Removal of Radioactive Krypton and
Xenon from Contaminated Nuclear
Process Off-Gas Streams
J. R. MERRIMAN, Section Head
M. J. STEPHENSON, Development Engineer
J. H. PASHLEY, Department Head
Process Systems Development Department
Gaseous Diffusion Development Division
Oak Ridge Gaseous Diffusion Plant
Union Carbide Corporation
Nuclear Division
Oak Ridge, Tennessee
INTRODUCTION
One group of waste products generated by the nuclear industry is comprised of
radioactive isotopes of the noble gases, krypton and xenon. These isotopes, generated
during the nuclear fission process, eventually contaminate nuclear process off gas
streams in a number of instances. For example, when nuclear fuel is reprocessed to
reclaim valuable uranium and plutonium, these gases are released as the fuel elements
are opened and dissolved. Also, in some types of nuclear reactor designs now under
study, krypton and xenon isotopes are steadily produced and released to the reactor
core vessel, where they mix with the core cover gas. Further examples include releases traceable to a variety of failure situations, ranging from minor releases from a
few leaky reactor fuel elements to those which would accompany the postulated
worst accident situation, complete core meltdown.
In many respects, control of radioactive krypton and xenon releases has not
been so important in the past as control over other, more toxic, fission products. In
fact, current noble gas releases are generally well below present limits. The nuclear
industry is growing, however, and fission product generation will increase accordingly. At the same time, the already stringent fission product release limits are being
looked at critically from the standpoint of setting them as much lower as is practicable in order to provide a further margin of public safety. These factors will combine to challenge existing pollution control measures and will result in development
of improved waste management schemes.
For many years, the U. S. Atomic Energy Commission has been vigorously
pursuing technology which would permit even safer utilization of nuclear energy. As
an example, the AEC's Environmental and Sanitary Engineering Branch, Division of
Reactor Development and Technology, initiated work in the latter part of 1966 at
the Oak Ridge Gaseous Diffusion Plant on the engineering scale demonstration and
evaluation of a krypton and xenon release control process. This project, which
centers around a selective absorption technique, is described in this paper following
a brief review of previous work in this general field.
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