Relative radiotoxicity

Table 11.2 Classification of isotopes according to relative radiotoxicity per unit activity...

Table 10.2 Classification of isotopes according to relative radiotoxicity per unit activity The isotopes in each class are listed in order of increasing atomic number...

Table 9.2. The categorization of radionuclides according to their relative radiotoxicity [19]... 

FIG. 21.19. Relative radiotoxicity after 3 y cooling. From top spent ftiel, HLW, HLW after removal of all Am and Cm, and after additional removal of all Sr and Cs. 

Relative radiotoxicity. (Data and graph from Sylvain David, Institute de Physique Nucleaire d Orsay, Orsay, France.)... 

One of the benefits of UNF recycling as depicted in Figure 14.33 is that the radiotoxicity level of recycled UNF implying the combination of partitioning of minor actinides and fast reactor technology will reach the uranium ore relative radiotoxicity level in 300 years as opposed to the 300,000 years required by a direct disposal of UNFl. Thus, the difference between the costs of recycling and direct disposal will be reduced, because it will take only 300 years to reach an acceptable level of environmental radiotoxicity. 

In addition to the isotope s relative radiotoxicity, another important factor in determining the maximum level of radioactivity that may... 

There is some consideration of ultimately disposing of these bottles into the sea. This may be well justified because of the relatively short half-life, the low radiotoxicity, and the chemical inertness of Kr. It may even reduce the Kr hazard in comparison with surface storage of high-pressure bottles. At present, however, the London Convention on sea disposal of radioactive waste permits only disposal of solid waste. 

Military uses (fission bombs based on U) and accidental releases of radionuclides such as during the Chernobyl accident may lead to the contamination of large areas. However, the contribution of uranium and its decay products to the radiotoxicity of nuclear fallout is marginal. Most of the acute and protracted dose is caused by relatively volatile and soluble fission or activation products such as Sr, Cs... 

Both a- and jS-emitters are used in luminescent paint. The fluoresc t material is usually ZnS. T and are preferred sources since their j3-energies are low, but Kr, Sr, and Pm are also used. The amount or radioactivity varies, depending on the need (watches, aircraft instruments, etc.) but it is usually < 400 MBq (< 10 mCi), although larger light panels may require > 50 GBq (several Curies). For such high activities only T or Kr are acceptable because of their relatively low radiotoxicity. 

Relative ingestion radiotoxicity of representative fission products and some actinides in spent fuel as a function of time after discharge from a pressurized water reactor (PWR) (NAS 1996) (Courtesy of the Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy (1995))... 

What Fig. 61.2 actually shows is the ingestion radiotoxidty of the various nucKdes. However, larger radiotoxicity means larger activity/number of atoms/mass of the given radionuclide per mass unit, i.e., the shapes of the curves are also characteristic of the relative amounts of radionuclides (p. 2808). 

For localized deposits of radionuchdes with high radiotoxicity (e.g. trarrsuranic elements) in a woimd, it is usttally advisable, subject to medical advice, to excise the contamirration soon after the irrtake. Radiochemical analysis of excised tissue by destractive and/or non-destractive methods can provide irrfonrration on the radionuclides and their relative concentratiorrs, and may assist in assessing the uptake to blood and in determining the cotuse of further actiorrs. 

The relatively high core bum-up of 65 GW d/t and SNF recycle would result in low SNF and waste volumes. An option to recycle minor actinides (MAs) could be considered to reduce long-term radiotoxicity of waste. 

The radioactivity of the SNF evolves over time as the various elements decay. The same is true of its radiotoxicity (expressed in Sv/metric tonne ) versus natural uranium that of fission products decreases very rapidly in a few hundred years and then persists at low level for millions of years, because of the presence of long-lived fission products. In fact, after approximately 600,000 years, the radioactivity of untreated spent fuel comes down to that of the natural uranium Irom which the fuel was made. The radioactivity of the SNF in fact decays by a factor of 65 within 1 year after unloading from the reactor core as a result of the decay of relatively short-lived fission products and actinides. The radioactivity of plutonium (mostly of half-lives 24,000, 6500, and 87 years) represents less than 10% of the total toxicity of the spent fuel when it comes out of the reactor. With the passage of time and the disappearance of the short-lived products, this proportion increases. In addition, MAs (Np, Am, Cm) significantly contribute to the radiotoxicity balance during a few thousand years. After several thousands of years, plutonium dominates and represents nearly 90% of the radiotoxicity. 

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