Fission products from

The main drawback to nuclear power is the production of radioactive waste. Spent fuel from a nuclear reactor is considered a high-level radioactive waste, and remains radioactive for a veiy long time. Spent fuel consists of fission products from the U-235 and Pu-239 fission process, and also from unspent U-238, Pu-240, and other heavy metals produced during the fuel cycle. That is why special programs exist for the handling and disposal of nuclear waste. 

The degradation of 4-chlorobiphenyl by Sphingomonas paucimobilis strain BPSl-3 formed the intermediates 4-chlorobenzoate and 4-chlorocatechol. Fission products from the catechol reacted with NH4+ to produce chloropyridine carboxylates (Davison et al. 1996) (Figure 2.2c). 

THE NEW VISION INCLUDES VIABLE PROGRAMS FOR MANAGEMENT OF THE BY-PRODUCTS OF THE NUCLEAR FISSION PROCESS, INCLUDING RECYCLEOF ALL FISSIONABLE MATERIALS AND LONG-TERMISOLATION OF UNWANTED FISSION PRODUCTS FROM THE BIOSPHERE. 

Viable programs for management of the by-products of the nuclear fission process, including recycle of all fissionable materials and long-term isolation of unwanted fission products from the biosphere... 

Table 4 summarizes the geographical behavior of fission products at the Oklo reactors compared with the behavior of fission products from neutron-irradiated uranium dioxide. The reactor zones RZ 1-9 are exposed on the ground, while RZ 10-16 are situated below the ground, all quite deep except RZ 15. 

After the separation of the actinides from the high-level waste, it is desirable to remove certain other fission products from the nuclear wastes. Some Cs and Sr are low-charged cations that react well with macro-cyclic ligands (e.g., crown ethers, calixarenes). Research to synthesize and investigate the properties of macrocyclic ligands for application in nuclear waste treatment has been an active effort internationally. Some of the results obtained are discussed in section 12.7. 

Humans are exposed to radiation from the testing and explosion of nuclear weapons and the wastes of nuclear reactors and power plants. Strontium-90 is a fission product from nuclear reactors. It is of particular concern because it has a long half-life of 38 years and becomes concentrated in the food chain, particularly plants-to-milk. The ban on atmospheric testing of nuclear weapons has reduced this hazard. Strontium-90 does have some industrial uses. Most people in developed countries receive minor exposure to radiation through medical procedures such as X-ray and various treatments for some diseases. 

This paper deals mainly with the condensation of trace concentrations of radioactive vapor onto spherical particles of a substrate. For this situation the relation between the engineering approach, the molecular approach, and the fluid-dynamic approach are illustrated for several different cases of rate limitation. From these considerations criteria are derived for the use of basic physical and chemical parameters to predict the rate-controlling step or steps. Finally, the effect of changing temperature is considered and the groundwork is thereby laid for a kinetic approach to predicting fallout formation. The relation of these approaches to the escape of fission products from reactor fuel and to the deposition of radon and thoron daughters on dust particles in a uranium mine is indicated. 

An important parameter in the evaluation of the safety of a reactor system is the release of fission products from the fuel. The fuel in the high-temperature gas-cooled reactor (HTGR) consists of spherical particles (U, ThC2) that are coated with a material presenting a diffusion... 

Calculations for Figure 14 illustrate a recoil source with the same parameters as those used in the study depicted by Figure 11, except that a buffer carbon layer 0.0006 cm. thick with a diffusion coefficient of 10"6 cm.2/sec. was placed between the coating and the kernel. Distribution coefficients were taken as unity. A recoil range of 0.0006 cm. was assumed in both the kernel and coating materials. Results of this calculation differ considerably from those for experiments with no recoil. These differences are consistent with. —4.5% release from the kernel during irradiation. After release of this quantity of fission product from the particle, the releases begin to approach those of the bare kernel. The recoil effects were unimportant after releases of 7 to 8%. 

Numerous studies by other workers (I, 10) have shown that the releases of iodine and the noble-gas fission products from pyrolytic carbon-coated fuel particles are controlled by diffusion of these nuclides through grain boundaries, cracks, and defects in the isotropic pyrolytic carbon coating. When coatings are intact, however, the release of these fission product nuclides is low. However, the pyrolytic carbon coating constitutes only a delaying barrier to the metallic nuclides barium and strontium through which they diffuse with diffusion coefficients of the order of 10 9 cm.2/sec. (at — 1400°C.). The steady-state release of these metallic nuclides is controlled instead by diffusion out of the fuel kernel,... 

In considering the operational safety and accident analyses of sodium-cooled fast reactors, similar information on the release of fission products from sodium is needed. Although the extent of vaporization can often be calculated from thermodynamic considerations (3, 4), appropriate transport models are required to describe the rate phenomena. In this chapter the results of an analytical and experimental investigation of cesium transport from sodium into flowing inert gases are presented. The limiting case of maximum release is also considered. 

Just as earlier we were able to observe mass-yield distributions of the fission products from the fissionable nuclide used in the Chinese nuclear device, it is possible to see part of the mass-yield curve from the fission of 244Pu, which was synthesized originally in a supernova. Figure 6 shows the mass-yield distribution of the excess fissiogenic xenon observed in the meteorite Pasamonte (15). 

Storm of Nov. 15-17, 1966. The fission product ratio data by nuclear event for this storm are given in Table VII. The storm occurred 18 days after the reported Chinese fourth nuclear weapon test of about 20 lalotons on Oct. 28, 1966 and 190 days after the Chinese third nuclear explosion of about 200 kilotons on May 9, 1966. Also listed is the series of tests conducted by the French in the Southern Hemisphere (near Tahiti) in the time period between these two Chinese tests. A further possible source of fission products was the vented U.S.S.R. underground nuclear explosion of Oct. 27, 1966 (14). The extent of venting is not reported, and contributions to the storm deposition, if any, would appear as part of the fission products from the China-3 explosion. However, the venting process may result in significant fractionation of the fission products. 

Fuel reprocessing has three objectives (a) to recover U or Pu from the spent fuel for reuse as a nuclear reactor fuel or to render the waste less hazardous, (b) to remove fission products from the actinides to lessen short-term radioactivity problems and in the case of recycle of the actinides, to remove reactor poisons, and (c) to convert the radioactive waste into a safe form for storage. Fuel reprocessing was/is important in the production of plutonium for weapons use. 

The most important liquid wastes are the high-level effluents, containing fission products from fuel reprocessing. They contain >99% of the fission products in the fuel with small quantities of U and Pu. Medium-level liquid waste has an activity of 4 GBq/L and results from various steps in fuel reprocessing. Low-level (<0.1GBq/m3) waste is treated or concentrated. Liquid organic waste is usually incinerated or chemically destroyed. 

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