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Closing In on Finishing the ESBWR Design Review

Michael Mayfield
Director, Advanced Reactor and Rulemaking Program
 

After a lot of technical discussions, the NRC is ready to take the next step in considering whether GE-Hitachi’s Economic Simplified Boiling Water Reactor meets our standards for U.S. use.

esbwrWe’ve been reviewing this new reactor design for several years. This design includes new types of safety systems that would use gravity to direct cooling water into the core during an emergency, even when electrical power is lost. Our review path took a major turn in 2011.

In March of that year we issued our technical conclusions on the design. The NRC then drafted a regulation that would approve the ESBWR, but later in 2011, we received additional information related to the steam dryer design that made us pause. (The steam dryer prevents excess moisture from damaging the plant’s turbine.)

We spent 2012 and 2013 making sure we had all the necessary information from GE-Hitachi on the ESBWR steam dryer design.  We’ve completed the review of the additional steam dryer design information and now have what we need to complete the design certification.

The NRC expects to seek public comment on a supplemental proposed certification rule next month and to send a draft final rule to the five-member Commission in July. This process could lead to final certification of the ESBWR later this year.

Utilities interested in new reactors can reference NRC-certified designs to simplify parts of their license reviews. The utilities applying for licenses to build ESBWRs, Detroit Edison in Michigan and Dominion in Virginia, will have to update their applications to account for any changes to the design.

Our letter to GE-Hitachi on these developments is available in the NRC’s electronic document database.

 

 

NRC Science 101 — Different Types of Radiation

Donald Cool
Senior Radiation Safety Advisor

science_101_squeakychalkIn earlier Science 101 posts, we talked about what makes up atoms, chemicals, matter and ionizing radiation. In this post, we will look at the different kinds of radiation.

There are four major types of radiation: alpha, beta, neutrons, and electromagnetic waves such as gamma rays. They differ in mass, energy and how deeply they penetrate people and objects.

The first is an alpha particle. These particles consist of two protons and two neutrons and are the heaviest type of radiation particle. Many of the naturally occurring radioactive materials in the earth, like uranium and thorium, emit alpha particles. An example most people are familiar with is the radon in our homes.

The second kind of radiation is a beta particle. It’s an electron that is not attached to an atom (see previous blog post). It has a small mass and a negative charge. Tritium, which is produced by cosmic radiation in the atmosphere and exists all around us, emits beta radiation. Carbon-14, used in carbon-dating of fossils and other artifacts, also emits beta particles. Carbon-dating simply makes use of the fact that carbon-14 is radioactive. If you measure the beta particles, it tells you how much carbon-14 is left in the fossil, which allows you to calculate how long ago the organism was alive.

The third is a neutron. This is a particle that doesn’t have any charge and is present in the nucleus of an atom. Neutrons are commonly seen when uranium atoms split, or fission, in a nuclear reactor. If it wasn’t for the neutrons, you wouldn’t be able to sustain the nuclear reaction used to generate power.

The last kind of radiation is electromagnetic radiation, like X-rays and gamma rays. They are probably the most familiar type of radiation because they are used widely in medical treatments. These rays are like sunlight, except they have more energy. Unlike the other kinds of radiation, there is no mass or charge. The amount of energy can range from very low, like in dental x-rays, to the very high levels seen in irradiators used to sterilize medical equipment.

fordoncools101As mentioned, these different kinds of radiation travel different distances and have different abilities to penetrate, depending on their mass and their energy. The figure (right) shows the differences.

Neutrons, because they don’t have any charge, don’t interact with materials very well and will go a very long way. The only way to stop them is with large quantities of water or other materials made of very light atoms.

On the other hand, an alpha particle, because it’s very heavy and has a very large charge, doesn’t go very far at all. This means an alpha particle can’t even get through a sheet of paper. An alpha particle outside your body won’t even penetrate the surface of your skin. But, if you inhale or ingest material that emits alpha particles, sensitive tissue like the lungs can be exposed. This is why high levels of radon are considered a problem in your home. The ability to stop alpha particles so easily is useful in smoke detectors, because a little smoke in the chamber is enough to stop the alpha particle and trigger the alarm.

Beta particles go a little farther than alpha particles. You could use a relatively small amount of shielding to stop them. They can get into your body but can’t go all the way through. To be useful in medical imaging, beta particles must be released by a material that is injected into the body. They can also be very useful in cancer therapy if you can put the radioactive material in a tumor.

Gamma rays and x-rays can penetrate through the body. This is why they are useful in medicine—to show whether bones are broken or where there is tooth decay, or to locate a tumor. Shielding with dense materials like concrete and lead is used to avoid exposing sensitive internal organs or the people who may be working with this type of radiation. For example, the technician who does my dental x-rays puts a lead apron over me before taking the picture. That apron stops the x-rays from getting to the rest of my body. The technician stands behind the wall, which usually has some lead in it, to protect him or herself.

Radiation is all around us, but that is not a reason to be afraid. Different types of radiation behave differently, and some forms can be very useful. For more information on radiation, please see our website.

Don Cool, who holds a Ph.D. in radiation biology, advises the NRC on radiation safety and for 30 years has been active on international radiation safety committees.

April Showers Also Bring Seasonal Power Plant Refueling Outages

Neil Sheehan
Public Affairs Officer
Region I

 

The robins are chirping, the daffodils are pushing out of the cold ground and the sun is shining for an additional minute or two every day. It’s finally spring in the U.S., which for many nuclear power plants heralds the start of refueling and maintenance outages.

npp2Every 18 to 24 months, nuclear power plants shut down to allow for the replacement of about a third of the fuel in the reactor with fresh rods. The outages also make it possible for plant personnel and contractors to perform a number of projects, such as the refurbishment or replacement of pumps and valves, and inspections of components not accessible when the reactor is operating.

Hundreds of contractors assist with this work, making these outages periods of intense, round-the-clock activity for at least several weeks. No doubt nearby coffee shops do a booming business, not to mention area hotels and restaurants.

The NRC also beefs up its inspection footprint during these shutdowns, which are usually scheduled for spring and fall because those are the times when the demand for electricity is generally lower. Resident Inspectors assigned to the plant on a full-time basis and specialist inspectors observe select work activities to ensure adherence to safety regulations. They are also able to glean information about what employees and contractors are learning as they put eyes on key pieces of equipment.

There are procedures that help guide NRC inspectors during outages, including one that helps target and prioritize areas for review. A key, though, is remaining flexible while maintaining a holistic view of what almost overnight becomes a particularly bustling workplace.

Nuclear power plants are baseload electricity generators designed to run at 100 percent, but they need to occasionally take a strategic timeout to refuel and kick the tires, so to speak. With careful planning, a focus on safety and an attention to detail, the tasks can be effectively completed and the unit restored to service in time to help meet the additional cooling demands of the ensuing summer or the warming needs of the following winter.

 

Change is in the Air: NRC Launches New Career Opportunities Website

Kristin Davis
Senior Human Resources Specialist
 

With April showers comes the countdown to graduation, and some student’s thoughts turn to the job market. Even those already employed may be getting the urge for a change of scenery. In that spirit the NRC has launched a new Career Opportunities website to attract the technologically savvy job seekers of today.

careerpictureOur website is often the first introduction prospective applicants have to the NRC and our important mission. This redesign allows us to improve that first impression with enhanced maneuverability and the most up-to-date information, all while embodying the NRC work style and attitude.

The fresh new look gives the NRC an entirely new online presence that aligns seamlessly with our overall recruitment campaign and conveys to prospective applicants that NRC has career opportunities for motivated, bright and dedicated experienced professionals as well as recent college graduates.

To attract top talent to fill our mission critical positions, we must develop relationships with potential candidates long before we need them. The Career Opportunities website is just one of the many avenues we use to do just that. We also attend college and professional career fairs, place ads in professional journals and post jobs on online job boards.  

Each year, the NRC hires about 200 new staff members in fields such as engineering, nuclear science and security.

Fukushima Lessons: Updating Earthquake Hazards at U.S. Nuclear Plants

Scott Burnell
Public Affairs Officer
 

The NRC is examining new earthquake-related information from U.S. nuclear power plants, and we’re making that information available over the next week or so. We’d like to summarize how we got here and what the next steps are.

seismicgraphicNuclear power plant designs set a basic standard for reactors to completely and safely shut down after an earthquake, based on site-specific information. Plant construction methods and other design factors add to a reactor’s capacity to safely withstand stronger motions than what the basic design describes.

The end of March marked an important milestone for our post-Fukushima activities. We received 60 reports from central and eastern U.S. nuclear power facilities updating the seismic hazard at their individual reactors. The NRC staff is making these reports available through its normal process. The NRC will post each plant’s report on the agency website’s Japan Lessons-Learned Activities page.

We will require the same updates of the three western power plants (Palo Verde in Arizona, Columbia Generating Station in Washington, and Diablo Canyon in California), but delayed by one year because of the more complex geology in that region of the country. Each western plant is individually looking at the seismic sources and local ground motion characteristics that could affect it. This Senior Seismic Hazard Analysis Committee process will inform the overall seismic hazard reassessment that the western plants are completing.

Our staff will spend the next month going over the submissions carefully, checking for errors, before confirming which plants will be required to do more extensive analysis of their ability to respond safely to a significant earthquake event.

These reports mark the first step in a comprehensive process to keep safety at U.S. plants up-to-date with the latest understanding from the earth sciences on the processes that create earthquakes in the U.S.  In 2012, the Department of Energy, Electric Power Research Institute and the NRC joined forces to update the “seismic source model” for the central and eastern U.S. This was based on a new understanding of what creates earthquakes on the North American tectonic plate, with a focus on the New Madrid fault zone near St. Louis, the Charleston fault zone near Charleston, S.C., and other updated information.

The data on seismic sources will be used in conjunction with a ground motion model for the central and eastern U.S. as well as data from individual plants on the localized geology, topography, soil cover, and other data to create a picture of the “ground motion response spectra” for each plant. This new ground motion response spectrum at each plant will be compared with that developed in the past to see if the new data suggests the plant could see higher ground motions than previously thought. If that is the case, the plant will be considered to have “screened in” to further detailed seismic hazard analysis.

Those plants that “screen in” will be required to do a seismic “probabilistic risk assessment” or a seismic “margin analysis” to evaluate in detail how the existing plant structures and systems would respond to the shaking from the range of earthquakes that could affect the plant based on our current understanding of seismic sources. This assessment is extensive, involving experts from a variety of fields, and will require at least 3 years to complete. Once these assessments are complete, the NRC will decide if significant upgrades to plant equipment, systems, and structures are required.

In the meantime, to ensure that the plant is safe, the NRC requires that by the end 2014, plants have reported the interim actions they will take to ensure the safety of the plants before the assessment is complete. Such measures could include re-enforcing existing safety-significant equipment or adding equipment.

It’s important to remember that significant earthquakes at central and eastern U.S. plants are unlikely. But it is our job to ensure that these plants are ready for all that nature might throw at them. And it is our job to keep up with the changes in the science to ensure that plants are as safe as they can be.

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