The Aircraft Reactor Experiment was designed for operation at temperatures in the region of 1500ºF (1100 K) at a power of 1-3 MWt with a fluoride-salt fuel circulating in a heterogeneous core. The moderator was hot-pressed BeO blocks cooled by circulating sodium. The heat produced was dissipated in water through hot liquid-to-helium-to-water heat exchange systems. All sodium and fuel circuit components were made of Inconel fabricated by inert-gas (Heliarc) welding. The system was heated to design temperature by means of electrical heating units applied over all parts of the system. Instrumentation and control of the experiment were fairly conventional. For the most part, standard instruments were modified slightly for the hightemperature application. The reactor system was constructed and operated in a building specifically provided for the purpose.The Aircraft Reactor Experiment (ARE) to be described in this paper was originally conceived in a very different form from that in which it was ultimately constructed. In fact, the original high-temperature reactor design did not employ a fluoride-salt fuel, and, in order to understand some of the features incorporated in the ARE, a certain amount of historical background is necessary.By 1950, at various places in the country, work had progressed on the handling of hightemperature sodium metal to the point that it was being seriously considered as a coolant for nuclear reactors. Accordingly, a group of engineers and physicists at ORNL started design work on a solid-fuel-pin sodium-cooled reactor, with the fuel consisting of 235 U (as UO 2 ) canned in stainless steel. It was decided to make this a thermal reactor and to use BeO blocks as the moderator. The circulating sodium was to extract heat from the fuel pins and at the same time to remove heat from the moderator blocks. The design of this solid-fuel-pin, BeO-moderated, sodium-cooled reactor proceeded to the point of purchase of the BeO moderator blocks. These blocks, as fabricated for the original reactor design, are shown in Figure 1.The solid-fuel-pin thermal reactor design was found to possess a serious difficulty when the design concept was projected to cover a relatively high-power reactor. The problem was the positive temperature coefficient of reactivity associated with the cross section of xenon at elevated temperatures. This xenon instability was considered to be serious enough to warrant abandoning the solid-fuel design concept, because of the exacting requirement placed on any automatic control system by this instability.An obvious way to avoid the control problem would be to incorporate a liquid fuel that would have a large density change for a given change in temperature. If, upon heating and expanding, a portion of the fuel could, in effect, be made to leave the critical lattice, a selfstabilizing reactor would result.

No abstract

The necessity for prudent conservation of potable water, the need for protecting water supplies from contamination, and the increased cost of dual water distribution systems serving an expanding nuclear complex, generated an interest at Oak Ridge National Laboratory in the reduced pressure principle backflow preventer. This device, despite its advantages of economy and convenience, has been only partially accepted as a substitute for air-gap separation in preventing pollution of potable water.Previous tests generally reported dynamic or maltreatment conditions. To provide additional assurance of the safety of the device, a reduced pressure principle backflow preventer was tested under five different static conditions. A solution of manganese and potassium nitrates was used as a nonradioactive tracer. Activation and radiochemical analyses having a sensitivity of -0.2 parts per billion of manganese proved there was no detectable backflow from the discharge side to the supply side. Potassium analyses also showed no detectable backflow, but with a lesser sensitivity.The "Protection Factor" (P.F.) for the device is defined as:Reagent concentration in the discharge zone Reagent concentration in the supply zone due to backflow ' P.F. =The minimum protection factor proven in these tests based upon the limit of the sensitivity of manganese analysis is 6.5 x lo8. This factor provides a rational basis for installation where the concentration of radioactivity or other contaminant can be estimated, measured or limited.Criteria for RPPBP installations at ORNL include purchase specifications, inspection requirements, approvals required for use in three levels of hazard, installation requirements and maintenance considerations.

This aanual is designed to assist local civil defense organiza tions prepare plans consistent with the changing strategic conditions of the seventies. The Defense Civil Preparedness Agency is aoving into a new program of "all-hazards, all-contingencies" planning which will involve developing a crisis-oriented evacuation capability. This capability will increase the survivability of the population in the event of a. nuclear attack and will be a counter agrinst certain "nuclear blackmail" threats. Planning for t>e development of shelter capabilities for either an "in-place" or evacuated posture will re quire an ability to rapidly build large numbet3 of new expedient skelters in addition to upgrading existing f&llout shelters. {Ex pedient shelters are shelters which can be built under crisis con ditions, within 48 hours using only locally available materials, equipment, and labor.)Detailed step-by-step instructions and pictorial design draw ings of fifteen expedient shelters are included in the Appendices. The instructions and drawings for any of these shelters can be pre printed by local CD. organizations for rapid dissemination in a crisis. The shelter designs are simple enough that thev can be built by ordinary Americans, even ones who have had no previous building experience and who have no guidance other than these draw ings in! instructions. Many of the designs have been proof-tested (i.e., built under simulated crisis conditions by unskilled urban or rural people with no prior preparation other than reading these instructions for building one of these shelters). Designs and in structions for building Kearny A>.r Pumps (KAI-'s) and an expedient, quick-closing blast door are also included in the Appendices.It is recommended that all of these shelters, especially the designs that have not yet been built by average citizens, be proof-tested under simulated crisis conditions by ordinary civilians and that the experiences so gained be used to refine and improve the designs and instructions. It is recommended that all of these shelters, especially the designs that have not yet been bu.Ut by average citizens, be proof-tested under simulated crisis conditions by ordinary civilians and that the experiences so gained be used to refine and improve the designs and Instructions.

No abstract