PNNL-13501 - Pacific Northwest National Laboratory

Development of High-Temperature Sensing Technology for On-Line Ceramic Melter
Processing Control
Morris S. Good, Michael J. Schweiger, Pavel R. Hrma, Hong Li, Aaron A. Diaz, Chester L. Shepard,
Margaret S. Greenwood
Study Control Number: PN00032/1439
Vitrification of high-level radioactive waste is a major aspect of dealing with the large volumes of legacy waste from
nuclear weapons production. The vitrification process is highly temperature-dependent. This project has developed a
method to detect the sludge level and formation of crystals that develop when the temperatures drop below the melting
point. The ability to more accurately sense temperature and crystal formation will lead to greater control and more
efficient vitrification densities.
Project Description
We are developing a new method to quantify the sludge
level in a waste melter for process control. High-level
radioactive waste melters handle material rich in various
metal oxide constituents that precipitate in the form of
spinel crystals and settle onto the floor during
vitrification. This can cause melter failure. Spinel
settling is a primary factor in determining waste loading.
Benefits of monitoring spinel settling for process control
of melter operation include the following:
• preventing electrical shorting of electrodes
• increasing melter life
• increasing or maintaining the production rate.
The current need to avoid accumulation of noble metals in
significant amounts results in considerable conservatism
in melter operating life projections and waste loading
specifications. A method to mitigate that risk would
allow an increase in waste loading by several percent and
therefore, could save DOE-EM billions of dollars over the
lifetime of the River Protection Project’s Waste
Treatment Plant at the Hanford Site. One approach is in
situ measurement of spinel layer growth; however,
measurement techniques must be compatible with high
operating temperatures and melter operation. A potential
solution is advance ultrasonic sensing technology that was
evaluated using room temperature surrogates of molten
glass and sludge. We concluded that spinel-layer can be
detected and quantified, and we recommended that future
work should entail high-temperature tests.
Introduction
Noble metal precipitation and settling in a melter has been
observed numerous times and has led to melter failure.
390 FY 2000 Laboratory Directed Research and Development Annual Report
Cooper et al. reported in 1994 an occurance during
research scale melter tests at Pacific Northwest National
Laboratory. Whittington et al. in 1996 reported an
accumulation on the melter floor. Mini-melter tests
conducted at Savannah River Technology Center revealed
noble metal particles dispersed in the glass during minimelter
tests (a) . The accumulation of noble metals at the
melter floor has caused electrical shorting as was the case
at the PAMELA vitrification plant in Mol, Belgium (b) .
Krause and Luckscheiter reported in 1991 a melter failure
attributed to noble metal accumulation and subsequent
shorting of the electrode. Electrical shorting occurred
since noble metal crystals are electrical conductors.
High-level wastes at Hanford have been shown to be rich
in iron (Fe2O3) with lower quantities of nickel (NiO),
chromium (Cr2O3), magnesium (MnO), and ruthenium
(RuO2) and these constituents in waste borosilicate
glasses can induce crystallization of spinel phases, a solid
solution of (Nix, Mny, Fe1-x-y)(Fez, Cr1-z)2O4 (Hrma et al.
1994, Vienna et al. 1996).
Acoustic measurements for process control have been
made for more than 50 years (Lynnworth 1989) and has
been configured to withstand hostile environments. It has
also been introduced as a tool for making real-time
process analytical measurements (Workman et al. 1999)
such as to characterize the degree of mixing (Bond et al.
1998). Ultrasonic technology has been utilized in a wide
variety of diagnostic applications. However, no
(a) Nakaoka RK and DM Strachan. 1990. Melter performance
evaluation report. Milestone report HWVP-90-1.2.2.04.08B.
Pacific Northwest Laboratory, Richland, Washington.
(b) Collantes CE, LK Holton, JM Perez Jr., and BA Wolfe.
1987. Research facilities in the Federal Republic of Germany &
the PAMELA facility workshop: “vitrification operational
experience.” Foreign trip report. Pacific Northwest Laboratory,
Richland, Washington.