Hardware implementation of the ORNL fissile mass flow monitor Page: 1 of 8
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HARDWARE IMPLEMENTATION OF THE ORNL FISSILE MASS FLOW MONITOR
Jim McEvers, James Sumner, Richard Jones, Regina Ferrell, Carl Martin, Taner Uckan, Jos6 MareLeIeuba
Oak Ridge National Laboratory,' P. O. Box 2008, Oak Ridge, TN 37831-6010 H E CE1 VED
This paper provides an overall description of the implementation of the Oak Ridge National Laboratory
(ORNL) Fissile Mass Flow Monitor, which is part of a Blend Down Monitoring System (BDMS) developed
by the U. S. Department of Energy (DOE). The Fissile Mass Flow Monitor is designed to measure the mass
flow of fissile material through a gaseous or liquid process stream. It consists of a source-modulator
assembly, a detector assembly, and a cabinet that houses all control, data acquisition, and supporting
electronics equipment. The development of this flow monitor was first funded by DOE/NE in September
95, and an initial demonstration by ORNL was described in previous INMM meetings. This methodology
was chosen by DOE/NE for implementation in November 1996, and the hardware/software development is
complete. Successful BDMS installation and operation of the a complete BDMS has been demonstrated in
the Paducah Gaseous Diffusion Plant (PGDP), which is operated by Lockheed Martin Utility Services, Inc.
for the US Enrichment Corporation and regulated by the Nuclear Regulatory Commission (NRC).
Equipment for two BDMS units has been shipped to the Russian Federation (R.F.)
Recent HEU Transparency agreements between the United States (US) and the R. F. provide for the
monitoring of the blending of highly enriched uranium (HEU) at an assay of -90% with low enrichment
blend stock uranium (LEU) at an assay of-1.5% to produce reactor-grade material at an assay of-4% to be
used in U.S. nuclear power plants. The BDMS has been developed to provide unattended monitoring of the
HEU blending operations at the R.F. facilities. It is configured to monitor the mass flow rate and 235U
isotopic enrichment of gaseous UF6 in these three separate flow streams. The ORNL Flow Monitor
component of the BDMS has been developed by the Oak Ridge National Laboratory. It measures the mass
flow rate of gaseous UF6 flowing through a process pipe, without requiring direct contact with the gas in the
pipe. The ORNL Flow Monitor also traces fission products generated in the HEU stream through the
blending operation and into the product LEU stream, thus confirming HEU blending. The instruments that
measure flow and enrichment are placed around existing process piping and do not require direct contact
with the UF6 gas or piping penetrations for operation of the BDMS.
OPERATING PRINCIPLES OF ORNL FISSILE MASS FLOW MONITOR
The ORNL Flow Monitor has two functions: measure the mass flow rate of fissile material in a process pipe
and trace the flow of the fissile material from the HEU leg to the product LEU leg. To achieve these
functions, the Flow Monitor induces fissions in the fissile stream and detects the delayed gamma rays
emitted by fission fragments at a downstream detector location (See Figure 1). The induced fissions are
modulated using a neutron-absorber shutter to create a time signature that is detected by the downstream
detectors. The Flow Monitor determines the fissile mass flow rate by relying on two independent
measurements: (1) the time required for the fission fragments to travel along a given length of pipe, which is
inversely proportional to the fissile material flow velocity, and (2) an amplitude measurement, which is
proportional to the fissile concentration (e.g., grams of 235U per length of pipe). Fissile traceability is
Managed by Lockheed Martin Energy Research Corp. For the U.S. Department of Energy under contract DE-AC05-960R22464
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McEvers, J.; Sumner, J.; Jones, R.; Ferrell, R.; Martin, C.; Uckan, T. et al. Hardware implementation of the ORNL fissile mass flow monitor, article, November 1, 1998; Tennessee. (digital.library.unt.edu/ark:/67531/metadc687044/m1/1/: accessed September 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.