L-25-160, Emergency License Amendment Request for Technical Specification 3.3.9 to Allow Use of Alternate Neutron Instrumentation
| ML25229A001 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 08/17/2025 |
| From: | Winn H FirstEnergy Nuclear Operating Co, Vistra Corp |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-25-160 | |
| Download: ML25229A001 (1) | |
Text
August 17, 2025 L-25-160 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Davis-Besse Nuclear Power Station, Unit No.1 Docket No. 50-346, License No. NPF-3 Davis-Besse Nuclear Power Station Heather J. Winn Plant Manager 5501 N. State Route 2 Oak Harbor, Ohio 43449 10CFR50.90 10CFR50.91 Emergency License Amendment Request for Technical Specification 3.3.9 to Allow Use of Alternate Neutron Instrumentation In accordance with the provisions of Section 50.90 of Title 10 of the Code of Federal Regulations (10 CFR), Vistra Operating Company LLC is submitting a request for an amendment to the facility operating license for Davis-Besse Nuclear Power Station, Unit No.1 (DBNPS). The proposed change would revise Technical Specification (TS) 3.3.9 Source Range Neutron Flux, to allow the use of alternate neutron instrumentation during startup from the current forced outage and through the end of the current operating cycle (Cycle 24), which is scheduled to end in March 2026.
The proposed license amendment is being requested on an emergency basis for DBNPS pursuant to 10 CFR 50.91(a)(5).
The proposed changes have been reviewed and approved by the Plant Operations Review Committee in accordance with administrative procedures and the quality assurance program manual. provides a description and evaluation of the proposed changes including a discussion of the emergency circumstances at DBNPS. Attachment 2 provides the proposed changes to the TS. Attachment 3 provides TS pages re-typed for information and attachment 4 provides markups of TS Bases pages for information.
Vistra Operating Company LLC requests approval of the proposed license amendment as soon as possible and no later than August 17, 2025 to support resumption of operation.
Davis-Besse Nuclear Power Station, Unit No. 1 L-25-160 Page2 There are no regulatory commitments contained in this submittal. If there are any questions, or if additional information is required, please contact Mr. Jack Hicks, Senior Manager, Licensing, at Jack.Hicks@vistracorp.com.
I declare under penalty of perjury that the foregoing is true and correct. Executed on August 17, 2025.
Sincerely, Attachments:
- 1.
Evaluation of the Proposed Change
- 2.
Proposed Technical Specification Pages Markup
- 3.
Proposed Technical Specification Pages Re-typed (for information only)
- 4.
Proposed Technical Specification Bases Page Markups (for information only) cc:
NRC Region III Administrator NRC Resident Inspector NRC Project Manager Utility Radiological Safety Board Executive Director, Ohio Emergency Mgmt. Agency
L-25-160 Evaluation of the Proposed Change Page 1 of 8
Subject:
Emergency License Amendment Request for Technical Specification 3.3.9 to Allow Use of Alternate Neutron Instrumentation 1.0
SUMMARY
DESCRIPTION 2.0 DETAILED DESCRIPTION 2.1 System Design and Operation 2.2 Current Technical Specification Requirements 2.3 Reason for the Proposed Change 2.4 Description of the Proposed Change 2.5 Emergency Circumstances
3.0 TECHNICAL EVALUATION
3.1 Defense-in-Depth 3.2 Safety Margin Evaluation 3.2 Compensatory Measures 3.3 Evaluation of Risk Impacts
4.0 REGULATORY EVALUATION
4.1 Applicable Regulatory Requirements I Criteria 4.2 No Significant Hazards Consideration Analysis 4.3 Conclusion
5.0 ENVIRONMENTAL CONSIDERATION
L-25-160 Page 2 of 8 1.0
SUMMARY
DESCRIPTION Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.90, Application for amendment of license, construction permit, or early site permit, and 10 CFR 50.91(a)(5), Notice for public comment; State consultation, Vistra Operations Company (Vistra OpCo) is requesting an emergency license amendment to the Davis-Besse Nuclear Power Station, Unit No. 1 (DBNPS) Technical Specifications (TS).
The proposed change would revise Technical Specification (TS) 3.3.9, Source Range Neutron Flux, to allow the use of alternate source range neutron monitoring instrumentation (Gamma-Metrics) per TS Table 3.3.17-1, Post Accident Monitoring Instrumentation, Function 17, during startup from the current forced outage. The proposed change is only applicable during the current operating cycle (Cycle 24), as Davis-Besse intends to perform permanent repairs no later than the March 2026 refueling outage.
2.0 DETAILED DESCRIPTION 2.1 System Design and Operation The Reactor Protection System (RPS) source range neutron flux channels provide the operator with an indication of the approach to criticality at lower power levels than can be seen on the intermediate range neutron flux instrumentation. These channels also provide the operator with a flux indication that reveals changes in reactivity and helps to verify that shutdown margin (SDM) is being maintained.
The source range instrumentation has two redundant count rate channels originating in two high sensitivity proportional counters. Two source range detectors are externally located on opposite sides of the core 180°. These channels are used over a counting range of 0.1 counts per second (cps) to 1E6 cps and are displayed on the operator's control console in terms of log count rate. The channels also measure the rate of change of the neutron flux level, which is displayed for the operator in terms of startup rate from -0.5 decades to +5 decades per minute. An interlock provides a control rod withdraw "inhibit" on a high startup rate of +2 decades per minute in either channel.
The proportional counters of the source range channels are BF3 chambers. The detector high voltage is automatically turned off when the flux level is approximately one decade above the useful operating range. Conversely, the high voltage is turned on automatically when the flux level returns to within approximately one decade of the detectors' maximum useful range. High voltage will be turned off automatically when the flux level is above 1E-9 amp in both intermediate range channels, or 10% power in power range channels (i.e., NI-5 or NI-6 and NI-7 or NI-8).
The source range neutron flux channels have no safety function and are not assumed to function during any Updated Final Safety Analysis (UFSAR) design basis accident or L-25-160 Page 3 of 8 transient analysis. However, the source range neutron flux channels provide on scale monitoring of neutron flux levels during startup and shutdown conditions. Therefore, they are being retained in Technical Specifications.
Two source range neutron flux channels shall be OPERABLE in MODE 2 to provide redundant indication during an approach to criticality. Neutron flux level is sufficient for monitoring on the intermediate range and on the power range instrumentation prior to entering MODE 1; therefore, source range instrumentation is not required in MODE 1.
2.2 Current Technical Specification Requirements Limiting Condition of Operations (LCO) 3.3.9 requires two source range neutron flux channels to be OPERABLE in MODES 2, 3, 4, and 5. If one source range neutron flux channel is inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux channels, the channel must be restored to OPERABLE status prior to increasing neutron flux. If one or more source range neutron flux channels are inoperable with neutron flux > 1E-10 amp on the intermediate range neutron flux channels, action to restore the channel(s) to OPERABLE status must be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
2.3 Reason for the Proposed Change This change would allow the use of Gamma-Metrics neutron flux detectors to monitor neutron flux during power accension when a source range instrument is inoperable.
The Gamma-Metrics detectors are included in Davis-Besse Technical Specifications 3.3.17-1.
2.4 Description of the Proposed Change The proposed change would credit the use of TS Table 3.3.17-1 Function 17 Neutron Flux (Source Range) as part of LCO 3.3.9 Condition A and C Required Actions if one source range neutron flux channels is inoperable. Source Range Neutron Flux (Gamma-Metrics) is a Category 1 variable provided to verify the reactor is subcritical.
Gamma-Metrics instrumentation consists of two channels. Each channel consists of a fission chamber with a range from 1E-1 cps to 1E5 cps. Continuous indicators have been provided in the PAM panels located in the control room. This change is only appliable during Cycle 24. The included attachments illustrate the proposed changes to TS 3.3.9.
2.5 Emergency Circumstances Why the Condition Occurred:
On August 12, 2025, Davis-Besse entered a forced outage to repair a leak on a steam generator level transmitter sensing line. During Mode 4 operations on August 13th at approximately 0930, SRNI2 failed to zero cps. A Problem Solving Decision Making Team was formed, and has been working both shifts since the beginning of the forced outage.
L-25-160 Page 4 of 8 Why the Situation Could Not Be Avoided:
The team performed a failure modes analysis and efforts to rule out failure modes, have guided the troubleshooting, from the detector to instrumentation cabinet and indicators.
There have been substantial efforts to restore SRNI2 to operable status through maintenance and engineering activities involving site and Vistra fleet subject matter experts and specialized vendor services.
With submittal of this request, the inoperability of SRNI2 remains the single resolution required prior to the resumption of power operation.
3.0 TECHNICAL EVALUATION
3.1 Defense-in-Depth The Reactor Protection System (RPS) source range neutron flux channels provide on scale monitoring of neutron flux levels during startup and shutdown conditions over a counting range of 10E-1 cps to 10E+6 cps. The channels also measure the rate of change of the neutron flux level, which is displayed for the operator in terms of startup rate from -0.5 decades to +5 decades per minute. The RPS source range channels are de-energized with neutron flux > 1E-10 amp on the intermediate range channels.
In a comparable manner, the Gamma-Metrics neutron flux detectors consist of two (2) safety grade, Class 1E, electrically independent, physically separated fission chamber radiation level instrument strings, with the capability of a calibrated range to include a source range (10E-1 to 10E+5 cps) and wide range indication (10E-8 to 2 x 10E+2 percent power) indications in the Control Room. The two (2) Gamma-Metrics neutron flux detectors are physically located on opposite sides of the reactor vessel as are the RPS source range nuclear instruments.
3.2 Safety Margin Evaluation Neither source range nor intermediate range neutron flux channels have a safety function and are not assumed to function during any UFSAR design basis accident or transient analysis. These neutron flux channels provide on scale monitoring of neutron flux levels during startup and shutdown conditions A control rod withdraw "inhibit" on a high startup rate of +2 decades per minute from the operable source range channel as well as +3 decades per minute in either Intermediate Range RPS nuclear instrument channel. These source and intermediate range functions are the same as Three Mile Island Unit One, for which the respective Limiting Condition requires 1 minimum channel operable and zero minimum degree of redundancy. Per UFSAR 7.8.1, a functioning interlock from either the source or intermediate range is not assumed in any accident analysis.
L-25-160 Page 5 of 8 3.3 Compensatory Measures No compensatory measures are needed as a result of the proposed change.
3.4 Evaluation of Risk Impacts NRC Regulatory Guide 1.174 provides an approach that is acceptable to the staff of the U.S. Nuclear Regulatory Commission (NRC) for developing risk-informed applications for a licensing basis change that considers engineering issues and applies risk insights.
It provides general guidance concerning analysis of the risk associated with proposed changes in plant design and operation.
NRC Regulatory Guide 1.177 provides an approach that is acceptable to the staff of the U.S. Nuclear Regulatory Commission (NRC) for developing risk-informed applications for changes to completion times (CTs) and surveillance frequencies (SFs) of plant technical specifications (TS). This RG provides specific guidance for considering engineering issues and using risk information to evaluate nuclear power plant TS changes to CTs and SFs. Section 2.4 (Acceptance Guidelines for Technical Specification Changes) of Regulatory Guide 1.177 Rev. 2 provides (in part) the following related to one-time CT changes:
The following TS acceptance guidelines specific to one-time only CT changes are provided for evaluating the risk associated with the revised CT:
- a. The licensee has demonstrated that implementation of the one-time only TS CT change impact on plant risk is acceptable (Tier 1):
- 2. ICCDP of less than 1.0x10-5 and an ICLERP of less than 1.0x10-6 with effective compensatory measures implemented to reduce the sources of increased risk.
- b. The licensee has demonstrated that there are appropriate restrictions on dominant risk significant configurations associated with the change (Tier 2).
- c. The licensee has implemented a risk-informed plant configuration control program, including the procedures to use, maintain, and control such a program (Tier 3).
The three tiers of the guidelines are assessed below:
Tier 1:
The source range neutron flux channels have no safety function and are not assumed to function during any UFSAR design basis accident, transient analysis, or PRA modeled accident sequence. Therefore, the source range neutron flux channels are not modeled in the PRA and the proposed change does not result in an increase in Core Damage Frequency or Large Early Release Frequency.
L-25-160 Page 6 of 8 Thus, ICCDP and ICLERP are zero, which is well below the acceptance criteria specified in Regulatory guide 1.177.
Tier 2:
Since there is no change in CDF or LERF due to this change, there are no dominant risk significant configurations associated with the change, and no additional restrictions are required.
Tier 3:
Configuration risk is managed in accordance with 10CFR50.65(a)(4), using Phoenix Risk Monitor to track planned and emergent work to determine impact to configuration risk. Since this change does not impact plant risk, continued normal online risk management will adequately monitor plant risk.
4.0 REGULATORY EVALUATION
4.1 Applicable Regulatory Requirements / Criteria This activity involves changes to the operating license Appendix A, Technical Specifications; therefore, in accordance with 10 CFR 50.90, this activity requires an amendment. As such, NRC approval is required prior to making the proposed changes in this license amendment request.
10 CFR 50.91(a)(5) provides the requirements to be met to allow the NRC to perform expedited approval of a license amendment in an emergency situation. Vistra Operating Company LLC (Vistra OpCo) is requesting emergency processing of this license amendment request, as a delay in approval of the proposed changes would result in derating or shutdown of a nuclear power plant, or in prevention of either resumption of operation or of increase in power output up to the plant's licensed power level.
Accordingly, this license amendment request satisfies the criteria for the Commission to issue a license amendment under the emergency provisions of 10 CFR 50.91(a)(5).
10 CFR 50.36(c)(2) requires that TS include Limiting Condition for Operation (LCOs).
Per 10 CFR 50.36(c)(2)(i), LCOs are the lowest functional capability or performance levels of equipment required for safe operation of the facility. The regulation also requires that when an LCO of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the TS until the condition can be met.
The source range neutron flux channels have no safety function and are not assumed to function during any UFSAR design basis accident or transient analysis and are not credited in the safety analysis. However, the source range neutron flux channels provide on scale monitoring of neutron flux levels during startup and shutdown conditions.
L-25-160 Page 7 of 8 The proposed change does not affect compliance with these regulations or guidance and will ensure that the lowest functional capabilities or performance levels of equipment required for safe operation are met.
4.2 No Significant Hazards Consideration Analysis Vistra Operating Company LLC. (Vistra OpCo) is proposing to amend Renewed Facility Operating License No. NPF-3 for Davis-Besse Nuclear Power Station, Unit No. 1 (DBNPS). The proposed change would revise Technical Specification (TS) 3.3.9, Source Range Neutron Flux, to allow the use of alternate source range neutron monitoring instrumentation, when one source range neutron flux channel is inoperable, for the remainder of Cycle 24.
Vistra OpCo has evaluated whether or not a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, Issuance of amendment, as discussed below.
- 1. Does the proposed amendment involve a significant increase in the probability or consequences of an accident previously evaluated?
Response: No.
The source range neutron monitoring instrumentation and the proposed alternate instrumentation are not accident initiators. The source range instrumentation provides a rod withdraw block, which is retained by the unaffected channel. The source range rod withdraw block is not credited in the accident analysis. Monitoring of the core reactivity state will continue to be provided by the unaffected source range neutron monitoring instrumentation channel and the alternate instrumentation. The alternate instrumentation is not new equipment and is required by other Technical Specifications.
Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?
Response: No.
The proposed change does not alter the design function or operation of the source range neutron monitors or alternate instrumentation. There are no new or failure mechanisms, malfunctions, or accident initiators created by the allowance for the use of alternate instrumentation to provide additional indication of the core reactivity.
Therefore, the proposed amendment does not create the possibility of a new or different kind of accident from any previously evaluated.
- 3. Does the proposed amendment involve a significant reduction in a margin of safety?
L-25-160 Page 8 of 8 Response: No.
The proposed change will not adversely affect the operation of plant equipment or the function of equipment assumed in the accident analyses. The source range instrumentation is not credited in the accident analyses. The proposed change does not alter any design basis or safety limits.
Therefore, the proposed amendment does not involve a significant reduction in a margin of safety Based on the above, Vistra OpCo. concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and, accordingly, a finding of "no significant hazards consideration" is justified.
4.3 Conclusion In conclusion, based on the considerations discussed above, (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 Commissions 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.
5.0 ENVIRONMENTAL CONSIDERATION
A review has determined that the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or a significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment
L-25-160 Proposed Technical Specification Pages Markup (2 pages follow)
Source Range Neutron Flux 3.3.9 Davis-Besse 3.3.9-1 Amendment 279 3.3 INSTRUMENTATION 3.3.9 Source Range Neutron Flux LCO 3.3.9 Two source range neutron flux channels shall be OPERABLE.
NOTE--------------------------------------------
High voltage to detector may be de-energized with neutron flux
> 1E-10 amp on intermediate range channels.
APPLICABILITY:
MODES 2, 3, 4, and 5.
ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. One source range neutron flux channel inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux channels.
A.1 Restore channel to OPERABLE status.
Prior to increasing neutron flux B. Two source range neutron flux channels inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux channels.
B.1
NOTE--------------
Plant temperature changes are allowed provided the temperature change is accounted for in the calculated SDM.
Suspend operations involving positive reactivity changes.
AND B.2 Initiate action to insert all CONTROL RODS.
AND Immediately Immediately OR A.2 ---------NOTE----------------
Only Applicable during Cycle 24.
Verify Neutron Flux (Source Range) instrumentation channels required by Table 3.3.17-1 Function 17 are OPERABLE.
Immediately AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter
Source Range Neutron Flux 3.3.9 Davis-Besse 3.3.9-2 Amendment 301 ACTIONS (continued)
CONDITION REQUIRED ACTION COMPLETION TIME B. (continued)
B.3 Open CONTROL ROD drive trip breakers.
AND B.4 Verify SDM is within the limits specified in the COLR.
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1 hour AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter C. One or more source range neutron flux channels inoperable with neutron flux
> 1E-10 amp on the intermediate range neutron flux channels.
C.1 Initiate action to restore affected channel(s) to OPERABLE status.
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.3.9.1 Perform CHANNEL CHECK.
In accordance with the Surveillance Frequency Control Program SR 3.3.9.2
NOTE------------------------------
Neutron detectors are excluded from CHANNEL CALIBRATION.
Perform CHANNEL CALIBRATION.
In accordance with the Surveillance Frequency Control Program OR C.2 ---------NOTE----------------
Only Applicable during Cycle 24.
Verify Neutron Flux (Source Range) instrumentation channels required by Table 3.3.17-1 Function 17 are OPERABLE.
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter
L-25-160 Proposed Technical Specification Pages Re-typed (for information only)
(3 pages follow)
Source Range Neutron Flux 3.3.9 Davis-Besse 3.3.9-1 Amendment 279 3.3 INSTRUMENTATION 3.3.9 Source Range Neutron Flux LCO 3.3.9 Two source range neutron flux channels shall be OPERABLE.
NOTE--------------------------------------------
High voltage to detector may be de-energized with neutron flux
> 1E-10 amp on intermediate range channels.
APPLICABILITY:
MODES 2, 3, 4, and 5.
ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. One source range neutron flux channel inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux channels.
A.1 Restore channel to OPERABLE status.
OR A.2
NOTE--------------
Only applicable during Cycle 24.
Verify Neutron Flux (Source Range) instrumentation channels required by Table 3.3.17-1 Function 17 are OPERABLE.
Prior to increasing neutron flux Immediately AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter
Source Range Neutron Flux 3.3.9 Davis-Besse 3.3.9-2 Amendment 301 ACTIONS (continued)
CONDITION REQUIRED ACTION COMPLETION TIME B. Two source range neutron flux channels inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux channels.
B.1
NOTE--------------
Plant temperature changes are allowed provided the temperature change is accounted for in the calculated SDM.
Suspend operations involving positive reactivity changes.
AND B.2 Initiate action to insert all CONTROL RODS.
AND B.3 Open CONTROL ROD drive trip breakers.
AND B.4 Verify SDM is within the limits specified in the COLR.
Immediately Immediately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1 hour AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter
Source Range Neutron Flux 3.3.9 Davis-Besse 3.3.9-3 Amendment 301 ACTIONS (continued)
CONDITION REQUIRED ACTION COMPLETION TIME C. One or more source range neutron flux channels inoperable with neutron flux
> 1E-10 amp on the intermediate range neutron flux channels.
C.1 Initiate action to restore affected channel(s) to OPERABLE status.
OR A.2
NOTE--------------
Only applicable during Cycle 24.
Verify Neutron Flux (Source Range) instrumentation channels required by Table 3.3.17-1 Function 17 are OPERABLE.
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1 hour AND Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.3.9.1 Perform CHANNEL CHECK.
In accordance with the Surveillance Frequency Control Program SR 3.3.9.2
NOTE------------------------------
Neutron detectors are excluded from CHANNEL CALIBRATION.
Perform CHANNEL CALIBRATION.
In accordance with the Surveillance Frequency Control Program
L-25-160 Proposed Technical Specification Bases Page Markups (for information only)
(7 pages follow)
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-1 Revision 32 B 3.3 INSTRUMENTATION B 3.3.9 Source Range Neutron Flux BASES BACKGROUND The Reactor Protection System (RPS) source range neutron flux channels provide the operator with an indication of the approach to criticality at lower power levels than can be seen on the intermediate range neutron flux instrumentation. These channels also provide the operator with a flux indication that reveals changes in reactivity and helps to verify that SDM is being maintained.
The source range instrumentation has two redundant count rate channels originating in two high sensitivity proportional counters. Two source range detectors are externally located on opposite sides of the core 180°.
These channels are used over a counting range of 0.1 cps to 1E6 cps and are displayed on the operator's control console in terms of log count rate. The channels also measure the rate of change of the neutron flux level, which is displayed for the operator in terms of startup rate from -0.5 decades to +5 decades per minute. An interlock provides a control rod withdraw "inhibit" on a high startup rate of +2 decades per minute in either channel.
The proportional counters of the source range channels are BF3 chambers. The detector high voltage is automatically turned off when the flux level is approximately one decade above the useful operating range.
Conversely, the high voltage is turned on automatically when the flux level returns to within approximately one decade of the detectors' maximum useful range. High voltage will be turned off automatically when the flux level is above 1E-9 amp in both intermediate range channels, or 10% power in power range channels (i.e., NI-5 or NI-6 and NI-7 or NI-8).
APPLICABLE The source range neutron flux channels are necessary to monitor SAFETY core reactivity changes. It is the primary means for detecting and ANALYSES triggering operator actions to respond to reactivity transients initiated from conditions in which the Reactor Protection System (RPS) is not required to be OPERABLE. It also triggers operator actions to anticipate RPS actuation in the event of reactivity transients during startup and shutdown conditions. However, the source range neutron flux channels are not credited in the safety analysis.
The source range neutron flux channels have no safety function and are not assumed to function during any UFSAR design basis accident or transient analysis. However, the source range neutron flux channels provide on scale monitoring of neutron flux levels during startup and shutdown conditions. Therefore, they are being retained in Technical Specifications.
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-2 Revision 32 BASES LCO Two source range neutron flux channels (i.e., the channels associated with the RPS) shall be OPERABLE whenever the control rods are capable of being withdrawn to provide the operator with redundant source range neutron instrumentation. The source range instrumentation is the primary power indication at low power levels 1E-10 amp on intermediate range instrumentation and must remain OPERABLE for the operator to continue increasing power.
A Note has been added allowing detector high voltage to be de-energized with neutron flux > 1E-10 amp on the intermediate range channels.
Above this point, the source range instrumentation is no longer the primary power indicator. As such, the high voltage to the source range detectors may be de-energized.
APPLICABILITY Two source range neutron flux channels shall be OPERABLE in MODE 2 to provide redundant indication during an approach to criticality. Neutron flux level is sufficient for monitoring on the intermediate range and on the power range instrumentation prior to entering MODE 1; therefore, source range instrumentation is not required in MODE 1.
In MODES 3, 4, and 5, source range neutron flux instrumentation shall be OPERABLE to provide the operator with a means of monitoring changes in SDM and to provide an early indication of reactivity changes.
The requirements for source range neutron flux instrumentation during MODE 6 refueling operations are addressed in LCO 3.9.2, "Nuclear Instrumentation."
ACTIONS A.1 and A.2 The Required Action for one channel of the source range neutron flux indication inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux instrumentation is to delay increasing reactor power until either the channel is repaired and restored to OPERABLE status or to verify the source range ex-core neutron flux detectors required by Table 3.3.17-1 Function 17 indications in the main control room post-accident monitoring panels are OPERABLE. A Note for A.2 allows the verification of the source range ex-core neutron flux detectors during Cycle 24 only. The verification is performed immediately and once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter. This limits power increases in the range where the operators rely solely on the source range instrumentation for power indication. The Completion Time ensures the source range is available prior to further power increases.
B.1, B.2, B.3, and B.4
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-3 Revision 32 With both source range neutron flux channels inoperable with neutron flux 1E-10 amp on the intermediate range neutron flux instrumentation, the operators must take actions to limit the possibilities for adding positive reactivity and to verify adequate SDM. This is done by immediately suspending positive reactivity additions, initiating action to insert all
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-4 Revision 32 BASES ACTIONS B.1, B.2, B.3, and B.4 (continued)
CONTROL RODS, and opening the CONTROL ROD drive trip breakers and verifying SDM is within limit within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Periodic SDM verification is then required to provide a means for detecting the slow reactivity changes that could be caused by mechanisms other than control rod withdrawal or operations involving positive reactivity changes. Since the source range instrumentation provides the only reliable direct indication of power in this condition, the operators must continue to verify the SDM every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> until at least one channel of the source range instrumentation is returned to OPERABLE status. Required Action B.1, Required Action B.2, and Required Action B.3 preclude rapid positive reactivity additions. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Completion Time for Required Action B.3 and Required Action B.4 provides sufficient time for operators to accomplish the actions. The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency for performing the SDM verification ensures that the reactivity changes possible with CONTROL RODS inserted are detected before SDM limits are challenged.
Required Action B.1 is modified by a Note which permits plant temperature changes provided the temperature change is accounted for in the calculated SDM. Introduction of temperature changes, including temperature increases when a positive MTC exists, must be evaluated to ensure they do not result in a loss of required SDM.
C.1 With neutron flux > 1E-10 amp on the intermediate range neutron flux instrumentation, continued operation is allowed with one or more source range neutron flux channels inoperable. The ability to continue operation is justified because the instrumentation does not provide a safety function during high power operation. However, actions are initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to either restore the channel(s) to OPERABLE status for future availability or to verify the source range ex-core neutron flux detectors required by Table 3.3.17-1 Function 17 indications in the main control room post-accident monitoring panels are OPERABLE. Note C.2 allows the verification of the source range ex-core neutron flux detectors during Cycle 24 only. The verification is performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter. The Completion Time of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is sufficient to initiate the action. The action must continue until channels are restored to OPERABLE status.
SURVEILLANCE SR 3.3.9.1 REQUIREMENTS Performance of the CHANNEL CHECK ensures that a gross failure of instrumentation has not occurred. A CHANNEL CHECK is normally a
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-5 Revision 32 comparison of the parameter indicated on one channel to a similar parameter on other channels. It is based on the assumption that instrument channels monitoring the same parameter should read approximately the same value. Significant deviations between the two instrument channels could be an indication of excessive instrument drift in one of the channels or of something even more serious. CHANNEL
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-6 Revision 32 BASES SURVEILLANCE REQUIREMENTS SR 3.3.9.1 (continued)
CHECK will detect gross channel failure; therefore, it is key in verifying that the instrumentation continues to operate properly between each CHANNEL CALIBRATION.
Agreement criteria are determined by the unit staff, based on a combination of the channel instrument uncertainties, including isolation, indication, and readability. If a channel is outside the criteria, it may be an indication that the detector or the signal processing equipment has drifted outside its limit. If the channels are within the criteria, it is an indication that the channels are OPERABLE. If the channels are normally off scale during times when surveillance is required, the CHANNEL CHECK will only verify that they are off scale in the same direction. Off scale low current loop channels are verified to be reading at the bottom of the range and not failed downscale.
The Surveillance Frequency is controlled under the Surveillance Frequency Control Program. The CHANNEL CHECK supplements less formal, but more frequent, checks of channel OPERABILITY during normal operational use of the displays associated with the LCO's required channels. When operating in Required Action A.1, CHANNEL CHECK is still required. However, in this condition, a redundant source range is not available for comparison. CHANNEL CHECK may still be performed via comparison with Post Accident Monitoring source range detectors, if available, and verification that the OPERABLE source range channel is energized and indicating a value consistent with current unit status.
Source Range Neutron Flux B 3.3.9 Davis-Besse B 3.3.9-7 Revision 32 BASES SURVEILLANCE REQUIREMENTS (continued)
SR 3.3.9.2 For source range neutron flux channels, CHANNEL CALIBRATION is a complete check and readjustment of the channels from the preamplifier input to the indicators. This test verifies the channel responds to measured parameters within the necessary range and accuracy.
CHANNEL CALIBRATION leaves the channel adjusted to account for instrument drift to ensure that the instrument channel remains operational between successive tests.
The SR is modified by a Note excluding neutron detectors from CHANNEL CALIBRATION. It is not necessary to test the detectors because generating a meaningful test signal is difficult. The detectors are of simple construction, and any failures in the detectors will be apparent as a change in channel output.
The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.
REFERENCES None.