Andrew T. Nelson

Small-Scale Testing of In-Core Fast Reactor Materials

Part of the Fuel Cycle R&D (FCRD) initiative in the USA is to investigate materials for high dose application. While mechanical testing on large samples delivers direct engineering data, these types of tests are only possible if enough sample material and required hot cell capabilities are available. Smallscale materials testing methods in addition to large-scale materials testing allows insight on the same specimen and direct probing into areas of interest which are not accessible otherwise. In order to establish an empirical and research-based relationship between small-scale and large-scale materials testing, several different mechanical testing techniques were conducted on the same specimen irradiated in the Swiss spallation source irradiation program (STIP) at the Swiss spallation source (SINQ) at the Paul Scherrer Institute (PSI) up to a dose of 19 dpa. It is shown that the yield strength measured by tensile testing, microcompression testing and microhardness testing all show the same trend. In addition, focused ion beam (FIB)-based techniques also are used to produce local electrode atom probe (LEAP) samples. This procedure allows cutting samples of such a small size that no radioactivity on the prepared sample can be measured.

Neutron Imaging at LANSCE—From Cold to Ultrafast

In recent years, neutron radiography and tomography have been applied at different beam lines at Los Alamos Neutron Science Center (LANSCE), covering a very wide neutron energy range. The field of energy-resolved neutron imaging with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as quantitative density measurements, was pioneered at the Target 1 (Lujan center), Flight Path 5 beam line and continues to be refined. Applications include: imaging of metallic and ceramic nuclear fuels, fission gas measurements, tomography of fossils and studies of dopants in scintillators. The technique provides the ability to characterize materials opaque to thermal neutrons and to utilize neutron resonance analysis codes to quantify isotopes to within 0.1 atom %. The latter also allows measuring fuel enrichment levels or the pressure of fission gas remotely. More recently, the cold neutron spectrum at the ASTERIX beam line, also located at Target 1, was used to demonstrate phase contrast imaging with pulsed neutrons. This extends the capabilities for imaging of thin and transparent materials at LANSCE. In contrast, high-energy neutron imaging at LANSCE, using unmoderated fast spallation neutrons from Target 4 [Weapons Neutron Research (WNR) facility] has been developed for applications in imaging of dense, thick objects. Using fast (ns), time-of-flight imaging, enables testing and developing imaging at specific, selected MeV neutron energies. The 4FP-60R beam line has been reconfigured with increased shielding and new, larger collimation dedicated to fast neutron imaging. The exploration of ways in which pulsed neutron beams and the time-of-flight method can provide additional benefits is continuing. We will describe the facilities and instruments, present application examples and recent results of all these efforts at LANSCE.