ML23321A122
| ML23321A122 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/17/2023 |
| From: | Scott Wall NRC/NRR/DORL/LPL3 |
| To: | Scarpello M Indiana Michigan Power Co |
| Wall S | |
| References | |
| L-2023-LLA-0011 | |
| Download: ML23321A122 (9) | |
Text
From:
Scott Wall Sent:
Friday, November 17, 2023 10:17 AM To:
Michael K. Scarpello Cc:
Helen L Levendosky; Bradford M Culwell
Subject:
FINAL RAI - D.C. Cook 1 & 2 - License Amendment Request Regarding Neutron Flux Instrumentation (EPID No. L-2023-LLA-0011)
Dear Mr. Scarpello,
By letter dated January 26, 2023, (Agencywide Documents Access and Management System Accession No. ML23026A284), as supplemented by letters dated August 2, 2023 (ML23214A289), Indiana Michigan Power company (I&M, the licensee) submitted a license amendment request for the Donald C. Cook Nuclear Plant, Unit Nos. 1 and 2 (CNP). The amendment would revise Technical Specification (TS) Table 3.3.3-1, Post-Accident Instrumentation. Specifically, the proposed changes would remove Function 1, Neutron Flux, from the list of required post-accident monitoring (PAM) instrumentation.
The NRC staff has reviewed the submittals and determined that additional information is needed to complete its review. The specific questions are found in the enclosed request for additional information (RAI). During a telephone call on November 16, 2023, the I&M staff indicated that a response to the RAIs would be provided by December 21, 2023.
If you have questions, please contact me at 301-415-2855 or via e-mail at Scott.Wall@nrc.gov.
Scott P. Wall, LSS BB, BSP Senior Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation 301.415.2855 Scott.Wall@nrc.gov Docket Nos. 50-315 and 50-316
Enclosure:
Request for Additional Information cc: Listserv RAI (Neutron Flux Instrumentation)
REQUEST FOR ADDITIONAL INFORMATION NEUTRON FLUX INSTRUMENTATION
INDIANA MICHIGAN POWER COMPANY DONALD C. COOK NUCLEAR PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-315 AND 50-316 INTRODUCTION By letter dated January 26, 2023, (Agencywide Documents Access and Management System Accession No. ML23026A284), as supplemented by letters dated August 2, 2023 (ML23214A289), Indiana Michigan Power company (I&M, the licensee) submitted a license amendment request (LAR) for the Donald C. Cook Nuclear Plant, Unit Nos. 1 and 2 (CNP). The amendment would revise Technical Specification (TS) Table 3.3.3-1, Post-Accident Instrumentation. Specifically, the proposed changes would remove Function 1, Neutron Flux, from the list of required post-accident monitoring (PAM) instrumentation.
The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing the application and has determined that the following additional information is required in order to complete the review.
REGULATORY BASIS Title 10 Code of Federal Regulations (CFR) Part 50, Section 50.36, Technical Specifications, requires, in part, that the TS shall be included by applicants for a license authorizing operation of a production or utilization facility. 10 CFR 50.36(c) requires that TS include items in five specific categories related to station operation. These categories are (1) Safety limits, limiting safety system settings, and limiting control settings, (2) Limiting conditions for operation (LCOs)
(3) Surveillance requirements, (4) Design features, and (5) Administrative controls. The regulation at 10 CFR 50.36(c)(2)(ii)(C) requires that TS LCOs of a nuclear reactor be established for a structure, system, or component (SSC) that is part of the primary success path and which functions or actuates to mitigate a design-basis accident (DBA) or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.
In CNP Updated Final Safety Analysis Report (UFSAR), Section 1.4, Plant Specific Design Criteria (PSDC) (ML22340A150), states that the CNP specific design is committed to meet the intent of the proposed GDC published in the Federal Register on July 11, 1967.
CNP PSDC CRITERION 12, Instrumentation and Control Systems, states, in part:
Instrumentation and controls shall be provided as required to monitor and maintain within prescribed operating ranges essential reactor facility operating variables.
Instrumentation and controls are provided to monitor and maintain all operationally important reactor operating parameters such as neutron flux, system pressures, flow rates, temperatures, levels and control rod positions within prescribed operating ranges. The quality and types of instrumentation provided are adequate for safe and orderly operation of all systems and processes over the full operating range of the plant.
Process variables, which are required on a continuous basis for the startup, power operation and shutdown of the plant, are indicated in, recorded in, and controlled as necessary from the control room, which is a controlled area.
CNP PSDC CRITERION 13, Fission Process Monitors and Controls, states, in part:
Means shall be provided for monitoring or otherwise measuring and maintaining control over the fission process throughout core life under all conditions that can reasonably be anticipated to cause variations in reactivity of the core.
The primary function of nuclear instrumentation is to safeguard the reactor by monitoring the neutron flux and generating appropriate trips and alarms for various phases of reactor operating and shutdown conditions. It also provides a secondary control function and indicates reactor status during startup and power operation.
REGULATORY GUIDANCE Regulatory Guide (RG) 1.97, Revision 3, Instrumentation for Light-Water-Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident, dated May 1983, (ML003740282) describes a method acceptable to the NRC staff for complying with the NRCs regulations to provide instrumentation to monitor plant variables and system during and following an accident in a light-water-cooled nuclear power plant.
RG 1.97 states, in part:
Examples of serious events that could threaten safety if conditions degrade are loss-of-coolant accidents (LOCAs), overpressure transients, anticipated operational occurrences that become accidents such as anticipated transients without scram (ATWS) and reactivity excursions that result in releases of radioactive materials. Such events require that the operators understand, within a short time period, the ability of the barriers to limit radioactivity release, i.e., that they understand the potential for breach of a barrier or. whether an actual breach of a barrier has occurred because of an accident in progress.
Regarding pressurized water reactors (PWR) plants, the applicable table in RG 1.97 specifies that neutron flux monitoring capability should be provided as a parameter to be monitored during and following an accident. The NRC staff position shown in the table of PWR parameters indicates that Neutron flux is considered as a key variable for post-accident monitoring of the accomplishment of critical safety functions. The qualification requirements for key variables are Category 1, which requires, among other things, that the parameter monitoring equipment is qualified for the environment where it is located.
RG 1.97 also states, in part:
A key variable is that single variable (or minimum number of variables) that most directly indicates the accomplishment of a safety function (in the case of Types B and C) or the operation of a safety system (in the case of Type D) or radioactive material release (in the case of Type E). It is essential that key variables be qualified to the more stringent design and qualification criteria. The design and qualification criteria category assigned to each variable indicates whether the
variable is considered to be a key variable or for system status indication or for backup or diagnosis, i.e., for Types B and C, the key variables are Category 1.
RG 1.97, Tables 2 and 3 (which include those variables mentioned in these sections), should be considered as the minimum number of instruments and their respective ranges for accident-monitoring instrumentation for each nuclear power plant.
RG 1.97 further states, in part:
In general the measurement of a single key variable may not be sufficient to indicate the accomplishment of a given safety function. Where multiple variables are needed to indicate the accomplishment of a given safety function, it is essential that they each be considered key variables and be measured with high-quality instrumentation.
BACKGROUND The PAM instrumentation LCO provides OPERABILITY requirements for RG 1.97 Type A and Category 1 instruments which provide information required by plant operators to perform certain actions specified in CNP Emergency Operations Procedures (EOPs). These manual actions ensure that a system can accomplish its safety function and are credited in the plant safety analyses.
Typically, the plant safety analyses incorporate the modeling of a range of accidents, which include dynamic information based on realistic assumptions and modeling of accident progression. The instrumentation selected for use as Accident Monitoring parameters has been selected to be capable of response times that are consistent with the modeling and analyses results.
In the LAR, the licensee states, in part:
In a design basis accident, wide range neutron flux instrumentation provides information to control room operators in two situations - to check if the reactor is no longer critical and to monitor the core for unexpected additions of reactivity after reactor shutdown has been achieved.
In the LAR, Section 2.3, the licensee described the reason for and details of the proposed changes. The licensee stated, in part:
During the most recent CNP Unit 2 refueling outage, while performing testing on the TS-required wide range neutron flux instrumentation, small leaks were detected in the jacketing of the cable for 2-NRl-21, Nuclear Instrumentation Channel I Wide Range Radiation Detector. While the jacket breach does not interfere with the ability of 2-NRl-21 to provide reliable indication in a non-adverse containment environment, it does cause 2-NRl-21 to not meet EQ
[environmental qualification] acceptance criteria.
l&M is actively engaged with the instrument vendor to address the inoperable equipment. The vendor was not available for emergent support for repair or replacement during the most recent CNP Unit 2 refueling outage and has notified l&M of their intent to discontinue maintenance and support of these instruments
at the end of 2024. The vendor also stated that certain spare parts and consumables could become unavailable prior to the end of 2024, due to supplier availability or regulatory restrictions.
In this LAR, the licensee proposed to change the categorization of the Neutron Flux Post-Accident Monitoring channels from Type B Category 1 to Type B Category 3. The NRC staff has previously not approved attempts to change the categorization of this function. In its review of Topical Report (TR) WCAP-15981-NP-A, Post Accident Monitoring Instrumentation Re-Definition for Westinghouse NSSS Plants, (ML103560687) within the NRC staffs final SE (ML080380350), the staff stated, in part:
Neutron Flux (Source Range) instrumentation provides this information. In a letter dated August 22, 2007 (Reference 14) [ML072360096], the PWROG
[Pressurized Water Reactor Owners Group] provided additional clarification to support the RAI responses documented in a letter dated June 28, 2007. The letter dated August 22, 2007 (Reference 14), states that RCS [Reactor Coolant System] Boron concentration provides information to ensure adequate shutdown margin. However, TR WCAP-15981-NP has not proposed that RCS Boron Concentration be upgraded to a Category 1 variable in lieu of Neutron Flux (Source Range). Based on the information provided, the NRC staff does not agree with the proposed reclassification of Neutron Flux (Source Range) and concludes that Neutron Flux (Source Range) should be included in the PAM TS.
In licensing documents identified by the licensee as precedents (LAR References 5, 6, and 7 (ML17264A259, ML100351277, and ML20094L410, respectfully)), the NRC staff did not approve a LAR to change the categorization of an existing Type B Category 1 variable to a Type B Category 3 variable, but rather had granted limited approvals of a PAMS commitment plan in response to Generic Letter 82-33, Supplement 1 to NUREG-0737 - Emergency Response Capability, for which the affected licensee could not commit to the installation of a new environmentally-qualified neutron monitoring parameter as a key variable to be measured with high-quality instrumentation.
In the LAR and supplement, the licensee described the current operation of CNP, Units 1 and 2, and provided its technical analysis of the proposed changes. In its analysis, the licensee proposes that the aggregate of indications of core exit temperature, hot leg temperature, cold leg temperature, boron concentration, and assurance of boron injection will provide information sufficient for plant operators to determine that the reactor is no longer critical and to monitor the core for unexpected additions of reactivity after reactor shutdown has been achieved. However, the NRC staff is aware that several modeling studies have been performed that indicate that there may be significant deviations between indicated and actual core temperature by the core exit thermocouples, as well as significant lag times between changes occurring in core temperature and indications of that change at the location of the core exit thermocouples. In addition, it is not clear whether the response times from the hot leg and cold leg temperature devices are adequate to enable a timely response by plant operators to identify and perform mitigative actions when the reactor coolant pumps may not be running after a LOCA accident has occurred.
INSTRUMENTATION & CONTROLS BRANCH (EICB) REQUEST FOR ADDITIONAL INFORMATION (RAI)
EICB-RAI-1 In the LAR, the licensee states, in part, that:
In a design basis accident, wide range neutron flux instrumentation provides information to control room operators in two situations - to check if the reactor is no longer critical and to monitor the core for unexpected additions of reactivity after reactor shutdown has been achieved.
During an accident that involves normal containment conditions, the neutron flux monitoring instrumentation is expected to be available for use. Under these conditions, control room operators are able to monitor the reactivity state of the core by evaluating neutron flux behavior measured by all of the neutron flux monitoring instrumentation (Gamma-Metrics in addition to Westinghouse power range, intermediate range, and source range Westinghouse instruments) as well as Core Exit Thermocouple (CET) temperatures, Reactor Coolant System (RCS) hot leg and cold leg temperatures, and boron concentration.
..Additionally, the shutdown margin would be verified by measuring boron concentration. The EOPs would also direct the operators to assure that boric acid injection is taking place, adding negative reactivity to ensure that the core remains shut down.
CNP Unit 1 and Unit 2 EOPs also require control room operators to monitor RCS temperature using CETs and RCS hot leg and cold leg instruments, and to monitor boron concentration and the assurance of boron injection.
Please provide information regarding how the indication of boron concentration and the assurance of boron injection instrumentation or sampling process may each be considered as key variables and be measured with high-quality instrumentation, in lieu of neutron flux monitoring (source range).
o Describe the response time characteristics of instrumentation used for responding to a change in boron concentration and for assuring boron injection is taking place.
o Describe whether the use of instrumentation measuring boron concentration will enable plant operators to take timely mitigative action in an event of a return to criticality following a LOCA event.
EICB-RAI-2 Currently the Neutron Flux are fulfilling the requirements of 10 CFR 50.36(c)(2)(ii), as are the RCS Hot Leg Temperature (Wide Range), RCS Cold Leg Temperature (Wide Range), and CET monitoring instrumentations. If during an accident that involves elevated temperature containment conditions the neutron flux instrument is not available, the operators will be relying on boron concentration and the assurance of boron injection as key variables. Per RG 1.97 Revision 3, key variable should be qualified to meet Category design specifications. The CNP TS Bases states that the PAM instrumentation TSs ensures the operability of RG 1.97 Type A and Category 1 variables so that the control room operating staff can (among other items):
Perform the diagnosis specified in the emergency operating procedures (these variables are restricted to preplanned actions for the primary success path of DBAs),
e.g., LOCA.
Take the specified, pre-planned manually controlled actions, for which no automatic control is provided, and that are required for safety systems to accomplish their safety functions.
Determine whether systems important to safety are performing their intended functions.
Provide the basis for concluding that boron concentration monitoring instrumentations and the assurance of boron injection is not required to be added to the PAM table.
EICB-RAI-3 Currently the Neutron Flux monitoring instrumentations are Category 1, as are the RCS Hot Leg Temperature (Wide Range), RCS Cold Leg Temperature (Wide Range), and CET monitoring instrumentations. Describe how the boron concentration monitoring instrumentations meets the qualifications of Category 1. If not currently at Category 1 qualification, are there any plans to upgrading the qualification of boron concentration instrumentation to Category 1? Please describe if so.
EICB-RAI-4 In the LAR, the licensee indicates that a DC Cook plant operator would rely on indications from core exit temperatures, hot and cold leg temperatures, boron concentration, and assurance of boron injection to verify that there is no continued or unexpected reactivity occurring. Any actions to be taken by the operator must be taken timely enough during the event to have a high degree of success in achieving or returning to cold shutdown, and hence a safe reactor state.
- a. Demonstrate whether there will be adequate time for detection of process changes at the location of the CETs and whether there is appropriate instrument response time and sufficient time available from the onset of reactor shutdown, for an operator relying on CET or Hot/Cold Leg Temperature, and boron concentration indications to verify that reactor shutdown has been successfully accomplished through the insertion of the control rods or boron addition during an accident with energy added to the containment.
- b. Demonstrate whether there will be adequate time for process changes at the location of the instruments and whether there is appropriate instrument response time and sufficient time available from the onset of unexpected reactivity, for an operator using CET or Hot/Cold Leg Temperature indications and boron concentration to observe that unexpected reactivity is occurring to enable timely action to mitigate this condition.
- c. Please provide an overview of an evaluation of expected process variations and the expected response of the CET and Hot/Cold Leg Temperature instruments to those variations regarding the time delay needed to allow for process changes to occur at the location of the Hot/Cold Leg Temperature instruments in response to those process variations.
o Describe the expected response of these instruments to enable plant operators to take appropriate mitigative actions to recover from the accident and avoid further adverse consequences of the event.
o Include your assumptions and conditions regarding whether the evaluation assumes whether the reactor coolant pumps are running and whether vessel or piping voiding conditions are occurring.
EICB-RAI-5 In the LAR, the licensee states, in part, that:
In addition, neutron flux instrumentation is not always proportional to reactor power, and therefore may provide anomalous indications which can potentially mislead the operator. Excore neutron flux instrumentation response is dependent on the location of voiding in the core and/or downcomer, the degree of core uncovery, and detector location. This is particularly likely for accidents which produce harsh containment environments since reactor vessel voiding may be occurring. Anomalous neutron flux indication (i.e., indication not proportional to reactor power) was observed at the Three Mile Island accident (Reference 3 [of LAR]) and has been demonstrated in NRC financed experiments (Reference 4
[of LAR]).
The NRC staff notes that one outcome of the Three Mile Island (TMI) recommendations was to have all PWR plants install a reactor vessel level indication system (RVLIS) to detect and monitor recovery from inadequate core cooling (ICC). All PWR plants were required to have redundant, environmentally qualified Class IE ICC systems. These systems were required to be functional during and following LOCA events. As described in Summary Report, Westinghouse Reactor Vessel Level Instrumentation System for Monitoring Inadequate Core Cooling dated December 1980 (ML18139B695), Westinghouse-designed RVLIS systems are capable of monitoring reactor vessel upper head and plenum, and wide range (dynamic) level. Indication from this level system should be capable of informing plant operators of the location of any voiding occurring inside reactor vessel. Information regarding the location of voiding in the reactor vessel should serve to support interpretation of readings from the neutron detectors outside reactor vessel which appear to be anomalous.
Please describe the RVLIS installed at CNP and confirm that it meets the TMI recommendations for monitoring ICC following a LOCA event.
Please provide a description of the process or procedure the plant operators would use to interpret potentially anomalous neutron source range readings by using information from the RVLIS regarding the location of potential reactor vessel voiding.
Hearing Identifier:
NRR_DRMA Email Number:
2314 Mail Envelope Properties (SA1PR09MB9605575AE59CA824DFD5C92692B7A)
Subject:
FINAL RAI - D.C. Cook 1 & 2 - License Amendment Request Regarding Neutron Flux Instrumentation (EPID No. L-2023-LLA-0011)
Sent Date:
11/17/2023 10:17:27 AM Received Date:
11/17/2023 10:17:30 AM From:
Scott Wall Created By:
Scott.Wall@nrc.gov Recipients:
"Helen L Levendosky" <hllevendosky@aep.com>
Tracking Status: None "Bradford M Culwell" <bmculwell@aep.com>
Tracking Status: None "Michael K. Scarpello" <mkscarpello@aep.com>
Tracking Status: None Post Office:
SA1PR09MB9605.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 22366 11/17/2023 10:17:30 AM Options Priority:
Normal Return Notification:
No Reply Requested:
No Sensitivity:
Normal Expiration Date: