TECHNOLOGY
Power Sources Draw Attention At Geneva Russia unveils system that converts heat in high-temperature, fast-neutron reactor directly to electricity, but omits details "The word 'Romashka' is getting to be as popular as 'sputnik.' " So declared A. M. Petrosyants, head of the U.S.S.R State Committee for Utilization of Atomic Energy (the Soviet AEC) and head of the Soviet delegation to the recent Third International Conference on Peaceful Uses of Atomic Energy, held at Geneva. He was referring, at a press conference, to the new direct conversion reactor unveiled at Geneva that converts heat produced in a high-temperature, fast-neutron reactor directly to electricity in a thermoelectric unit without a coolant. It was obviously something of a propaganda ploy with perhaps a bit of humor thrown in. And Mr. Petrosyants was wringing every drop of value from Romashka that he could. Still, even though talk of "another big Russian first in atomic energy" by some of the press had grown a bit more subdued by the end of the conference, many who viewed the Soviet Romashka exhibit at the show (run in conjunction with the conference) and who had heard the technical paper on the subject seemed to agree that the development is new and interesting, that it came as a surprise, but that it is apparently somewhat primitive compared to the U.S.'s SNAP (Systems for Nuclear Auxiliary Power) program. At the same time, however, the Soviet development may be long on potential with its direct use of heat and high temperatures. The trouble is that the Soviets as usual are playing it close to the vest when it comes to giving out technical details. Here are some of the basic facts about Romashka so far revealed: • Thermal power: 40 kw. •Electrical power: 500 to 800 watts (depending on temperature). • Reactor type: high-temperature, fast-neutron. • Fuel: uranium dicarbide enriched to 90% with U 2 3 5 (total weight of U 2 3 5 is 108 lb.). • Core cladding: graphite. 56
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FAST NEUTRONS. This model of Romashka, the Russian's direct-conversion reactor, was shown at the exhibit held in conjunction with the Third International Conference on Peaceful Uses of Atomic Energy held at Geneva
• Reflector: beryllium. • Thermoelectric converter: silicon-germanium . • Central core temperature: 3270° F . • Maximum reflector temperature: 2200° F . Space Use? Romashka (which is the Russian name for the camomile flower) began generating electricity Aug. 14, now has more than 500 hr. under its belt. One of the big questions: Is Romashka designed for space use? The answer seems to be yes and no. N. N. Ponomarev-Stepnoy, who gave
the paper on Romashka at the session on direct conversion of nuclear power into electricity, indicated that the unit, at least in its present form, isn't likely to get off the ground. With auxiliary equipment, the system is heavy and bulky. But Mr. Petrosyants at the Soviet press conference certainly didn't close the door to this possibility. Replying to a question as to whether Romashka would be used in space, he said: "We have been working in this direction for quite some time and have gotten interesting results. Romashka will find use in many fields." So it's really anybody's guess as to just where the Romashka program stands.
Thus, Romashka has technically beaten SNAP 10A, the U.S. reactorpowered thermoelectric converter, into operation. But SNAP 10A has been fully component-tested and is due for a full space flight test next April. Unless the Soviets have something more up their sleeves, Romashka will still be very much in the development stage at that time. SNAP 10A, developed by Atomics International, is designed to produce 500 watts (electrical). The system uses a 34-kw. (thermal) homogeneous reactor of fully enriched U 2 3 5 , zirconium-hydride moderated. Heat from the reactor is supplied to the thermoelectric converter through a recirculating NaK system. The converter is made up of germanium-silicon alloy thermocouples operating at an average hot-junction temperature of 902° F . and a temperature difference of 310° F. Total weight of the system is 950 lb. Describing SNAP 10A, H. M. Dieckamp of Atomics International told the Geneva conference that fast reactors were eliminated early in the reactor concept stage because of the high cost of the uranium inventory (about $1 million) and the more complex control problems involved. SNAP 10A is just the beginning, Mr. Dieckamp indicates. Future communications satellites, he says, will require power levels of up to about 100 k w ( e ) . and three to five years' life. Large manned space stations could easily require 50 k w ( e ) . , and bases on the moon and Mars would spell even larger power requirements—in the 1000-kw(e). range. Such power systems, he says, will require a reactor source. Meanwhile, SNAP 50, which will be in the 300- to 1000-kw(e). range, is scheduled for ground testing in the early 1970 , s. Thermionic Generators. But thermoelectric converters aren't the only devices being studied. "Thermionic generators are particularly suitable where fission heating is involved, since, if the emitter contains fissile material, it may be part of the fuel element in a reactor and readily raised to a high temperature, , , P. D. Dunn, United Kingdom Atomic Energy Authority, Atomic Energy Research Establishment, Harwell, told the Geneva conference. Thermionic generators could provide power densities in the 5- to 20watt-per-square-centimeter range, output voltage of 1 volt, rejection temper-
atures in the 1300° to 1800° F. range, with conversion efficiencies of 10 to 25%, Mr. Dunn says. "Single diodes of about 15% efficiency can be developed reasonably quickly, but their usefulness as reactor elements will depend on life and reliability," he says. Basic problem in such generators is choice of suitable emitters. Uranium monocarbide looks promising, and adding zirconium carbide as cladding raises resistance to thermal stress with little effect on electronic emission. Possible uses of thermionic generators are in space vehicles and as "toppers" for nuclear power stations. In another paper submitted to the conference, U.S. authors from several firms and laboratories discussed cesium plasma cells using uranium carbide and tungsten emitters. Purpose of the cesium is to increase rate of emission. A recent experiment produced a converter efficiency of 14%, according to the authors. Longest lifetime to date is about 500 hr. Goal of an in-pile test program is to develop a nuclear fuel rod with a 10,000-hr. life and a power output in the 1- to 10-watt-per-square-centimeter range. MHD Converters. In another approach, Pierre Ricateau, of the French Commissariat a l'Energie Atomique, told the conference about French research in magnetohydrodynamic (MHD) converters. (MHD conversion is a process aimed at generating electrical power by direct interaction of a fluid moving in a magnetic field.) CEA, jointly with the French Oil Institute, is pushing a program involving both open-cycle and closed-cycle M H D conversion. In the open cycle, combustion gases from fossil fuels are passed through the M H D converter and exhausted to the atmosphere. In the closed cycle, rare gases such as argon or helium (alkaline-seeded with low concentrations of potassium or cesium) are heated by a source that could be nuclear and circulated in a closed loop through the M H D converter. So far, preliminary studies of closed systems have been aimed at obtaining the highest possible gas conductivities. In another paper submitted but not delivered to the conference, I. I. Bondarenko and others noted that thermoelectric devices are useful in the 10- to 100-kw. range, M H D devices in the 100,000- to 1 million-kw. range, while thermionic generators have advantages in the mid-power range.
Vacuum Spectrophotometer Lowers Ultraviolet Range Molecular studies in the ultraviolet region down to 584 A. are possible with a vacuum ultraviolet spectrophotometer developed by Jarrell-Ash Co., of Waltham, Mass. Few other companies have vacuum ultraviolet spectrophotometers commercially available, and none in this far-ultraviolet range. For example, one commercially available vacuum ultraviolet spectrometer has a lower wave length of about 1600 A. Two completely integrated units are offered by Jarrell-Ash. By a completely integrated unit the company means a complete double-beam spectrometer, sources, chart-recorder, readout, detectors, and monochromator. Both units are alternating current, line operated and do not include the sample cell, which varies according to proposed use. One spectrometer unit (Model 84500) has a range down to 1200 A. It is based on the 0.5-meter Evert spectrometer and includes high-intensity sources of xenon, krypton, and argon. A hydrogen source is used to give continuous operation from 3500 to 1200 A. Model 84-510 is a double-beam spectrometer based on the 1-meter, 15° (fixed angle between entrance and exit beams) Robin vacuum spectrometer. This model permits absorption down to 584 A. This model also includes a helium source. The price of the first unit is $32,000 and the price of Model 84-510 is $42,000. Vacuum UV Sources. Several significant achievements made resolution to 584 A. possible, the company says. The primary factor is the present availability of vacuum ultraviolet sources and particularly that of a helium source. The helium source is used in the 1100 to 584 A. range. The approximate range of the other sources: xenon, 2000 to 1500 A.; krypton, 1500 to 1300 A.; and argon, 1300 to 1100 A. Development of a 1-meter evacuable spectrometer unit was also important. The Robin mount monochromator is an automatically focusing 15°, concave grating instrument with 1meter radius of curvature. The grating is coated with magnesium fluoride. According to the company, magnesium fluoride enhances the reflectivity of optics in the ultraviolet region. The pumping system is a 71/2-in. SEPT. 21, 1964 C & E N
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