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Category Archives: Radioactive Waste

Taking a Look at an Independent Review of Spent Fuel Pool Safety and Security

Scott Burnell
Public Affairs Officer

 A recently published National Academy of Sciences report includes the academy’s latest thoughts on enhancing the safety and security of spent nuclear fuel storage. The NRC gave NAS the funding for the study at the direction of Congress. This report is Phase 2 of the NAS work; we’ll recap Phase 1 in a moment.

The agency sponsored the two-phase NAS study to identify lessons learned from the Fukushima accident and to follow up on previous NAS recommendations on spent fuel safety and security. The earlier NAS work looked at these same topics after the Sept. 11, 2001, terrorist attacks, and led to a 2004 report (our response to Congress about the 2004 report is on the agency’s website).

As the NAS gathered information for the latest report, they talked with NRC staff and received NRC documents related to relevant regulatory programs and requirements.

Our first look at the Phase 2 NAS report did not identify any safety or security issues that would require immediate action by the NRC. U.S. nuclear power plant security is extremely robust; the plants are some of the best protected facilities in the world. We have a long record of studying and analyzing the safety and security of spent fuel storage. Some of these studies have resulted in security enhancements. For example, after the 9/11 terrorist attacks, the NRC’s security assessments resulted in improvements to security at nuclear power plants, and strengthened the plants’ coordination with other federal and state agencies in responding to security threats.

Our post-Fukushima requirements for U.S. reactors have enhanced spent fuel pool safety. For example, we required plants to improve the ability of operators to monitor the water level in spent fuel pools. We also required plants to develop new strategies for adding water to these pools to keep them cool, even under the conditions that might exist following an extreme natural event, like a severe earthquake or flood.

Looking at all the available information, we remain confident U.S. spent fuel is safely and securely stored. The Phase 2 NAS report looks ahead to some areas that NAS believes warrant further study or action. We’ll evaluate the NAS report and its recommendations to see if we need to take any further action in the long run. The staff plans to provide the Commission with its assessment of the NAS Phase 2 report later this year.

We know the public has questions about safely and securely storing spent nuclear fuel, so the NRC website includes key points and frequently asked questions and answers. We expect to update this information once we’ve finished assessing the NAS report.

We looked at the NAS Phase 1 report in 2014. That report looked at the causes of the Fukushima accident and also identified lessons for improving nuclear power plant safety systems and operations. The staff provided the Commission an assessment of the Phase 1 report in SECY-15-0059. In our final assessment of the Phase 1 report, we determined that all of the NAS recommendations were being addressed by completed and ongoing NRC activities.

WCS Sends NRC Interim Storage Application

Mark Lombard
Director, Division of Spent Fuel Management

You may have heard that the NRC has received an application today for a centralized storage facility for spent nuclear fuel. We thought this would be a good time to talk about what that facility would do, and how we will review the application.

First some background. “Spent fuel” is the term we use for nuclear fuel that has been burned in a reactor. When spent fuel is removed from a reactor, it is very hot, so it is put immediately into an onsite pool of water for cooling. Initially, the plan in the ‘70s had been to send the spent fuel for “reprocessing” prior to final disposal, so usable elements could be removed and made into fresh fuel. But reprocessing fell out of favor in the United States in the ‘80s.

Officials from Waste Control Specialists deliver its application to construct and operate a consolidated interim storage facility to Joel Munday, Acting Deputy Director of the NRC’s Office of Nuclear Material Safety and Safeguards.

Officials from Waste Control Specialists deliver its application to construct and operate a consolidated interim storage facility to Joel Munday, Acting Deputy Director of the NRC’s Office of Nuclear Material Safety and Safeguards.

To manage their growing inventory, nuclear utilities turned to dry storage. The idea behind dry storage casks is to cool the fuel passively, without the need for water, pumps or fans. The first U.S. dry storage system was loaded in 1986. In the past 30 years, dry storage has proven to be safe and effective.

Against this backdrop, a Texas company, Waste Control Specialists (WCS), filed an application with us today for a dry cask storage facility to be located in Andrews County. WCS plans to store spent fuel from commercial reactors; initially, from reactors that have permanently shut down.

The application discusses utilizing dry storage casks that have previously been approved by the NRC. The spent fuel would arrive already sealed in canisters, so the handling would be limited to moving the canisters from transportation to storage casks.

Ever since Congress enacted the first law for managing spent nuclear fuel in 1982, federal policy has included some centralized site to store spent fuel before final disposal in a repository. Congress made DOE responsible for taking spent fuel from commercial reactors. It gave NRC the responsibility to review the technical aspects of storage facility designs to ensure they protect public health and safety and the environment.

We conduct two parallel reviews – one of the safety and security aspects, the other of potential environment impacts.

But before those reviews get underway, we will review the application to see if it contains enough information that is of high enough quality to allow us to do the detailed reviews. If it doesn’t, WCS will have a chance to supplement it. If we find the application is sufficient and accept it, we will publish a notice in the Federal Register. This notice will alert the public that we have accepted the application for technical review, and offer an opportunity to ask for a hearing.

Then we begin our reviews. At the beginning of our safety and security review, NRC staff will hold a public meeting near the site to answer questions about our process. We’ll also have public meetings with WCS as needed so the staff can ask questions about the application. We will document this review in a Safety Evaluation Report.

Once we get public and stakeholder input on the scope of our environmental review, we will conduct the review and document the results in a draft Environmental Impact Statement (EIS). We’ll ask the public and stakeholders to comment on the draft. After considering those comments, we’ll finalize it.

We expect the review process to take us about three years, assuming WCS provides us with good information in a timely way during our review.

If interested parties ask for a hearing, and their petition is granted by our Atomic Safety and Licensing Board, then the board will consider specific “contentions,” or challenges to our reviews of the safety, security or environmental aspects of the proposed facility. The board will hold a hearing on any contentions that cannot be resolved. We can’t predict how long this hearing process would take.

The Safety Evaluation Report, the EIS and the hearing need to be complete before the NRC staff can make a licensing decision. If the application meets our regulations, we’re legally bound to issue a license. We don’t consider whether there’s a need for the facility or whether we think it’s a good idea. Our reviews look at the regulatory requirements, which are carefully designed to ensure public health and safety will be protected, and at the potential environmental impacts and applicant’s plans for mitigating them.

Incidentally, we are expecting an application for a second centralized interim storage facility Nov. 30. This one, to be filed by Holtec International, will be for a site in New Mexico. We’ll follow the same process in reviewing that application.

Dry Casks 101: Managing Heat

CASK_101finalCaylee Johanson
Mechanical Engineer

In this series we’ve been talking about storing spent nuclear fuel in dry casks. One major function of these casks is to cool the fuel. Keeping the spent fuel from getting too hot is one way to ensure casks will be safe. As the fuel cools, heat is transferred from inside the cask to the outside.

Our experts look at how the cask will perform this function. We require the cask and fuel to remain within a certain temperature range. Our review looks at four main areas:

Spent fuel releases heat as a result of its radioactive decay. This is called decay heat. A key function of dry storage casks is to move the decay heat from the cask to the outside environment to ensure the fuel and cask components do not get too hot. Our experts look at how that heat will move through the cask and into the environment.

The method used to remove heat has to be reliable and provable. Heat must also be removed in a way that is passive—meaning no electrical power or mechanical device is needed. Casks use conduction, convection and radiation to transfer the heat to the outside.

Heat Radiation Transparent 2The graphic shows the three heat transfer methods. As you can see, conduction transfers heat from the burner through the pot to the handle. The process of heat rising (and cold falling) is known as convection. And the heat you feel coming off a radiator, or a hot stove, is known as radiant heat.

These methods work the same way in a storage cask. Where the canister or metal structure containing the fuel touches the fuel assemblies, heat is conducted toward the outside of the cask. Most casks have vents that allow outside air to flow naturally into the cask (but not into the canister) and cool the canister containing the fuel (convection). And most casks would be warm from radiant heat if you stood next to them. (The heat generated by a loaded spent fuel cask is typically less than is given off by a home-heating system.)

We limit how hot the cask components and fuel materials can get because we want to protect the cladding, or the metal tube that holds the fuel pellets. Limiting the heat is one important way we can ensure the cladding doesn’t degrade. The cask must  keep spent fuel cladding below 752 degrees Fahrenheit during normal storage conditions—a limit that, based on the material properties of the cladding, will prevent it from degrading. The fuel must also remain below 1058 degrees in off-normal or accident conditions (such as if a cask were dropped while it is being positioned on the storage pad, or if a flood or snow were to block the vents).

We also confirm the pressure inside is below the design limit to make sure the pressure won’t impact the structure or operations. Our experts review applications for new cask designs carefully to verify the fuel cladding and cask component temperatures and the internal pressure will remain below specified limits.

Each storage cask is designed to withstand the effects from a certain amount of heat. This amount is called the heat load. We look at whether the designer correctly considered how the heat load will affect cask component and fuel temperatures. We review how this heat load was calculated.

We also verify that the cask designer looked at all the environmental conditions that can be expected because these will also affect the cask component and fuel temperatures. These may include wind speed and direction, temperature extremes, and a site’s elevation (which can affect internal pressure). To make sure the right values are considered, we verify they match the historical records for a site or region.

We review all of the methods used to prove that the storage system can handle the specified heat loads. We also verify any computer codes used in the analysis and the values that were plugged in. For example, we look at the material properties for cask components used in the code. We look at calculations for temperatures and pressure. We make sure the computer codes are the latest versions.

And we only allow designers to use codes that have been endorsed by experts. We might run our own analysis using a different computer code to see if our results match the application.

The analysis and review allow us to see whether and how the dry cask will meet the temperature limits. Our review ensures the temperature is maintained and the cladding is protected. Finally, our review confirms the cask designer used acceptable methods to analyze or test the system and evaluate the thermal design. If we have any questions or concerns, we ask the designer for more information.

Only when we are satisfied that our requirements are met will we approve the thermal analysis in a cask application.

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

Mark Lombard
Director, Division of Spent Fuel Storage and Transportation

refresh leafAs the country wrestles with how to manage the highly radioactive fuel left over from generating nuclear power, one question often comes up: “how do we know we can transport it safely from reactor sites to other locations for storage, testing or disposal.” For one thing, we periodically assess the risks. For another, spent fuel shipments are strictly regulated and have not released any radioactive materials since they began more than 30 years ago.

Our most recent risk assessment, published in 2014, confirmed that NRC regulations for spent fuel transport are adequate to ensure safety of the public and the environment. As more data become available and computer modeling improves, these studies allow the NRC to better understand the risks.

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 containers for the more hazardous radioactive materials, including spent fuel.

To be certified, a container 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. Containers 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 cask absorbs all the force) followed by a 1,475-degree Fahrenheit fire that engulfs the package for 30 minutes.

The 2014 Spent Fuel Transportation Risk Assessment modeled the radiation doses people might receive if spent fuel is shipped from reactors to a central facility. The study found:

  • Doses along the route would be less than 1/1000 the amount of radiation people receive from background sources each year
  • There is 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 Spent Fuel Transportation Risk Study examined how three NRC-certified casks 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 2014 study 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 1987 and 2000 found the risks were even smaller than the 1977 study predicted. Together with analyses we perform on major transportation accidents, these studies give the NRC confidence in the safety of spent fuel shipments.

For more information on how the NRC regulates spent fuel transportation, click on our backgrounder.

REFRESH is an occasional series where we revisit previous posts. This originally ran in September 2013

 

 

Dry Cask 101: Storage and Transport – The Right Materials for the Job

John Wise
Materials Engineer

CASK_101finalMaterials – the stuff of which everything is made. You might not give much thought to the materials around you: the metal in the door of your car, the plastic used in airplane windows, or the steel from which elevator cables are made. Yet, in each of these cases, the selection of appropriate materials is critical to our safety.

Systems that transport and store spent nuclear fuel and other radioactive substances are made of a variety of materials. All of them are reviewed to confirm that those systems can protect the public and environment from the effects of radiation. The NRC does not dictate what materials are used. Rather, the NRC evaluates the choice of materials proposed by applicants that want NRC approval of systems to transport or store radioactive substances.  We typically refer to these substances as radioactive materials, but that might make this discussion much too confusing.

What makes a material “appropriate” to transport and store radioactive substances depends on a number of factors.

First, materials must be adequate for the job. In other words, the mechanical and physical properties of the materials have to meet certain requirements. For example, the steel chosen for a transportation canister has to withstand possible impacts in a transport accident.  Neutron-absorber materials need to block the movement of neutrons to control nuclear reactions in spent nuclear fuel.

Next, when making complex metal system, parts often are fused together by partially melting, or welding, them in a way that ensures that the joints themselves are adequate for the job. It may not be obvious, but during the welding process, the welder is creating a new material at the joint with its own unique properties.  That’s why the NRC looks at how this is done, including the selection of weld filler metals, how heat is controlled to ensure good welds, and the use of examinations and testing to verify that no defects are present.

Horizontal storage systems under construction.

Horizontal storage systems under construction.

Finally, the NRC considers how materials degrade over time. In other words, we must take into account a material’s chemical properties – how it reacts with its environment. We’re all familiar with how iron rusts when it gets wet or how old elastic materials (e.g., rubber bands) become brittle. Often such degradation is not important. But sometimes it can cause concern. Thus, materials must be selected based on their present condition and their projected condition throughout their lifetimes.

Best practices for appropriately selecting materials and the processes used to join them often can be found in consensus codes and standards. These guidelines are typically developed over many years of experience and through industry-wide and government agreement.  But such guidelines may not cover all aspects of material selection. So we also rely on both historical operating experience and the latest materials testing data.

The NRC has a team of materials experts that reviews every application we receive for approval of spent fuel storage and transportation systems. These experts must be satisfied that every material and the processes used to join them are up to the job. The materials review is one part of a comprehensive review the NRC does on every application. We will focus on other parts of our reviews in upcoming blog posts.

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