.
The proposed TS changes are for both the current TS (CTS) and the improved TS (ITS). The CTS change is in Table 4.3-1 and the ITS changes are in SR 3.3.1.2 and its Bases. The ITS Bases changes also explain adjusting the PR neutron flux - high bistable settings to s 85 percent RTP when adjusting the NIS PR channel below 50 percent RTP or during a
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post refueling startup.
2.0 BACKGROUND
in 1996, Westinghouse identified that at less than about 70 percent RTP there is uncertainty in the calometric-power calculation that might result in non-conservative NIS PR channel calibration. Westinghouse issued Technical Bulletin ESBU-TB-9214 R1,"Decalibration Effects Of Calorimetric Power Measurements on the NIS High Power Reactor Trip At Power Levels Less Than 70% RTP," on February 6,1996, and made six recommendations to resolve the uncertainty.
SNC stated that feedwater flow measurement (typically measuring AP across a feedwater venturi) is the primary error contributor to instrument uncertainty when calculating secondary-side calorimetric power. While the AP measurement uncertainty remains constant as power Enclosure 9910070115 991001 PDR ADOCK 05000348 i
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i 2-decreases, the uncertainty increases as a square term when translated into flow. Thus, a 1 percent flow error at 100 percent power can approach a 10 percent error at 30 percent RTP even though the AP error has not changed. ESBU-TB-92-14 R1 described how the potential effects of this error increase at lower power levels. An example in the Technical Bulletin shows that for a 10 percent error in secondary-side calorimetric-calculated power, the NIS PR could be i
non-conservatively biased enough to prevent a reactor trip assumed in the safety analyses.
This event is rod withdrawal from 10 percent RTP for the Farley plant.
Westinghouse Technical Bulletin ESBU TB-92-14-R1 recommendation No. 6 conflicts with the Farley TS PR daily surveillance requirement. Recommendation No. 6 suggests that if the NIS PR indicates a higher power than the secondary side calorimetric-calculated power measurement at power levels below approximately 70 percent, the PR channel (s) should not be adjusted. However, the Farley TS requires PR channel adjustment whenever the absolute difference is > 2 percent above 15 percent RTP.
In response to ESBU-TB-92-14-R1, SNC determined that the 2 percent RTP calometric-calculated power measurement uncertainty is valid for power levels 2 50 percent RTP based on the Farley-specific calorimetric measurement procedure. Farley also determined that resetting the NIS PR high neutron flux-high setpoint reactor trip to s 85 percent RTP is an acceptable administrative addition to adjusting the NIS PR channel to reflect the calometric-calculated power below 50 percent RTP. SNC is adding this to the ITS Bases.
The Westinghouse Owners Group initiated a program (MUHP-3034) to obtain NRC approval to relax the present TS requirements to always adjust NIS channels when indicated power differs from calometric-calculated power by more than 2 percent. Farley is the lead plant for this generic program.
3.0 EVALUATION SNC analyzed the impact of the proposed NIS PR surveillance changes on the Farley licensing basis and demonstrated that the proposed changes will not adversely affect safe plant operation. We evaluate SNC's proposed TS changes below.
3.1 NIS PR Indication and Reactor Trip System (RTS) Functions When operating above 15 percent RTP, Farley plant operators daily normalize (i.e., calibrate) each PR channel to match thermal power calculation results from a secondary-side calorimetric heat balance, SNC's proposed changes to the NIS PR daily surveillance TS requirements potentially impact the following:
PR indications RTS functions control system functions a
l miscellaneous alarm functions We discuss each of these below.
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3-3.1.1 PR Indications SNC stated that plant operators monitor reactor power to ensure that they operate the unit within the limits of the Facility Operating License and safety analyses. SNC's proposed daily PR surveillance requirements will have a conservative effect on PR channel indication (i.e., indicated power will be greater than actual power). With regard to safety limits, reactor l'
power is one of the parameters used in the Revised Thermal Design Procedure (RTDP). The RTDP safety analyses assume a reactor power uncertainty of
- 2 percent RTP. The proposed
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i PR surveillance changes do not invalidate the Farley-specific uncertainty calculation.
Therefore, the RTDP and safety analyses reactor power uncertainty assumption of 2 percent RTP continues to be a bounding allowance for the core safety limits and safety analyses.
3.1.2 RTS Functions SNC performed plant specific calculations for the high neutron flux-high reactor trip setpoint, the high neutron flux-low reactor trip setpoint, and permissives P-8, P-9, and P-10. SNC's setpoint uncertainty calculations demonstrated that there is a conservative margin between the TS nominal trip setpoints and safety analyses limits. The proposed changes do not affect the
. PR high-positive and high-negative rate reactor trips since they are generated by relative comparison circuits.-
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'SNC also studied the effect of the proposed changes on the permissive P-10 reset delay and determined that the time for P-10 reset would be very short. During this brief period, the PR high neutron flux-high setpoint reactor trip would provide core protection. The PR high positive j
rate, overtemperature delta temperature, and overpower detta temperature reactor trips provide l
' additional protection. Therefore, the proposed TS changes do not adversely affect PR RTS functions. ~ '
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3.1.3 ' Control System Functions SNC studied the control functions affected by PR inputs including the following:
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' Control interlock C-2 which blocks automatic and manual control rod withdrawal.-
Nuclear power input signal PR-44 which controls reactor coolant system (RCS) i i
= temperature.
These controls are not required for plant safety. Furthermore, the proposed TS changes will not adversely impact the NIS PR control functions since the changes will limit the maximum allowed non-conservative calibration error.
3.1.4 Miscellaneous Alarm Functions L
The NIS PR channels provide input signals to the PR channel deviation, quadrant power tilt ratio (OPTR), and N-16 leakage detection systems. The proposed TS changes will not affect the PR channel deviation and QPTR alarms since they are generated by comparing PR channel outputs.
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The N-16 leakage detection system may cause some control room alarms because the 1
proposed TS changes will allow NIS indicated power to be greater than the calometric-calculated power. However, SNC considers such alarms to be acceptable on the following grounds:
The N-16 leakage detection system is a non-safety-related system used as an operational aid.
Other radiation monitors such as the air-ejector and steam generator blowdown monitors provide continuous primary to-secondary leakage indication.
TS surveillance requirements specify periodic RCS leakage checks.
a SNC uses radiochemistry analysis to determine primary-to-secondary leak rates.
Plant operators will adjust the PR channels daily when the plant is operating at nearly full power.
3.2 Loss-of-Coolant Accident (LOCA) and LOCA-Related Analyses SNC stated that the proposed TS changes do not adversely affect the following LOCA and LOCA-related analyses:
i large and small-break LOCA a
reactor vessel and loop LOCA blowdown forces post-LOCA long term cooling subcriticality post-LOCA long-term core cooling minimum flow hot-leg switchover to prevent boron precipitation The proposed TS changes do not affect normal plant operating parameters, safeguards systems actuation or accident mitigation capabilities important to LOCA mitigation, or LOCA related accident assumptions. The surveillance changes do not create conditions more limiting than those assumed in these analyses. Also, the proposed TS changes do not affect analysis methodology or assumptions and do not alter the steam generator tube rupture event analysis results.
3.3 Non-LOCA Related Analyses SNC stated that the proposed NIS PR surveillance TS changes do not adversely affected non-LOCA safety analyses presented in FSAR Chapter 15. These changes do not affect normal plant operating parameters, accident mitigation capabilities, non-LOCA transient assumptions, or create conditions more limiting than those enveloped by the current non-LOCA analyses. Therefore, the conclusions presented in the FSAR remain valid.
3.4 Mechanical Components and Systems SNC stated that the proposed TS surveillance changes do not affect RCS component integrity or the ability of a plant auxiliary system to perforrn its design function.
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3.5 Other Safety-Related Areas and Analyses SNC stated that the proposed TS surveillance changes do not affect the following safety-related areas and analyses:
containment integrity analysis (short term /long term LOCA release) main steam line break mass and energy release radiological analyses a
probabilistic risk assessment emergency response procedures 3.6 ITS Bases Changes The ITS Bases contain more information than the CTS Bases do. Accordingly, SNC added additionalinformation to the ITS Bases to explain adjusting the PR neutron flux high bistable setting to s 85 percent RTP 1) whenever the NIS PR channelis set below 50 percent RTP, or
- 2) during a post refueling startup and reset back to TS nominal setpoint of < 109 percent RTP when the thermal power is increased above 50 percent RTP. The CTS Table 3.3.1-1 PR neutron flux high reactor trip setting is 109 percent RTP which corresponds to a safety analysis limit of 118 percent RTP. Westinghouse Technical Bulletin ESBU-TB-92-14JR1 indicates that a two loop plant may have 10 percent normalization error at 30 percent RTP in the worst case.
This would cause about 40 percent RTP difference between indicated and actual power at 120 percent RTP. The staff determined that with the plant at 50 percent power and the PR neutron flux-high bistable set at 85 percent RTP, if thermal power increases to 120 percent RTP then the maximum difference between the indicated power and the calculated power will be about 24 percent RTP. This is equivalent to a 109 percent (85 percent + 24 percent) RTP reactor trip setting. This resolves the limitations mentioned in the Westinghouse Technical Bulletin. SNC is presently making this PR neutron flux-high bistable adjustment under a plant procedure ar.d proposes to continue adjusting it permanently.
3.7 Staff Conclusions SNC's proposed TS changes are based on Westinghouse Technical Bulletin ESBU TB-92-R1 recommendations and SNC's plant specific evaluations support the changes. Specifically, setting the PR neutron flux-high bistable to s 85 percent RTP 1) whenever the NIS indicated power is adjusted in the decreasing power direction below 50 percent RTP, or 2) before post refueling startup effectively addresses the current TS limitations mentioned in the Westinghouse bulletin. Based on the above Section 3.0 evaluation, the staff concludes that the proposed CTS and ITS changes are acceptable. We are processing the ITS changes separately under the ITS Conversion program.
4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the State of Alabama official was notified of the proposed issuance of the amendments. The State official had no comments.
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5.0 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 the surveillance requirements. The NRC 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
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occupational radiation exposure. The Commission has previously issued a proposed finding i
that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (64 FR 4160, dated January 27,1999). 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 environmental impact statement or i
environmental assessment need be prepared in connection with the issuance of the j
amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that (1) there is reasonable 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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
i Principal Contributors: H. Balukjian S. Mazumdar Date:
October 1, 1999 t
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