Potential for using coded aperture imaging for fuel motion detection measurement in the STF

At Sandia Laboratories, coded aperture imaging of both neutrons and γ-rays is being investigated for fuel motion detection in STF as part of the NRC Reactor Safety Research program. Based on work done for the development of a fuel motion detection system for the ACPR UPGRADE, coded aperture imaging of γ-rays will be capable of producing high-resolution images of at least up to seven fuel pins. However, because of the short mean free path of γ-rays in the test fuel, it is not clear that γ-ray imaging can provide useful information in the large-bundle tests to be made in STF. Investigation of these questions in detail has therefore commenced using γ-ray transport codes. Alternatively, fast neutrons have a somewhat longer mean free path than γ-rays, and it may be desirable to image with fast neutrons in the case of larger fuel bundles