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Testing Spent Fuel Transport Casks Using Scale Models

Bernard White
Senior Project Manager
Division of Spent Fuel Storage and Transportation

Before casks can be used to transport the most radioactive cargo—including spent nuclear fuel—the NRC requires them to undergo a thorough safety evaluation. Casks are evaluated for their ability to withstand vibration, water spray, free fall, stacking, penetration and fire. A cask must be able to contain and shield the spent fuel and keep it in a safe configuration under both normal and accident conditions. Typically, spent fuel casks are certified through a combination of engineering analyses and scale model or component testing.

People often ask why the NRC allows designers to test scale models instead of requiring tests on full-sized casks. The bottom line is scale-model testing provides the necessary information for the NRC staff to know that a cask loaded with spent fuel can be transported safely, even in the event of an accident.

scalemodel2First, it is important to understand what information comes out of these tests. Test casks are fitted with sensors to measure acceleration. These accelerometers are similar to the ones used in smart phones, video game remotes and pedometers to respond to the movements of the user. Knowing the cask’s acceleration allows designers and the NRC to understand the forces different parts of the cask will experience in different types of impacts. The design engineer generally calculates these impact forces first by hand or by computer. Tests on a scale model can be used to check the accuracy of these analyses.

Engineers follow a similar process to safety-test airplanes, ships, bridges, buildings and other large structures. Scale-model testing is a proven and accepted practice across engineering disciplines, and may be one of the oldest engineering design tools. (Ancient Egyptian, Greek, and Roman builders are known to have built small models to assist in planning structures.) Today, models allow oversized structures to be examined in wind tunnels, under different weight loads and on shake tables to provide key inputs into design and safety reviews.

Cost savings is a factor, but not the most important one. The biggest reason for using scale models is practicality. Transport casks for spent nuclear fuel are typically in the 25-ton to 125-ton range. There are very few testing facilities in the world that can put a 125-ton cask through the required tests.

For example, during 30-foot drop test, the test cask must strike the surface in the position that would cause the most severe damage. Cask designers often perform several drops to ensure they identify the correct position. After the 30-foot drop, the cask is dropped 40 inches onto a cylindrical puncture bar, then placed in a fully-engulfing fire for 30 minutes. Casks are also immersed in water to ensure they don’t leak. Measurements from these tests are plugged into computer programs that analyze the cask structure in great detail.

This analysis can determine the stresses placed on cask closure bolts, canisters and baskets that hold the spent fuel in place, and the spent fuel assemblies themselves. Computer simulations can be run for different scenarios, providing maximum flexibility to designers in understanding how best to design different parts of a cask’s structure.

In addition, NRC regulations specify that in the 30-foot drop test, the cask must hit an “unyielding” surface. This means the cask itself, which may be fitted with “impact limiters,” has to absorb all the damage. The impact limiters work much like the bumper that protects a car in a collision. The target surface cannot dent, crack or break in any way. In a real-world accident, a 125-ton cask would damage any surface significantly. It requires considerably more engineering work to achieve an unyielding surface for a full-sized cask than for a scale model, with no measurable advantage. The rule-of-thumb for testing is the impact target should be 10 times the mass of the object that will strike it. So a 125-ton cask would need to hit a 1,250 ton surface. A 30-ton cask would only need a 300-ton target.

Scale models are easier to handle and can be used efficiently for many drop orientations to meet the multiple test requirements. If a test needs to be run again, it can be done much more easily with a scale model. Design changes are also more easily tested on models. Together with extensive analyses of a cask’s ability to meet our regulatory requirements, the information from these tests allows the NRC to decide whether a cask can safely transport the radioactive contents.

In Honor of June – Fresh Fruit and Vegetables Month

fruitsandvegJune isn’t just about Father’s Day and graduations. It’s also Fresh Fruit and Vegetables Month. In honor of that designation, we bring you this question: Which of these fruits and vegetables contain naturally occurring radioactive potassium?

  1. a) White potatoes
  2. b) Carrots
  3. c) Lima beans
  4. d) Bananas
  5. e) All of the above

NRC — Ready for the 2015 Hurricane Season UPDATED

Update: Due to Hurricane Bill, the South Texas Project nuclear power plant, located near Bay City, Texas, has started tropical storm/hurricane procedures. Actions taken include performing a plant walkdown to secure and tie down anything that could be become a projectile missile or flying debris. The plant operator has implemented restrictions for employees to stay inside if winds get above 40 mph. Today, winds are projected to be sustained at 50 mph with gusts up to 60 mph. Both units are at full power unless winds reach speeds above 75 mph, but that is not expected at this time. They have additional staff onsite and supplies (cots, food, water). The resident inspectors are not evacuating and an additional group of NRC inspectors has been on site and will remain so to back up the residents if need be. (At this time the hurricane is not expected to affect River Bend or Waterford nuclear power plants, but the NRC’s Region IV will continue to monitor the projected path.)

Roger Hannah
Senior Public Affairs Officer
Region II

The hurricane season officially began June 1, but this year the Carolina coast experienced a tropical storm named Ana in early May. While Ana produced winds of more than 60 miles an hour near the Brunswick nuclear plant, there was no major damage. It did, however, serve as an early reminder of the NRC’s role in ensuring nuclear plants remain safe during damaging winds and storm surges.

A hurricane as seen by satellite. Be assured, it's not happening now.

A hurricane as seen by satellite. Be assured, it’s not a current photo and is NOT happening now.

The NRC has years of experience with hurricanes and other severe storms. Nuclear facilities were affected by Hurricane Andrew in Florida in 1992, by Katrina in Louisiana in 2005, by Sandy along the East Coast in 2012 and by many others. Although the National Oceanic and Atmospheric Administration predicts fewer storms this year than the historical average, any storm can be dangerous.

How does the NRC oversee the safety of nuclear plants and other facilities during these storms?

The NRC staff monitors tropical storms as they form, and if the projected path is towards the coast, the agency’s regional offices begin continuous tracking. If a storm’s path shows the possibility of it affecting a nuclear plant or other NRC-licensed facility, the NRC collects more information on the storm and NRC resident inspectors check the plant’s preparations. Depending on the projections, additional NRC inspectors may be dispatched to some nuclear plants.

Around 12 hours before predicted hurricane-force winds, nuclear facilities that may be in the path provide the NRC updates and NRC inspectors monitor the plant staff’s actions. Plant procedures require the plant operators to shut the reactor down if winds greater than a certain speed are expected on the plant site.

Nuclear plants are built to withstand all expected local meteorological events, including hurricanes, and actual storms have shown that plants can safely shut down and with little or no damage to important safety equipment.

The NRC stays in contact with plants and NRC inspectors on site as the storm passes over, and the agency has backup systems if regular communications channels are lost.

Once the storm is over, the NRC and FEMA assess damage and make sure local emergency response organizations can resume their normal roles. If the plant shut down, it will only be restarted after the NRC is satisfied there is no damage to safety equipment and emergency response capabilities have been restored.

Fortunately, most tropical storms and hurricanes do not adversely affect nuclear plants, but the NRC is ready in case one does.

Continually Improving Search to Enhance Openness

Patricia Hall
Chief, Information and Data Operations Branch

The NRC prides itself on being an open and transparent organization and we have an extensive web site and a comprehensive online document system to prove it. We also provide a handy search tool that facilitates some 5000 to 8000 search requests on the average work day.

searchBecause we understand that sometimes it can still be a bit difficult to easily find what you’re looking for we have improved our search function effective immediately.

Located at the top of each page at www.nrc.gov, the search retains many of the features of the prior site search. You can still:

  • Search the whole web site and the public part of the ADAMS document library
  • Refine your search in a variety of ways
  • Sort your results by relevance or date

Now, though, there are several new features. Your search will include thumbnail images (if images are part of the document) and you can search not just the website but also the agency’s social media platforms, including the blog, Facebook, Flickr and YouTube. You can also search the site glossary of nuclear terms.

Search suggestions will appear as you type in the search and there is a link on the results page to save your current search results for later viewing or sharing.

searchBut there’s more! New collection searches will be available for several types of NRC Generic Communications, including Information Notices, Regulatory Issue Summaries, Generic Letters, Bulletins, and Circulars. Searches of the Commission Speeches collection will include links to filter by specific NRC Commissioners and searches of the News Releases collection will include links to filter by NRC region.

This new and improved search aligns more closely with the search experience at www.google.com, so you can expect a level of user friendliness from our search similar to what they would expect with a Google search. For example, when you enter a search phrase consisting of several words, Google search will bring up Web pages and documents containing instances of the entire phrase before those matching only the individual words. Web pages and documents containing more instances of your exact phrase will be favored in the ranking, as will those where the phrase occurs in the title or near the top of the document.

We hope you will find the improved search tool easier to use and your searches to be more fruitful. If you have additional suggestions for improvements, please put them in the comments below.

Note: The graphic is just an illustration. The Search box looks exactly the same as it did previously.

Throwback Thursday – A Reactor Vessel’s Arrival

tbtchIn these photos, a reactor vessel is being towed (and then arrives) at the barge dock of an East Coast nuclear power plant site circa 1971 Can you name the power plant? Photo courtesy of the Department of Energytbtch1

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