ML18331A019
| ML18331A019 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/18/2018 |
| From: | Southern California Edison Co |
| To: | NRC Region 4 |
| References | |
| Download: ML18331A019 (7) | |
Text
Summary of the Root Cause and Apparent Cause Evaluations of August 2018 Download Event at SONGS Summary report prepared by Southern California Edison, October 2018 This is a summary of two cause evaluations. The cause evaluations do not attempt to make a determination as to whether any of the actions or decisions taken by management, vendors, internal organizations, or individual personnel at the time of the event were reasonable or prudent based on the information that was known or available at the time they took such actions or made such decisions. Any individual statements or conclusions included in this summary of the evaluation as to whether errors may have been made or improvements are warranted are based upon all of the information considered, including information and results learned after-the-
/act, evaluated in hindsight after the results of actions or decisions are known, and that do not reflect any conclusion or determination as to the prudence or reasonableness of actions or decisions at the time they were made.
PURPOSE OF REPORT The purpose of this report is to summarize two separate cause evaluations - the Root Cause Evaluation (RCE) prepared by Holtec and the Apparent Cause Evaluation (ACE) prepared by Southern California Edison (SCE). These cause evaluations are in response to the Aug. 3, 2018 abnormal handling event during downloading of a Holtec Multi-Purpose Canister (MPC) into the Independent Spent Fuel Storage Installation (ISFSI) at the San Onofre Nuclear Generating Station (SONGS).
Holtec performed a RCE to determine the cause of the event and to identify appropriate corrective actions. In parallel, SCE performed an ACE to determine why SCE oversight was not ef(ective to detect, correct, and prevent the event.
SUMMARY
OF AUGUST 2018 EVENT SCE is overseeing the movement of Multi-Purpose Canisters (MPCs, or "canisters 11
) containing spent nuclear fuel from each of the (SONGS) Units 2 and 3 spent fuel pools to the Independent Spent Fuel Storage Installation (ISFSI) by the contractor Holtec. The final evolution for each MPC is the lowering (or "downloading") of the MPC into a Cavity Enclosure Container (CEC), until the canister is resting at the bottom of the CEC. This was the 29th MPC (out of a total of 73) to be downloaded. Each loaded canister weighs approximately 54 tons. The downloading process takes about 15 minutes from start of the lowering of the MPC, until the time that the MPC rests on the bottom of the CEC. The outside diameter of the MPC is approximately 76 inches and the inside diameter of the Divider Shield Ring (DSR - the narrowest component inside the CEC) is approximately 76.5 inches. This provides a X inch radial clearance between the MPC and the DSR.
Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event MATING OEVICEAOA.PTER-,. *';(..,
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.* - -OIV1DER SHELL On Aug. 3, 2018, during the first few minutes of the downloading process, the MPC came to rest on the top of the DSR and against the inside surface of the Hi-TRAC (Holtec International Transfer Cask). The Vertical Cask Transporter (VCT - mobile crane) slings went slack indicating the M PC was hung-up. The crane operator could not see the MPC (because this is a condition commonly called a blind lift) and a spotter assigned to observe the MPC did not recognize the slack sling condition.
The Cask Loading Supervisor (CLS),
Rigger-in-Charge (RIC) and the SCE ISFSI Project Oversight Specialist were located 150 feet away in a low radiation dose area observing the slings from the rear of the VCT and believed, because the slings appeared to be taut, that the MPC was being lowered to the bottom of the CEC. However, elevated radiation measurements taken near the VCT indicated that the MPC had not been fully lowered to its final resting position. Actions were initiated immediately to raise the VCT, lifting the MPC off the DSR, thereby placing the MPC load back on the slings and the MPC was subsequently lowered to the bottom of the CEC.
SIGNIFICANCE OF EVENT Calculations performed by Holtec, and independently verified by SCE and third-party subject matter experts, show conclusively that:
The DSR is structurally capable of supporting the full weight of the loaded MPC with substantial margin.
MPCs maintain complete confinement integrity if subjected to a postulated uncontrolled free fall event from the DSR, with substantial margin.
A review of the MPC special lifting devices used in the lifting operation demonstrate large margins of safety against structural failure.
Therefore, this incident did not, even under the assumption of an uncontrolled free fall from the DSR height, pose a risk of breach of the confinement boundary. There was no risk of radioactive exposure to the public; the health and safety of the public would never be affected in a postulated fall scenario.
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Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event BACKGROUND On December 3, 2014, SCE signed a client-assisted, turnkey, contract with Holtec International (Holtec) for the construction of an expanded Independent Spent Fuel Storage Installation (ISFSI), supply of Multi-Purpose Canisters (MPCs - fuel storage containers), and movement of spent fuel from the spent fuel pool to the ISFSI. Holtec is an NRC Certificate of Compliance (C of C) holder for both the MPCs and the ISFSls, and has an approved 10CFR72 Quality Assurance Program. The contract was structured such that Holtec was to work to Holtec-developed procedures, training, and processes.
EXTENT OF EFFORT Importantly, both the RCE and ACE looked far beyond the downloading event itself. As part of the Extent of Condition and Extent of Cause analysis, every evolution in the movement of fuel from the spent fuel pools to dry storage was examined. This examination included review of processes, procedures, training, oversight, and equipment. As a result, some 80 Corrective Actions were developed for the RCE and ACE, most of which will be completed prior to recommencement of Fuel Transfer Operations (FTO).
Since the MPC download process was performed by Holtec, in accordance with their Quality Assurance Program, they performed a Root Cause Evaluation (RCE) to determine the root cause of the event. SCE and Holtec assembled a team of internal and external cause evaluation and technical experts to carefully evaluate the causes of the event. Information gathered from Holtec's internal task force established to identify any hidden vulnerabilities in the Holtec pool-to-pad operational infrastructure and the investigative work performed by a senior expert review team also fed into the final RCE document. The RCE was a rigorous, systematic effort that spanned more than two months. The resulting RCE was reviewed by SCE site personnel, SCE third-party expert reviewers, and approved through the SCE SONGS Corrective Action Process (CAP).
SCE further believed it was prudent to conduct a self-critical analysis to identify weaknesses in its oversight responsibility that could have precluded the incident. In response to this event, SCE formed a multidisciplinary team, including an independent cause analysis subject matter expert, to perform an Apparent Cause Evaluation (ACE). The ACE was a rigorous, systematic effort, conducted over several months. In addition to the normal site Corrective Action Program review process, SCE obtained independent third-party reviews to ensure that the ACE was comprehensive and on-target.
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Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event HOLTEC ROOT CAUSE EVALUATION AND CORRECTIVE ACTIONS Although the RCE was concerned with the MPC downloading event, it did not stop there. The actions taken by Holtec to determine the root cause included reviews of processes, procedures, training, equipment, and qversight used throughout the entire scope of moving spent fuel from the pools to dry storage. Included was an examination of the life cycle of the "UMAX" storage system, including design, fabrication, construction and deployment. This RCE was an extensive effort, by a large multidiscipline team, to completely uncover the causes of the incident and determine corrective actions in order to assure that this, or a similar incident, will never happen again.
Root Cause (summary):
Holtec concluded that its management did not completely recognize the complexity and risks associated with fuel transfer operations while using a relatively new system design (UMAX) in conjunction with a long duration campaign and thus did not implement all necessary program improvements or the necessary level of oversight.
Contributing Causes (summaries}:
Procedures lacked sufficient detail (for the workforce to be successful) to recognize special conditions related to a new equipment system (UMAX).
Certain aspects of design features were not adequately captured and mitigated during the design review process.
Communication protocols with a chain of command established during MPC movement were not well defined.
A continuous learning environment which promotes the use of internal and external operating experience was not thoroughly utilized.
The Holtec Training Program did not consider uniqueness of UMAX system relative to HI-STORM system, nor the uniqueness of challenges raised in a long-term project; training was not sufficient to provide for error-free performance.
Summary of Holtec RCE Corrective Actions and Corrective Actions to Prevent Reoccurrence (not all-inclusive)
Revise all Holtec procedures (e.g. Site Loading and Safety procedures) to provide increased level of clarity and detail of performance requirements.
Develop a site-specific training program for all of the Holtec FTO work at SONGS which includes the attributes of a systematic approach to training.
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Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event Provide training to all loading personnel, based on the requirements of the newly developed site-specific training program, to ensure all personnel are trained and qualified prior to re-commencing loading activities.
Strengthen the involvement of senior leadership and management oversight during the implementation of FTO.
Use engineered features to monitor load while performing downloading to provide continuous monitoring of equipment load and position.
Conduct an effectiveness review of corrective action implementation for this RCE.
Implement an improved continuous learning environment by including low thresholds for the reporting and handling of adverse conditions. Ensure that, by the end of each work shift, abnormal or unexpected conditions are used as learning opportunities with all of the work crews.
Increase Holtec corporate governance and oversight of the project by structuring focused Quality Assurance assessments, providing assessment reporting, including key performance indicators and providing trending results to the site leadership team.
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Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event SCE APPARENT CAUSE EVALUATION AND CORRECTIVE ACTIONS The purpose of the Apparent Cause Evaluation by SCE was to determine to what extent SCE's oversight was not effective in preventing the event and why the activity was not stopped while in progress. The ACE looked closely at the Aug. 3 event and probed further into SCE's oversight role when Holtec's loading procedures and training programs were approved by SCE prior to Fuel Transfer Operations (FTO). It is an SCE management expectation that SCE Oversight Specialists (OS) provide direct oversight and observation of critical or high risk activities to ensure applicable procedures and processes are adhered to during these evolutions and initiate a stop work if discrepancies or safety issues are identified.
Apparent Cause (summary):
SCE ISFSI project management failed to establish a rigorous process to ensure:
Technically accurate Holtec procedures, SCE and Holtec training to support procedure implementation, and Sufficiently detailed Oversight Specialist (OS) guidance.
Contributing Causes (summaries):
SCE ISFSI project management observations were not routinely performed; and SCE ISFSI project management has not consistently reinforced initiation of an Action Request (AR) into the Corrective Action Program (CAP) for deviations from normal, even if covered by procedure.
Summary of SCE ACE Corrective Actions and Actions to Prevent Recurrence (not all-inclusive)
Train Oversight Specialists (OS) on Holtec procedure changes and equipment modifications, Holtec and SCE training program improvements, including detailed criteria developed for operating and training procedure review, Oversight Database documentation expectations, and NUREG-0612 (Heavy Loads Program).
Reinforce to the OS the use of Human Performance tools, including revised Roles and Responsibilities, Task-Specific OS Guidelines, and use of Situational Awareness tools.
Develop an OS experience matrix to ensure optimal OS coverage during each FTO process evolution.
Ensure the Oversight organization has a low threshold to place issues into the Corrective Action Process (CAP).
Conduct an effectiveness review of corrective action implementation for this ACE.
To ensure and maintain a consistent high-level of OS performance, use SCE management and peer-to-peer observations of OS work, and provide critical feedback.
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Summary of the Root Cause and Apparent Cause Evaluations of the August 2018 Download Event SCE management to conduct critique of Holtec field performance during simulator practice runs and, looking forward, during all aspects of the Holtec work for FTO.
Ensure Operating Experience (from SONGS, other ISFSI sites, EPRI, NEI, etc.) is used to effectively improve performance.
Revise the SCE Contractor Oversight procedure to include rigorous review requirements for Vendor/Contractor Operations, Maintenance, Quality, and Training Programs, including all procedures that implement such programs.
Review the revised Holtec procedures, training, and corrective action process, and ensure they meet the required regulatory standards.
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