CNL-18-139, Proposed Technical Specifications (TS) Change TS-510 - Request for License Amendments - Maximum Extended Load Line Limit Analysis Information

Proposed Technical Specifications (TS) Change TS-510 - Request for License Amendments - Maximum Extended Load Line Limit Analysis Information

ML18348B156
Person / Time
Site:	Browns Ferry
Issue date:	12/14/2018
From:	Henderson E Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-18-139, EPID L-2018-LLA-0048
Download: ML18348B156 (9)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-18-139 December 14, 2018 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Units 1, 2, and 3 Renewed Facility Operating License Nos. DPR-33, DPR-52, and DPR-68 NRC Docket Nos. 50-259, 50-260, and 50-296

Subject:

Proposed Technical Specifications (TS) Change TS-510 - Request for License Amendments - Maximum Extended Load Line Limit Analysis Plus - Supplement 3, Responses to Requests for Additional Information

References:

1. Letter from TVA to NRC, CNL-18-002, "Proposed Technical Specifications (TS) Change TS-510 - Request for License Amendments - Maximum Extended Load Line Limit Analysis Plus," dated February 23, 2018 (ML18057B276)

2. Letter from NRC to TVA, Browns Ferry Nuclear Plant - Request for Additional Information Regarding Maximum Extended Load Line Limit Analysis Limit Plus License Amendment Request (EPID: L-2018-LLA-0048), dated November 20, 2018 (ML18312A427)

By the Reference 1 letter, Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for a Technical Specification (TS) amendment (TS-510) to Renewed Facility Operating License Nos. DPR-33, DPR-52, and DPR-68 for Browns Ferry Nuclear Plant (BFN) Units 1, 2, and 3, respectively. The proposed amendment allows operation in the expanded Maximum Extended Load Line Limit Analysis Plus (MELLLA+)

operating domain and use of the Detect and Suppress Solution - Confirmation Density (DSS-CD) stability solution. During their technical review of the LAR, the Nuclear Regulatory Commission (NRC) identified the need for additional information. The Reference 2 letter provided, in part, NRC Requests for Additional Information (RAIs) related to human factors. The due date for the responses to the human factors related NRC RAIs provided by the Reference 2 letter is December 14, 2018. The enclosure to this letter provides the responses to the human factors related RAIs included in the Reference 2 letter.

U.S. Nuclear Regulatory Commission CNL-18-139 Page 2 December 14, 2018 TVA has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration provided to the NRC in the Reference 1 letter. The supplemental information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the supplemental information in this submittal does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed license amendment. Additionally, in accordance with 10 CFR 50.91(b)(1), TVA is sending a copy of this letter to the Alabama State Department of Public Health.

There are no new regulatory commitments associated with this submittal. If there are any questions or if additional information is needed, please contact Michael A. Brown at (423) 751-3275.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 14th day of December 2018.

Respectfully, E. K. Henderson Director, Nuclear Regulatory Affairs

Enclosure:

Responses to NRC Requests for Additional Information APHB RAI-1, APHB RAI-2, and APHB RAI-3 cc:

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant State Health Officer, Alabama Department of Public Health

ENCLOSURE Responses to NRC Requests for Additional Information APHB RAI-1, APHB RAI-2, and APHB RAI-3

ENCLOSURE APHB RAI-1 Section 10.6 of Attachment 6, NEDC-33877, to the LAR dated, February 23, 2018, states that two new operator actions are required to operate in the MELLLA+ domain. Please confirm that these two new operator actions do not impact operator response times or actions associated with any ATWS or dual recirculation pump trip (2RPT) ATWS-Instability mitigation requirements. Explain how the operator actions associated with ATWS or 2RPT ATWS-Instability mitigation are implemented and controlled when operating in the MELLLA+

domain.

TVA Response The referenced operator actions are associated with new Technical Specifications and Renewed Facility Operating License Conditions restrictions to ensure operation is maintained within Maximum Extended Load Line Limit Analysis Plus (MELLLA+) analyzed conditions. The restrictions prohibit operation in the MELLLA+ region of the power to flow map when operating in Single Loop Operation or when operating with feedwater temperature reduced greater than 10°F below the feedwater design temperature. These new restrictions are not associated with any Anticipated Transient Without Scram (ATWS) or 2RPT ATWS-Instability (ATWS-I) operator mitigation actions, therefore operator response time and operator mitigation actions for ATWS or 2RPT ATWS-I are not impacted or changed.

The two actions referenced in Section 10.6 of NEDC-33877P, Safety Analysis Report for Browns Ferry Nuclear Plant Units 1, 2, and 3, Maximum Extended Load Line Limit Plus, deal with restrictions on operating parameters which would require plant operators to maneuver the plant when operating outside of an analyzed portion of the power to flow map; specifically exiting the MELLLA+ region when feedwater temperature is reduced greater than 10° below the feedwater design temperature, or when operating in Single Loop Operation. While not explicitly required by Technical Specifications or Renewed Operating License Conditions, current plant procedures and operator training direct operators to maneuver the plant to establish operation inside analyzed portions of the power to flow map if operation were to occur outside the analyzed region. Therefore, the new actions referenced in Section 10.6 of NEDC-33877P are actually a subset of already established operator actions. Cues to indicate that the new operating parameter restrictions have been met, requiring operator action, will be included in plant procedures and will be presented in training for licensed operators.

With respect to ATWS or 2RPT ATWS-I mitigation actions, these actions are documented in an Abnormal Operating Instruction (AOI) hard card located on the reactor control panel, directing the Reactor Operator (RO) to take the required ATWS/2RPT ATWS-I mitigation actions without direction from the Senior Reactor Operator (SRO), thus eliminating communication delays. The SRO continues to monitor and provide oversight for the actions being taken by the RO. The actions taken by the RO include shutdown of both Reactor Recirculation pumps, termination and prevention of injection to the Reactor Pressure Vessel (lowering Reactor Pressure Vessel water level), and injection of Standby Liquid Control (SLC).

For more information regarding ATWS/2RPT ATWS-I mitigation actions, see the response to APHB RAI-3.

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Enclosure APHB RAI-2 Section 10.5.3 of Attachment 5, NEDC-33877, to the LAR dated, February 23, 2018, states, in part:

The operator responses to anticipated occurrences, accidents, and special events for CLTP [current licensed thermal power] with MELLLA+

conditions are basically the same as for CLTP conditions.

Conditions during an ATWS are potentially more severe post-reactor RPT during MELLLA+ operation. At reduced flow rates with power at 120% of the OLTP [original licensed thermal power], the post-RPT power level may be slightly higher during MELLLA+ operation. RPV [reactor pressure vessel] water level would potentially drop quicker and containment heat up would initially be quicker if power level is slightly higher. This would potentially reduce the time for operator response and this was assessed for PRA impact.

The PRA impact review determined that the effect on operator response times is negligible and resulted in no changes to the human error probabilities associated with short-term ATWS response actions.

Describe how the impact of the potential reduction in time for existing operator response time described above was evaluated from a human factors perspective.

TVA Response The site-specific ATWS analysis determined that key operator actions and their associated required response times remained unchanged for MELLLA+. The human error probability (HEP) for actions taken during ATWS post Recirculation Pump Trip (RPT) under MELLLA+

conditions were evaluated for impact in the PRA model. BFN follows industry guidance and uses common industry software to perform human reliability analysis (HRA). The inputs in the HRA calculator for the ATWS actions were evaluated for operation in the MELLLA+

domain. The evaluation considered potential changes in cues and indications, procedures, training, timing analysis, cognitive analysis, execution performance shaping factors, and stress. The evaluation determined the following:

• The cues and indications remain unchanged by operating in the MELLLA+ operating domain.

• The ATWS emergency operating instructions (EOIs) do not change for operating in the MELLLA+ domain. Operator actions are driven by the ATWS EOI, and therefore are unchanged.

• Operator training on ATWS actions does not change for operation in the MELLLA+

domain.

• The time specified for successful completion of the ATWS actions does not change for operation in the MELLLA+ domain. Although there is a potential for slightly higher ATWS power post-RPT when operating in the MELLLA+ domain, there is no impact on the allotted time to complete the ATWS actions.

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Enclosure

• The cognitive analysis considered availability of information, failure of attention, potential to misread or miscommunicate data, misleading information, potential to skip a procedure step, potential to misinterpret instructions, misinterpret decision logic, and deliberate violations. It is not possible to quantitatively assess the magnitude of the impact on these attributes for operation in the MELLLA+ domain.

Because the time specified for completion of ATWS actions does not change for operation in the MELLLA+ domain, a qualitative analysis determined the impact of any change in these attributes to be bounded by the current assumptions in the baseline PRA.

• The execution performance shaping factors considered environmental factors, complexity of response, and equipment accessibility. The evaluation determined that these attributes remained unchanged for operation in the MELLLA+ domain.

• The evaluation determined that operation in the MELLLA+ domain would not affect stress levels of the operators performing the actions.

Because there was a potential to reduce operator time to respond due to the potential for slightly higher power during ATWS post-RPT, a sensitivity case was performed to assess the impact of HEPs on the PRA solution. The sensitivity case conservatively increased ATWS HEPs by 10% for each of the affected human failure events in the PRA model. The results of this sensitivity case is shown in the table below.

Unit Delta CDF (/yr) Delta LERF (/yr)

Unit 1 4.81E-08 1.73E-08 Unit 2 3.76E-08 1.77E-08 Unit 3 4.59E-8 1.89E-8 In addition to the evaluation described above, BFN time validated the ATWS response procedure to ensure key manual actions could be performed within the time limits specified in the BFN MELLLA+ safety analysis. There were 16 operating crews evaluated to ensure they could perform key manual operator actions during the ATWS event within the time constraints assumed in the MELLLA+ analysis. As described in BFN MELLLA+ LAR Supplement 2, Operator Training Results, the average operating crew time to complete key manual operator actions was significantly less than the time assumed in the analysis. This validation confirms that the HEPs for actions taken during ATWS post-RPT under MELLLA+

conditions in the PRA model are bounded by the current assumptions in the baseline PRA.

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Enclosure APHB RAI-3 The enclosure of the BFN letter dated July 23, 2018 (ADAMS Accession No. ML18205A498), reports average operator crew action times that appear to be very low relative to the average action times for other licensees implementing MELLLA+ at similar units. Please provide the raw results for crew operator action times including a listing of the action times for each crew including training failures that required remediation.

TVA Response The requested information is provided below. The specific crew times for recognition of an ATWS following a 2RPT will be provided in a separate RAI response by January 18, 2019.

BFN ATWS Actions Timing Data - Licensed Operator Requalification 2018 Time to Commence Reactor Water Time to Initiate Standby Liquid Level Reduction by Reducing Crew Control System Following Feedwater Flow Following Recognition of ATWS (seconds)

Recognition of ATWS (seconds)

Group 0 42.00 61.75 Group 1A 30.25 24.75 Group 1B 17.25 21.75 Group 1C 38.00 70.75 Group 2A 54.00 42.50 Group 2B 46.75 42.75 Group 2C 21.50 37.50 Group 3A 38.50 38.00 Group 3B 37.50 30.50 Group 3C 53.00 51.00 Group 4A 57.75 46.75 Group 4B 29.00 33.00 Group 4C 24.25 35.25 Group 5A 52.75 44.00 Group 5B 60.45 62.95 Group 5C 47.00 61.75 Average Time 40.62 44.06 (seconds)

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Enclosure All crews completed the actions well within the required time of 120 seconds with no problems or failures identified. As such, no remediation was required.

An external evaluation of BFN was conducted during the summer of 2016. An issue was identified during the simulator evaluation related to operator performance during simulated ATWS scenarios. The BFN crews did not demonstrate consistent performance among crews when taking ATWS actions.

In the summer of 2017, BFN was preparing to implement Extended Power Uprate (EPU),

raising reactor power to 120% of original rated reactor thermal power. One of the goals for implementation of EPU was to identify and mitigate any areas that could cause a challenge for the operators. The BFN Unit 3 simulator was upgraded to model EPU operation and it was identified that operator response to an ATWS from EPU conditions had the potential to be more critical. This condition would potentially become even more important for any future MELLLA+ operation.

Based on the identified issue described above, and the challenges created by EPU, the EPU project team (Operations, Reactor Engineering, and Operations Training) partnered to optimize the operator actions during an ATWS. The focus was on prioritization of terminating and preventing injection to the Reactor Pressure Vessel (RPV) in order to lower core inlet subcooling to mitigate the possibility of large irregular oscillations which could cause fuel damage. The BWR Owners Group (BWROG)

Emergency Procedure Committee Chairman, a BFN reactor engineer, was present during development and aided in the development of the optimized actions. On shift licensed operators, both ROs and SROs, were used to provide feedback and to refine the optimized actions. Approximately 50% of all licensed operators eventually participated in the ATWS action development, and the optimized actions were subsequently approved by Operations management.

No EOI changes were made to improve operator performance. The changes optimized and reordered the actions taken by the operators in the Abnormal Operating Instructions (AOIs) for a reactor SCRAM, including SCRAM with ATWS. The optimized actions fell into two categories which resulted in improved operator performance times.

The first was a delay in providing a full SCRAM report until after the ATWS operator actions were taken and RPV water level had been lowered. The previous revision of the AOI required a seven item SCRAM report for all SCRAMs, including ATWS. These seven items would be communicated by the RO to the SRO who would then repeat them back to the RO for confirmation. It was after this communication that the SRO would enter the EOI flowcharts. The full initial SCRAM report is appropriate for non-ATWS scrams but added unnecessary time delay to ATWS events, slowing action by the RO. The optimized action for ATWS is a three item initial SCRAM report followed by a notification from the RO that ATWS actions are continuing. The remainder of the SCRAM report is given only after reactor water level is lowered below the target value.

The second optimization was based on eliminated communication of directions from the SRO for actions taken by the RO. For an ATWS greater than 5% reactor power, the EOIs direct a specific and consistent set of actions taken every time. The previous strategy was for the SRO to direct each individual action to the RO. The action direction was then repeated by the RO, confirmed by the SRO, and then performed by the RO. The RO would then communicate that the action was complete, with repeat E-5

Enclosure back by the SRO and confirmation by the RO. This occurred for every action taken by the RO. This level of communication was evaluated and determined to not be required, and only served to delay operator action. The optimized action, documented in a hard card located on the reactor control panel, is for the RO to take the required ATWS actions without direction from the SRO, thus eliminating the communication delay. The SRO continues to monitor and provide oversight for the actions being taken by the RO. The actions taken by the RO include shutdown of both Reactor Recirculation pumps, termination and prevention of injection to the RPV (lowering RPV level), and injection of Standby Liquid Control (SLC).

These changes resulted in improved times for initiation of feedwater flow reduction and injection of SLC. The changes were well received by the operators as they matched the mental model of operator control during an ATWS with the RO performing actions and the SRO providing oversight. Training, followed by evaluation, was provided to all licensed operators over two training cycles with consistent results.

In August and November of 2017, the BWROG Emergency Procedure Committee reviewed the optimized actions taken by BFN Operations and these actions were adopted as the standard for ATWS performance by the BWROG for inclusion in EPG/SAG Revision 4, published in June 2018. During a 2018 external evaluation conducted at BFN, the improved operator performance and procedure revision associated with ATWS mitigation actions were recognized as a strength.

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