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Keeping Tabs on Diablo Canyon’s Evolving Seismic Situation

Lara Uselding
Public Affairs Officer
Region IV

diabloThe NRC has added two items to the growing list of documents on seismic issues related to the Diablo Canyon Power Plant, near San Luis Obispo, Calif. Our Region IV office in Arlington, Texas, sent the plant operator, PG&E, an inspection report and our headquarters Office of Nuclear Reactor Regulation in Rockville, Md. sent PG&E a letter about the plant’s seismic hazard reevaluation due in March 2015.

The Region IV inspection report discusses the agency’s independent assessment of the operability determination completed by PG&E associated with its September report on the Shoreline and other faults near the plant. PG&E provided the report to the state under California Assembly Bill 1632. That bill required the report so the California Energy Commission could assess if California’s largest baseload power plants are vulnerable to a seismic event as those plants age.

The NRC did not request this analysis, but PG&E committed to keep us updated on any new information that would indicate the Shoreline fault is more energetic or capable than was presented in the January 2011 Shoreline Fault Report. PG&E further committed to provide the NRC with an interim analysis of any new Shoreline-related information before the post-Fukushima evaluations are due in March 2015.

Our regional review of PG&E’s operability determination indicates there is considerable design margin for the plant’s systems, structure, and components. The staff did not identify any concerns with PG&E’s determination that the plant is operable. The analysis adds to the evidence that the plant’s systems, structures, and components would function properly after an earthquake and not pose undue risk to public health and safety.

Our letter from headquarters confirms PG&E will incorporate the September report’s findings into its ongoing, post-Fukushima, full seismic re-analysis due in March 2015. The NRC believes this more rigorous analysis will provide the most accurate assessment of faults affecting the site.

The bottom line is that the effect of earthquakes has been extensively evaluated during the construction, licensing, and operation of the plant. Diablo Canyon’s systems, structures, and components are designed to withstand the area’s earthquakes and perform their safety functions.

Sixty-Plus Years of Reactor Safety Advice — and Still Going Strong

Ed Hackett
Executive Director
Advisory Committee on Reactor Safeguards

For as long as the United States has worked on commercial nuclear power plants, a group of experts has given regulators independent safety advice. Since Congress passed the Atomic Energy Act of 1954, the group’s been called the Advisory Committee on Reactor Safeguards.

The committee’s dozen or so members contribute decades of academic and/or practical experience in their specialties, which include risk assessment, health physics, accident analysis and several types of engineering. Past and present committee members have also lent their expertise to international regulators.

Members of the ACRS brief the NRC Commission.

Members of the ACRS brief the NRC Commission.

When there’s an opening on the committee, the Commission chooses a replacement from nominees among the leading experts in a given specialty. Committee members are supported by a small group of NRC staff who focus solely on the committee’s independent activities.

The full committee meets 10 times a year, spending several days each time to discuss a broad range of topics. For instance, this month’s meeting agenda included a developing new rule related to safety enhancements based on lessons learned from the Fukushima nuclear accident. Other meetings have covered reviews of new reactor licensing topics and operating reactor license renewal, as well as proposed facilities to create radioactive material for medical uses.

Committee members ask detailed questions of both NRC staff and industry representatives. If members feel an issue needs more explanation or analysis, they’ll keep asking questions and challenging assumptions until they’re satisfied. All of this interaction contributes to the committee’s opinions on the topics.

The committee’s conclusions, which are independent of the NRC staff’s work, are provided in formal letters to the NRC’s Chairman. The Commission takes the committee’s views into account when it considers licensing or policy matters. The committee also meets publicly with the Commission at least once a year to discuss major topics. The Commission uses the advice provided by the committee, in addition to the information provided by the NRC staff, in reaching its decisions on regulatory matters.

The committee also has an obligation to advise the U.S. Navy on its nuclear reactor program, as well as the Defense Nuclear Safety Board, which deals with Department of Energy-controlled facilities.

The committee does all of this work according to the requirements of the Federal Advisory Committee Act. This means all committee meetings are public, except when discussing sensitive information the NRC needs to protect. It also means the public can speak and present information to the committee. Keep an eye on our schedule to see when we’ll discuss something you’re interested in. Also, see our YouTube videeo on the ACRS.

Improving NRC Processes—Part Two

Patricia Holahan
Director, Office of Enforcement

 

We wrote in June about steps we are taking to improve our “non-concurrence” process, which is a way for NRC staff to air a variety of views before final management decisions are made. Today, we’d like to fill you in on steps we are taking to improve our Differing Professional Opinions (DPO) process—used to bring NRC staff views on agency decisions to the highest levels of NRC management.

publicopinionBoth processes are important to creating an environment where NRC employees feel they can speak up when they disagree—the same safety conscious work environment we expect from our licensees.

First, a little context. The NRC makes hundreds if not thousands of decisions each year. To reach the best decisions, the agency encourages staff to bring their views forward throughout the process. This active engagement is essential.

NRC expects all employees to promptly discuss their views and concerns with their immediate supervisor on a regular basis. Employees are expected to raise concerns and propose solutions as early as possible in the decision-making process. In addition to informal discussions, which should be sufficient to resolve most issues, individuals have various options for expressing and having their differing views heard by decision makers.

In the vast majority of cases, an informal conversation is sufficient. But if not there are a number of avenues for elevating concerns. We have an Open Door policy that allows the staff to request a meeting with any manager at the NRC—including the Chairman and Commissioners—to raise concerns. This policy encourages employees to resolve their concerns informally. There is also the non-concurrence process, which allows the airing of issues through the concurrence chain before a decision is made. An employee who disagrees with an established position can use the DPO process.

The NRC is unique in not only having and promoting these programs, but in assessing them and reporting the results to the public. This transparency helps ensure that differing views do not get lost in the shuffle.

To gauge how well these processes are working, we used a variety of tools to measure user satisfaction and process effectiveness. As with our assessment of the non-concurrence process, the DPO assessment shows the process is sound. NRC staff knows about it and most would be willing to use it. Also like the earlier assessment, the DPO assessment has helped us to identify areas for improvement.

There have been 28 DPOs filed since 2004, or an average of two to three cases per year. In that same time frame, one DPO was withdrawn and 24 DPO decisions were issued. Given that so few NRC employees have direct experience with the process, we were encouraged to see from our agency-wide safety culture survey that only 15 percent of NRC employees would be unwilling to use it. While this number is small, it shows we have some work to do. We want all NRC employees to feel they can use the process, and that it will be effective and lead to better, more informed decision-making. We are also concerned about the 18 percent who worry using the process could impact career development and the 46 percent who are unsure.

These numbers present an opportunity to do more outreach and education to ensure NRC leadership is committed to the DPO process. We will also need to; develop clearer guidance and better tools and support the process; ensure training is readily available to all employees (including a focus on improved communications); and identify ways to address concerns about real and perceived  negative consequences for using the process.

publicopinionAs we work to make these improvements, we can also celebrate the things that make our DPO process strong. From looking at other agencies with similar processes, our assessment shows the NRC is unique in making summaries of our DPO decisions public and, if asked by those who file DPOs, releasing key DPO records.

We are also pleased by the feedback from DPO submitters. We surveyed the 12 who remain at the NRC and received nine responses. All nine reported their views were heard by management. Eight said the DPO panel was sufficiently knowledgeable, independent, impartial, timely, and thorough. The same number said they were understood and treated fairly. Seven said the process added value to the final decision, their views were fully considered, and their management was supportive. Six said they were recognized with a Special Act award or an NRC Team Player award.

As we move forward, we will build on these strengths and take additional steps to foster an organizational culture where employees take personal responsibility for their actions, feel part of a community and work toward shared goals. We value the feedback from these self-assessments and commit to responding constructively so we can continuously improve our performance.

NRC Team Ready to Get to Work at Pilgrim Nuclear Power Plant

Neil Sheehan
Public Affairs Officer
Region I
 

When the Pilgrim nuclear power plant got a second “white” performance indicator in the same area of performance in 2014 it meant we would ratchet up our level of scrutiny until the underlying issues were resolved.

pilgrimStarting Monday, that scrutiny will take the form of a team inspection at the Plymouth, Mass., facility. Eight NRC inspectors will begin performing evaluations in several key areas.

For one, they will review the evaluation done by Entergy, the plant’s owner and operator, looking at why the problems that triggered the indicator changes occurred. The team will also dig into the fixes, or corrective actions, put in place by the company to prevent the issues from happening again. They will also look at whether the issues could have affected other parts of plant operations. The timeframe for the inspection gave Pilgrim time to evaluate and fix the problems, so the NRC inspectors can make sure the corrective actions are adequate.

Another area the team will assess will be whether there were any safety culture weaknesses that caused or played a part in the performance issues. The NRC defines nuclear safety culture as values and behaviors that emphasize safety over competing goals to ensure protection of people and the environment.

Once the team’s on-site work is finished, the inspectors will brief Entergy at a high level regarding what it has found. That is followed by an inspection report issued within 45 days.

We also plan to conduct a public meeting with Entergy after the inspection is wrapped up. This meeting, which would likely occur in December or January near the plant, will provide a forum for the NRC and the company to discuss the performance issues, their underlying causes and any improvement steps.

The NRC will provide notice on the date, time and location for this session.

As a refresher on earlier developments, the Pilgrim plant’s performance indicator for Unplanned Scrams (shutdowns) with Complications crossed the threshold from “green” to “white” following the third quarter of 2013. Then, in the fourth quarter of last year, the performance indicator for Unplanned Scrams per 7,000 Hours of Operation also changed to “white,” something that occurs if a plant has more than three such shutdowns during the designated period. This placed Pilgrim in the Degraded Cornerstone Column of the Action Matrix used by the NRC to assess plant performance.

And that, in turn, requires the heightened NRC attention to be paid during the team inspection this week.

 

Science 101: How a Chain Reaction Works in a U.S. Nuclear Reactor

Paul Rebstock
Senior Instrumentation and Control Systems Engineer

 

science_101_squeakychalkThe primary active ingredient in nuclear reactor fuel is a particular variety, or “isotope,” of uranium, called U235. U235 is relatively rare — only about 0.7% of uranium as it exists in nature is U235. Uranium must be enriched to contain about 5% U235 to function properly as fuel for a U.S. commercial nuclear power plant.

U235 has 92 protons and 143 neutrons. Protons and neutrons are some of the almost unimaginably tiny particles that make up the nucleus of an atom — see Science 101 Blog #1. All other isotopes of uranium also have 92 protons, but different isotopes have slightly different numbers of neutrons.

Uranium is a radioactive element. Uranium atoms break apart, or disintegrate, into smaller atoms, releasing energy and a few leftover neutrons in the process. This happens very slowly for U235. If you have some U235 today, in about 700 million years you will have only half as much. You will have the remaining U235, plus the smaller atoms. The energy released will have gone into the environment too slowly to be noticed, and the extra neutrons will have been absorbed by other atoms.

While this happens very slowly, the disintegration of each individual atom happens very quickly, and the fragments are ejected at a very high speed. Those high-speed fragments are the source of the heat generated by the reactor. Under the right man-made conditions, the number of U235 atoms that disintegrate each second can be increased.

When a U235 atom disintegrates, it releases some neutrons. Some of those neutrons can be made to interact with other U235 atoms, causing them to disintegrate as well. Those “target” atoms release more neutrons when they disintegrate, and then those neutrons interact with still other U235 atoms, and so on. This is called a “chain reaction.” This process does not work well for other isotopes of uranium, which is why the uranium needs to be enriched in U235 for use as nuclear fuel.

Most of the energy released when a U235 atom disintegrates is in the form of kinetic energy — the energy of physical motion. The fragments of the disintegrated atom collide with nearby atoms and set them vibrating. That vibration constitutes heat. The fuel rods get hot as the reaction progresses. The faster the chain reaction — that is, the larger the number of U235 atoms that disintegrate each second — the faster energy is released and the hotter the fuel rods become.

The uranium in a U.S. commercial nuclear reactor is thoroughly mixed with neutral material and formed into pellets about half inch wide and three-quarters of an inch long. The pellets are stacked tightly in metal tubes, forming “fuel rods” that are several feet long. Each fuel rod is just wide enough to hold a single column of pellets. The fuel rods are sealed, to keep all of the radioactive materials inside. There are thousands of these fuel rods in a typical reactor. They contain around 60 tons of uranium – but only about three tons are U235. (The majority of the uranium in the reactor is in the form of the most abundant naturally occurring isotope of uranium, U238, which cannot sustain the fission process without the help of an elevated concentration of the isotope U235.)

The people in charge of the reactor can control the chain reaction by preventing some or all of the released neutrons from interacting with U235 atoms. The physical arrangement of the fuel rods, the low U235 concentration, and other design factors, also limit the number of neutrons that can interact with U235 atoms.

The heat generated by the chain reaction is used to make steam, and that steam powers specialized machinery that drives an electrical generator, generating electricity. Science 101 will look at how that works in more detail in a later issue.

The author has a BS in Electrical Engineering from Carnegie-Mellon University.

 

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