WASHINGTON, April 16 (UPI) -- (Editor's note: This is the second article in a four-part series from United Press International examining some of the scientific issues related to using Nevada's Yucca Mountain as a nuclear waste repository site. Congress has started a 90-legislative-business-day period where it must vote to override the state's objections to continue the project. The House Energy and Commerce Committee is to hold a hearing on the project on April 18.)
Those opposed to the proposed nuclear waste site at Yucca Mountain often refer to horrific scenarios involving anti-tank missiles being fired at transport casks filled with waste, but the science of the matter is less dramatic.
Although the current debate in Congress involves whether the site itself is suitable for a long-term storage facility, opponents also are focusing on the risks of transporting waste from more than 100 sites around the country.
Both rail and road shipments are possible, though no railroad to Yucca exists. Failure to build one would mean more than 100,000 casks of spent nuclear power plant fuel and other waste would have to travel by truck, said Robert Halstead, an adviser to the state of Nevada, which is fighting the Yucca proposal.
"If rail access is achieved, the combined number of rail and truck shipments could be reduced to 36,400," Halstead said. "That works out to roughly between 1,000 and 2,900 shipments per year over 38 years."
Halstead and Rep. Shelley Berkley, D-Nev., are among those who have publicized a video taken during a test of a shipping cask. The warhead of a TOW antitank missile placed against the sidewall of the cask is detonated, putting a hole through the diameter of the container.
Thousands of TOW missiles exist around the world, Halstead said. The radioactivity released by such an attack in an urban area could kill several people immediately, and eventually could cause at least 3,000 deaths from cancer, he said.
Antitank missiles and their effects present a possibly serious situation, but on a much smaller scale than envisioned by Yucca opponents.
A shipping cask consists of an outer jacket of steel a few inches thick, several feet of lead shielding and spent fuel assemblies at the center. The assemblies are tubes of zirconium cladding surrounding ceramic uranium fuel pellets, said Edwin Lyman, scientific director and upcoming president of the Nuclear Control Institute, a group advocating stronger security at nuclear power plants and more effective handling of weapons-grade nuclear materials.
When the protection requirements for transport casks were written, intentional attack was not considered, Lyman told United Press International. Sandia National Laboratories later determined such an attack might cause casualties.
"On that basis the Nuclear Regulatory Commission imposed a restriction that basically banned casks from going through urban areas," Lyman said. "That was based on a postulated release without technical backup."
Further investigation involved tests similar to that shown in the video.
Antitank warheads also are called shape charges, where high explosive surrounds a hollow cone of copper, glass, or another dense material, said Charles Cutshaw, a former U.S. Army officer who specialized in antitank weapons and now is an editor with Jane's Infantry Weapons. When the charge hits an object, the extremely rapid detonation of the explosive forces the cone into a thin jet of molten material, whose velocity and density forces its way through armor plate.
"It does not actually 'burn through' the armor," Cutshaw told UPI. "As it goes through, it loses weight off the jet, but if it does penetrate, you find a slug of the metal behind the armor."
NRC tests showed only the material directly in the path of the jet would be shattered, and half of the zirconium tubes would be ruptured, Lyman said. There also are inert gases present in the fuel assemblies, but there is nothing in the cask to cause a secondary explosion after the warhead detonates, he said.
The tests concluded casualties from such an event would be limited to a few latent cancer cases, prompting the NRC to replace the urban transport ban with a requirement for armed escort in such areas, Lyman said. But those tests failed to take into account radioactive gases, such as krypton-85, which are generated by the fuel pellets after use in a reactor, Lyman said.
"If (the cladding) is punctured, that gas will be vented," Lyman said. "There are also some isotopes that become gaseous at moderate temperature. Cesium-137 is probably the worst actor, because it becomes volatile at a temperature of about 1,000 degrees Fahrenheit and it's a long-lived isotope."
Lyman recalculated the consequences based on the additional materials and determined Sandia's first estimates of several hundred possible latent cancer cases are probable.
All of this assumes use of an advanced, actively guided antitank missile, which is not the most likely situation, Cutshaw said.
"You don't always look at the worst-case threat, but what constitutes a reasonable threat," Cutshaw said. "First of all, getting a TOW and maneuvering it into position is going to be really problematic."
The missile is several feet long and together with its launcher weighs more than 200 pounds. The system is mounted on a vehicle or carried by a team of several people -- not something a terrorist could toss in a backpack and lug around, Cutshaw said.
The system is not "fire and forget," either. It requires an operator to keep the guidance scope centered on a moving target for the entire flight of the missile, possibly in the face of return fire from armed escort. This is something reliably achieved only with regular training unavailable outside military installations.
A more probable attack, Cutshaw said, would involve human-portable antitank weapons such as rocket-propelled grenades or the LAW and AT4 systems in the U.S. inventory. While these weapons are more easily obtained, they have smaller warheads, less range and are far less accurate, Cutshaw said.
"I'm not sure a LAW or an AT4 would completely penetrate a cask. I'm not even sure it would even get through one side," Cutshaw told UPI.
Another factor to consider is how the warhead would hit a cask, since the molten jet travels in a straight line. Scenarios such as those Lyman and the NRC investigated assume the warhead hits the sidewall within a few degrees of perpendicular in order for the jet to pass through the center of the cask. Less-than-perfect shots, even with a TOW, would only affect the lead shielding or fail to penetrate the entire cask.
Lyman and others have suggested terrorists could cause much greater damage with demolition charges. This scenario, however, would require attackers to gain full physical control of a cask, Lyman said.