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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.

Updating Radioactive Materials Transportation Regulations

Emma Wong
Project Manager

10cfrIf you have ever wondered about the safety of packaging and transporting radioactive materials, now is the perfect opportunity to learn about it. The NRC is kicking off the process of updating our requirements in 10 CFR Part 71.

We do this periodically to reflect new information. Changes to international packaging and transportation standards published by the International Atomic Energy Agency, which serve as a standard for the U.S. and other nations, can also trigger revisions. Stringent safety requirements, as well as coordination among federal agencies, international regulators, and tribal, state and local officials, help to ensure radioactive materials shipments are made safely.

The U.S. Department of Transportation has primary responsibility for regulatory materials transport, while the NRC regulates packages for larger quantities. This structure provides many layers of safety.

When it is time to review our requirements, the NRC coordinates with DOT to ensure the two agencies have consistent regulatory standards. The process may take several years. We are also working to align our regulations with the IAEA’s.

To encourage public input, we are publishing an “issues paper” that outlines areas we have identified for possible revision. We’ll take comments on it for 60 days. We plan to use that input to develop a draft regulatory basis—a document that identifies a regulatory issue, and considers and recommends a solution. Once finalized, the draft regulatory basis will be made available for public comment. After taking comments on the draft, we can publish a final regulatory basis.

At that point, if our Commission agrees that revision to our requirements are needed, we would move into developing a proposed rule, then a final rule. Each step in the process takes about a year. Details on how to submit comments can be found in a Federal Register notice that will be published on November 21. This information and additional details about the rulemaking will be available on the federal rulemaking website.

We’re also planning a public meeting on Dec. 5-6 at NRC headquarters in Rockville, Md., to discuss the paper and answer questions. Details on participating, including by teleconference and webinar, can be found in our meeting notice.

img_0230While the regulations are being updated, the fact remains that radioactive materials are transported safely all the time. Millions of these shipments are made each year and arrive at their destination without incident. Occasionally, a carrier might be involved in a traffic accident. But in decades of experience, there has never been an accident that resulted in injury from exposure to the radioactive contents.

All shipments of radioactive material must also be made in compliance with DOT regulations. Smaller shipments pose extremely low risk. The larger the amount of radioactive materials, the more stringent DOT’s requirements are. DOT limits how much radioactivity can be transported in each package. That way, no transport accident involving these shipments would pose a significant health threat.

But what about larger amounts of radioactive materials? What about spent nuclear fuel?

In addition to meeting DOT requirements, larger shipments of radioactive cargo such as spent nuclear fuel and fissile material must meet NRC regulations for packaging and transport in Part 71. These regulations include very detailed requirements for shipping under normal conditions, as well as stringent tests to show the packages can withstand hypothetical severe accidents. These are the regulations we are updating now. If you would like to learn more about the transportation of spent fuel and radioactive materials, see our website.

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.

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