25th Annual Report, Volume II, Exhibit D.9, Diablo Canyon Independent Safety Committee Report on Fact Finding Meeting at DCPP on May 20–21, 2015 by Per F. Peterson, Member, and David C. Linnen, Consultant

1.0 Summary

The results of the May 20–21, 2015 fact-finding trip to the Diablo Canyon Power Plant in Avila Beach, CA are presented. The subjects addressed and summarized in Section 3 are as follows:

  1. Plant Health Committee Meeting
  2. Discussion with NRC Senior Resident Inspector
  3. Office Seismic Safety
  4. Discussion with PG&E Chief Nuclear Officer
  5. Seismically Induced System Interactions (SISI) Housekeeping Program
  6. Seismic Reviews of DCPP’s Replacement Steam Generators and New Reactor Vessel Heads
  7. Benchmarking Program
  8. Operating Experience Program
  9. Potential for Chloride Stress Corrosion Cracking (CSCC) of Multi-purpose Canisters (MPCs) in the Independent Spent Fuel Storage Installation (ISFSI)
  10. External Flooding Assessment
  11. Quarterly Station Performance Review Meeting

2.0 Introduction

This fact-finding trip to the DCPP was made to evaluate specific safety matters for the DCISC. The objective of the evaluation was to determine if PG&E’s performance is appropriate and whether any areas revealed observations which are important enough to warrant further review, follow-up, or presentation at a Public Meeting. These safety matters include follow-up and/or continuing review efforts by the Committee, as well as those identified as a result of reviews of various safety-related documents.

Section 4—Conclusions highlights the conclusions of the Fact-finding Team based on items reported in Section 3—Discussion. These highlights also include the team’s suggested follow-up items for the DCISC, such as scheduling future fact-finding meetings on the topic, presentations at future public meetings, and requests for future updates or information from DCPP on specific areas of interest, etc.

Section 5—Recommendations lists specific recommendations to PG&E proposed by the Fact-finding Team. These recommendations will be considered by the DCISC. After review and approval by the DCISC, the Fact-finding Report, including its recommendations, is provided to PG&E. The Fact-finding Report will also appear in the DCISC Annual Report.

3.0 Discussion

3.1 Plant Health Committee Meeting

The DCISC Fact-finding Team (FFT) observed a routine weekly meeting of the Plant Health Committee (PHC). The DCISC last reviewed such a meeting in April 2015 (Reference 6.1), when it concluded the following:

The April 22, 2015 DCPP Plant Health Committee (responsible for plant system health), meeting was focused on improving the system health of the 480Volt Vital and Non-Vital systems. The meeting was conducted crisply and effectively. The DCISC should observe these meetings regularly.

The PHC is governed by DCPP Procedure OM4.ID16, “Plant Health Committee” and is a management team responsible for:

The membership of the PHC Core Team, which is the Decision Making (i.e. voting) group of the PHC, is as follows:

Also, any other Director may serve as a Decision Making Member at the discretion of the Chairman.

The PHC is also supplemented by a group of Supporting (non-voting) Members as shown below:

Plant health issues that require PHC periodic review include:

Prior to the Fact-finding Visit, the DCISC Fact-finding Team reviewed its most recent copy of DCPP’s most recent monthly Plant Performance Improvement Report (PPIR) (released April 16 for March 2015 data) which, among many other things, provides a listing of plant systems whose Health has been rated Red (Unsatisfactory) or Yellow (Deficient), for Unit 1, Unit 2, or Both. The following systems were on those lists:

Red

Yellow

The agenda for this meeting included the following:

The meeting was conducted with great efficiency, and the agenda was covered as scheduled. It was evident that discussion by focus groups prior to the meeting helped the attendees prepare for the meeting. Great emphasis was placed on plant safety and reliability throughout the discussion.

A portion of the meeting was designated for discussion of the Units 1 and 2 Reactor Coolant Systems (RCS), both of which are rated as Yellow (Unhealthy) and have been Unhealthy for about a year. The discussion was classified as a “6-month Review” of this topic. The RCS System Health Reports had been distributed to the attendees for their review prior to the meeting. Also, the most recent Plant Performance Improvement Report indicates that those systems are expected to return to Healthy status during Refueling Outages 1R19 (i.e. 4th Quarter 2015) and 2R19 (i.e. 1st Quarter 2016) respectively. The DCISC’s most recent review of these systems was in September 2014.

Throughout the meeting attendees actively engaged in providing their input and in asking questions of others. The meeting Chairman encouraged this interaction. This included providing differing opinions, having questioning attitudes, and yet reaching agreement on issues being discussed. Participants appeared to be well prepared for the meeting and knowledgeable of the topics being discussed. During the discussion, a plant announcement was made over the P/A system, and discussion immediately ceased so that all attendees could hear the announcement.

The objective of maintaining safe and reliable nuclear plant operation was stated on a number of occasions. Actions were assigned to participants as the meeting progressed and captured for future reference. Participants readily accepted responsibility for these future actions as the needs arose.

Conclusions:
The Plant Health Committee meeting was conducted efficiently and effectively. Members and presenters appeared to be well prepared. Discussion was active, thoughtful, and probing, with a focus on safety. The DCISC should consider conducting a Fact-finding review of the Reactor Coolant Systems of both Units prior to the 4th Quarter of 2015 since both systems have been rated as Unhealthy for about a year.
Recommendations:
None

3.2 Discussion with NRC Senior Resident Inspector

The DCISC Fact-finding Team met with Mr. Thomas Hipschman, DCPP’s NRC Senior Resident Inspector. The DCISC last discussed issues/topics pertaining to DCPP with the station’s NRC Resident or Senior Resident Inspector during DCISC’s April 2015 Fact-finding Visit (Reference 6.2), when it concluded:

The DCISC periodic meetings with the NRC Resident and/or Senior Resident Inspector continue to be beneficial for sharing of information on important DCPP issues.

Topics that were discussed by the DCISC Fact-finding Team and Mr. Hipschman included the following:

Conclusions:
DCISC meetings with the NRC Resident, or Senior Resident, Inspector continue to be beneficial with regard to sharing information and to understanding issues important to the NRC and DCISC. Because it could be beneficial to have a future DCISC Public Meeting scheduled in the same week as a NRC public meeting, the DCISC should follow up to see if this can be coordinated in the future.
Recommendations:
None

3.3 Office Seismic Safety

The DCISC Fact-finding Team met with Tom Baldwin, Site Services Director, to discuss DCPP’s continuing efforts to address office seismic safety. The DCISC last reviewed this topic during its December 2-3, 2014 Fact-finding Visit (Reference 6.3), when the DCISC concluded:

DCPP has been making good faith efforts in recent years with regard to Office/Personnel Seismic Safety. Much progress has been made, and status is at the point where an Action Plan is no longer needed. However, it is likely that some potential hazards may have been overlooked and could pose a risk to employees and/or might impede employee response to an earthquake. DCPP should consider ways to encourage its employees to self-report items of potential risk. Also, PG&E’s methods of responding in its corporate offices in San Francisco after the 1989 Loma Prieta earthquake, which shook all of San Francisco and environs and caused dozens of deaths, might be helpful to DCPP.

The initial portion of this fact-finding meeting was devoted to reviewing activities that have taken place within DCPP with regard to office seismic safety, as well as actions that have been taken by the DCISC to encourage appropriate station efforts with respect to this issue. In Mr. Baldwin’s new position as Director of Site Services, he has taken a proactive approach to gain a clearer understanding of the DCISC’s view of DCPP’s current status. To assist in this, the Fact-finding Team provided Mr. Baldwin with copies of some of DCISC’s past Fact-finding reports on this topic.

Although the DCISC has been reviewing DCPP’s plant seismic safety since the Committee’s inception, Office Seismic Safety was not examined and reported as a distinct topic until May 2010. Since then the DCISC has reviewed this specific issue at least annually, and more often during the last two years. Likewise, DCPP has more actively focused on this specific topic since 2010 and has made considerable progress, which has involved:

Nevertheless, during various Fact-finding Visits over the most recent two years, the DCISC Fact-finding Teams continue to identify heavy, tall office furniture that needs to be braced in order to avoid harming personnel in the event of a significant earthquake. During this particular Fact-finding (FF) Visit in May 2015, the FF Team was able to identify a number of tall, heavy, unsecured pieces of office furniture that would be expected to topple during an earthquake. The furniture is located on the 5th Floor of DCPP’s Administration Building. Mr. Baldwin accompanied the FF Team throughout this review. During a portion of this inspection, the FF Team was also accompanied by DCPP’s Fire Captain, Dan Ensminger. Captain Ensminger noted that a Station Notification (50705251) has been written to provide for coordinating future seismic safety inspections with fire safety inspections. The DCISC Fact-finding Team believes that such coordination will be beneficial to the quality of both inspections.

Conclusions:
Although DCPP has made much progress in recent years in the seismic bracing of tall furniture, there continue to be instances where seismic bracing is needed. The recent personal involvement of a senior station manager in this issue is a noteworthy expression of the station’s interest in completely resolving the issue. DCPP’s intent to conduct seismic safety inspections in conjunction with fire safety inspections can be expected to increase the safety benefit of each type of inspection. The DCISC should consider reexamining this issue in mid-2016.
Recommendations:
None

3.4 Discussion with PG&E Chief Nuclear Officer

DCISC Member, Per F. Peterson, met with PG&E’s Senior Vice President and Chief Nuclear Officer, Ed Halpin. Discussion included topics pertaining to this Fact-finding Visit and other items of mutual interest.

3.5 Seismically Induced Systems Interaction (SISI) Housekeeping Program

The DCISC Fact-finding Team met with Rich Harvey, Work Week Manager, and Craig Stolz, Seismically Induced Systems Interaction (SISI) Housekeeping Program Owner. The DCISC last reviewed this topic in May 2011 (Reference 6.4), when it concluded:

Performance appears to have improved considerably in the area of DCPP’s Seismically Induced Systems Interaction Housekeeping Program since the DCISC Fact-finding Team’s last review of this topic in July 2010. Recognizing that increased effort and attention to detail on this issue will be needed as a result of the accidents at Fukushima, the DCISC should review this topic on a periodic basis through Fact-finding trips and/or through DCPP presentations at Public Meetings.

Station performance with respect to Seismically Induced Systems Interaction is governed by procedure AD4.ID3, “SISI Housekeeping Activities.” The procedure specifically notes that SISI applies to any of the following:

The procedure also specifies that it does not apply to SISIP evaluations associated with design modifications. These evaluations are specifically governed by other station procedures.

The objective of the SISI Housekeeping Program is to ensure that safe-shutdown systems, structures, and components, as well as certain accident-mitigating systems, will function properly during and following an earthquake. The procedure’s intent is to ensure that needed components and equipment will not be impacted during an earthquake by improperly positioned or restrained transient equipment or alterations made to systems, structures, or components.

The procedure provides a lengthy list of examples of temporary equipment and components that could damage plant equipment if stored unrestrained in unacceptable areas of the plant, and/or inadequately secured, and if an earthquake were to occur. Some examples are tools, ladders, gas bottles, work-benches, rigging equipment, test equipment, temporary power load centers, and parts resulting from operations, maintenance, modifications, or testing activities.

One method to help prevent an undesirable seismic impact on plant systems has involved the designation of “SISI Safe Areas,” which have been evaluated by Engineering and are predesignated throughout the plant. As such, these areas are intended for repeated use and do not require an SISI evaluation by engineering when the need occurs to store items temporarily in those areas. Such areas are identified by NOTICE signs located throughout the Turbine Building, Auxiliary Building, and Fuel Handling Building.

The Engineering Evaluation resulting in the identification of an “SISI Safe Area” involves identifying potential “Targets,” which are defined by Procedure AD4.ID3 as systems, structures, and components that are required to “safely shutdown the plant, maintain the plant in a safe shutdown condition, and/or maintain the function of accident mitigating systems.” Targets also include related tubing, instrumentation, electrical circuitry, and component supports that are necessary to ensure that the associated systems, structures and components can perform their design functions. Thus, the “SISI Safe Areas” are locations where stored equipment, tools, or components could not negatively affect “Targets” and therefore could not have a negative on impact nuclear safety in the event of an earthquake.

Procedure AD4.ID3 also provides guidance to help inspect for and evaluate potential SISI housekeeping issues. As would be expected, this process depends to a great extent on examining areas outside the “SISI Safe Areas” as well as examining the adequacy of restraints applied to materials being temporarily stored in the vicinity of SISI “Targets.”

DCPP has a programmatic requirement to perform, and to report on, a quadrennial SISI Program Self-assessment. The results of the most recent Self-assessment, conducted in August 2014, were provided to the DCISC Fact-finding Team. Since it had been four years since its previous, formal self-assessment, DCPP contacted another station by phone prior to performing the self-assessment to determine any lessons learned from that station’s self-assessment.

DCPP’s formal Self-assessment had one Deficiency, no Strengths, six positive findings, and six gaps representing opportunities for improvement. The Deficiency was that DCPP did not have an SISI Walkdown Checklist for conducting area walkdowns. Strengths included the overall conservatism of the program, plant cleanliness and housekeeping, procedure adherence by workers, worker knowledge of SISI Program requirements, definition of General Plant Personnel Responsibilities, and a number of effective procedural elements. The gaps primarily pertained to clarity of some aspects of procedures, to the inadequacy of some performance metrics for clearly identifying some trends and for providing insights, and to not modeling SISI concepts in training labs.

Station performance with respect to the SISI Housekeeping Program is reported in DCPP’s monthly Plant Performance Improvement Report. Each monthly report tracks SISI performance for each month during the prior twelve. Performance is graded each month on a point basis with 100 being the maximum achievable. However, points are subtracted from 100 for each of the following types of deficiencies that are noted during the month:

The resulting monthly point scores are then translated into performance categories, as follows:

Because a number of years had transpired since the DCISC’s last Fact-finding review of this topic, the DCISC Fact-finding Team examined DCPP’s reported monthly performance from January 2013 to the present. From January 2013 through January 2014, each of the monthly indicators was Green. In February 2014 two issues were identified, which resulted in a White rating. In March 2014, five issues were reported, yielding a Red rating; and April and May 2014 were rated Green. The indicator for June 2014 was Red due to some issues identified by the NRC during plant inspections. The monthly indicators then returned to Green from July 2014 through April 2015, except for September 2014, which was White due to some outage work related issues.

Conclusions:
DCPP’s Performance with respect to its Seismically Induced Systems Interaction Program appears to have been reasonably strong and stable during the past few years, with the exception of a few nonconformances. Given the heightened attention to seismicity during this same period, DCISC should review this program at a frequency of at least once every 2 years.
Recommendations:
None

3.6 Seismic Reviews of DCPP’s Steam Generators and Reactor Vessel Heads

The DCISC Fact-finding Team met with Nozar Jahangir, Seismic Engineering Manager, and Kristin Zaitz, Engineer. Although this is DCISC’s first review of this specific collective topic, the DCISC has been actively following station progress with respect to the updated seismic evaluation of the entire plant facility and site, which has direct implications for this topic. The DCISC’s most recent review of PG&E’s Site Seismic Study was conducted on March 30, 2015 at PG&E’s corporate office in San Francisco, as part of the DCISC’s March 30—April 1, 2015 Fact-finding Visit (Reference 6.5), where the DCISC Fact-finding Team concluded:

PG&E submitted its most recent report to the NRC on the site seismic hazard in mid-March 2015. The work contained in this report is clearly a major advance over previous analyses. It will be reviewed in the near future both by the NRC staff and by other outside experts. The DCISC should continue to review this topic too, by studying the underlying technical data and reports and reviewing the reviews of others.

However, even more recently, during the DCISC’s review of the status of DCPP’s Licensing Basis Verification Project in its April 2015 Fact-finding Visit (Reference 6.6), the DCISC Fact-finding Team drew the following conclusion with respect to the seismicity of DCPP’s Steam Generators and Reactor Vessel Heads:

DCPP’s Licensing Basis Verification Project (LBVP) continues to progress on schedule with a completion date of year-end 2015. An issue identified by the Project, incorrect specification of the seismic and loss-of-coolant accident loads on the new reactor vessel heads and steam generators, is being re-evaluated, and is expected to be completed by September 2015.

PG&E is also engaged in a “Seismic Fragility Probabilistic Risk Assessment (PRA).” This topic was last reviewed by the DCISC in August 2014 (Reference 6.7) when it concluded:

DCPP is proceeding satisfactorily with its Seismic Fragility Probability Risk Assessment (SFPRA) analysis using the latest methodology and seismic response spectra. SFPRA is a very useful tool, because it provides information about the likelihood of different plant damage states caused by earthquakes. Because the seismic PRA provides improved information on the most probable plant damage states that could be caused by an earthquake, the DCISC recommends that this information be used in developing the DCPP FLEX strategy to respond to beyond design basis earthquakes. Although early, there have been no problems identified. The DCISC should continue to monitor this analysis, and review how the DCPP FLEX program uses SFPRA results to develop mitigation strategies for beyond design basis earthquakes.

As noted above, the DCPP-specific requirements for procurement of these major pieces of equipment had been overlooked when they were ordered as replacements, and this equipment had been designed rather to generic industry seismic load requirements and those pertaining to Loss of Coolant Accident (LOCA) loads. This particular issue is being addressed through a re-analysis being performed as part of the LBVP, and this re-analysis is expected to be complete by September 30, 2015.

There is an additional commonality between the hazards to the New Steam Generators and hazards to the New Reactor Vessel Heads. That is, since both types of equipment are replacements for original equipment, both also may need to be examined collectively, as well as individually, for their ability to withstand a Loss of Coolant Accident (LOCA) occurring simultaneously with an earthquake, as were the original pieces of equipment.

In addition, it may be advisable to install seismic instrumentation on these large vessels in order to be able to verify how any future seismic ground motion and acceleration affects the shaking of this equipment. Nevertheless, it can be stated that thus far, since the replacement of this large equipment, all of this equipment has been functioning properly.

Conclusions:
Ongoing seismic re-evaluations include verifying the capability of DCPP’s Steam Generators and Reactor Vessel Heads to withstand a Design Basis Earthquake. They have also been separately analyzed to withstand a Design Basis Loss of Coolant Accident. However, more analysis may be needed in to confirm that this equipment can also withstand a Design Basis Earthquake that occurs concurrently with a Design Basis Loss of Coolant Accident. Also the re-analysis of the seismic and loss of coolant accident loads on this equipment is expected to be complete by September 2015. In addition, it may be appropriate to install seismic instrumentation on this equipment in order to verify how future seismic events affect the motion of this equipment.
Recommendations:
None

3.7 Benchmarking Program

The DCISC Fact-finding Team met with Derek Schmidt, Senior Performance Improvement Coordinator. The DCISC last reviewed DCPP’s Benchmarking Program in January 2013 (Reference 6.8), when it concluded:

The Benchmarking Program appears to be active and productive. It continues to provide for formal and informal examinations of a broad range of nuclear plant performance areas. The material provided by DCPP’s Program Owner to the Fact-finding Team was especially well organized and extensive. This program appears to warrant DCISC’s to warrant DCISC’s review no more frequently than biennially.

Station Procedure OM15.ID4, “Self-Assessment and Benchmarking Procedure, OM15.ID4,” defines benchmarking as “A study which first identifies best practices in one or more organizations and subsequently compares DCPP programs, processes, products, and services to identify gaps, develop recommendations, and set targets to improve performance.” “Formal” benchmarking is a highly structured process that involves scheduling, planning, training, conducting a site visit by a DCPP team, documenting results in written reports, planning and tracking corrective actions, and evaluating the resultant changes. “Informal” benchmarking may consist of telephone interviews, surveys, resource sharing, attendance at industry meetings, querying site visitors, or internal benchmarking. Informal benchmarking may also include a site visit or a trip to a vendor or another plant, but without the structure of a formal program.

The station’s Self-assessment Review Board (SARB) is the governing and reviewing body for all formal benchmarking. It is a group composed of appropriate members of the leadership team to provide oversight of benchmarking schedules, plans, and results, as well as oversight of operating experience and other station programs.

Station departments have the latitude to conduct informal benchmarking without having to schedule them through SARB. These can be conducted by phone or e-mail. Also, effectiveness reviews are expected to be conducted at the department level for Benchmarking activities.

As a part of DCPP’s routine correspondence, DCISC is provided with copies or summaries of various station reports and other documents, some of which report the Benchmarking activities that are conducted by DCPP. Examples of the topics of some of these Benchmarking reports that have been reviewed by DCISC during the past year are as follows:

  1. Feedwater Iron Strategies
  2. “Fix It Now” Benchmark Report
  3. Design Drafting and Drawing Incorporation
  4. Work Week “T+1” Meeting
  5. Functioning of the Equipment Reliability Working Group
  6. Evaluation of Operating Crew Performance in the Simulator
  7. Operations Training Program
  8. Pressurized Water Reactor Owners Group Procedure Subcommittee Meeting, with special focus on Emergency Operating Procedures, Severe Accident Management Guidelines, Extreme Damage Mitigation Guidelines, and Fukushima Response Support Guidelines

Information in the reports reviewed by the DCISC Fact-finding Team appeared to be clear and focused, and would be expected to be of potential help to the station.

Conclusions:
The Benchmarking Program appears to continue being an active and productive method for obtaining information supporting the achievement and maintenance of safe and reliable nuclear plant operation. It continues to provide for formal and informal examinations of a broad range of nuclear plant performance areas. The program again appears to warrant DCISC’s review no more frequently than biennially.
Recommendations:
None

3.8 Operating Experience Program

The DCISC Fact-finding Team met with Derek Schmidt, Senior Performance Improvement Coordinator. The DCISC last reviewed DCPP’s Operating Experience Program in September 2013 (Reference 6.9), when it concluded:

The DCPP Operating Experience Program is well established and, though below DCPP’s desired goal in performance, is improving. DCPP is taking actions to benchmark industry best performance and practices and incorporate them.

Industry operating experience information comes from two primary sources:

  1. An Industry Consolidated Event System (ICES)
  2. Other, including NRC, industry vendors, etc.

The former has the most extensive collection of operating event information.

The Plant receives 15-20 Operating Experience (OE) documents weekly from a variety of sources as noted above. These OEs are screened and information considered to be relevant to DCPP is transmitted to department Subject Matter Experts (SMEs) who review the material for specific applicability to their areas and determine appropriate action. The process and requirements for reviewing, screening, disseminating, and evaluating this industry OE are described and controlled by plant procedure: “Assessment of Industry Operating Experience.” In addition to receiving industry OE, DCPP also provides its own operating experience reports to both NRC and for others in the industry.

The DCISC Fact-finding Team (FFT) reviewed DCPP OE Program Health for the month of February 2015 as shown in DCPP’s Plant Performance Improvement Report (PPIR), dated March 16, 2015. The health report measures the following attributes:

A system of point values and weighting values is used for assessing performance of each of the above attributes, which are combined to assess overall OE Program Performance.

The scale on which performance is reported is:

OE Program Health had been Red (Unacceptable) for the period ending two months prior to the report, then improved to Yellow (Needs Improvement) for the period ending one month prior to the report, and again improved to Green for the most recent month. These overall improvements were due almost exclusively to improvements in Evaluation Quality and Timeliness. The DCISC Fact-finding Team also reviewed prior monthly PPIRs dating back through May 2014 to discern DCPP monthly performance over a longer time span. In none of those prior months was DCPP’s OE overall performance rated as Red. One overall rating was Yellow (November 2014) and the ratings in the other months were Green and White. The predominant reasons for these lower ratings involved timeliness of both evaluations and processing of the industry documents.

DCPP also continues to engage with others in the industry in order to adopt and maintain best industry practices and has also continued to review industry performance metrics to identify top performers.

Conclusions:
DCPP continues to maintain an active and effective Operating Experience Program. DCISC should continue to examine this topic on a frequency no greater than biennially.
Recommendations:
None

3.9 Potential for Chloride Stress Corrosion Cracking (CSCC) of Multi-purpose Canisters (MPCs) in the Independent Spent Fuel Storage Installation (ISFSI)

The DCISC Fact-finding Team met with Larry Pulley, Used Fuel Storage Manager, to discuss the Potential for Chloride-induced Stress Corrosion Cracking (CSCC) of Multi-purpose Canisters (MPCs) in the Independent Spent Fuel Storage Installation (ISFSI). This is the DCISC’s first review of this topic.

After each nuclear fuel cycle, the operating unit is shut down, and a portion of the nuclear fuel is removed from that reactor and replaced with new nuclear fuel. The spent nuclear fuel assemblies are then temporarily stored (for a number of years) in the Unit’s Spent Fuel Pool. However, each Spent Fuel Pool, one for each operating Unit, has a capacity that is limited. Therefore, DCPP has constructed an Independent Spent Fuel Storage Installation (ISFSI) pad above the plant on a hill to the east of the plant, on which this spent nuclear fuel is stored after undergoing a highly controlled transfer process. The spent fuel assemblies (32 in each movement) are inserted into a stainless steel MPC-32 which is then sealed and welded, and is eventually transferred into a thick concrete and steel High Integrity Storage Module (HI-STORM), which is then fastened to a reinforced concrete pad at the ISFSI. A more detailed description of this transfer process from the Spent Fuel Pool is as follows:

The key points for the purpose of this issue are:

Mr. Pulley noted that the industry is pursuing this issue and that he is a member of the Electric Power Research Institute’s (EPRI’s) Technical Advisory Committee on Stress Corrosion Cracking. DCPP is part of an EPRI pilot program where some sample swabs have been taken from the surfaces of some MPCs, from the circumferential weld at the midpoint as well as from an axial weld. The samples were analyzed, and found to contain chlorides. He noted further that different types of stainless steel have differing degrees of susceptibility to chloride stress induced corrosion cracking, and he noted that lower carbon content in stainless steel tends to reduce its susceptibility to this type of corrosion. He mentioned four types in particular: 304 (austenitic), 304L (L means lower carbon), 316, and 316L. The 304 stainless were determined to be the most susceptible to this corrosion, and Mr. Pulley noted that the first two sets of DCPP’s casks (16 casks in total) transferred to the ISFSI in 2009 and 2010 contain MPCs made of 304 stainless.

On November 14, 2012, the Nuclear Regulatory Commission issued NRC Information Notice (IN 2012-20) to all holders and applicants for an independent spent fuel storage installation (ISFSI) license. The reason for this notice was “To inform addressees of recent issues and technical information concerning the potential for chloride-induced stress corrosion cracking (SCC) of austenitic stainless steel dry cask storage system canisters. Significant SCC could affect the ability of the spent fuel storage canisters to perform their confinement function during the initial license or license renewal storage period(s). The NRC expects that recipients will review this information to determine how it applies to their designs and facilities and consider actions, as appropriate, to avoid these potential problems. However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.”

The NRC’s Information Notice further provides background information, as follows:

“SCC is induced from the combination of tensile stress and a specific corrosive environment. Austenitic stainless steels under tensile stress are known to be susceptible to SCC when exposed to chlorides in the environment. A literature survey has revealed failures attributed to chloride-induced SCC in the types of austenitic stainless steels typically used in dry cask storage system canisters when these materials are exposed to atmospheric conditions near salt-water bodies. This phenomenon is of concern at temperature and relative humidity combinations that allow the chloride compounds to deliquesce (i.e. to become soft or liquid with age). It is thought that airborne salts could deposit on the material surface, then form chloride-rich deliquescent brines in conditions of high relative humidity. Laboratory data suggests that chloride-induced SCC is of particular concern as the canister surface temperature decreases to the level where salt will deliquesce.”

“Researchers do not yet fully understand the relationship between the proximity to a salt-water body and the potential for chloride deposition on a dry cask storage system canister. However, it should be noted that many ISFSIs are located near salt-water bodies or other sources of chlorides, such as salted roads or condensed cooling tower water. These canisters may have high tensile residual stresses from welding or other fabrication processes.”

NRC Information Notice 2012-20 further states:

“The NRC is currently evaluating data to determine the level of susceptibility and potential safety significance for existing licenses and certificates. The NRC has engaged the Nuclear Energy Institute (NEI) to describe information related to structures, systems, and components important and to understand industry plans for generically addressing this issue. The NRC also has communicated concerns and technical information regarding this topic at several stakeholder meetings. At this point, no immediate safety concern has been identified with currently approved licenses that would warrant a backfit analysis under 10CFR 72.62, ‘Backfitting.’ However, maintenance and surveillance programs during initial license periods and aging management programs (AMPs) during license renewal periods are required to address aging effects, such as chloride-induced SCC, as appropriate for the relevant canister design(s), operating conditions, specific site environmental conditions, and proposed license renewal periods.”

As stated above, NEI has been engaged in supporting the industry on this issue. In an October 29, 2014 letter to the NRC, NEI concluded, and informed the NRC and the industry, that this issue “Has not reached a level of urgency of safety significance to qualify it for the NRC’s generic safety issue process because testing is inconclusive (laboratory conditions do not accurately represent in-situ conditions at ISFSI sites), actual conditions (atmospheric and cask) vary from site to site and from model to model and cask to cask; and actual field data is insufficient. Since there is not an immediate safety concern, use of this protocol permits a deliberate yet timely approach to understanding the issue and creating the necessary tools for licensing and implementing prevention and mitigation strategies, as necessary.” NEI’s stated goal at that time was to finalize and send to the NRC by June 2015 “Industry Susceptibility Criteria that can be used by ISFSI licensees to evaluate the potential for Chloride Induced Stress Corrosion Cracking to occur on canisters at their site.”

Measurement of the surface temperature of the canisters in the DCPP ISFSI, along with the outside ambient temperature, provides a way to verify that the canister surface temperatures are sufficiently high to make deliquescence impossible, even if the air relative humidity is 100%. The rate of decay heat generation in the canisters currently in storage is sufficiently high that this condition exists and deliquescence is impossible. One concern is that in coming decades, decay heat generation will drop and ISFSI canisters may then become vulnerable to deliquescence and SCC. Given the age of the spent fuel in storage in the ISFSI, the dominant heat generation comes from decay of Cs-137 and Sr-90, which have 30-year half-lives, so heat generation can be expected to drop by about half every 30 years. However, if the canister temperatures are monitored, it will be possible to block air vent holes in the over pack containers to reduce air flow, and thus to maintain appropriate canister temperatures over extended periods of time if required.

PG&E and the state of California are also examining the possibility of installing salt-water cooling towers as an option to once through cooling. To the extent possible it would be advisable to examine the potential impact of such cooling towers on salt deposition rates at the ISFSI, and the accompanying impact on the possible deliquescence and SCC phenomena for the ISFSI Multipurpose Canisters.

Conclusions:
DCPP is participating in an industry initiative to determine the impact of atmospheric chlorides on the corrosion rate of ISFSI Multipurpose Canisters (MPCs). It is expected that these corrosion rates will be individually dependent upon the material properties of the individual MPCs and the atmospheric conditions at each ISFSI. DCPP’s initial 16 MPCs that were used for transfer of used nuclear fuel to the ISFSI are made of 304 austenitic stainless steel, which tends to be somewhat more susceptible to chloride induced stress corrosion cracking than other types of stainless steel that are used for this purpose. Deliquescence that can cause stress corrosion cracking can be made impossible if the canister surface temperatures are maintained sufficiently above outside ambient temperatures, so periodic monitoring of canister temperatures is valuable. Because PG&E and the state of California are examining the possibility of installing salt-water cooling towers as an option to once through cooling at DCPP, it would be advisable, to the extent possible, to examine the potential impact of such cooling towers on the rate of salt aerosol deposition at the ISFSI.
Recommendations:
None

3.10 External Flooding Assessment

The DCISC Fact-finding Team met with Scott Maze, Fukushima Project Supervisor; Behooz Shakibnia, Civil Supervisor, Design Engineering; Julio Barbosa, Mechanical Design Engineer; Allen Clark, Architect, Civil Group; and Hector Garcia, Mechanical Design Engineering Supervisor. Although the DCISC has examined tsunami risk in earlier Fact-finding Visits, this is DCISC’s first Fact-finding review of this collective topic.

This PG&E assessment of external flooding was conducted in response to an NRC Request for Information dated March 12, 2012. In it the NRC requested DCPP to re-evaluate site seismic and flooding hazards using updated flooding information and present-day regulatory guidance and methodologies. In essence, the review was to be conducted in the same way as if DCPP were a new plant. With respect to the flooding aspects, PG&E’s 90 day response letter, DCL-12-058, stated that PG&E would submit the flooding hazards reevaluation to the NRC by March 12, 2015. (PG&E’s Response was submitted on March 11, 2015 in PG&E Letter DCL-15-034.) PG&E further committed that if its flooding reevaluation was not bounded by the Current Licensing Basis (CLB), then PG&E would evaluate and/or discuss mitigation actions in an Integrated Assessment by March 2017.

In addition to following the NRC’s formal regulatory guidance for a response to a Request for Information, PG&E adhered to the requirements of the following NRC documents pertaining to this specific request:

The analysis was performed in a hierarchical fashion. That is, the most conservative assumptions were embedded in the first analysis, such as assuming that no active components remain functional and the site drainage network is completely blocked. After this, another analysis was performed using assumptions that were more realistic. This progression of analyses is referred to as a Hierarchical Hazard Assessment (HHA).

Historical data was used to determine the values that are relevant. For example, to obtain Probable Maximum Precipitation (PMP) historical California data was extracted for all-season data, seasonal data, and local storm data. Local Intense Precipitation (LIP) (i.e. microbursts) was also examined over the entire site drainage basin.

Tsunami/Ocean analyses had been performed to calculate the effects of distant and near source tsunamis due to earthquakes as well as offshore landslides, including the effects of updated hydrostatic and hydrodynamic forces, debris and water-borne projectiles, and sediment & erosion. Likewise storm surges were also incorporated using historical wave data.

The historical records of local intense precipitation (LIP) were also reexamined along with the flow paths for the accumulating water that could enter the plant and affect equipment. To determine areas and equipment that could be affected, site walkdowns were performed, including the identification of potential entry points providing flow paths to equipment that is important to safety. The determination of maximum water surface elevations then allowed the assessment of whether equipment would be affected. This reanalysis indicated that there is a potential for inundation of power block structures during a LIP event. PG&E’s Letter DCL-15-034 noted: “The flood hazard reevaluations are distinct from the current design and licensing bases of DCPP and do not alter the terms of the license. NRC staff considers the flood hazard reevaluations being performed to be beyond the current design/licensing basis of operating plants (NRC, 2012c).”

Findings of the report are as follows:

Based on the determination of the potential impact of a local intense precipitation event on plant safety, this type of event will be examined further and addressed in an Integrated Assessment that is required to be submitted to the NRC prior to March 13, 2017.

Conclusions:
PG&E’s Flood Hazard Reevaluation of the DCPP site appears to be detailed and thorough. Local intense precipitation (LIP) was determined to present the only potential risk of inundation of the power block structures. PG&E further noted that NRC has considered LIP to be beyond the current design and licensing basis of the plant. In conformance with a commitment that PG&E made to the NRC, PG&E will conduct further examination of LIP and address the results in an Integrated Assessment that will be submitted to the NRC prior to March 13, 2017.
Recommendations:
None

3.11 Quarterly Station Performance Review Meeting

The DCISC Fact-finding Team attended the first 90 minutes of a 3½ hour Quarterly Station Performance Review Meeting (PRM). The DCISC last attended such a meeting in July 2012 (Reference 6.10), when these meetings were held on a monthly basis, and when the DCISC concluded:

The DCPP Monthly Performance Review Meeting was well structured and focused and was conducted effectively. The focus was primarily on topics related to current station initiatives on Event Free Operations, Performance Improvement, and Regulatory Excellence. The DCISC should consider reviewing the elements of DCPP’s station initiative for achieving Event Free Operations either in a future Fact-finding Visit or Public Meeting.

The overall expressed purpose of these meetings is to align the station leadership team on actions needed to help drive positive performance. Participants in the meeting were largely senior manager and manager level personnel, over 20 in number, from a wide range of technical disciplines. During the course of the meeting individual attendees provided brief summaries (about 5 minutes each) of over 20 key areas of station performance in which their individual areas of responsibility had the lead. The desired outcomes of these discussions were to:

Since it was often the case that other station work groups provided support to performance areas being discussed, those other managers would inject their own comments regarding the subject activities. These same individuals would also summarize their own responsibilities for assisting in addressing issues for which another group had the lead.

The Chairman of the meeting was actively engaged in frequently summarizing the material being presented and ensuring that the appropriate individuals understood their specific responsibilities. He also provided positive feedback with regard to progress that was being achieved in various areas. He occasionally asked questions regarding the degree to which presenters needed help from others in order to address specific issues. He emphasized the importance of maintaining effective alignment between DCPP’s managers, which is the manifestation of organizational alignment.

A listing of Action Items stemming from the previous Station Performance Review Meeting (February 19, 2015) was also reviewed. All but three of the 14 had been completed, and the remaining three were administrative in nature.

Conclusions:
The quarterly Performance Review Meeting was well structured, appropriately focused, and conducted efficiently and effectively. The meeting provided a framework for DCPP management personnel to stay updated on key station issues and associated responsibilities, and it fostered an atmosphere of teamwork. The change in frequency of this meeting from monthly to quarterly appears appropriate, recognizing the nature of this meeting and the time required for all participants to prepare for, and participate in, this important meeting.
Recommendations:
None

4.0 Conclusions

4.1
The Plant Health Committee meeting was conducted efficiently and effectively. Members and presenters appeared to be well prepared. Discussion was active, thoughtful, and probing, with a focus on safety. The DCISC should consider conducting a Fact-finding review of the Reactor Coolant Systems of both Units prior to the 4th Quarter of 2015 since both systems have been rated as Unhealthy for about a year.
4.2
DCISC meetings with the NRC Resident, or Senior Resident, Inspector continue to be beneficial with regard to sharing information and to understanding issues important to the NRC and DCISC. Because it could be beneficial to have a future DCISC Public Meeting scheduled in the same week as a NRC public meeting, the DCISC should follow up to see if this can be coordinated in the future.
4.3
Although DCPP has made much progress in recent years in the seismic bracing of tall furniture, there continue to be instances where seismic bracing is needed. The recent personal involvement of a senior station manager in this issue is a noteworthy expression of the station’s interest in completely resolving the issue. DCPP’s intent to conduct seismic safety inspections in conjunction with fire safety inspections can be expected to increase the safety benefit of each inspection. The DCISC should reexamine this issue in mid-2016.
4.4
DCPP’s Performance with respect to its Seismically Induced Systems Interaction Program appears to have been reasonably strong and stable during the past few years, with the exception of a few nonconformances. Given the heightened attention to seismicity during this same period, DCISC should review this program at least once every 2 years.
4.5
Ongoing seismic re-evaluations include verifying the capability of DCPP’s Steam Generators and Reactor Vessel Heads to withstand a Design Basis Earthquake. They have also been separately analyzed to withstand a Design Basis Loss of Coolant Accident. However, more analysis may be needed in to confirm that this equipment can also withstand a Design Basis Earthquake that occurs concurrently with a Design Basis Loss of Coolant Accident. Also the re-analysis of the seismic and loss of coolant accident loads on this equipment is expected to be complete by September 2015. In addition, it may be appropriate to install seismic instrumentation on this equipment in order to verify how future seismic events affect the motion of this equipment.
4.6
The Benchmarking Program appears to continue being an active and productive method for obtaining information supporting the achievement and maintenance of safe and reliable nuclear plant operation. It continues to provide for formal and informal examinations of a broad range of nuclear plant performance areas. The program again appears to warrant DCISC’s review no more frequently than biennially.
4.7
DCPP continues to maintain an active and effective Operating Experience Program. DCISC should continue to examine this topic on a frequency no greater than biennially.
4.8
DCPP is participating in an industry initiative to determine the impact of atmospheric chlorides on the corrosion rate of ISFSI Multipurpose Canisters (MPCs). It is expected that these corrosion rates will be individually dependent upon the material properties of the individual MPCs and the atmospheric conditions at each ISFSI. DCPP’s initial 16 MPCs that were used for transfer of used nuclear fuel to the ISFSI are made of 304 austenitic stainless steel, which tends to be somewhat more susceptible to chloride induced stress corrosion cracking than other types of stainless steel that are used for this purpose. Deliquescence that can cause stress corrosion cracking can be made impossible if the canister surface temperatures are maintained sufficiently above outside ambient temperatures, so periodic monitoring of canister temperatures is valuable. Because PG&E and the state of California are examining the possibility of installing salt-water cooling towers as an option to once through cooling at DCPP, it would be advisable, to the extent possible, to examine the potential impact of such cooling towers on the rate of salt aerosol deposition at the ISFSI.
4.9
PG&E’s Flood Hazard Reevaluation of the DCPP site appears to be detailed and thorough. Local intense precipitation (LIP) was determined to present the only potential risk of inundation of the power block structures. PG&E further noted that NRC has considered LIP to be beyond the current design and licensing basis of the plant. In conformance with a Commitment that PG&E made to the NRC, PG&E will conduct further examination of LIP and address the results in an Integrated Assessment that will be submitted to the NRC prior to March 13, 2017.
4.10
The quarterly Performance Review Meeting was well structured, appropriately focused, and conducted efficiently and effectively. The meeting provided a framework for DCPP management personnel to stay updated on key station issues and associated responsibilities, and it fostered an atmosphere of teamwork. The change in frequency of this meeting from monthly to quarterly appears appropriate, recognizing the nature of this meeting and the time required for all participants to prepare for, and participate in, this important meeting.
5.0 Recommendations:
None
6.0 References
6.1
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.8, Section 3.7 “Attend Plant Health Committee Meeting.”
6.2
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.8, Section 3.1, “Meeting with NRC Senior Resident Inspector.”
6.3
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.5, Section 3.4, “Office/Personnel Seismic Safety. ”
6.4
“Diablo Canyon Independent Safety Committee Twenty-First Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2010—June 30, 2011”, Approved October 5, 2011, Volume II, Exhibit D.11, Section 3.6, “Seismically Induced System Interactions Housekeeping Program.”
6.5
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.7, Section 3.2, “PG&E Seismic Study.”
6.6
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.8, Section 3.9, “Licensing Basis Verification Project Issues.”
6.7
“Diablo Canyon Independent Safety Committee Twenty-Fifth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2014—June 30, 2015”, Approved October 21, 2015, Volume II, Exhibit D.2, Section 3.7, “Seismic Fragility PRA Update.”
6.8
“Diablo Canyon Independent Safety Committee Twenty-Third Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2012—June 30, 2013”, Approved October 9, 2013, Volume II, Exhibit D.6, Section 3.6, “Benchmarking Activities.”
6.9
“Diablo Canyon Independent Safety Committee Twenty-Fourth Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2013—June 30, 2014”, Approved October 14, 2014, Volume II, Exhibit D.3, Section 3.1, “Operating Experience Program Update.”
6.10
“Diablo Canyon Independent Safety Committee Twenty-Third Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations, July 1, 2012—June 30, 2013”, Approved October 9, 2013, Volume II, Exhibit D.2, Section 3.7, “Observation of DCPP Monthly Performance Review Meeting.”

For more information contact:

Diablo Canyon Independent Safety Committee
Office of the Legal Counsel
857 Cass Street, Suite D, Monterey, California 93940
Telephone: in California call 800-439-4688; outside of California call 831-647-1044
Send E-mail to: dcsafety@dcisc.org.