RESEARCH

Cu Helps Reactor Run Smoothly, Safely Salts catalyze formation of water from H2

and 02 in homogeneous reactor, prevent explosive gas mixtures

Small amounts of copper salts play a big role in homogeneous nuclear reac­tors—where the fuel is an aqueous uranyl sulfate solution. Reason: The salts catalyze tfre recombination of hydrogen and oxygen formed in the solution, prevent formation of an ex­plosive gas mixture.

A research group at Oak Ridge Na­tional Laboratory discovered copper's catalytic activity, an important factor in the operation of ORNL's experi­mental homogeneous reactors, HRE-1 and HRE-2. Without copper, the hydrogen-oxygen-steam mixture in the reactor may fall within the explosive range. A reactor makes about 10 cu. ft. per min. of a 2:1 hydrogen-oxygen mixture for every 1000 kw. of fission energy. A reactor of the size needed at a power station might pro­duce 1000 times as much.

Besides the explosion hazard itself, there are other complications:

• An explosion might release the intensely radioactive fuel solution.

• Sudden formation or removal of gas bubbles in the reactor core could cause surges of nuclear fission. Con­cern over this point delayed early homogeneous reactor development from 1944 until 1949.

Gas Disposal. Normally, the sim­plest way to get rid of an explosive gas mixture is to dilute it with large volumes of air and disperse it in the atmosphere. This cannot be done for reactor-produced gases for two rea­sons. First, the mixture as it comes from the reactor contains highly ra­dioactive fission gases. Secondly, the hydrogen is present as deuterium (from the heavy water used as the fuel solvent). Its loss would be very expensive.

Another way to dispose of the gases is to bum them. When ORNL started up HRE-1 in April 1952, the

46 C & E N FEB. 29, 1960

hydrogen-oxygen mixture passed through a throttling valve to atmos­pheric pressure and burned in a unit resembling a household gas stove burner. Injection pumps returned the resulting water to the fuel solution to maintain its composition. A heated bed of platinized alumina pellets re­moved remaining traces of hydrogen and oxygen, while charcoal beds ad­sorbed the noncondensable radioac­tive gases.

This system—satisfactory for a small experimental reactor—is less attractive for large-scale reactors. Too large a volume of gas would have to be han­dled outside the reactor core.

Reaction Studies. Several chemi­cal research groups, directed by Dr. C. H. Secoy of ORNL, had studied the behavior of uranyl sulfate solutions at elevated temperatures and in the presence of reactor radiation. The scientists suspected, and later proved in laboratory experiments, that uranyl sulfate solutions themselves could cat-alytically combine hydrogen and oxy­gen at rates which accounted for the steady-state pressures observed in the reactor at temperatures above 200° C. Other laboratory tests show that many other solutes can catalyze the reac­tion. Copper salts seem to have out­standing catalytic activity, according to Dr. H. F. McDuffie, leader of the group which investigated this phase of the work. Other members of this group were Dr. E. L. Compere, H. H. Stone, and L. F. Woo.

The reaction is first order, both in concentration of dissolved copper and in the concentration of dissolved hy­drogen, says Dr. Compere. Activa­tion energy for the reaction is ap­proximately 24 kcal, per mole. The kinetic studies have been declassified [/. Phys. Chem. 62, 1030 (1958)].

The ORNL group tested some 80 different chemicals for possible cat­

alytic activity, says Mr. Stone. So far, copper salts are the most effective catalysts. Ionic platinum, palladium, osmium, iridium, and rhodium are quickly reduced to the metallic state. Then they act as very effective het­erogeneous catalysts, often initiate ex­plosions of the confined gas. Explo­sions are not observed with catalysts that remain in solution.

How Much Cu? Finding the re­quired copper concentration involves several factors—fission density (which controls gas production), hydrogen pressure, and temperature. Copper sulfate was tested in the HRE-1 fuel solution during December 1953 and January 1954. These tests showed that all the radiolytic gas recombined with a concentration of 0.07 molar copper, a fuel temperature of 260° C , a total pressure of 1200 p.s.i.g., and a reactor power level of 1280 kw. The catalyst appeared to have no adverse effects. If anything, the reactor was slightly more stable. The first ex­perimental reactor has now been dis­mantled and replaced by the HRE-2. It has operated for several thousand hours with a copper catalyst at a power level up to 5 megawatts and at pressures up to 2000 p.s.i.

Fused Salts Hold Key to Titanium Process Two Canadian scientists believe that it is practical to make titanium elec-trolytically in a low temperature salt bath—with "substantial" advantages over the usual reduction methods. While studying the e.m.f. of com­pounds in fused salts, Dr. Spyridon N. Flengas and Dr. Thomas R. Ingraham of the Department of Mines and Tech­nical surveys, Ottawa, found that titanium tetrachloride dissolves in molten salts containing KCl. This dis­covery may lead to the new process, they say.

Dr. Flengas and Dr. Ingraham made a KCl-NaCl eutectic containing U7r Ti at 690° C , feel that this is due to KoTiCl«; in the melt. They pre­pared this compound from KCl and TiCl4, determined its stability by measuring TiCl4 vapor pressure over the pure material. Their finding: KoTiCl«; begins to decompose at about 300° C. Therefore, high temperature melts such as KCI-NaCl don't favor the solubility of TiCl4.

KCI-LiCI Shows Promise. A low temperature melt such as KCI-LiCI would permit operation of electrolytic

cells at temperatures where the inter­mediate is stable. This mixture melts at about 250° C , but it presents a problem of its own. Air oxidizes the lithium chloride to the oxide. A sim­ple way to convert the oxide back to the chloride would make low tem­perature baths practical for an elec­trolytic process, Dr. Flengas and Dr. In graham say.

These investigators observed that the discharge potential for Ti ions is less than 2 volts, and for Na ions, 3.4 volts. In a cell with a controlled potential, they say, it should be pos­sible to deposit titanium without dis­charging Na or Κ ions.

Merck and Molecular Electronics Merck jumps into molecular electron­ics with a new way to make silicon p-n layers directly from vapor phase growth of single crystals. The proc­ess deposits alternate ρ and η crystal layers from the vapor phase. Merck says the method is a new approach to making semiconductor junctions now made by alloy or diffusion processes.

A wide range of p-n junctions are possible, Merck says. Resistivity of

the ρ or η layer can be varied from a degenerate level to several hundred ohms per centimeter. The method was developed by John Allegretti and Donald Shombert, Merck Research Laboratories' advanced electronic ma­terials section. Merck is now pre­paring to distribute samples of junc­tions for evaluation by manufacturers.

BRIEFS

Cadmium sulfide transistor has been developed experimentally by General Motors Research Laboratories. Differ­ence from other transistors: Light and other radiations affect the CdS's electrical properties, make it useful as a phototransistor, GMRL says.

Antibody molecules can be measured using an electron microscopic method developed by Dr. C. E. Hall at Ros-well Park Memorial Institute, Buffalo, N.Y! Minute particles of platinum are evaporated across an antibody field on a mica surface and pile up against the antibody molecules. From the shad­ows cast by the Pt drift lodged against the molecules, their size and shape can be determined.

Old Newspapers Plus H3B03 Yield Insulation The product that makes this picture possible is made from old newspapers and boric acid. Here it shows what it can do by insulating a man's hand from a 4000° F. flame used to melt the penny he is holding. Called Thermo-K, the product was developed by United States Insulation, Carson City, Nev. The material has a thermal conductivity of 0.19, much lower than other insulation materials, the company says. Added advan­tages: lightweight, water resistant. U.S. Insulation is showing Thermo-K at the Chemicals and Synthetics Exhibit at the Department of Commerce building, Washing­ton, D.C., under auspices of the Patent Office. The office of Naval Research, Army Chemical Corps, and 16 industrial companies got together to put on the exhibit, which shows progress made by inventors in the chemical field.

FEB. 29, 1960 C & E N 47

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