Contamination, radioactive tritium

This section of the chapter will briehy review the LANL held studies and the results of these studies. The signihcance of each of these experiments will be examined in the Discussion section of this chapter. Field research was conducted at LANL during 1994, 1995, and 1996. The study site was located adjacent to a 7-million-liter, radioactive waste lagoon that contained known bioavailable contamination including tritium, cobalt-56, cobalt-60, manganese-54, sodium-22, and tungsten-181. The lagoon was the nearest source of water for the colonies in the experiment. 

DOE — Organics, PCBs, petroleum/fuel hydrocarbons, solvents, TCE, unspecified VOCs, and unspecified SVOCs are among the contaminants found. Metals cited most often include lead, beryllium, mercury, arsenic, and chromium. Radioactive contaminants are present at most installations the most frequently cited are uranium, tritium, thorium, and plutonium. In addition, mixed waste containing both radioactive and hazardous contaminants is of particular concern to the DOE because of the lack of an acceptable treatment technology. 

Schell, W.R., Sanzay, G. Payne, B.R. (1974) World distribution of environmental tritium. In Physical Behaviour of Radioactive Contaminants in the Atmosphere, pp. 396-400. Vienna IAEA. 

Analysis is best carried out by a fluorescence activated cell sorter (see 10.7.5) but, if the cells are pulse labelled with [3H]-thymidine immediately before harvesting the proportion of cells in S-phase in the various fractions can be estimated by autoradiography (see 12.3). The problem with this procedure is that the machines can become contaminated with radioactivity and the tritium may interfere with subsequent enzyme assays. Labelling of a sample after fractionation is a poor alternative, but prior pulse labelling with bromodeoxyuridine allows S-phase cells to be detected using a fluorescent antibody 12.7.5. 

The main aspects for the selection of plasma facing materials for ITER are the requirements of plasma performance (minimize impurity contamination), engineering integrity, component lifetime and safety (e.g., minimize tritium and radioactive dust inventories) [7]. Currently, the ITER design uses beryl-... 

The nature of our concern is best illustrated by a specific example. Blank and Kidwell use a cocaine solution of 100,000 ng/mL for their contamination experiments, to which they add approximately 1 pCi of tritium-labeled cocaine, i.e., approximately one million counts per minute. Therefore, they have approximately a sensitivity of 10 cpm/ng of sample. Decontamination of hair means that residual drug concentration must drop below the endogenous cutoff level of 5 ng/10 mg of hair, i.e., to 50 cpm/10 mg hair. Now if the labeled cocaine has a radiochemical impurity of as little as 0.1%, this corresponds to 1000 cpm or to 100 ng of residual cocaine equivalents. Since self-irradiation of tritium-labeled material tends to form polymeric impurities, and since these are likely to preferentially bind to hair, one incurs a major risk of concluding erroneously that the residual radioactivity represents residual cocaine contamination rather than contamination by polymeric degradation products. 

The experiments have proved that membrane distillation can be applied for radioactive wastewater treatment. In one-stage installation the membrane retained all radionuclides and decontamination factors were higher than those obtained by other membrane methods. The distillate obtained in the process was pure water, which could be recycled or safely discharged into the environment. It seems the process can overcome various problems of evaporation such as corrosion, scaling, or foaming. There is no entrainment of droplets, which cause the contamination of condensate from thin-film evaporator. Operation at low evaporation temperature can decrease the volatility of some volatile nuclides present in the waste, such as tritium or some forms of iodine and ruthenium. The process is especially economic for the plants, which can utilize waste heat, e.g., plants operating in power and nuclear industry. 

Contamination from a fission reaction can last for thousands of years because of the long half-life of the fission-produced radioactive isotopes. If, by an unusual set of circumstances a plot of ground becomes contaminated with a hazardous amount of tritium the area would be safe within a few decades because of the short half-life of the tritium. 

In a water-cooled reactor the coolant is processed continuously for control and removal of chemical and radioactive contaminants. In a PWR the lithium formed by (n, a) reactions in dissolved boron will add to whatever natural lithium is present as a contaminant and for corrosion control, but the continued processing will hold it at some steady concentration. For the purpose of this estimate we shall assume a concentration of 1.0 ppm of lithium in the coolant and will neglect the additional Li produced by reaction (8.50), However, after the coolant lithium has been exposed to thermal neutrons for a few years it will become depleted in the Li, because of the high absorption cross section of Li. A typical isotopic composition of lithium in the coolant of a PWR is 99.9 percent Li [S2]. Applying Eq. (8.55) for tritium produced by Li(n, a) yields the yearly production of 34 Ci listed in Table 8.10. The yearly production of the tritium from Li reactions is estimated at 4 Ci [S2]. 

It is unusual to think of any type of atmospheric contamination - especially by a radioactive species -as beneficial however, bomb-produced radiocarbon (and tritium) has proven to be extremely valuable to oceanographers. The majority of the atmospheric testing, in terms of number of tests and production, occurred over a short time interval, between 1958 and 1963, relative to many ocean circulation processes. This time history, coupled with the level of contamination and the fact that becomes intimately involved in the oceanic carbon cycle, allows bomb-produced radiocarbon to be valuable as a tracer for several ocean processes including biological activity, air-sea gas exchange, thermocline ventilation, upper ocean circulation, and upwelling. 

LS counters are suitable for measuring radionuclides that emit only very low-energy beta particles or electrons, notably tritium (Emax = 18.6 keV). When tritium is measured as tritiated water and its activity is reported relative to water weight or volume, no yield measurement is needed. Liquid samples, e.g., water from the environment, process streams, urine, or dissolved solids, can be counted directly or purified by distillation. Results for purified samples are more reliable to the extent that the radioelement can be identified, quenching is stabilized, and luminescent contaminants are removed. Reagents may have to be added to the distillation flask to hold back other potentially volatile radionuclides, such as radioactive iodine, carbon, ruthenium, or technetium. 

Automatic sample preparation methods for the determination of oarbon-14 and/or tritium, and carbon-14 and/or sulfur-36 in dual labelled samples by liquid scintillation counting are presented. The sample is burnt in a stream of oxygen, and the combustion products carrying radioisotopes are subsequently separated and collected for radioactivity determination. Tritium is measured as water, carbon-14 as "carbamate" and sulfur-35 as sulfuric acid. The procedures run automatically, they are free of memory effect and cross contamination, and provide quantitative recovery. 

Singleton and Yaimopoulos (1975) have used Sc and Y films (500-1200 nm thick) for fabrication of radioactive electron emitters (tritriated electron sources). The stability of the sources in flow gas streams increases from Ti to Y to Sc. Once again, it is shown that the surface contamination has a profoimd influence on both the loading and loss of tritium in the films. Bacon et al. (1984) have manufactured SCD2 and ScDT thin film targets (10-50 pm) for neutron protection inside an intense neutron source for use in cancer therapy. The films must not be heated at temperatures over 723 K to maintain their chemical stability. 

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