trial applications and of direct relevance to present committee hearings on the systems for nuclear auxiliary power programs. These two reactor systems— (1) Thermionic-reactor space power system; and (2) Compact ZrH-U reactor for terrestrial power have been intensively investigated by General Atomic over the past 2 years and now appear promising for Government development as advanced compact reactor power systems. Thermionic-reactor space power system Development of the first reactor systems for space, SNAP 2 and 8, currently underway by the AEC will provide electrical power up to 30 ekw. with specific weights down to about 50 pounds/ekw. Power requirements for future space programs employing electrical propulsion or supporting manned missions will need space power systems with much higher electrical output (from 100 tc 10,000 ekw.) and with much lower specific weights (below 10 pounds/ekw.) As current systems under development cannot meet these requirements, new systems need to be investigated. Thermionic-reactor space power systems under development at General Atomic have a great potential for achieving very low specific weights (below 5 pounds/ ekw.) at high power levels. Studies of reactor systems employing thermionic energy converters in a reactor indicate that thermionic power systems at 300 ekw. could weigh about the samę (1,500 pounds) as the SNAP-8 operating at 30 ekw. Additionally the problems presented by rotating equipment and phase separation of the coolant common with Rankine cycle (such as SNAP 2 and 8) systems could be eliminated. Considerable progress has been made at General Atomic on the research and development of nuclear reactor thermionic power conversion. In early 1960 a milestone in thermionic development occurred when General Atomic conducted an in-pile test of a fission heated thermionic cell applicable to space power systems. This test achieved 90 watts of electrical power at 10 percent efficiency and high power densities (12 watts/cm.2). Since that time significant progress has been made toward the solution of the formidable metallurgical problems facing the development of thermionic reactor power systems. However, considerable research and development remains to be accomplished, particularly in the area of long life operation and in understanding the interaction of the reactor environment on thermionic cell performance. Although more data are required before a thermionic reactor can be designed, the potentially superior space power systems which can be obtained by employing thermionic reactors make this reactor power system a promising approach to advanced space power systems. Compact ZrH-U power reactors Over the past 5 years General Atomic has developed a class of reactors, known as TRIGA, which are completely safe to operate; that is, no conceivable accident can cause a nuclear excursion which damages the core and releases fission products to the atmosphere. The high degree of reactor safety is obtained through a special reactor design which employs ZrH-U fuel-moderator elements and water coolant. Control rods or other mechanical devices need not, therefore, be relied upon for safety. These reactors have demonstrated their complete safety through repeated tests of the instantaneous insertions of excess reactivity up to $3 with no damage to the fuel elements, and hence no danger of fission product release. Ten reactors of this type have been built and operated and another 14 are under construction. The concept of inherently safe reactors employing water-cooled, ZrH-U fuelmoderator elements has been investigated by General Atomic for the application of compact pressurized-water reactor systems. Compact power reactors using the inherently safe ZrH-U core could be used for a broad range of applications of interest to the Government, such as remote power stations, submersible power systems, and other portable applications of use to the military. General Atomic believes that the development of highly compact reactor systems which are inherently safe can now be undertaken. Sufficient data exists on the ZrH-U fuel element and the physics of the reactor to warrant a development program aimed at producing an inherently safe compact reactor. The successful development of the ZrH-U inherently safe compact reactor could be considered a second generation compact water reactor and would open up new and broader avenues where portable nuclear reactor systems could be employed. Very truly yours, FREDERIC DE HOFFMANN, Senior Vice President, General Dynamics Corp., and President, General Atomic Division. NOTE. A photo of the TRIGA reactor is shown on the next page. Assembly containing cesium cell thermionic converter is lowered into TRIGA atomic reactor at General Atomic Division of General Dynamics Corp. for in-pile experiment in which 90 watts of electric power were produced directly from the heat of nuclear fission. The tiny cesium cell converter-only about a half-inch in length is located near the bottom of the 12-foot aluminum tube which also contains the electrical leads carrying the electricity from the converter to a bus bar outside the reactor. The cesium cell converter contained a nuclear fuel element made of uranium carbide and zirconium carbide. During the series of in pile tests conducted in April 1960, the conversion of fission heat to electrical energy, as measured at the bus bar, showed overall efficiencies as high as 10 percent. Mr. JAMES T. RAMEY, Executive Director, Joint Committee on Atomic Energy, WESTINGHOUSE ELECTRIC CORP., DEAR JIM: We appreciate the opportunity to describe our experience with space auxiliary reactors and other compact nuclear power sources and to express some viewpoints on them. As you know from our testimony on other occasions, we have had an active interest in this part of the nuclear technology and remain convinced of its importance in our space and defense efforts. The establishment of the Westinghouse Astronuclear Laboratory several years ago to focus our capabilities on space applications and other highly developmental aspects of nuclear energy, including these small, lightweight, high performance powerplants, is ample testimony to our convictions. Specific work in the field has been extensive. Westinghouse made a preliminary design study of a 300 kw.(e) SNAP-type powerplant in connection with the SPUR program. The design details are classified, but the plant has a long-endurance nuclear reactor which supplies thermal power to a turbine generator for conversion to electrical power. The turbine would operate on a modified Rankine cycle using metal vapor as the working fluid. We are also carrying forward design studies for NASA of similar but larger units for space auxiliary powerplants up to low megawatt ratings. In this NASA study, several types of nuclear reactors were analyzed, and a number of liquid and vapor metals were studied for suitability as working fluids. In addition, direct cycle and dual cycle systems were analyzed and the problem of environmental testing was investigated. These are but a few of the problems we looked at, but they describe the type of effort. The results of these studies have been incorporated in a preliminary design of a 1 mw.(e) powerplant. In addition to the studies of turbine-generator-type SNAP systems, we have had broad investigatory programs in static conversion including the development of thermoelectric materials and devices. We have conducted a study for the Navy on possible application of thermoelectrics to a wide range of Navy nuclear devices. In addition, we have an AEC program for the development of thermoelectric materials for use in the core of a reactor. Westinghouse thermoelectric generators have found application in some of the low-power SNAP's, including work now in progress for SNAP-10A. Remarkable improvements have been made in these devices. However, a major improvement is required before the thermoelectric generators will be efficient for the higher power ratings. Another static conversion scheme which holds some promise for application to a nuclear reactor is the thermionic generator. In this case, Westinghouse is conducting basic research into the properties of cesium diodes and an engineering development of the diodes for specialized application of thermal to electrical power conversion. In addition, the Atomic Power Division has made a conceptual design study of a nuclear reactor with an assembly of electrically cascaded thermionic diodes distributed throughout the core. This reactor-thermionic generator was designed for an electrical output of 1 MW. An experimental diode which was prepared as a demonstration prototype was tested in the Westinghouse testing reactor, using nuclear heat to generate electrical power from an in-pile assembly. Recently, a Westinghouse research effort on heat diode converters was started for the Air Force. In support of the development of SNAP-type plants, we have important research and development programs looking at materials and equipment. These include investigations of high temperature fuel and structural materials for reactors. We have been looking at ways to improve instrumentation, particularly the nuclear detectors themselves. An effort also has been underway on the development of high performance rotating generators for high temperature operation. There is an associated development in electrical insulation, bearings, and magnetic materials. In turbine studies, there have been preliminary selections of working fluids (mercury, sodium, potassium, cesium and rubidium vapors were considered) and the associated thermodynamic analysis has established reference operating conditions. The effort on materials for the turbines and associated piping and vessels has been directed toward special alloy development involving the refractory metals. Westinghouse has accepted manufacturing contracts from NASA-Lewis for fabrication of turbine parts for metal vapor turbine development at that laboratory. In addition, a fabrication order was accepted from ÑASA-JPL for special tubing to be made from some refractory alloys newly developed by Westinghouse. This tubing is for use by JPL in evaluation tests with metal vapors for use with metal vapor work at that laboratory. In brief, these are some of our technical efforts in this important field. We believe that the uncertainties in the technology have been identified and are.defined to the point where a development program can now be undertaken on a powerplant in the megawatt range with a flyable weight of less than 10 pounds per kilowatt. We believe that the SNAP technology is mature and will be able to support demands for big blocks of electrical energy in space-particularly the demands for power for electrical propulsion engines. This, in turn, could contribute to U.S. leadership in astronautics, since auxiliary power will be a vital element in space missions of the future. Sincerely, J. W. SIMPSON, STATEMENT OF W. E. ZISCH, EXECUTIVE VICE PRESIDENT, AEROJET-GENERAL CORP., Azusa, CALIF. Subject: Aerojet-General Corp. work in the fields of compact nuclear power systems Aerojet-General Corp. has long been vitally interested in the SNAP programs (system for nuclear auxiliary power). The evolution of today's advanced state of industrial and military technology has largely been made possible through the availability of electrical power. Unquestionably, the exploration and conquest of space will be even more dependent on the availability of electrical power for such things as electric propulsion systems, communication, and life support. Latitude in mission capability depends on availability of large quanties of electrical power as well as large boosters. In space, nuclear energy is the only practical energy source for developing the higher power levels we will need. The energy released in fissioning 1 pound of uranium would produce about 150 kilowatts of electrical power for 1 year in space. If this same energy were to be produced by burning hydrogen and oxygen the weight of combustibles required would be in the millions of pounds. Aerojet's activities and progress on the development of nuclear power systems requiring highly compact nuclear power supplies of the SNAP type can be described in three categories: SNAP-8, SPUR (space power unit reactor), and a nuclear thermionic system. SNAP-8 SNAP-8 is a nuclear turboelectric, two-loop Rankine cycle, space power system. The design permits a single or a dual power conversion system to be coupled with a single nuclear reactor to provide a capability for either 30 or 60 kw (e) output. Operation is initiated in orbit. The system has a specific weight of 50 to 60 pounds per lb/kw(e). The life is 10,000 hours (over 1 year). |