Nuclear Weapons & Materials Monitor
2/1/99


A classified Los Alamos National Laboratory program that has raised questions with the Defense Nuclear Facilities Safety Board involves confinement vessel explosives tests, apparently using plutonium-242 at the lab’s new Dual-Axis Radiographic Hydrotest Facility, according to declassified documents and Energy Departmental sources. Details about the experiments, apparently to be conducted later this year are highly classified, and simply the fact that there is now a public discussion going on regarding the apparent use of plutonium-242 in the tests has prompted inquiries by the Department of Energy about a possible breach of security, NW&M Monitor has learned.

Experts say use of the plutonium-242 isotope in explosives tests would allow a full-scale nuclear weapon mockup to be detonated without resulting in any nuclear yield, an experiment that would allow detailed hydrodynamical study of the early stages of the implosion of a nuclear weapon. But while there have been hints in the public record about the possibility of such tests being planned for DARHT, details have been tightly classified.

The mask slipped slightly with the public release of a Dec. 17 letter from Assistant Energy Secretary Vic Reis to the Defense Nuclear Facilities Safety Board. The unclassified letter, which accompanied a classified report, discusses issues related to “confinement vessel integrity” associated with upcoming work to be done at Los Alamos. Reis’ letter came in response to a Nov. 17 letter from the board to the DOE complaining about a classified research project about to get underway. The letter questioned “efforts to startup certain classified activities at the Los Alamos National Laboratory,” offering no details. Reis’s response revealed that the tests involved “more challenging charge loadings” involving “confinement vessel(s)”.

Classification around the project remains tight, but sources familiar with the work left a trail of bread crumbs leading inexorably to the apparent fact that the tests in question involve the use of plutonium-242 at DARHT. The crumb trail starts in 1995, when a series of documents published by the Energy Department led to questions about plutonium use in high explosive tests. Conducted at least as far back as the 1950s, the tests involve detonating various materials in sealed steel vessels and using very high-powered x-rays to image the process. Some 40 to 60 of various types of such hydrotests are conducted annually at test facilities at Los Alamos and Lawrence Livermore Nationally Laboratory. To beef up its capability to do such tests, the department is near completing DARHT at Los Alamos, which offers more powerful x-rays, with the x-ray images to be taken from two directions, allowing three-dimensional images of imploding objects to be taken. The first axis of DARHT is scheduled to be completed and ready for tests this summer.

In an environmental impact statement produced for DARHT in 1996 after activists sued trying to block the project, there were unclassified discussions of the use of various materials in DARHT tests, but details of plutoniurn usage in the facility were confined to a classified appendix. In addition, the department’s Environmental Impact Statement on the stockpile stewardship program, which came out around the same time, included a similar classified annex dealing with plutonium-242 being produced at Savannah River. At the time, smart activists and journalists put two and two together and inferred that the purpose of the SRS plutonium-242 was for use in DARHT.

Basic physics provides a rationale. When weapons-grade plutonium-239 reaches a critical mass, a nuclear chain reaction begins, a phenomenon that severely limits the type of nuclear weapons testing that can be done in a test ban environment. But plutonium-242 is much less fissionable. That means an identical mass of plutonium to that used in a weapon could be imploded with a full charge of high explosives with no nuclear yield resulting. While that won’t help weapons scientists understand the physics of the nuclear blast itself, it could allow them to analyze in great detail the behavior of the plutonium as it liquifies and is squeezed inward by the high explosive blast used to set off a nuclear weapon.

As plutonium ages and develops imperfections, the behavior of the material in that crucial instant becomes one of the key questions facing the weaponeers as they cope with an aging arsenal that they are not permitted to test directly with underground blasts.

There was a feud within the Energy Department in 1996 over the classification of the use of plutoniuin-242 in the DARHT tests, with classification and weapons program officials favoring declassifying it, while nonproliferation officials opposed any such move. Thus, the potential use of plutouium-242 at DARHT remains officially classified, but officials speaking with NW&M Monitor confirmed the general outlines of a program in which plutonium-242 will be detonated in containment vessels at DARHT. Whether that plutonium-242 would actually be assembled into a warhead configuration remained unclear.

In his letter to the DNFSB, Reis offered assurances that the work would be done safely. Any containment vessel blasts with larger explosive charges than those already approved will not be done until full safety analyses are completed, Reis said.

(Courtesy of Exchange/Monitor Publications, Inc.)