Experience with Palladium Diffusers in Tritium Processing Page: 6 of 16
13 p.View a full description of this article.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
service around 1983 (Fig. 2). These
commercially available units use a 75%
palladium 25% silver alloy for the diffusion
coil (a coiled tube), which has both a higher
hydrogen permeability and higher strength.
They can be connected in multiple stages as
required. The RSI diffusers have replaceable
heaters and thermocouples. The coils have
lasted for varying times between 4 months
and 5.5 years. Most of these failures are
believed to be caused by mercury present in
this system (see below). Four RSI diffusers
installed in a new tritium facility are expected
to have a considerably longer service life
because mercury is not present in the new
system. Additionally, there were frequent
failures of the stainless steel to palladium-
silver transition joint in earlier RSI units.
Savannah River Site personnel worked with
RSI to improve the braze design to prevent
this type of failure.
The RSI diffuser consists of five coiled
palladium-silver permeation tubes, mounted
in parallel in a single chamber to reduce the
pressure drop associated with high tube-side
gas flows. The diffuser is heated by five
replaceable cartridge heaters mounted in wells
which are coaxial with the five permeation
coils. Each heater is monitored by a
thermocouple to detect failure of the heater. A
failed heater cartridge can be replaced without
shutting down the entire system. Also,
operation can continue on the four remaining
heaters until the fifth one is replaced. A sixth
temperature control thermocouple is inserted
in a well near the center of the cluster of
permeation coils.
The RSI diffusers have many advantages
compared to the old Multistage Palladium
Diffuser units. They are not susceptible to
cooling water corrosion and O-ring gasket
leaks. The RSI design allows each stage to be
repaired independently; the older diffuser had
to be taken apart to be repaired. Because the
RSI diffuser is commercially available,
replacement parts are less expensive.
Johnson Matthey Incorporated
Two diffusers manufactured by Johnson
Matthey, Inc. (JMI) were installed in the
Tritium Facility diffuser system and tested as
possible replacements for RSI diffusers.
Having an alternate diffuser supplier was
desirable because of cost, quality (braze jointfailures), and delivery time concerns related to
RSI diffusers.
The JMI diffuser incorporated several
design improvements over the RSI diffuser
(Fig. 3). The feed inlet tubing was coiled
around the diffuser shell, under the insulation,
to preheat the feed gas prior to entering the
palladium coil. The JMI diffuser used only a
single heater cartridge to heat the coils.
Burnout of a heater cartridge was rare, and the
single heater allows for better control of the
palladium-silver coil temperature.
Tests at SRS revealed that the JMI diffuser
was not equivalent to the RSI diffuser in
separation performance. When operated at
the same feed rate, the product rate of the JMI
diffusers was about half that of RSI diffusers.
Much of the product remained in the
byproduct stream. When operated at the
minimum byproduct rate, the JMI diffusers
had about one-fourth the product rate of RSI
diffusers and still did not produce acceptable
byproduct. The JMI diffusers were designed
for permeation from the shell to the coil rather
than from the coil to the shell as in the RSI
diffuser designs. The JMI design allows
hydrogen isotopes in the feed to bypass the
palladium coil and show up in the byproduct.
The two JMI diffusers were used in
Tritium Facility for four years. During that
time, no failures of the units occurred.
Adolph Coors Company
The Adolph Coors Company was
contracted to manufacture a palladium
diffuser similar to the RSI unit. This was
done to develop another alternate commercial
diffuser supplier. The Coors design
incorporated the preheater and single heater
design of the JMI diffuser but retained the coil-
to-shell product gas pathway of the RSI design
(Fig. 4). In the Coors unit the close tolerance
between the heater cartridge and its well
(required to maximize the heat transfer
efficiency) has caused warping of the well or
heater cartridge. The heater is then wedged in
the cartridge, rendering the unit useless.
Adjusting the tolerance would allow the
replacement of heater cartridges, while still
providing for adequate heater performance.
These diffusers were installed in 1993, and
performance testing is underway.2
-.z-:.. .?:sr _r -i :er ;.-r. .. .. >.x-. s: <_ ___c,"r h ,..' ; si. ;.i: _ :~ .. >:.
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Motyka, T.; Clark, E. A.; Dauchess, D. A.; Heung, L. K. & Rabum, R. L. Experience with Palladium Diffusers in Tritium Processing, article, January 27, 1995; Aiken, South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc1312072/m1/6/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.