DEMONSTRATION OF EMITTED-NEUTRON COMPUTED TOMOGRAPHY TO COUNT FUEL PINS

Year
2012
Author(s)
P. A. Hausladen - Oak Ridge National Laboratory
P. Marleau - Sandia National Laboratories
E. Brubaker - Sandia National Laboratories
D. L. Chichester - Idaho National Laboratory
M. A. Blackston - Oak Ridge National Laboratory
Abstract
In this paper, we report demonstration of emitted-neutron computed tomography using fast fission neutrons to infer the geometry of sources of special nuclear material (SNM) such as fuel pins. In a proof-of-concept measurement at the Idaho National Laboratory’s (INL’s) Zero Power Physics Reactor (ZPPR) facility, an array of unirradiated plutonium mixed-oxide (MOX) fuel rodlets in a can was imaged, and a bias defect consisting of a single rodlet containing plutonium replaced by one containing depleted uranium (DU) was detected. The imaging system employed in the demonstration is based on a newly constructed array of pixelated neutron detectors that are suitable for arrangement in a close-packed imaging array and whose active volume consists of liquid scintillator EJ-309, which allows neutron-gamma discrimination via pulse shape to enable pure fast-neutron imaging. The imaging array was used along with a radial collimator aperture in order to perform high-quality fast-neutron imaging where tomographic reconstruction of slices through an object resolves neutron sources similar in dimension to a fuel pellet, or about 1 cm. Measurements were performed at Oak Ridge National Laboratory (ORNL) with neutron sources in addition to those performed at the INL’s ZPPR facility with plutonium MOX fuel rodlets. An analogous capability to detect single-pin defects in spent fuel assemblies would be desirable, such as for safeguards verification measurements of spent fuel assemblies just prior to transferring them from the spent-fuel cooling pool to long-term dry cask storage. This paper describes the design and construction of the present imager, characterization measurements with neutron sources at ORNL, measurements with SNM at INL’s ZPPR facility, and feasibility of building an analogous imager for spent fuel measurements.