Polonium alloys

Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. The element has been used in devices for eliminating static charges in textile mills, etc. however, beta sources are both more commonly used and less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, minimizing hazards to the user. 

One of the earliest reported uses was for the improvement of the cold starting properties of internal combustion engines, the polonium being incorporated into the sparking plug electrode alloy (38), but its effectiveness for this purpose has been disputed (40) and a health hazard would certainly arise from the burning off of the polonium from the electrode and its discharge into the air. 

Commercial uses of Se, Te, and Po are limited, though selenium is used to make red colored glass and in photocopiers (see the Interlude at the end of this chapter). Tellurium is used in alloys to improve their machinability, and polonium (2i0po) has been used as a heat source in space equipment and as a source of alpha particles in scientific research. 

In case of steam generator tube failure and depressurization of the secondary circuit, PbBi alloy can find its way into the secondary circuit and water can be contaminated by polonium. In this case basic amount of polonium is kept in the alloy, condensate saturation activity of lO-s-lO" Bq/kg is reached, and SG inner surfaces become contaminated owing to polonium sorption from the water. Water evaporation determines radioactivity level in the turbine hall. 

The major reason for its radiation danger is the formation of radioactive polonium aerosols when hot LBC contacts with air. It could happen under conditions of emergency tightness loss of the primary circuit and coolant spillage. In this case, as the RI operation experience at the NS has displayed, the yield of Po aerosols and air radioactivity (according to the thermodynamics laws) reduce quickly with temperature decreasing and spilled alloy solidifying. Fast solidification of spilled LBC restricts the area of radioactive contamination and simplifies its removal in the form of solid radioactive wastes. 

For almost half a century scientists had to be satisfied to work only with polonium compounds (usually in rather small amounts). The pure metal was prepared only in 1946. High-density layers of metallic polonium prepared by vacuum sublimation have a silvery colour. Polonium is a pliable low-melting metal (melting point 254°C, boiling point 962°C), its density is about 9.3 g/cm . When polonium is heated in the air it readily forms a stable oxide its basic and acidic properties are weakly manifested. Polonium hydride is unstable. Polonium forms organometallic compounds and alloys with many metals (Pb, Hg, Ca, Zn, Na, Pt, Ag, Ni, Be). When we compare Mendeleev s predictions with these properties we see how close they are to the truth. 

Polonium (Po) is a radioactive element that was discovered in 1898 by Marie Sklodowska-Curie and Pierre Curie. Po is used in brushes to remove dust from photographic films and to avoid charge static accumulation produced by several processes, such as the rolling of paper, wire, and sheet metal. In addition, Po has been alloyed with beryllium to be used as a neutron source. All these and other applications depend on Po s structural properties. Po is the only element of the periodic table that adopts the simple cubic (sc) structure at ambient pressure (a few other elements such as Ca-III and As-II present the sc, but only at high pressure [1]), and this structure has a low atomic packing factor and is rare in nature. The first experimental studies of Po s crystal structure, by using electron diffraction, were reported in 1936 by Rollier et al. [2]. Several years later, Beamer and Maxwell [3,4] and Sando and Lange [5] reported on their X-ray diffraction experiments on metallic Po. From these reports, we know that Po exhibits two structural phases the a phase (a-Po), which has the sc structure p Pmim)], a = 3.345(2) A [4], and the /3 phase (/3-Po), stable above 77(9)°C, which has the rhombohedral (r) structure [Df (/ 3m)], a = 3.359(1) A, and a = 98.22(5)°. 

The other possibility is a liquid metal. Mercury was used in an experimental reactor in America, but the use of mercury poses some obvious hazards. A lead bismuth alloy is a possibility, since it has a low melting point (having the coolant freeze in the reactor is not a good move) but bismuth absorbs neutrons and decays to become radioactive polonium. The only other feasible option is to use sodium... 

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