High fluence neutron source for nondestructive characterization of nuclear waste. 1998 annual progress report

Technical Report · Mon Jun 01 00:00:00 EDT 1998

DOI:https://doi.org/10.2172/13431· OSTI ID:13431

Pickrell, M M

'The author is addressing the need to measure nuclear wastes, residues, and spent fuel in order to process these for final disposition. For example, TRU wastes destined for the WIPP must satisfy extensive characterization criteria outlined in the Waste Acceptance Criteria. Similar requirements exist for spent fuel and residues. At present, no nondestructive assay instrumentation is capable of satisfying all of the requirements. One of the primary methods for waste assay is by active neutron interrogation. The authors plan to improve the capability of all active neutron systems by providing a higher intensity neutron source (by about a factor of 1,000) for essentially the same cost, power, and space requirements as existing systems. This high intensity neutron source will be an electrostatically confined (IEC) plasma device. The IEC is a symmetric sphere that was originally developed in the 1950s as a possible fusion reactor. It operates as D-T neutron generator. Although it was not believed to scale to fusion reactor levels, these experiments demonstrated a neutron yield of 2 x 1010 neutrons/second on table-top experiments that could be powered from ordinary laboratory circuits (1 kilowatt). The basis for scaling the output up to 1x1011 n/s has been established. In addition, IEC devices have run for cumulative times approaching 10,000 hours. The essential features of the IEC plasma neutron source, compared to existing sources of the same cost, size and power consumption, are: neutron yield of 1011 compared to 108, lifetime of 10,000 hours compared to 500, and operation is pulsed or steady state compared to pulsed. The design of a conventional IEC source is a spherical vacuum chamber containing a spherical grid. The grid is raised to a high negative potential. A breakdown develops between the chamber wall and the grid, and this plasma becomes a source of positive deuterium and tritium ions. These ions are accelerated to the center of the vacuum chamber sphere where they may collide. If the grid is raised to a nominal 100 kV, the coulomb barrier for D-T fusion, then the fusion cross section becomes quite large and the neutron production proceeds. The limiting factor has been high densities associated with the Paschen breakdown curve. Because of the high densities, the ions tend to collide multiple times before reaching the center and do not collide with the full accelerating potential. The Los Alamos IEC uses a triple grid design. In the triple grid IEC device, the inner grid is the accelerating grid and serves the same function as the single grid in conventional IEC systems. The central grid serves as electrical isolation, and is held at ground potential. The outer grid is raised to a modest positive potential, say 200 volts. Dispenser cathodes around the vacuum chamber wall inject electrons. The electrons are trapped and orbit around the outer grid, ionizing a local plasma. Because of the modest potential, the breakdown occurs at a different point on the Paschen curve, at a much lower density. The limit is further relaxed by the injected ionization from the dispenser cathodes. The result is a lower density plasma. The result is a tight focus of fully accelerated ions that collide in a beam-beam mode. The collision energy and neutron yield are large.'

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
• OSTI ID: 13431
• Report Number(s): EMSP-54751-98; ON: DE00013431
• Country of Publication: United States
• Language: English

Related Subjects

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Progress Report
Measuring Instruments
Measuring Methods
Radioactive Wastes
Chemical Wastes
High-Level Radioactive Wastes
Radioactive Materials
Remedial Action
Spent Fuels
PROGRESS REPORT
MEASURING INSTRUMENTS
MEASURING METHODS
RADIOACTIVE WASTES
CHEMICAL WASTES
HIGH-LEVEL RADIOACTIVE WASTES
RADIOACTIVE MATERIALS
REMEDIAL ACTION
SPENT FUELS