Sandia National Laboratories researchers and partners recently completed a 14,500-mile test to gather data on the stresses spent nuclear fuel experiences during transportation.

Nuclear power supplies almost 20 percent of U.S. electricity and is a leading carbon-neutral power source. However, it produces between 2,200 and 2,600 tons of spent fuel in the U.S. each year. Fuel rods become brittle and highly radioactive while powering the nuclear reactor, making safe transportation important.

Route of sea, rail, and truck test route. Credit: Sandia National LabRoute of sea, rail, and truck test route. Credit: Sandia National LabA nuclear waste transportation and storage cask was loaded with three surrogate fuel rod assemblies from the U.S., Spain and South Korea. It traveled from Spain to Colorado and back again by truck, ship and train. Zirconium alloy tubes filled with lead rope, lead pellets or molybdenum pellets imitated the uranium oxide pellets inside a spent nuclear fuel rod.

“All of our preliminary data suggests that the likelihood of a fuel rod breaking during routine handing and transportation is low," said Sylvia Saltzstein, Sandia's manager of the transportation projects.

Sandia collaborated on the test with Equipos Nucleares S.A. (ENSA), the Spanish cask designer and manufacturer, and Empresa Nacional de Residuos Radiactivos S.A. (ENRESA), the company responsible for nuclear waste management in Spain. The Korea Radioactive Waste Agency (KORAD), Korea Atomic Energy Research Institute (KAERI) and Pacific Northwest and Argonne national laboratories also took part in the test.

A grid of almost 300 rods makes up a fuel assembly and the cask used in the test can hold 32 assemblies in a specially designed basket. The mock fuel rods within the three assemblies were outfitted with accelerometers and strain gauges before they went into the cask. The cask and basket were similarly equipped.

The accelerometers and strain gauges measured each bump, rattle and jolt the mock fuel experienced during the trip, yielding data that can be used to quantify the safety margins of transporting spent nuclear fuel.

Test cask is loaded onto a barge. Credit: Sandia National LaboratoryTest cask is loaded onto a barge. Credit: Sandia National LaboratoryAlthough Sandia has tested the robustness of nuclear waste casks during decades of simulated catastrophic transportation accidents, another challenge is the stress from everyday transportation on the fuel rods inside the cask. Researchers worry that repeated jostling may lead to a fuel rod snapping, like bending a soda can tab one too many times.

The rail cask test generated about eight terabytes of shock and vibration data. Saltzstein expects the full analysis to take nearly a year. Data from the test also will be used to validate computer models of the stresses experienced by spent fuel during normal transportation.

The test was partially funded by the Department of Energy Office of Nuclear Energy’s Spent Fuel and Waste Science and Technology program.

Ongoing Tests

The recent test was the fourth to examine stresses encountered in transporting spent nuclear fuel.

The first used a large shaker table to test Sandia’s sensor-studded mock fuel assembly, with lead rope in zirconium alloy tubes to mimic the weight of uranium pellets. The researchers programmed the table to reproduce the shocks and vibrations from traveling by truck and measured the strain experienced by the fuel rods. The table only went up and down, so more testing was needed.

The second test placed the same assembly on a truck trailer loaded with 50,000 pounds of concrete, the same as a transportation cask, and took it on a 38-mile trip on highways, city streets and dirt roads. This test showed similar, low levels of strain on the mock fuel. However, since spent nuclear fuel mostly will travel by train, a third test was launched to measure the shocks and vibrations experienced on railroads.

Sandia researchers took shock and vibration data provided by the Association of American Railroads to set up a shaker table that could move in six directions instead of just up and down, simulating the strain and acceleration of train travel. They also replaced the lead rope in some of the rods with lead and molybdenum pellets for a better approximation of spent fuel.

This test agreed with two earlier tests: the stresses from normal transportation are about 100 times lower than the stresses known to damage nuclear fuel rods.

For the fourth test, researchers moved an actual spent fuel cask provided by a Spanish partner, but similar to those used in the U.S. The cask also was moved from one mode of transportation to another to obtain data closer to real-world conditions.

Spain to Colorado and Back

The test started in northern Spain, where the cask traveled by heavy-haul truck for about 250 miles through main roads and highways. After a layover to download data from the sensors, the cask was transferred to a barge, which sailed along the coast of France to Belgium. After a layover in Belgium, the cask was transferred to a cargo ship. Then the ship crossed the Atlantic to Baltimore through sometimes rough seas. This took two weeks.

In Baltimore, the cask was transferred to a dedicated flatbed train car and traveled west about 2,000 miles through 12 states. Then, in partnership with the Association of American Railroads, the cask and fuel assemblies were tested at the Transportation Technology Center Inc. facility near Pueblo, Colorado. The center has almost 50 miles of test track, permitting such controlled scenarios as joining two rail cars together or passing over a track crossing. After these trials, the cask with its sensors reversed course and returned to Spain.