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Category Archives: Operating Reactors

REFRESH — Where There’s Steam, There’s … a Steam Generator

Kenneth Karwoski
Senior Advisor for Steam Generators

refresh leafWhen the NRC talks about “steam generators,” we’re not talking about teakettles. Steam generators provide vital technical and safety functions at many U.S. nuclear power plants.

In the United States, steam generators are only found in pressurized-water reactors, one of the two types of U.S. reactors. There can be two to four steam generators for each reactor unit. The generators mark the spot where two closed loops of piping meet. The first loop sends water past the reactor core to carry away heat, and this loop is at such high pressure that the water never boils. The second loop is at a lower pressure, so the water in this loop turns to steam and runs the plant’s turbine to generate electricity.

The steam generator’s main technical job is to let the first loop pass its heat to the second loop as easily as possible. To do this, a steam generator packs thousands of small tubes closely together, allowing the maximum area for heat to pass through the tubes and into the second loop’s water.

At the same time, the steam generators provide an important safety barrier – the first loop can contain radioactive material, so the tubes must keep the two loops of water separate. NRC rules require plants to closely monitor the second loop and immediately shut the reactor down if a tube leak exceeds very strict limits.

pwr[1]The NRC’s rules for inspections, maintenance and repair of steam generator tubes help ensure the tubes continue providing the safety barrier. If an inspection shows a tube is starting to get too thin, the plant will repair or even plug a tube to maintain safety.

Steam generator tube material has improved over time. The first steam generators had tubes made from a type of stainless steel that experience showed could be corroded by the chemicals, temperatures and pressures in the first and second loop. Over time, plants have replaced those steam generators with ones using more advanced alloys that are less likely to corrode.

Steam generator replacement only happens when the reactor is shut down for refueling, and plant owners bring in hundreds of specialized workers to safely remove the old generators and install the new ones. The old generators have to be safely disposed of as low-level radioactive waste.

REFRESH is an occasional series where we revisit previous posts. This first ran in July 2013.

NRC Begins Significant Activity under Heightened Oversight at Pilgrim Nuclear Plant

Neil Sheehan
Public Affairs Officer
Region I

A significant activity at the Pilgrim nuclear power plant gets underway today when a team of inspectors arrives at the Plymouth, Mass., facility to examine a variety of aspects of its operation.

Included on the 20-member team will be inspectors tasked with evaluating the state of equipment reliability, human performance, plant procedures and the plant’s corrective action program.

What’s more, the team will look carefully at the plant’s safety culture. Among other things, safety culture encompasses the willingness of plant employees to raise safety concerns without fear of reprisal.

This inspection is being performed as part of NRC increased oversight of Pilgrim, which was initiated in September 2015. That occurred after performance issues triggered a change in where the plant falls on the agency’s Action Matrix. The matrix uses inspection findings and performance indicators to guide the level of scrutiny at each plant.

The “95003” inspection process spells out the steps to be taken by the NRC staff to ensure a plant’s owner has taken the appropriate actions to remedy deficiencies. Two earlier team inspections, carried out in January and April, were also part of this oversight regimen.

The inspection beginning today will involve three weeks of on-site reviews. Any findings coming out of the evaluation will be made available in a report due out within 45 days of the inspection’s conclusion.

More information on the NRC review activities regarding Pilgrim can be found on a webpage devoted to that subject.

Different Control Rooms – Same Stringent Requirements for Operators

Roger Hannah
Senior Public Affairs Officer
Region II

ap1000_controlU.S. commercial nuclear power plant operators must have the training, experience and skills to safely operate the reactor — and they must possess a license issued by the NRC.

The nation’s four new nuclear units being built, two at the Vogtle site in Georgia and two at the Summer site in South Carolina, will need licensed teams of operators and the companies building those plants are working with the NRC to ensure those operators will be ready when the plants are finished.

The control rooms for those new units replace the traditional layout packed with levers, switches, dials and lighted indicators with large digital screens and plant equipment interfaces as part of the Westinghouse AP1000 design. Even older nuclear plants use digital screens in the control rooms to augment the information for operators, but the new plants will be the first in this country equipped with the new control rooms. While the look may be different, the operator qualifications do not change.

“Requirements for obtaining an operator license for the new nuclear plants and the previous generation plants are equally stringent,” said NRC Region II License Examiner Mark Bates. “The licensing process requires that all operators be evaluated based on their competence in areas important for safe operation.”

The NRC issues licenses to reactor operators, who handle the controls of the plant, and senior reactor operators, who oversee and direct the licensed activities of the reactor operators. To become a reactor operator, an applicant must have at least three years of power plant experience and at least six months as a non-licensed operator. Senior reactor operator applicants must have at least 18 months experience as a qualified non-licensed operator, plant engineer or manager at a commercial nuclear power plant.

Reactor operator candidates do not need a college degree, but they must have the required experience and training. A college degree in engineering, engineering technology, or related sciences is typically required for anyone testing directly for a senior reactor operator license. However, a reactor operator with at least a year of active experience at a similar nuclear plant may take the senior reactor operator exam, whether or not they have a college degree.

Applicants for operator licenses must complete rigorous training provided by the company operating the plant before taking the NRC’s detailed written examination and a hands-on operating test on a simulator exactly like the plant’s control room. Although the company prepares and administers the tests, the NRC approves the test material and grades the applicants.

Even after receiving a license, operators continue to train on a regular basis every few weeks and as part of an NRC-approved requalification program, both reactor operators and senior reactor operators must pass an operating test every year and a written examination every two years to maintain their license.

More information on the licensing process for nuclear reactor operators, including more specific training and qualification requirements, can be found on the NRC website.

Five Questions With: Andrea Veil

Andrea Veil is the Executive Director for the Advisory Committee on Reactor Safeguards

  1. How would you briefly describe your role at the NRC?

5 questions_9with boxI serve as the liaison between the ACRS and the NRC staff at all levels and the NRC Commissioners. I also manage the technical and administrative staff who support the ACRS as it meets its obligation to provide the Commission with independent and timely technical advice. By the way, the ACRS full committee just held its 638th meeting last week.

  1. What is your foremost responsibility at work?

Ensuring that the ACRS members have everything that they need to provide effective and timely technical advice to the NRC Commission. That means researching issues, getting answers to questions, pulling together legal and regulatory documents, talking to stakeholders, reviewing reports and all other kinds of support actions. The independence of ACRS is truly unique among government agencies. The ACRS provides independent advice to the Commission on issues related to nuclear reactors safety and security, and nuclear waste and materials, so facilitating the technical reviews and meetings required to fulfill the ACRS mission is of utmost importance.

  1. What is your most significant challenge in the workplace?

andreaThe challenge to continue adapt to agency-wide changes that may affect the ACRS workload and independent function.

  1. What do you consider one of your most notable accomplishments at the NRC?

I would say one of my biggest job successes is becoming the first female Executive Director of the ACRS since its beginning in 1954.

  1. What is one quality of the NRC that more people should know?

The NRC is a regulatory authority and does not have promotion of nuclear energy as part of its mission. Our stance is if there is to be nuclear power in this country, it will be done safely. We don’t advocate for or against nuclear power, nor do we have any say in the energy generation mix in this country (that’s Department of Energy). In addition, over regulation by the NRC is sometimes cited as the reason for the permanent closure of a plant. The decision by a utility to permanently close a plant is a business/economic decision by that licensee.

Five Questions is an occasional series in which we pose the same questions to different NRC staff members.

An Explanation of Capacity Factor

Neil Sheehan
Public Affairs Officer
Region I

Earlier this year, the nuclear power industry announced it had set a record for reliability in 2015. The measuring stick for this achievement is what is known as “capacity factor.” But what exactly is that?

Put simply, capacity factor compares how much energy was generated against the maximum that could have been produced at continuous full-power operation during a specific period of time. It’s similar to baseball’s on-base percentage, which counts how many times a hitter reaches base versus the number of opportunities in the batter’s box.

Nuclear is one part of the energy generation mix.

Nuclear is one part of the energy generation mix in the U.S.

The Nuclear Energy Institute, the industry’s trade organization, preliminarily pegged the capacity factor average for all of the nation’s reactors at 91.9 percent last year. It added that this was a new record, edging out the previous one set in 2007.

An update issued by the U.S. Energy Information Administration on June 24 upped the 2015 total to 92.2 percent. EIA also lists nuclear power’s capacity factor in 2014 as 91.7 percent and 2013 as 89.9 percent.

For comparison purposes, other segments of the energy production sector had the following reliability ratings in 2015 (according to the EIA): Coal – 54.6 percent; natural gas-fired combined cycle – 56.3 percent; conventional hydropower – 35.9 percent; wind – 32.5 percent; solar photovoltaic – 28.6 percent; solar thermal – 22.7 percent; landfill gas and municipal solid waste – 67.6 percent; other biomass, including wood – 52.9 percent; and geothermal – 71.7 percent.

EIA allows visitors to its website to check capacity factors dating back to 1973. A review of this data shows that reactor reliability rates started out in the upper 40s/low-to-mid-50s percent range during the U.S. commercial nuclear power fleet’s early days.

By 1991, the level had climbed to 70.2 percent and in 1998 to 85.3 percent. Since the start of the new millennium, the capacity factor average has been in the upper 80s/lower 90s range.

Then-NRC Chairman Nils Diaz, in congressional correspondence issued in March 2001, wrote that increases in capacity factor could be attributed to decreases in the amount of time that plants were shut down for repairs, refueling and maintenance.

For its part, the NRC focuses not on the number of operational hours for plants but rather that they remain safe whether or not they are operating. The agency does, however, track the number of unplanned shutdowns as a measure of plant performance.

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