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NRC Science 101 – About Spent Nuclear Fuel Part II

Greg Casto
Branch Chief
Division of Reactor Safety Systems

 
science_101_squeakychalkOur last post talked about the fuel that powers nuclear reactors. Today, we’ll talk about what happens to that fuel when it’s removed from a reactor.

You’ll recall that fuel becomes very hot and very radioactive as it is used in the reactor core to heat water. After about five years, the fuel is no longer useful and is removed. Reactor operators have to manage the heat and radioactivity that remains in the “spent fuel” after it’s taken out of the reactor. In the U.S., every reactor has at least one pool on the plant site where spent fuel is placed for storage. Plant personnel move the spent fuel underwater from the reactor to the pool. Over time, as the spent fuel is stored in the pool, it becomes cooler as the radioactivity decays away.  

These pools contain an enormous quantity of water—enough to cover the fuel by about 20 feet. The water serves two purposes: it cools the fuel and shields workers at the plant from radioactivity. Having 20 feet of water above the fuel means there is a lot more water than is needed for cooling and shielding the workers. Also, because of the extra water and the simple design of the pool, there is a lot of time for plant personnel to add water to the pool if needed for any reason.

fuelpoolThe pools are built to meet strict NRC safety requirements. They have very thick, steel-reinforced concrete walls and stainless-steel liners, and are protected by security personnel. There are no drains that would allow the water level to drop or the pool to become empty. The plants have a variety of extra water sources and equipment to replenish water that evaporates over time, or in case there is a leak. Plant personnel are also trained and prepared to quickly respond to a problem. They keep their skills sharp by routinely practicing their emergency plans and procedures.

When the plants were designed, the pools were intended to provide temporary onsite storage. The idea was for the spent fuel to sit in the pool for a few years to cool before it would be shipped offsite to be “reprocessed,” or separated so usable portions could be recycled into new fuel. But reprocessing didn’t end up being an option for nuclear power plants and the pools began to fill up.

In the early 1980s, nuclear plants began to look for ways to increase the amount of spent fuel they could store at the plant site. One way was to replace spent fuel storage racks in the pools with racks containing a special material that allowed spent fuel to be packed closer together. Another way was to place older, cooler and less radioactive fuel in dry storage casks that could be stored in specially built facilities at the plant site. We’ll talk more about dry spent fuel storage in future blog posts.

Most plants today use both re-designed storage racks and dry storage facilities to store spent fuel. All storage methods must be reviewed in detail and approved by the NRC before a plant is allowed to change storage methods.

OIG Audits NRC’s Scientific Research Program

Stephen Dingbaum
Assistant Inspector General for Audits

An Office of the Inspector General audit regarding the NRC’s process for ensuring integrity in scientific research is now available here. The audit set out to determine if the NRC has the controls is place to oigassure that scientific research is objective, credible, and transparent.  

The NRC’s regulatory research program conducts research in the areas of nuclear reactors, nuclear materials, and radioactive waste. Scientific information that supports research includes factual inputs, data, models, analyses and technical information, or scientific assessments. This scientific information often informs NRC regulations.

The OIG found that while the NRC has controls in place, the way it manages scientific information, including information associated with scientific research, needs to be strengthened. Specifically, the NRC must improve the internal controls associated with responding to public requests to correct scientific information and for designating it as influential scientific information. Additionally, the OIG audit states the NRC must adopt required guidelines on conducting peer review of its information products associated with scientific research.

The audit also states the NRC must have effective controls in place to ensure that its information products are objective, credible, and transparent. Without effective controls, an opportunity for maximizing the quality, objectivity, utility, and integrity of NRC scientific information is being missed and may result in compromising stakeholder confidence in NRC’s ability to regulate in an unbiased, trustworthy, and open manner.

The report makes five recommendations specific to the way the NRC handles scientific information, to ensure that the NRC adopts federal requirements on peer review, and to ensure that internal guidance that may be impacted by new or revised federal guidance is regularly reviewed to determine if revisions are necessary.

NRC management stated their general agreement with the audit findings and recommendations.

 

EXIT — A Good Sign of Radiation

Maureen Conley
Public Affairs Officer

refresh leafMost people know radioactive energy can be harnessed to provide electricity and even to diagnose and treat certain illnesses. But would it surprise you to learn that radioactive materials also perform an important safety function by lighting emergency EXIT signs?

Look for the EXIT sign the next time you go to work, school, a sporting event, religious service, the movies, or the mall. If the sign glows green or red, chances are it contains a radioactive gas called tritium. The tritium, a radioactive isotope of hydrogen, is sealed into glass tubes lined with a chemical that glows in the dark. Tritium emits low-energy radiation that cannot penetrate paper or clothing and even if inhaled, it leaves the body relatively quickly. As long as the tubes remain sealed, the signs pose no health, safety, or security hazard.

exit3We estimate there are more than 2 million of these signs in use in the United States. To ensure safety in handling and the manufacturing process, we and our Agreement State partners regulate the manufacture and distribution of tritium EXIT signs. Companies have to apply for and receive a license before they can manufacture or distribute one of these signs.

But because the signs are designed to be inherently safe, the NRC does not require any special training before a building can display the signs. Users are responsible for meeting the requirements for handling and disposal of unwanted or damaged signs and for reporting any changes affecting the signs.

exit2Proper handling and disposal is the most important safety requirement for these signs. A damaged sign could contaminate the immediate area and require an expensive cleanup. That is why broken or unwanted signs must be return to a licensed manufacturer, distributer, radioactive waste broker or radioactive waste disposal facility.

Tritium EXIT signs are one of several types of radioactive consumer products that we allow. These products can be produced and sold ONLY if they have a benefit that outweighs any radiation risk. See our earlier blog post for more information on how we regulate these products.

REFRESH is an occasional series where we revisit previous blog posts.

Inspector General Report on Spent Fuel Pools Makes Recommendations To Improve Oversight

Stephen Dingbaum
Assistant Inspector General for Audits

oigAn Office of the Inspector General audit regarding the NRC’s oversight of spent fuel pools is now available here. The audit set out to determine if the NRC’s oversight of spent fuel pools — and the nuclear fuel they hold — provides adequate protection for public health and safety, and the environment.

The NRC is responsible for developing the regulatory framework, analytical tools, and data needed to ensure safe and secure storage, transportation, and disposal of spent nuclear fuel. In the U.S. today, there are 93 spent fuel pools currently storing spent fuel. Recent NRC staff studies demonstrating the safety of spent fuel pools and the safety of continued storage of spent fuel at reactor sites highlight the need to make sure the pools operate safely for longer periods than originally envisioned.

The OIG found the NRC does provide adequate oversight of spent fuel pools and the fuel they contain, but opportunities exist for improvement. Specifically, we found that regulatory uncertainty exists in the NRC’s evaluation of the analytical methods used to prevent a chain reaction in the spent fuel pools. In addition, there are gaps in NRC’s spent fuel pool inspection program as inspections of spent fuel pools greatly vary between licensee sites and are limited in scope.

As part of its mission, the NRC must inspect and assess licensee operations and facilities to ensure compliance with its regulatory requirements. The NRC should also regulate in a manner that clearly communicates requirements and ensures regulations are consistently applied and practical. The OIG believes an absence of effective spent fuel pool guidance for both licensees and NRC staff may reduce program efficiency and effectiveness.

The report makes four specific recommendations to improve NRC oversight, including developing and issuing new guidance for licensees and developing new NRC inspection procedures. NRC management stated their general agreement with the findings and recommendations.

 

IMPEP — Evaluating the NRC’s Radioactive Materials Program

David Spackman
Health Physicist

For the NRC and each of the 37 states that regulate radioactive materials under agreements with us, a time comes every few years when we start talking about “IMPEP.” The acronym is spoken about as frequently as the top 10 new words added to Webster’s Dictionary every year – that is to say a lot.

IMPEP may be very easy to say, but understanding its true value requires a closer look.

IMPEP stands for the Integrated Materials Performance Evaluation Program. Think of it like an audit. It is the NRC’s primary tool for assessing how well radioactive materials programs are agreementstatenesperforming. Every Agreement State and NRC program is evaluated under IMPEP every four to five years. A rotating team of experts from the Agreement States and the NRC do the reviews. The teams focus on specific areas of a radioactive materials program that have the potential to affect public health and safety. The reviews are very detailed, typically lasting a full week.

Once an IMPEP review team has looked at everything they need to see on-site, they document their findings. They write a report and recommend a “grade” on the program’s performance to the Management Review Board, which is comprised of senior NRC managers and a state program manager who keeps in touch with the other Agreement States. The board holds a public meeting to talk about what the team saw and assigns the overall program rating: “Satisfactory,” “Satisfactory but Needs Improvement,” or “Unsatisfactory.”

Recently it was the NRC’s turn to undergo an IMPEP review. From Dec. 8-11, a team of experts from Ohio, Tennessee, and the NRC reviewed the NRC’s Sealed Source and Device (SS&D) Evaluation Program. This program performs engineering and radiation safety evaluations of sealed radioactive sources and the devices that use them.

Sealed sources are just what the name says—radioactive sources sealed in a capsule to prevent leakage or escape of the material. The devices are used for many things, but generally they measure something, such as soil density, fluid levels, the thickness of a pipe, and whether metal and welds are sound. They can also help to map geologic formations from inside a gas or oil well. The NRC needs to do adequate technical evaluations of SS&D designs to ensure they’ll maintain their integrity and their designs are adequate to protect public health and safety.

During the four-day IMPEP review at NRC Headquarters, the team looked at the NRC program’s technical quality, staffing and training, and any defects or incidents involving SS&Ds. Most of the work was done through in-depth staff interviews and targeted document reviews. S

Since finishing the evaluation in mid-December, the team has drafted their report. They expect to recommend to the board that the NRC’s SS&D program be rated Satisfactory – the highest possible rating. Furthermore the review team commended NRC staff for performing very competent technical SS&D reviews. Although this is an excellent result so far, there is still one more important step to complete the IMPEP review process – the public meeting.

This meeting allows the review team to present its findings and formally recommend the overall program rating. While the structure of these meetings is simple, it is very common to see a spirited discussion of the strengths, weaknesses, innovations and shortcomings of the program under review.

This is where the true value of IMPEP is laid bare. If all goes right, the end result is improving a program’s ability to protect public health and safety and the environment – even if the program gets the highest rating.

The MRB’s public meeting to discuss NRC’s SS&D program will be held at NRC Headquarters in Rockville, Md., on March 5, 2015. The meeting details are available on the NRC website at http://meetings.nrc.gov/pmns/mtg. We encourage members of the public to come or listen in by phone.

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