To Yucca from plant

The 25-year transportation programme to move spent fuel from commercial reactors around the USA to a proposed repository at Yucca Mountain, Nevada, will not be simple matter of loading casks on a fleet of trucks and driving to the desert. Even if the repository programme were running smoothly, which it most definitely is not, transportation issues would require millions of dollars and years of effort before the first cask ever hits the roads – or the rails. Among the big ticket items are a new railroad spur to the proposed repository site, full-scale crash and fire testing of typical spent fuel casks, and then procurement of an entire fleet of existing and custom designed casks.

However, all bets may be off as a result of a 9 July federal appeals court decision that threw out the federal government’s licensing standard for Yucca Mountain, finding that the 10,000-year compliance period did not go far enough in protecting the public from radiation releases.

Illustration of rail transport of spent nuclear fuel cask

Department of Energy (DoE) officials have said publicly since the decision that they still intend to submit a repository licence application to the Nuclear Regulatory Commission (NRC) in December 2004, and will leave it up to NRC or the courts to halt the process. However, Nevada officials consider the repository programme dead, at least in its present form, Robert Loux from the Nevada Agency for Nuclear Projects told NEI. State officials who have talked to NRC said licensing is in limbo, since there is no valid rule on which to base a licensing decision.

Until July, DoE officials talked about having the repository built and accepting spent fuel by 2010. As part of this ambitious schedule, DoE had to select a transportation scenario from among those presented in its February 2002 final environmental impact statement. In December 2003, DoE selected a scenario that calls for most of the waste to be transported to the repository by rail, but a small quantity of waste would be transported by truck from power plants not accessible by railroad. DoE also is considering transporting some waste by barge from power plants to the nearest railroad.

UP TO 10,000 TRAINLOADS

DoE’s transportation plan, which calls for shipping three casks per trainload, anticipates 3000-3300 train shipments over the 24-year operating life of the repository. Shipments of only one cask per train would result in 9000-10,000 shipments over the life of the repository. In addition, DoE expects to make about 1000 legal-weight truck shipments from power plants lacking rail access.

Under this mostly rail scenario, DoE would be required to build a rail spur in Nevada to transport the waste the final distance to the repository, since Yucca Mountain does not have an existing rail line. The department looked at five possible rail corridors from existing rail lines in Nevada, and selected the one known as the Caliente Corridor. The corridor originates at an existing siding to the mainline railroad near Caliente, Nevada, and extends west to the northwest corner of the Nevada Test and Training Range. It then turns south-southeast to the proposed repository site.

UNPRECEDENTED VOLUME

Given plans that called for the first shipments of nuclear waste to start heading for a repository within a decade, the US National Academy of Sciences (NAS) brought together an expert panel to identify key technical and societal issues that would affect decisions on transporting nuclear material from around the country to a repository. Physicist Neal Lane, a Rice University expert in science and technology policy, heads the 16-member panel, which was due to hold its final meeting on 21-23 July 2004, in Albuquerque, New Mexico, and to issue its report in early 2005.

The NAS Committee on Transportation of Nuclear Waste is focusing on the principal risks of transporting radioactive waste and how they compare with other societal risks and the principal technical and societal concerns, and what additional work is needed to address these concerns.

The volume of waste shipped to Yucca Mountain will be unprecedented in US history, Kevin Crowley, staff director of the NAS Board on Radioactive Waste Management, told the waste transportation panel in its 5-7 May 2004 meeting in Washington, DC. Once the repository is fully operational, each year’s shipments will approximately equal total US spent fuel shipments in the 33 years from 1964 to 1997, between 2000 and 2500 metric tons of heavy metal (MTHM).

He also pointed out that there is very little US experience with rail shipments; most shipments in the USA have been by truck. In researching the history of US spent fuel shipments, Crowley was able to find fewer than 300 rail shipments overall.

On a worldwide basis, total historical spent fuel shipments are about the same as the legal limit on disposal at Yucca Mountain – 70,000 MTHM. By far, the majority of these have been rail shipments, Crowley found, noting that they included shipments through urban areas. He also observed that most of these shipments covered a shorter distance (less than 1000km) than most of the planned US shipments, but also involved younger, hotter fuel since it was being shipped for reprocessing.

Some environmentalists, however, contend that no Yucca Mountain shipments will go the whole route on rail, at least not in the early years of repository operation. The Caliente rail spur is not likely to be completed for at least six years after the repository opens, said Michele Boyd from the activist group Public Citizen. This means that DoE will have to offload the spent fuel casks to trucks somewhere in Nevada and complete the journey by road. Pointing out that DoE had specifically rejected this option in the final environmental impact statement, she called the need for offloading a “significant change that should be evaluated.”

Loading a spent nuclear fuel cask onto a truck

CLASHING ON CRASH TESTS

The most hotly debated issue at the May NAS panel meeting was the need for crash and fire tests involving full-scale transportation casks, rather than the use of computer simulations and scale model tests. Industry representatives and some scientists contend the full-scale tests are expensive and unnecessary – they produce almost no information that could not be gained by other means. Environmentalists and local officials see the full-scale tests as the gold standard for demonstrating cask durability.

NRC, responsible for conducting these tests as part of the so-called Package Performance Study, made its decision to go with the full-scale tests several days after the May panel meeting. NRC establishes design standards for casks used to transport licensed spent fuel, and reviews and certifies cask designs prior to use. The Nuclear Waste Policy Act requires DoE to use casks certified by NRC if it transports spent fuel and high-level waste to the repository.

On 12 May, the NRC commissioners approved an NRC staff recommendation that the agency should begin preparing for a high-speed crash test of a cask, and set the plans in motion by directing the NRC staff to begin procuring a full-scale certified rail cask. In authorising the cask purchase, the commissioners directed the NRC staff to develop the test protocol in such a way that additional tests – and procurement of additional casks – would not be necessary.

In announcing the decision, NRC chairman Nils Diaz agreed that current computer and scale-model tests provide a reasonable scientific assurance that NRC certified casks can survive a transportation accident, but added: “The full-scale tests will enhance public confidence about how demanding our requirements really are.”

Industry does not object to full-scale testing per se, but does object to making it a regulatory requirement because it results in unnecessary expense, said Steve Kraft from the Nuclear Energy Institute. “If DoE wants to make full-scale testing a requirement for procurement of casks, then that is a cost issue DoE will have to deal with,” Kraft said, arguing that from a safety standpoint, computer models were better than physical testing. “They’re less expensive and you can simulate more conditions.”

Spent nuclear fuel cask illustration

Earl Easton from the NRC said that the commission’s certification requirements allow for the use of full-scale testing, half-scale testing or computer modelling. NRC requires “whatever it takes” to demonstrate that a package can meet Type B requirements.

In the past, NRC has required full-scale tests for casks that were a new design or a design that raised a lot of questions. For example, NRC required full-scale tests of the TRUPACT II cask that DoE uses to ship transuranic waste to the Waste Isolation Pilot Plant near Carlsbad, New Mexico. Although DoE uses the TRUPACT II to ship defence waste to a DoE facility, Congress required that NRC certify the WIPP shipping casks. Because the TRUPACT II uses a new cask design with much thinner walls than other casks, and a number of unusual features, NRC determined that full-scale testing was needed.

NRC also anticipates requiring full-scale crash tests if the commission receives an application to certify the German CONSTOR cask in the USA, Easton said. As with TRUPACT II, the CONSTOR differs from most US casks in a number of ways.

Boyd used several recent accidents in the Washington, DC area to highlight the need for full-scale testing. These include a fire in a Baltimore, Maryland railroad tunnel that involved flammable hazardous material and a highway accident in which the driver of a gasoline tanker truck suffered a heart attack and flipped his truck 60 feet over a highway overpass, creating a fireball and an uncontrolled blaze that burned for hours.

One member of the NAS panel pointed out that full-scale testing and computer modelling both have positive and negative aspects. Full-scale testing has become a ‘mantra’ among the public and many scientists, including the former head of the National Transportation Safety Board, he said. On the other hand, modelling proponents often ignore the fact that computer modelling is neither simple nor easy. Benchmarking any computer code is no easy task, yet it is a critical step if the model is to have validity.

Crash tests validate models

Crash tests are used to demonstrate the validity of analytical tools and scale modelling techniques to predict damage from accidents, not to validate regulatory standards, said Doug Ammerman from Sandia National Laboratory, which has conducted most of the US tests. Crash tests allow analysts to predict damage from accidents by comparing results predicted by the models to the actual tests results and to gain knowledge about extreme accident environments.

A number of insights for future testing can be gained from the last major campaign of cask testing in the 1970s, Ammerman said. These include:

• Use the same casks and transport systems that will be used for the actual shipping campaign.

• Include properly simulated fuel assemblies, with cladding and fuel pellets.

• Use modern inelastic dynamic analysis computational methods and the best-available materials property data and models.

• Use larger scale models to aid the analyst with the structural evaluation of the transport environment, because materials and components such as bolts often behave differently at smaller scales.

• Use analysis tools to help instrument hardware.

• Include more instrumentation.

At several points, members of the NAS panel asked for more details on how spent fuel pellets would behave under accident or fire conditions. They called for more examination of the possibility of pellet fracturing and the production of respirable particles from damaged pellets.

Angled impact is another area that needs more analysis, according to Brandon Hoffman from Public Citizen. US automakers have found that such impacts can cause more damage than two vehicles hitting head on at high speed.

As well as accidents, several speakers noted that there is another even more uncomfortable issue to be considered: careless or deliberate violations of codes and standards in the fabrication, use and servicing of casks. When Crowley asked if NRC keeps data on cask and transportation violations, Easton responded that the Department of Transportation, not NRC, is responsible for tracking violations. NRC does, however, inspect casks during fabrication.

On the issue of tunnel fires, panel vice-chairman Thomas Deen, a transportation consultant, noted that the Baltimore tunnel fire had become the ‘poster child’ for the ultimate nightmare accident. He suggested that writing regulations to ban spent fuel carriers from tunnels might solve the problem. As a practical matter, US spent fuel carriers already avoid tunnels for security and safeguards reasons, Kraft said. Shipments are seen as more vulnerable to attack or diversion in a tunnel. A representative from the environmental group Nuclear Information and Resource Service (NIRS) countered that DoE has been deliberately ambiguous on tunnels: sometimes the department says tunnels will be avoided, but at other times, it includes conditions for tunnel transport or identifies proposed routes that include tunnels.

TRANSPORTATION INTEGRATES

Transportation will be the ‘biggest integrator’ on the Yucca Mountain project, according to Ned Larson from the transportation office in DoE’s Office of Civilian Radioactive Waste Management (OCRWM), the office responsible for the Yucca Mountain project. Transportation touches all aspects of the programme: waste generators; the transportation industry; cask vendors; state, tribal and local governments; the repository; and other federal agencies, including NRC, the Department of Defense and the Department of Transportation.

Transporting a spent nuclear fuel cask by road

Just acquiring the casks that DoE needs to ship spent fuel will be a major challenge, Larson said. Since there is no standard fuel configuration for US reactors, the casks must accommodate a broad range of fuel types, and must be adaptable to utilities with a wide range of fuel handling and cask loading capabilities. Current cask designs are market-driven and tailored to dry storage requirements. In addition, casks are a long-lead-time item. Four or more years are required to design, certify and fabricate significant quantities of a new cask system.

DoE also is hampered in its ability to develop schedules based on the point of origin of the spent fuel, the fuel type or fuel characteristics, Larson said. The standard contracts DoE signed with the utilities in the 1980s determine many shipping priorities, and utilities have the choice of what fuel to ship first. Finally, spent fuel characteristics are a moving target. New fuel types are constantly being developed or modified.

OCRWM also is identifying ‘orphan fuel types’ for which there are no currently certified shipping casks. Larson expects most commercial fuels will be able to use currently available casks, but much of DoE’s own waste from the old weapons production sites will require custom casks. DoE plans to issue a professional services contract this autumn to develop certificates of compliance for casks for the orphan fuels. These casks could either be modifications of existing casks, or totally new designs.

In November 2003, the department issued a notice of programme interest seeking to determine which vendors could provide what kinds of casks in what quantities. DoE can place purchase orders with any cask vendor that has an NRC certificate of compliance. DoE’s schedule calls for it to issue a draft cask procurement request for proposals (RFP) this summer and the final RFP this fall. DoE hopes to start placing orders for existing, modified and new casks sometime in 2007.

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All images in this article are courtesy of the Nuclear Energy Institute