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
about the size of a
baseball, the Laboratory ’s
criticality safety and
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
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
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
Technicians at the
improvised some of
tools for handling
here is a grasping
tool fashioned from
a standard kitchen
used in canning. It
was modified to
securely hold the
sphere so that it
could not be
when being moved.
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