Advanced technologies for decontamination and conversion of scrap metals Page: 4 of 24
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INTRODUCTION
Recycle of radioactive scrap
metals (RSM) from decomissioning of
DOE uranium enrichment and nuclear
weapons manufacturing facilities is
mandatory to recapture the value of
these metals and avoid the high cost of
disposal by burial. The scrap metals
conversion project detailed below
focuses on the contaminated nickel
associated with the gaseous diffusion
plants.
Nickel represents 80 percent of
the scrap value of all metals that will
come from the dismantlemnt of the
gaseous diffusion plants. The current
DOE nickel inventory is approximately
60,000 tons. 10,000 tons of this material
was melted as part of the Cascades
upgrade program in the 1970's. There
are an additional 50,000 tons in the
diffusion plants, much of which is porous
and has been in itimate contact with
uranium compounds and fission
products. Because of the intricacy of the
pourous nickel the contamination is not
readily removed. Technetium-99 is
known to be particularly troublesome in
that regard and is an element that makes
a significant contribution to the measured
radioactivity.
The melting performed in the
1970's converted 10,000 tons of
diffusion plant nickel into 1 ton
cylindrical ingots. No refining of the
technetium was accomplished and the
cast metal is bulk contaminated with 5 to
10 parts per milllion by weight (wppm)
Technetium. At these contamination
levels the nickel activity is 3,000 to 6,000
Bequerels per gram (Bq/gm).
Ultimately recovery of the
contaminated nickel will be possible only
if the developed reuse process iseconomically viable and there is a market
for the products. The available markets
include domestic restricted end use and
international unrestricted use.
Restricted End Use
It is likley that the nickel could
find utility in restricted end use products
in lieu of domestic unrestricted
commerce having no bulk contamination
release critera. In that regard the clean-
up levels of the bulk material will be less
restrictive. As an economic option it is
therefore the intent of this study to
develop methods to utilize the nickel
without decontamination.
Potential restricted end use
products may be stainless steel containers
for: Vitrification casks; uranium
hexafluoride storage; and drums and
boxes for waste handling. In addition
high nickel alloys represent a product for
restricted end use particularly as alloy
825 (a 42% nickel alloy), a candidate
material for the multipurpose cask.
Part of this phase one study
incorporated the vacuum induction
melting (VIM) of clean stainless steel
using commercially available alloys to
generate the alloy loss profile peculiar to
MSC's steel making process. The alloy
loss profile is characteristic to a furnace
lining, geometry and melt practice and is
necessary information when making
steels with precise compositional
tolerances.
Using the alloy loss profile data
and contaminated nickel as an alloy
addition, S30400 stainless steel and
inconel 825 were produced.
Ferrochromium, ferromanganese,
ferrosilicon, and iron. were added as in
conventional steels to produce the alloys.-208-
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Muth, T.R.; Moore, J.; Olson, D. & Mishra, B. Advanced technologies for decontamination and conversion of scrap metals, report, December 31, 1994; United States. (https://digital.library.unt.edu/ark:/67531/metadc685276/m1/4/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.