Information Notice No. 96-51: Residual Contamination Remaining in Krypton-85 Handling System After Venting
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, DC 20555
September 11, 1996
NRC INFORMATION NOTICE 96-51: RESIDUAL CONTAMINATION REMAINING IN
KRYPTON-85 HANDLING SYSTEM AFTER VENTING
All material licensees.
The U.S. Nuclear Regulatory Commission is issuing this information notice to
make licensees aware of a possible contamination problem in krypton-85 (Kr-85)
handling systems. It is expected that recipients will review the information
for applicability to their facilities, to ensure that this information is
considered when decommissioning one of these systems. However, suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action nor written response is required.
Description of Circumstances
Recently, NRC was informed of several cases where a licensee found residual
contamination remaining in some components of Kr-85 handling systems after the
standard decommissioning process. Although these incidents only involved Kr-
85, the inherent concerns extend to all gas handling systems that subject a
radioactive gas to vacuum/pressure cycling.
The current process for cleaning these systems during decommissioning is to
flush and vent them until the readings from the exhausted air are below
release limits. The readings on the outside of the components of the system
are also checked to make sure that they are below acceptable limits.
During cleaning and decommissioning of some of these systems, it has been
reported that a varnish-like residue has been found on the inside of some of
the system components (i.e., storage tank and the compressors). The residue
is probably the result of the oils and dust in the system plating on the
inside of the components through the repeated vacuum and pressure cycles.
This residue is not removed by the flushing process currently used to clean
the systems. It has been reported that several of the commonly used solvents
have been tried, but that the residue was not easily removed. The residue can
be removed by exposing the internal surfaces of the components and scraping
the residue. Residues containing up to 29.6 gigabecquerels (800 millicuries)
have been reported. Due to the low levels of gamma radiation emitted by Kr-85
and the robust construction of the air storage tank and other components, the
presence of the residue is not detectable by measurements of the outside of
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September 11, 1996
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There is a concern that systems released as �cleaned� under the current
decommissioning procedures may still contain the residue and be released into
the scrap stream for later reuse. In particular, there is a concern that the
components could be later cut up, exposing the Kr-85 residue or that the
storage tank may be reused as a tank or pressurization chamber.
Licensees decommissioning or receiving these systems, or components from these
systems, should be aware of the potential for residual contamination, and take
This information notice requires no specific action nor written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate regional office.
Donald A. Cool, Director
Division of Industrial and
Medical Nuclear Safety
Office of Nuclear Material Safety
Technical contact: Michele Burgess, NMSS
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