Weapons Plutonium Disposition: MOX
Gets Go Ahead; Immobilization Dead in Water
Long a disputed issue, the disposal of excess weapons
plutonium seems to be headed for technical resolution in U.S. national policy.
In a report posted on the Internet, the National Academy of Sciences Committee
on International Security and Arms Control (CISAC) has concluded that
irradiating the plutonium in MOX (mixed oxides of uranium and plutonium) in a
once-through nuclear reactor fuel cycle would meet its "spent-fuel" standard
for resistance to theft and proliferation.
A close look at the report also indicates that previously
considered methods of immobilization by underground burial are
not now approved or available for weapons plutonium.
Because of the longstanding debate about plutonium
disposition, it's a little odd that these significant NAS results have not
gotten more public attention. I've been following this issue for years, partly
in connection with a book being prepared with some colleagues about Cold-War
nuclear arsenals and legacies, yet it was only this year (2001) that I noticed
the July 1999 "Interim Report." No final report is available, although it was
scheduled for the Fall of 1999.
It seems strange that all three of their significant
conclusions-regarding MOX burning, immobilization, and demilitarization-are
only published in an unheralded interim report. It is hard not to wonder
whether the apparently imminent final report was not issued because it was
considered ideologically unacceptable in certain quarters.
CISAC adopted for their 1999 review a systematic methodology
to compare options for plutonium disposal. Perhaps because it is only
"interim," the 1999 report is difficult to read and understand, with many of
its important findings rather obscure or relegated to footnotes. It is not a
simple matter to sort through the jargon, but a careful reading indicates that
today's state of the art does not permit the spent-fuel standard to be met
through immobilization (either by vitrification or can-in-canister).
Those of us who have long been calling attention to the
advantages of isotopic "denaturing" of weapons plutonium can find some
satisfaction in a footnote (no. 13) in the CISAC report. For the first time in
print, the official body explicitly acknowledges that any attempt to insert
isotopically demilitarized plutonium in existing weapon configurations would
be "likely" to run into an abundance of difficulties, such as "design
modifications and . . . new nuclear-explosive tests . . .
to confirm that the change in isotopic composition had not unacceptably
The chairperson of CISAC, John Holdren, explained his own
views about reactor-grade plutonium in an article he wrote for The Bulletin
of the Atomic Scientists in 1997:
. . .because the isotopics are different, weapons using this
plutonium would have to be redesigned, which would require nuclear tests. That
means the path to reuse of spent fuel would be more difficult technically and
politically-as well as easier to detect-than reusing weapons plutonium
extracted from glass.
Thus the Committee has definitively embraced the proposition
that demilitarized plutonium is really not useful for making military-quality
weapons. This has important implications in evaluating treaty-breakout
scenarios for nuclear-weapons states after deep cuts in arsenals have taken
place. The report now effectively supports the contention that isotopic
demilitarization would make plutonium inherently unsuitable for rapid recovery
into weapons. Demilitarized plutonium is more securely protected against
reversal into high-quality weapons than is buried "immobilized" plutonium that
has not been put through a reactor fuel cycle.
After deciphering the oblique vocabulary of the report, it
looks as though the Academy is saying not only that MOX irradiation (which
results in chemical, metallurgical, and isotopic demilitarization of
plutonium) meets the disposition standard, but that irradiation in reactors is
the only practical way currently available to dispose of weapons
Am I the only one who has noticed this progress?
Retired from Argonne National Laboratory
21302 W. Monterrey Dr., Plainfield, IL 60544