Transporting Spent Nuclear Fuel: How Do We Know It’s Safe?

John Cook
Senior Transportation Safety Scientist
Division of Spent Fuel Storage and Transportation
 

In May, we talked about changes to NRC regulations regarding shipments of nuclear materials – including spent fuel. This month, we wanted to share the results of a periodic evaluation of the risk posed by spent fuel shipments. The NRC expects to publish the final study later this year. A draft was published in 2012.

Microsoft Word - diagram-typical-trans-cask-system-2.docSpent fuel shipments are strictly regulated and have not released any radioactive materials since they began more than 30 years ago. But the NRC still periodically evaluates the risks. As more data become available and computer modeling improves, these studies allow us to refine our understanding of these risks.

The latest study, Spent Fuel Transportation Risk Assessment, modeled the radiation doses people might receive if spent fuel is shipped between various sites. The study confirmed that NRC regulations for spent fuel transport are adequate to ensure safety of the public and the environment.

Both the NRC and the U.S. Department of Transportation oversee radioactive material transport. DOT regulates shippers, vehicle safety, routing, and emergency response. The NRC certifies shipping packages for the more hazardous radioactive materials, including spent fuel.

To be NRC-certified, a package must provide shielding, dissipate heat, and prevent a nuclear chain reaction. It must also prevent the loss of radioactive contents under both normal and accident conditions. The package must be able to survive a sequence of tests meant to envelope the forces in a severe accident. These tests include a 30-foot drop onto an “unyielding” surface (one that does not give, so the package absorbs all the force), a puncture test drop onto a steel peg, and then a 1475-degree Fahrenheit fire that engulfs the package for 30 minutes.

The 2013 risk assessment examined how three NRC-certified packages would behave during both normal shipments and accidents. It modeled a variety of transport routes using population data from the 2000 census, as updated in 2008. It used actual highway and rail accident statistics. It considered doses from normal shipments to people living along transportation routes, occupants of vehicles sharing the route, vehicle crew and other workers, and anyone present at a stop. And it used state-of-the-art computer models. The risk assessment found:

 Doses from routine transport would be less than 1/1000 the amount of radiation people receive from background sources each year

 There is less than a 1 in 1 billion chance that radioactive material would be released in an accident

 If an accident did release radioactive material, the dose to the most affected individual would not cause immediate harm

The 2013 risk assessment builds on earlier studies of transportation risks. It uses real-world data and equipment in place of generic designs and conservative assumptions. The first study, done in 1977, allowed the NRC to say that its transport regulations adequately protect public health and safety. Other studies done in in 1987 and 2000 found the risks were even smaller than the 1977 study predicted. These studies, together with analyses we perform on major transportation accidents, previous physical testing of package performance, and the global experience with thousands of completed spent fuel shipments, give the NRC confidence in the safety of spent fuel shipments.

For more information on how the NRC regulates spent fuel transportation, click here. To read our updated backgrounder on the subject, click here.

Two Separate NRC Efforts Address Spent Fuel Safety

David McIntyre
Public Affairs Officer
 

Today, the NRC is making publicly available four documents relating to the safe storage of spent nuclear fuel. The first three represent the agency’s work to date on revising its waste confidence rule and analyzing the environmental effects of extended spent fuel storage. The fourth is a draft study examining whether earlier transfer of spent fuel from pools to dry cask storage would significantly reduce risks to public health and safety.

Although both waste confidence and the spent fuel pool study discuss the safety of spent fuel, these are two separate efforts with distinct goals. So we wanted to explain the processes here on the blog to help avoid confusion.

dropquotedaveThe waste confidence documents represent a major milestone in the NRC’s effort to address last year’s U.S. Appeals Court decision striking down our waste confidence rule. The court directed the agency to analyze the environmental effects of never having a permanent repository for the nation’s commercial spent fuel, as well as the effects of spent fuel pool leaks and fires.

The three waste confidence documents being posted today on the NRC website are:

• A staff paper to the Commission (SECY-13-0061) recommending publication of a proposed rule and draft generic environmental impact statement, or GEIS, for public comment;

• A draft Federal Register notice containing the proposed rule and a “Statement of Considerations,” or preamble, that explains the rule, the conclusions in the GEIS that support the rule, and the changes in format that the NRC is recommending as part of this rulemaking (Enclosure1); and

• The draft generic environmental impact statement on the effects of continued storage of spent fuel (Enclosure 2); it serves as the regulatory basis for the proposed rule. A list of reference documents used in preparing the GEIS is also being posted on the NRC’s waste confidence webpage.

These documents are now before the Commission and are being made publicly available under standard agency procedure. The Commission may approve, modify or disapprove these documents, so we are not yet seeking public comments. We hope to publish them officially for comment in late August or early September, but that timeframe depends on Commission approval.

When they are published, the 75-day official public comment period will begin. During that period, we will hold 10 public meetings around the country to present the proposed rule and draft GEIS and receive your comments. Two of these meetings will be at NRC headquarters in Rockville, Md. The rest will be in New York, Massachusetts, Colorado, southern California, central California, Minnesota, Ohio, and North Carolina.

Details will be announced closer to the dates on the NRC’s public meetings webpage and the waste confidence webpage.

reportsThe spent fuel pool study is being published for public comment. A Federal Register notice to be published soon will set a 30-day deadline and explain how to submit comments.

The NRC began this study after the Fukushima nuclear accident in March 2011. Although the spent fuel pools at Fukushima did not fail, the accident sparked debate in this country over whether it might be safer to transfer spent fuel from pools to dry cask storage sooner than is the norm.

The study considered a pool at a boiling-water reactor with Mark 1 containment (the type used at Fukushima and 23 U.S. reactors) and an earthquake several times stronger than the pool was designed to withstand. It examined both a “full” pool and one with less fuel and more space between the assemblies, with and without emergency procedures to add water to the pool in the unlikely event an earthquake causes the pool to drain.

The pool study and the waste confidence review are separate efforts. The draft GEIS does not explicitly reference the pool study, though the waste confidence staff worked closely with the staff preparing the pool study while developing relevant chapters of the draft GEIS. If a final version of the study is published before the final waste confidence GEIS, the staff will incorporate a reference to it in the final GEIS.

These four documents represent two distinct NRC efforts on one very important subject: the safe storage of spent fuel and its environmental impacts. We look forward to your comments on the draft spent fuel pool study now, and on the waste confidence proposed rule and draft environmental study in the fall.

Updating Nuclear Materials Transportation Regulations

Jessica Umaña
Project Manager, Division of Spent Fuel Storage and Transportation
 

The idea of transporting nuclear materials can make people nervous. It’s easy to imagine worst-case accidents on the highway or involving a train. But stringent safety requirements, as well as coordination among federal agencies, international regulators, and state and local officials, help to ensure these shipments are made safely. This structure provides many layers of safety.

From time to time, the requirements are updated to address new information. The International Atomic Energy Agency (IAEA) and U.S. Department of Transportation recently updated their requirements. The NRC is now amending ours to reflect those updates, as well as to make some changes we feel are needed based on recent experience. You can read the Federal Register notice on the proposed rule.

mapWhile the rules are being updated, the fact remains that nuclear materials are transported safely all the time. By far the majority of shipments involve small quantities of nuclear materials. Millions of these shipments are made each year and arrive at their destination without incident. Occasionally, the carrier might be involved in a traffic accident. But in decades of transporting nuclear materials, there has never been an accident that resulted in a radioactive release.

Smaller shipments must be made in compliance with DOT regulations for shipping hazardous materials. The greater the potential risk of the contents, the more stringent DOT’s packaging requirements are. The DOT regulations limit how much radioactivity can be transported in each package. That way, no transport accident involving these small shipments would pose a serious health threat.

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

In addition to having to meet DOT requirements, more radioactive cargo such as spent fuel must meet NRC regulations for nuclear materials packaging and transport in 10 CFR Part 71. These regulations include very detailed requirements for shipping under normal conditions, as well as stringent tests to show the packages can withstand 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 newly updated backgrounder.

When Problems Are a Sign of Success

Chris Allen
Project Manager
Division of Spent Fuel Storage and Transportation
 

Can a problem show that our regulatory system works? If you don’t think so, read on.

Two weeks ago, the NRC published an “information notice” about moisture causing problems for dry spent fuel storage casks. Information notices are one way the NRC communicates formally with licensees. We send these notices when we want all licensees to be aware of a particular problem found with just one or only a handful of licensed facilities or equipment so they can prevent similar problems.

Spent fuel dry casks
Spent fuel dry casks

The problem in this case centers on dry spent fuel storage casks that store used nuclear fuel after it’s been cooled for several years in spent fuel pools. The NRC reviews the designs of these casks to make sure they will safely cool the fuel and contain the radiation it emits.

In this case, two different sites using two different storage designs had unanticipated problems on the outside of the system caused by moisture. The structural integrity of the systems was never compromised and the radiation levels at both sites remained very low.

The first problem dates to 2007 at a facility in Idaho that stores spent fuel debris from the damaged Three Mile Island reactor. The system uses thick concrete for shielding and protection from earthquakes and other natural forces. The operator saw that cracks in the concrete—originally thought to be cosmetic and trivial—were spreading. The licensee’s evaluation found water had entered bolt holes on top of the casks, froze, thawed and cracked the concrete. The evaluation also identified repairs, ways to prevent more water from getting in and a program for monitoring cracking.

The second problem, at the Peach Bottom reactor site in Pennsylvania, was identified on October 11, 2010, when an alarm sounded. That alarm was designed to be an early warning that the helium inside might be leaking. On examination, the licensee found rust beneath a metal weather cover and moisture around the bolts holding the cask lid in place. An outer lid seal was leaking more helium than the NRC license allowed. An inner seal kept the spent fuel and radioactivity confined inside the cask.

From the time these issues were discovered, we made information available through licensee event reports, NRC inspection reports, letters and other communications with licensees. Our licensees and some trade publications that follow NRC activities closely knew of the issues.

The licensees talked with one another as well at industry-wide workshops and conferences. And our inspectors, who also talk with one another, always look for evidence that dry storage casks are in good condition.

So how does this mean the process worked?

Alarms like the one at Peach Bottom and follow-up evaluations like the one in Idaho are examples of the monitoring and periodic examinations that the NRC requires all cask users to perform. These provide warnings long before a problem could develop that might affect public health and safety or the environment. We also require periodic examinations of dry storage casks so any potential issues can be identified early.

The NRC stayed up-to-date as the licensees learned more about the cause of their problems, how to prevent such problems in the future, and how to fix the problems on their existing systems. In this case, the NRC took the extra step of issuing the information notice even though communication between the NRC and licensees as well as among licensees meant that, when the information notice came out last week, it was actually “old news.”