Nuclear Thermal Rocket Element Environmental Simulator (NTREES) Upgrade Activities

To support the on-going nuclear thermal propulsion effort, a state-of-the-art non nuclear experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The facility to perform this testing is referred to as the Nuclear Thermal Rocket Element Environment Simulator (NTREES). This device can simulate the environmental conditions (minus the radiation) to which nuclear rocket fuel components will be subjected during reactor operation. Test articles mounted in the simulator are inductively heated in such a manner so as to accurately reproduce the temperatures and heat fluxes which would normally occur as a result of nuclear fission and would be exposed to flowing hydrogen. Initial testing of a somewhat prototypical fuel element has been successfully performed in NTREES and the facility has now been shutdown to allow for an extensive reconfiguration of the facility which will result in a significant upgrade in its capabilities. 1 . The NTREES facility is designed to perform realistic non-nuclear testing of nuclear thermal rocket (NTR) fuel elements and fuel materials. Although the NTREES facility cannot mimic the neutron and gamma environment of an operating NTR, it can simulate the thermal hydraulic environment within an NTR fuel element to provide critical information on material performance and compatibility. The first phase of the upgrade activities has been now been completed. This upgrade in part consisted of an extensive modification to the hydrogen system to permit computer controlled operations outside the building through the use of pneumatically operated variable position valves. The new setup also allows the hydrogen flow rate to be increased to over 200 gm/sec. Other aspects of the upgrade included reworking NTREES to reduce the operational complexity of the system. To this end, many of the controls were consolidating on fewer panels. Additionally, the purge system was modified so as to permit simplified purging operations. As part of this upgrade activity, the Safety Assessment (SA) and the Standard Operating Procedures (SOPs) for NTREES were extensively rewritten. In the second stage of modifications to NTREES, which is currently underway, the capabilities of the facility will be increased significantly. In particular, the current 50 kW induction power supply will be replaced with a 1.2 MW unit which will allow more prototypical fuel element temperatures to be reached. To support this power upgrade, the water cooling system will also be upgraded to so as to be capable of removing 100% of the heat generated during testing and the nitrogen system will be upgraded to increase the nitrogen flow rate from its current 1.2 lb/sec to at least 4.5 lb/sec. The new setup will require that the NTREES vessel be raised onto a platform along with most of its associated gas and vent lines. The induction heater and water systems will be located underneath the platform. The new design will also allow for additional upgrades which could raise the power level of NTREES to 5 MW. Once fully operational, the 1.2 MW NTREES test chamber will be capable of testing fuel elements and fuel materials in flowing hydrogen at pressures up to 1000 psi at temperatures up to and beyond 3000 K and at near-prototypic reactor channel power densities. NTREES will also be capable of testing potential fuel elements with a variety of