Development Testing A number of component development programs will be conducted prior to the nuclear subsystem qualification test. A critical prenuclear subsystem test is the fuel fabrication task. Fuel beads will be manufactured, qualified, and characterized by a commercial bead supplier. Fuel element extrusions, both with and without fuel beads, will be performed to assure that the extrusion process will not damage the fuel beads. Fuel elements will be manufactured and coating of the fuel element surfaces with ZrC will be demonstrated. In-reactor fuel tests will also be conducted. Several material-related tasks, as well as nuclear subsystem component tests will be performed prior to the nuclear subsystem qualification test. They include hydraulic tests to confirm the flow distribution and testing of the reactor control components. Qualification Testing Upon completion of the development tests, it will be necessary to perform qualification tests. This ground test program will be designed to ensure that the system meets design specifications including all design margins and to give a high level of confidence in achieving a successful space mission. The system level tests will be conducted on a test article which is prototypic of the flight system to the extent possible, except as modified to accommodate minor changes that may be necessary to conduct the tests. The test article will be manufactured from the same drawings, using the same materials, tooling, and methods as those for the flight hardware. Ground testing of the open cycle system presents some challenge. During the 1960s when the NERVA engines were tested, environmental requirements were less stringent. The engines were tested without containment, and the exhaust was discharged without a cleanup system. In the early 1970s, Los Alamos National Laboratory (LANL) tested a cryogenic scrubber system with atmospheric burning of hydrogen that was satisfactory for exhaust cleanup, but the system received only limited testing. Idaho National Engineering Laboratory (INEL) then built upon that
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