Radionuclides total activity

Liquid HLW from reprocessing of SNF may consist of 50-60 elements, including about 90 radionuclides of 35 chemical elements of fission products (FP) and more than 120 radionuclides due to FP decay. The total activity of HLW may achieve 1016 Bq/m3 (Nikiforov el al. 1985). The HLW elements can be divided into four groups ... 

Based on the negligible annual dose to individuals of 10 pSv and assumed scenarios for unrestricted disposal of waste, IAEA has developed recommendations on exemption levels for radionuclides in solid waste (IAEA, 1995) the recommended exempt concentrations have values in the range of about 0.1 to 104 Bq g 1 depending on the radionuclide. IAEA also has issued recommendations on total activities and activity concentrations of radionuclides that could be exempted from any requirements for notification, registration, or licensing of sources or practices, based on the same exemption principles and assumed scenarios for exposure of the public (IAEA, 1996). The recommended exemption levels for naturally occurring radionuclides are limited to their incorporation in consumer products, use as a radioactive source, or use for their elemental properties. 

Another example involves classification of average commercial low-level radioactive waste. The total activities of the dominant radionuclides in the waste, as obtained from data for all Class-A, -B and -C low-level waste emplaced in near-surface disposal facilities in the United States in 1990, are given in Table 7.4 (DOE, 1993b). These estimates do not account for decay that would occur during the 100 y institutional control period. That is, inadvertent intrusion is assumed to occur at the time of facility closure. Radionuclide concentrations are based on the estimated volume of waste and an... 

Szilard-Chalmers reactions are characterized by the enrichment factor (i.e. the ratio of the specific activity of the radionuclide considered after separation to the average specific activity before separation), and by the yield (i.e. the ratio of the activity of the radionuclide obtained after separation to its total activity). Enrichment factors of up to about 1000 or more may be obtained, and yields of about 50 to 100% are of practical interest. 

No. of pieces or weight Total activity and radionuclide used Exported imported into Germany... 

Assinder et al. (1985) reported that the behaviour of radionuclides in the Esk Estuary was determined by its physical characteristics and by its location close to the Sellafield discharge point. Relatively high specific activities of radionuclides in the dissolved phases of waters were encountered. They found that sediment reworked from earlier deposits within the estuary formed a major part of the sediment load of the tidal waters and therefore provided a significant part of the total activity of the particulate phase. The temporal and spatial variation of the total water activity for radionuclides such as Pu follows the pattern for suspended sediment concentration whereas, for conservative radionuclides (e.g. Cs), the... 

The specific activity of a radionuclide relates activity (A) (the number of radioactive atoms decaying) to the total number (N) or total mass of atoms present ... 

Total activity of the element whose principal radionuclide(s) is (are) listed above. 

Radionuclides of high specific activity are produced either through accelerator irradiation or through secondary reactions in the target ( 15.6) in a reactor. Maximum specific activity is obtained when the radioactive nuclide is the only isotope of the element. This is not possible to achieve in regular reactor irradiation through (n,y) capture processes. For example, reactor-produced Na may be obtained in specific activities of 2 X 10 Bq g while the specific activity of accelerator-produced Na may exceed 10 Bq g however, the total activities available are usually the inverse. 

Radioactive material means any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in ADR. 

Class 7 material (radioactive material) shall mean any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in paragraphs 401-406 of the Regulations for the Safe Transport of Radioactive Material, (1996) IAEA Safety Standards Series No. ST-1. UN 2.7.1... 

During the period 1986-97, a complex for HLW vitrification on the basis of two EP-500 ceramic melters were operated at the Mayak power unit (Fig. 1). For six years exploitation of a ceramic melter EP-500/lp, under conditions of remote operation, about 12,500 m liquid HLW were transferred into glass-type matrices based on phosphate glass (Table 1). The total activity of radionuclides incorporated in glass is 285 million Ci on P-emitters and 2.5 million Ci on a-emitters [1]. 

The term "total" activity measurement is, however, somewhat misleading. There is no method available which can cover all radionuclides equally. 

Even the total activity measurement displays a greater or lesser degree of selectivity, with the result that the selection of the method inevitably implies a decision as to which radionuclides are to be measured and which are not. 

Depending on the type of radiation emitted, at least three different types of measuring instruments will be required in order to be able to carry out total activity measurements for all radionuclides or radionuclide groups ... 

If a selective radiochemical separation of individual radionuclides is performed instead of determination of the total activity, smaller quanti-... 

For the U-Al alloy fuel assemblages, a faster rate of release was given to some of the more soluble and mobile radionuclides of the fission product inventory, typically 20% of the total activity. 

In the dawn of the history of nuclear science, the neutron flux density (/) of Ra-Be source was only 10 -10 n cm s The total activity produced by such neutron sources via (n,y) reaction was very low and so was the specific activity of the radionuclides. The Szilard-Chalmers process, however, could dramatically increase the specific activity the improvement could reach orders of magnitude. In the measurement of P radioactivity, which was a frequent task in early days of nuclear science, samples with low specific activity brought sometimes troublesome problems of self-absorption corrections. By the introduction of the Szilard-Chalmers process, however, this difficulty could be avoided, because the measurement could be performed within small statistical errors using a sample with high specific activity. Therefore, the Szilard-Chalmers process became one of the useful means of preparation of radioisotopes for measurement, as Szilard and Chalmers (1934b) recognized the importance of this technique in their early work. 

---