Existing and planned DOE neutron sources, such as the Intense Pulse Neutron Source (IPNS) and the Spallation Neutron Source (SNS), generate pulses of cold neutrons for materials research. The usefulness of such facilities depends on the efficiency of the components that convert the fast neutrons to a cold neutron beam. Although the existing solid methane moderator at IPNS has high efficiency, the design cannot be scaled to the high power levels planned for the SNS. An alternative cold moderator concept, which uses solid methane pellets and was proposed in 1988, would be capable of high power operation; however, the technology for producing and transporting the solid pellets have not yet been developed. This project will apply practical pellet fabrication and transport technologies, previously developed for the DOE fusion program, to the production of methane pellets. Phase I demonstrated the production of high quality frozen methane and ammonia pellets. Tests showed that the pellets could be transported into a small scale moderator cell, and refrigerated to temperatures below 20K. The ammonia pellets were shown to fill the cell with a packing density of 60 percent. Phase II will de-velop a methane and ammonia pellet fabrication and transport system with the capability of periodically filling a full size cold moderator cell with pellets. The pellets will be refrigerated to below 20K. A method of rapidly replacing the pellets in the moderator cell, which was tested in the Phase I project, will also be demonstrated with the full scale system.
Commercial Applications and Other Benefits as described by the awardee: The cold moderator should enhance the operation of high power spallation neutron sources, which are used for materials and biological science research, by doubling the output of cold neutrons. The technologies developed will also be useful for the production of other cryogenic pellets, such as dry ice, used commercially.
