Lab builds world's first neptunium sphere

Not much is known about the properties of neptunium, a highly radioactive man-made material that is a byproduct of nuclear reactors, except that it emits alpha, beta and gamma radioactivity. The critical mass is not well known, with documented values covering a very wide range of masses.

“We were starting from scratch when this project began back in 1997,” said Stanley Bodenstein,, who led the project in its early stages.

“Nothing like this had been done before with neptunium. We were going to cast, machine and clad a sphere of material that is pyrophoric, meaning it can catch fire if exposed to oxygen, and so radioactive it must be handled remotely, completely hands-off.”

The neptunium sphere team included Actinide Chemistry Research and Development (NMT-11), Materials Technology: Metallurgy (MST- 6), CMR Facility Management (NMT-13), Experimental and Diagnostic Design (DX-5), Advanced Nuclear Technology (NIS-6), Security (S) Division, Environment Safety and Health (ESH) Division, and the Department of Energy ’s Los Alamos Area Office and Albuquerque Operations Office.

Before the creation of the 3.25-inch-diameter sphere, about the size of a baseball, the Laboratory ’s criticality safety and nonproliferation work dealt with neptunium in a variety of other shapes.

“No direct measurements for neptunium critical mass have been done,” said Rene Sanchez of NIS-6.“ The Laboratory possessed some quantities of neptunium, but not the right amounts or shapes.

With this new sphere we now have the capability to go beyond the current data that are only estimates.”

Creating the sphere from scratch is no exaggeration. “We had to ramp-up the entire process from basically nothing,” said Bodenstein..“The whole thing had to be done in an ‘alpha box ’ placed inside a ‘hot cell.’ Special tools had to be designed, built and tested by the technicians so they could be used with remote manipulators, one-of-a-kind melting and molding equipment had to be created and then all of it had to go through a DOE readiness assessment.”

The alpha box and hot cell are equipment at the CMR building. An alpha box is a large, highly specialized containment vessel built for a specific job intended to prevent the spread of radioactive particulate inside the hot cell. The work was accomplished inside one of CMR ’s 16 hot cells, small rooms that are heavily shielded with three-foot-thick walls for radiation protection and outfitted with lead glass, oil-filled windows and remote handling arms.

“There were many challenges along the way,” said Bob Romero,,team leader at the hot cell facility. “We were in the midst of removing a lot of materials at CMR, we were influ- enced by an upgrade schedule that called for technical improvements to the hot cells and we were faced with changing security and safety requirements. We were interrupted several times because of funding, stand-downs, management changes, a division reorga- nization and of course, the Cerro Grande fire in May 2000.”

And the team realistically had only one shot at getting it right. “All of the equipment, tooling, work instructions, hazard control plans, training, security plans, everything was prepared to give the team the highest reasonable probability to perform the task correctly and safely on the first attempt. Resource restrictions would have made a second attempt doubtful,” said Bodenstein.

Getting everything in place for the DOE Readiness Assessment (RA) was a major success, according to team members, but the real accomplishment was how the assessment and final fabri- cation processes were completed. “Often an RA and comment resolution process leading to the DOE approval of a project ’s ‘readiness to proceed ’ takes about six months..Then the project itself typically takes many weeks to complete,” said Bodenstein.“With close coordination between our team and the DOE RA team we were able to complete the RA in just nine days.Then, with total involvement from the whole team, we were able to deliver a finished product only four days later. Thirteen days, start to finish, this was unprecedented.

As the team looks back on this major success they agree that communication is what made this project work.“Security was a major driver that required detailed planning and coordination,” said Romero..“People worked weekends and evenings to prepare, sometimes into the wee hours of the night.It was a very intense effort.When problems occurred,we ’d step back and evaluate what to do — we really used the five--step Integrated Safety Management process effectively to solve problems fast with worker safety at the forefront.”

“There was total involvement across all organizations.Technicians were involved in development of the hazard control plan and procedures.MST personnel developed and supervised the melting and casting of the materials,and folks from DX-5 worked through the night machining the protective tungsten outer shell of the final casting,” said Dave Yeamans,who led the project in its final stages.Sanchez added,“This was one of those projects that makes you very proud to be a Laboratory employee.”

One technological advance was the fabrication of the one-of-a-kind,yttrium-oxide-coated graphite mold.The specialized design integrated several thermocouples,a highly sensi- tive type of thermometer,to help control the cooling process of the molten neptunium. “From a metallurgist ’s point of view,a sphere is the hardest shape to cast,” said Sanchez.. “From a physicist ’s point of view,it ’s the best shape for experimentation.”

“We ’ve already learned many things from this project about how neptunium reacts to melting and cooling,how hard the finished product becomes — it turns out to be harder than steel,something we did not expect — and how difficult it is to machine,,” said Yeamans..

“There is still so much more to learn and there is a lot of interest in neptunium,” said Romero.“An internal Los Alamos Neptunium Working Group sponsored by the Glenn T.

Seaborg Institute for Transactinum Science has already begun to think about new studies with neptunium.”

The principal funding sources for the neptunium sphere project were DOE Defense Programs,Office of Emergency Response and DOE Nuclear Nonproliferation, Nonproliferation Research and Engineering.

Starting from scratch, a team of Laboratory scientists and technicians have fashioned an 8- kilogram, tungsten- and nickel-clad sphere of neptunium. The sphere, about the size of a baseball, will be used in criticality safety and nuclear nonproliferation experiments.

Technicians at the CMR facility improvised some of tools for handling the highly radioactive neptunium sphere during its fabrication and machining. Shown here is a grasping tool fashioned from a standard kitchen gadget normally used in canning. It was modified to securely hold the sphere so that it could not be accidently dropped when being moved.

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