Technetium release

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

A selective separation of fission technetium induced by fission of can be performed by stopping the speed of the Tc nuclides in solid KCl and SrClj catchers. At temperatures of 300 to 750 °C, 30% to 85% of Tc is selectively released. Purified nitrogen is used for the transportation of the nuclides from the target to the detector. The release is accelerated by increasing the temperature and adding ZrCl as a carrier. 

Long-lived ty = 2.1 x 10 years) Tc, present as TCO4 in Purex process HNO3 feed solutions, is partially coextracted with uranium and plutonium in the first cycle. Unless separated in the Purex process, Tc contaminates the uranium product subsequent processing of the U02(N03)2 solution to UO2 can release some of the technetium to the environment. The presence of technetium in the purification steps as well as in the uranium product causes several other complications. Thus it is desirable to route all Tc into the high-level waste. Efforts in this direction have been described in some recent flow sheets [37]. 

An unusual reaction pattern has been found for the electrochemical and chemical (by ascorbic acid) reduction of the rhenium(II) thioether complex [Re(9S3)2] " (9S3 = 1,4,7-trithiacyclono-nane). Instead of the formation of the corresponding rhenium(I) complex, C bond cleavage and the release of ethene was observed and the brown rhenium(III) species [Re(9S3)(SC2H4SC2H4S)]" (250) was isolated as a BF4 salt. Lfpon electrochemical reduction of [Re(9S3)(SC2H4SC2H4S)]" further loss of ethene was observed while the analogous technetium complex can be reversibly reduced to [Tc(9S3)(SC2H4SC2H4S)]. 

Making metastable technetium-99 is an expensive business. A cheaper, common alternative tracer is iodine-131, which emits a gamma ray when it decays. But the iodine isotope also releases beta particles that can damage tissues, making it less attractive as an imaging agent. 

W.L. Ebert, S.F. Wolf, and J.K. Bates, The release of technetium from defense waste processing facility glasses, Mater. Res. Soc. Symp. Proc., 412 (1996) 221-227. 

Nuclear chemistry (radiochemistry) has now become a large and very important branch of science. Over four hundred radioactive isotopes have been made in the laboratory, whereas only about three hundred stable isotopes have been detected in nature. Three elements —technetium (43), astatine (85), and promethium (61), as well as some trans-uranium elements, seem not to occur in nature, and are available only as products of artificial transmutation. The use of radioactive isotopes as tracers has become a valuable technique in scientific and medical research. The controlled release of nuclear energy promises to lead us into a new world, in which the achievement of man is no longer limited by the supply of energy available to him. 

Radioiodine uptake can be used to test thyroid function, though technetium would be more usual. Scanning may be used for the identification of solitary nodules, and in the differential diagnosis of Graves disease from the less common thyroiditides (e.g. de Quervain s thyroiditis). In the latter, excessive thyroid hormone release caused by follicular cell damage can cause clinical and biochemical features of hyperthyroidism, but uptake is reduced. 

However, lipophilic d,l-HMPAO is easily transformed into a charged complex, which cannot pass the BBB. Once inside the brain, this secondary complex is trapped and is released very slowly (Neirinckx et al. 1987). The Tc-HMPAO complex is also used for labeling leukocytes with technetium. 

Calculations of the absorbed radiation dose resulting from inhalation of Tc-milli-microspheres are based on technetium-labeled aerosols (ICRP Publication 53, International Commission on Radiological Protection 1987b). It is assumed that the label is released in the lung slowly, with a biological half-time of 24 h, and that the activity is excreted by the kidneys. The effective dose equivalent is 0.015 mSv/MBq. The dose to the bladder wall after inhalation of 150 MBq (4 mCi) is 1.95 mCy. The effective whole-body dose in adults (70 kg) resulting from inhalation of 150 MBq of Tc-millimicro-spheres is 2.3 mSv. 

Taking into account the kind of sources and the chemistry of technetium, c will be released to the environment as pertcchnetate. Its behavior in the environment attracted much attention during the last two decades due to the long physical half-life of I c and the solubility and mobility of TCO4 in aquatic systems. Considerable effort has been made to understand the long-term biogeochemical behavior of c, its transfer in food chains and the mechanisms controlling its mobility in diverse environments [17]. 

Based on surveys before and after the discharges in 1994, 30 TBq (March-April) and 32 TBq (Septem-ber-October), the transit time for technetium from the Irish Sea to the North Sea was calculated to be considerably faster than previous estimations of transit times for released radionuclides. This faster transport is demonstrated by measurements indicating that the first discharge plume of Tc had reached the south coast of Norway before November 1996 in about 2.5 years compared to the previously estimated transit time of 3-4 years. 

Technetium has been transferred to terrestrial and aquatic ecosystems due to the fallout from atmospheric nuclear weapons tests. It is assumed that 1 Mt fission energy corresponds to 1.45 x 10 fissions and that Cs is produced with a representative fission yield of 5.57%. Assuming that the global stratospheric injection of nuclear debris was 168.5 Mt and a fission yield of Tc of 6%, similar to that of Cs, the global activity of Tc released into the stratosphere is 160 TBq. When local fallout is included, the total release of Tc into the environment from nuclear weapons tests between 1945 and 1963 should be within 180-200 TBq. Any releases from underground nuclear weapon tests are assumed to have a local impact only. 

During release and initially after deposition of fission products, fractionation between volatile elements associated with condensed particles ( Cs, °Sr) and refractory elements associated with fuel particles Nb) may take place. The behavior of Tc in the environment will, therefore, depend on whether technetium is released as such or formed from precursors after deposition. Technetium-99 is believed to be released from the nuclear fuel cycle as the volatile heptaoxide (TcaOy) in air emissions or as soluble and highly mobile pertechnetate (TcO T) in effluents. 

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