IR 05000263/2020015

NRC Inspection Report 05000263/2020015

ML20314A103
Person / Time
Site:	Monticello
Issue date:	11/09/2020
From:	Jim Beardsley Engineering Branch 3
To:	Conboy T Northern States Power Company, Minnesota
References
EA-20-111 IR 2020015
Download: ML20314A103 (11)

Text

November 9, 2020

SUBJECT:

MONTICELLO NUCLEAR GENERATING PLANT - NRC INSPECTION REPORT 05000263/2020015

Dear Mr. Conboy:

On September 30, 2020, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Monticello Nuclear Generating Plant and discussed the results of this inspection with you and other members of your staff. The results of this inspection are documented in the enclosed report.

No NRC-identified or self-revealing findings were identified during this inspection.

A licensee-identified violation which was determined to be of very low safety significance is documented in this report. We are treating this violation as a non-cited violation (NCV)

consistent with Section 2.3.2 of the Enforcement Policy.

If you contest the violation or the significance or severity of the violation documented in this inspection report, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial, to the U.S. Nuclear Regulatory Commission, ATTN:

Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region III; the Director, Office of Enforcement; and the NRC Resident Inspector at Monticello Nuclear Generating Plant. This letter, its enclosure, and your response (if any) will be made available for public inspection and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document Room in accordance with Title 10 of the Code of Federal Regulations 2.390, Public Inspections, Exemptions, Requests for Withholding.

Sincerely, James D. Digitally signed by James D. Beardsley Beardsley Date: 2020.11.09 11:57:13 -06'00'

James D. Beardsley, Acting Chief Engineering Branch 3 Division of Reactor Safety Docket No. 05000263 License No. DPR-22

Enclosure:

As stated

Inspection Report

Docket Number: 05000263 License Number: DPR-22 Report Number: 05000263/2020015 Enterprise Identifier: I-2020-015-0000 Licensee: Northern States Power Company Facility: Monticello Nuclear Generating Plant Location: Monticello, MN Inspection Dates: July 01, 2020 to September 30, 2020 Inspectors: L. Kozak, Senior Reactor Analyst D. Szwarc, Senior Reactor Analyst Approved By: James D. Beardsley, Acting Chief Engineering Branch 3 Division of Reactor Safety Enclosure

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an NRC inspection at Monticello Nuclear Generating Plant, in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs program for overseeing the safe operation of commercial nuclear power reactors. Refer to https://www.nrc.gov/reactors/operating/oversight.html for more information. A licensee-identified non-cited violation is documented in report section: 7115

List of Findings and Violations

No findings or violations of more than minor significance were identified.

Additional Tracking Items

Type Issue Number Title Report Section Status URI 05000263/2020002-01 Partial Sample of FZ-08, 71152 Closed Cable Spreading Room Past Operability due to Installation of Heat Detectors with Incorrect Setpoint

INSPECTION SCOPES

Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with their attached revision histories are located on the public website at http://www.nrc.gov/reading-rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared complete when the IP requirements most appropriate to the inspection activity were met consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection Program - Operations Phase. The inspectors reviewed selected procedures and records, observed activities, and interviewed personnel to assess licensee performance and compliance with Commission rules and regulations, license conditions, site procedures, and standards.

71152 - Problem Identification and Resolution

Annual Follow-up of Selected Issues (IP Section 02.03) (1 Sample)

The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:

(1) The inspectors reviewed the licensee's investigation of the events that led to the installation of thermal heat detectors having incorrect setpoints in the cable spreading room. The inspectors also reviewed the licensee's risk evaluation associated with this issue. This completes the partial sample documented in Inspection Report 05000263/2020002 (ADAMS Accession Number ML20216A756).

INSPECTION RESULTS

Unresolved Item Partial Sample of FZ-08, Cable Spreading Room Past 71152 (Closed) Operability due to Installation of Heat Detectors with Incorrect Setpoint URI 05000263/2020002-01

Description:

The inspectors reviewed the licensee's evaluation of the degraded Halon suppression system and documented a licensee-identified violation in this report.

Corrective Action Reference(s): 501000038446, Replaced CSR [Cable Spreading Room]

Thermal Detector Issue Licensee-Identified Non-Cited Violation 71152 This violation of very low safety significance was identified by the licensee and has been entered into the licensee corrective action program and is being treated as a non-cited violation, consistent with Section 2.3.2 of the Enforcement Policy.

Violation: License condition 2.C.4 required the licensee to implement and maintain in effect all provisions of the approved fire protection program as described in the Updated Safety Analysis Report (USAR) and as approved through Safety Evaluation Report (SER) dated August 29, 1979, and supplements dated February 12, 1981 and October 2, 1985.

USAR Appendix J, Fire Protection Program, Fire Hazards Analysis Matrix for Fire Are VIII, Fire Zone 8 (the Cable Spreading Room) states that detection is provided, in part, by thermal detectors located within the fire zone and that automatic suppression is provided by an automatic total flooding Halon 1301 fire suppression system. It further states that calculation CA-02-174 addresses detection and suppression systems National Fire Protection Association (NFPA) code deviations. Section 2-2.1.1 of the code conformance review in calculation CA-02-174 states that the, CSR halon system is automatically actuated by 140°F fixed temperatureheat detectors.

Contrary to the above, from August 30, 2018 until March 5, 2020, the licensee failed to implement and maintain all provisions of the approved fire protection program. Specifically, the licensee failed to install 140°F fixed temperature heat detectors for three of four heat detector locations in the cable spreading room.

Significance/Severity: Green. The inspectors concluded that the finding was more than minor because it adversely impacted the attribute of protection against external factors (fire)and affected the mitigating system cornerstone because the finding adversely affected the suppression capability of fire suppression systems. Specifically, the higher than designed temperature actuation set point of three of four thermal detectors in the cable spreading room could have the potential for delayed Halon suppression system actuation.

In accordance with Inspection Manual Chapter (IMC) 0609, Significance Determination Process (SDP), Attachment 0609.04, Initial Characterization of Findings, Table 2, the inspectors determined the finding affected the Mitigating Systems cornerstone. The finding degraded fixed fire protection systems and the inspectors determined, using Table 3, that it could be evaluated using Appendix F, Fire Protection Significance Determination Process.

Inspectors assigned a Fixed Fire Systems; Fixed Suppression System - Automatic fire finding category in Step 1.2. In Step 1.3, inspectors did not assign a low fire degradation rating since greater than 10 percent fire detectors were degraded, and functional detection was available near combustibles. Inspectors assigned this finding to the Fixed Fire Systems, category in Step 1.4. Inspectors answered question 1.4.2-A Yes because the degraded thermal detectors did adversely affect the ability of the system to protect any equipment important to safe shutdown. Specifically, a fire in the cable spreading room that is allowed to grow, as a result of the delayed Halon actuation, could reasonably be expected to affect additional equipment important to safe shutdown.

The licensee performed an analysis of the finding using the existing fire Probabilistic Risk Assessment (PRA) and additional detailed fire modeling performed specifically for the finding.

The licensee initially estimated a change in core damage frequency of 4.7E-7/yr., which represents a finding of very low safety significance (Green). The NRC reviewed the licensee evaluation and determined it was not acceptable to screen the finding to Green in Step 1.5 of the fire protection SDP, Inspection Manual Chapter (IMC) 0609 Appendix F. The NRC concluded that the risk evaluation did not adequately capture the change in risk due to degraded Halon system performance (i.e., it did not capture the risk of the performance deficiency). The Halon suppression system response to fires, specifically timing, was not originally evaluated with analytical tools in the development of the baseline fire PRA scenarios. Therefore, it was difficult to estimate a change in risk using the existing fire PRA model because the target sets were developed using different fire growth and timing assumptions. The licensees risk evaluation showed a change in risk for fire scenarios in which current fire modeling showed little to no difference in the response of the system.

Conversely, the licensees risk evaluation also estimated no change in risk for other scenarios with many fire PRA targets and fire modeling indicating delayed Halon response. The results overall did not provide confidence that the finding should be screened to Green based on the licensee's evaluation. Because the finding could not be screened to Green, the NRC proceeded to perform a phase 2 and phase 3 (detailed risk evaluation) for the finding, given the safety significance of the Halon suppression system.

A Region III senior reactor analyst (SRA) performed a detailed risk evaluation by using fire modeling assumptions provided by fire protection inspectors, information from fire modeling performed by the licensee, information from the licensees fire PRA, and guidance from IMC 0609 Appendix F, to evaluate the degraded condition that existed. Additional references used included NUREG-2169, NUREG-CR/6850, and recently issued NUREG-2232.

The degraded condition under evaluation was an automatic Halon system that does not actuate at its normal setpoint of 140°F for an exposure period of 1 year. With three of the four heat detectors set at 275°F, additional fire damage could occur before the system can actuate to suppress the fire. The licensee performed fire modeling to estimate the time to automatic Halon actuation in both the degraded and non-degraded states. The inspector and the SRA used this information to focus the detailed risk evaluation on two areas of the cable spreading room designated as transient zone 1 and transient zone 2. These areas were farthest away from the single heat detector that was set at 140°F and the fire modeling results showed Halon actuation at up to 11 minutes after ignition, where normally the Halon system would be expected to actuate within 1 or 2 minutes. In these transient zones, there were many fire PRA targets - stacks of five, six, or seven horizontal cable trays with cables in vertical trays several feet apart routing cables in and out of the horizontal trays. A Halon actuation delay could lead to fire spread and damage through the cable tray stacks before Halon actuation. Under non-degraded conditions, the system would be able to reliably prevent this fire damage state. The plant fire PRA scenario development relied on the Halon system being in a non-degraded state.

The NRC developed six fire scenarios intended to be representative of the spectrum of fire scenarios that can occur in the two transient zones selected for further review in the cable spreading room. The complexity of the issue required judgment and some simplifying assumptions. Core damage frequency was considered to be the appropriate risk metric for this finding and large early release frequency was not evaluated. The change in core damage frequency for the degraded condition is estimated using the following equation and definitions:

CDF = FIF

• SF

• delta NSPfixed* NSPmanual

• CCDP FIF = Fire Ignition Frequency. The fire ignition frequency for transients and hot work (welding/cutting) was estimated using IMC 0609 Appendix F, Attachment 4, Guidance for Determining Fire Ignition Frequency. A medium likelihood for transient fires and a low likelihood for welding was assessed. For each fire scenario, the frequency was multiplied by 1/7 as a weighting factor to represent the frequency of fires only in the area that contributes to a change in risk for the performance deficiency. The weighting factor was chosen based on the licensees fire PRA which divided the room into seven zones for evaluating fire scenarios. Only fires in two of the zones were specifically evaluated, although some Halon actuation delays were estimated for other zones.

SF = Severity Factor. A severity factor of 0.1 was used for the transient zone 1 fire scenarios, based on engineering judgment consistent with recent guidance from NUREG-2232 which indicates the severity factors for transient combustible fires may be significantly lower than the guidance provided for determining severity factors in IMC 0609 or NUREG/CR-6850. For transient zone 2, the two fire scenarios were divided into four scenarios and weighted accordingly. A severity factor of 0.1 was used in two of the scenarios. A severity factor of 0.95 was used in the other two scenarios because the cable trays were very near to the floor and the guidance of IMC 0609 Appendix F Attachment 8 was considered to be more appropriate for the configuration, as the targets would likely be the flame zone of the postulated fire.

NSPfixed [non-suppression probability] = Change in the probability of automatic or manual non-suppression. The halon suppression system failure probability is estimated using the difference between the estimated time to damage and the time to fixed suppression system actuation provided in table A7.3 of IMC 0609 Appendix F, Attachment 7, Guidance for Non-Suppression Probability

Analysis.

In developing the time to Halon actuation, the NRC considered automatic and manual actuation of the Halon system. In the degraded case, Halon was assumed to actuate in 9.5 minutes manually. For the T1 scenario, the time to damage of a stack of cable trays was assumed to be 11 minutes and for the T2 scenario, 10 minutes. The difference between the actuation time and the damage time is used to estimate the system reliability. For T1 and T2 respectively, the Halon non-suppression probability was 0.95 and 0.80. For the non-degraded condition, the baseline risk Halon non-suppression probability would be approximately 0.1, significantly more reliable in preventing the postulated damage state.

NSPmanual = Probability of manual non-suppression. This was estimated using Table A7-2 of IMC 0609 Appendix F, Attachment 7 with the estimated of time to damage minus 2 minutes for detection. This estimate of non-suppression considers the fire brigade response and any other operator actions to suppress the fire.

CCDP = Conditional core damage probability. The licensees CCDPs for a medium zone of influence (ZOI) fire in the specific zone was used to represent the fire damage state. A medium ZOI fire damage state represents a damage to probabilistic risk assessment targets in which fire growth occurs beyond an initial damage state termed small ZOI. The halon system in an undegraded state is assumed to be able to prevent the medium ZOI damage state with a nominal reliability of approximately 5E-2. For T1 scenarios the medium ZOI CCDP was 0.01 and for T2 scenarios the CCDP was 0.15.

The estimated change in core damage frequency with the above assumptions was less than 1E-6/yr. The dominant core damage sequence is a transient combustible fire in T2 that is not suppressed within 10 minutes followed by the failure to safely shutdown. Based on the results of the analysis, the finding was determined to be of very low safety significance (Green).

Corrective Action References: 501000038446, Replaced Cable Spreading Room Thermal Detector Issue, 03/05/2020 Observation: Cable Spreading Room Degraded Halon Suppression System 71152 The inspectors reviewed Corrective Action Program item 501000038446, Replaced CSR Thermal Detector Issue, dated March 5, 2020 that documented the replacement of three of four thermal heat detectors in the cable spreading room with detectors having an incorrect actuation setpoint. During surveillance testing performed on March 5, 2020, the licensee identified that three of the four installed thermal heat detectors had incorrect actuation setpoints of 275°F versus the required 140°F.

The inspectors reviewed the licensees corrective actions that restored compliance and the apparent cause evaluation that reviewed how the issue occurred. The licensee determined that maintenance personnel inappropriately replaced the three thermal heat detectors having a setpoint of 140°F with detectors with a setpoint of 275°F on August 20, 2018 under Work Order 700007188-0010. Once the error was identified on March 5, 2020, the licensee immediately replaced the three detectors with detectors having the correct setpoint of 140°F.

The licensee performed an extent of condition and verified that no other thermal detectors were affected. The inspectors reviewed the licensees corrective actions and did not identify any concerns with the licensee's corrective actions.

A licensee-identified violation associated with this issue is documented in the preceding section.

EXIT MEETINGS AND DEBRIEFS

The inspectors verified no proprietary information was retained or documented in this report.

• On September 30, 2020, the inspectors presented the NRC inspection results to Mr. T. Conboy, Site Vice President and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection Type Designation Description or Title Revision or

Procedure Date

71152 Calculations CA-02-174 Evaluation of Fire Suppression and Detections Systems in 0

the Cable Spreading Room - Fire Area VI, Fire Zone 8

CA-03-201 Evaluation of Response Time for Heat Detectors Installed in 0

the Cable Spreading Room, Fire Area VI/Fire Zone 8

Corrective Action 501000038446 Replaced Cable Spreading Room Thermal Detector Issue 03/05/2020

Documents 501000038753 Misunderstanding Communicated to NRC 03/13/2020

Drawings NF-36738 Office & Control Building Heating and Ventilation Plan & E

Sections - Elevation 939'-0"

NX-20598-2 Monticello Nuclear Generating Plant C-108A Cable B

Spreading Halon System

NX-9276-1-1 Monticello Nuclear Generating Plant V-AH-6 Equipment & K

Cable Spreading Room (V-EF-33 RA Fan) - Honeywell H & V

Engineering N/A Preliminary Risk Significance of Delayed Halon Actuation 04/16/2020

Evaluations with Elevated Heat Detector Settings

N/A Risk Significance of Delayed Halon Actuation with Elevated 09/09/2020

Heat Detector Settings

N/A Supplemented Risk Significance of Delayed Halon Actuation 04/24/2020

with Elevated Heat Detector Settings

Procedures Ops Man C.4-B Operations Manual Section: Abnormal Procedure 33

C.4-B.08.05.A Plant Fire

Ops Man C.4-C Operations Manual Section: Abnormal Procedure C.4-C 51

Shutdown Outside Control Room

Work Orders 700007188 2016 Fire Protection FSA Paint Identified on Heat Detector 08/30/2018

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