Part IV Reactor Development AIRCRAFT REACTORS @Seeee Nuclear Propulsion for Manned Aircraft Direct cycle approach. The immediate objective of the direct cycle approach is to develop and ground test by the fall of 1960 a nuclear propulsion system consisting of a preprototype reactor with associated turbomachinery. The series of reactor experiments continued at the National Reactor Testing Station to ‘investigate materials, components, and nuclear aircraft engine operation. Two significant experiments were performed with the Heat Transfer Reactor Experiment No. 2 (HTRE-2) during the quarter. Ore was the test of an insert, consisting of unclad hydrided zirconium moderator and nichrome fuel elements. The second was a meltdown test of a fuel element to obtain data on the hazards associated with nuclear aircraft operation. _ The insert, the third of a series tested in the parent core of the HTRE-2, was designed primarily to determine the operational and engineering characteristics of unclad moderators for use in the first nuclear aircraft power plant. On April 14 this insert completed 100 hours operation with the moderator at the design condition of 1,200 degrees Fahrenheit. The test run was highly successful and the insert materials showed no significant change. Since this moderator material is to be used in the Heat Transfer Reactor Experiment No. 3 (HTRE-3) and is planned for use in the first nuclear aircraft power plant (the XMA), the results are encouraging, In the mel:jown experiment the element melted was of nichrome material in a configuration similar to that used in previous heat transfer reactor experiments. The element was melted in three to five seconds by a rise in temperature caused by restricting the airflow over the element. No interaction with the reactor moderator or other fuel elements occurred. Hazards data ~ ere obtained by extensive monitoring of the effluent in the ducting, in the stack, and up to 15 m ‘les downwind, and by taking measurements to determine all applicable meteorological parameters. The diffusion conditions were good and the release cloud followed the certerline of the instrumented test area. In general the experiment was a success. No hazard was incurred, and considerable data were obtained which will be under analysis for the next few months. The HTRE-3, which is the first of the HTRE series to have a horizontal configuration and to have a solid moderator, became critical in a series of low power experiments. Nuclear power operaticn with the associated turbojet engines was planned for September 1958. DOEARCHIVES oe ~ 726