by Theresa Pepin
Failures of nuclear facilities at Fukushima Daiichi and storage at Yucca Mountain highlight the importance of containment materials as a first line of defense for preventing the release of nuclear fission products.
Neutron imaging is an ideal diagnostic tool for evaluating the structural integrity of containment materials, with implications for safety, shipping and long term storage.
Eric Lukosi takes the first step in the long road towards achieving a next generation neutron-imaging sensor that will be able to characterize and confirm whether the materials we choose to use in critical applications remain effective and safe.
How ironic that we use the word for the material “iron” in the well known phrase “ironclad agreement.” Not nearly good enough. It should be “zirconium-clad.”
But although a far superior material for containment, even zirconium is not perfect. What particularly concerns us about the structural integrity of the zirconium cladding used in nuclear applications is the degree to which it can become less “homogeneous” and embrittled in the conditions it is subjected to. Obvious or catastrophic failure of the material is too late. Instead, we want to “see” when that process of embrittlement begins as clearly and as early as possible.
Next-generation neutron-imaging sensors require detectors with much higher spatial resolution (to the sub-ten micron) than is readily available today in combination with excellent timing resolution (one microsecond), high neutron sensitivity, and the ability to count neutrons almost instantaneously.
And, of course, do we need to mention that limiting the complexity of sensor fabrication is important so that all of this can come at an affordable cost?
In order to achieve this ambitious goal, Lukosi and his team, including graduate student Thomas Wulz, are making use of advanced laboratory facilities and instrumentation at UT that include a hot wall Chemical Vapor Deposition system and a new Microelectronic and Thin Film Fabrication facility. They will be used to produce solid-state neutron imaging detectors that can perform at this level.
Recent funding from the National Science Foundation will support experimental investigations and modeling of a full-scale neutron imager and its full capabilities. So, as in many cutting-edge endeavors, both theory and experiment must work hand in hand to achieve success.
Lukosi’s investigations are focused on a corresponding LDRD project headed by Yong Yan at ORNL involving a broader inquiry into studies of zirconium alloy cladding under various physical conditions using both destructive and nondestructive analysis.
For Lukosi, this joint work affords the chance to build a long-term relationship at ORNL and the Spallation Neutron Source (SNS)* while undertaking neutron diagnostics at an advanced level. Because substantial funding will be required for the successful outcome of this challenging research, the project is only the beginning of many grant opportunities Lukosi is already on the path to pursue.
The ultimate result is expected to be a vastly improved neutron imager than what is currently available at SNS—not to mention a much safer world once fabrication of the detector is proven and leads to widespread use in critical applications.
High spatial resolution neutron imaging sensors
Eric Lukosi, UT Nuclear Engineering Department
Non-destructive evaluation of hydrided Zr cladding by in-situ neutron scattering and tomography of hydrogen
Yong Yan, ORNL Fusion & Materials for Nuclear Systems Division