Fission products isotope proportions

As may be clear from Sections II and III, the proportions of the various fission product isotopes that might be released if there were a reactor accident, must depend to some extent on the type of reactor, the kind of accident that happens to it, its containment, and how safeguard devices perform. There is such a variety of reactors and such a plurality of failure modes, that one would be rash to attempt to make a single statement, however broad, intended to cover all such releases. Yet, if some coherent... 

In the case when defective fuel rods are present in the reactor core, the BWR reactor water contains the other fission products and the activation products released from the fuel in concentrations well below those of fission product iodine. This applies as well for fission product cesium, which is retained on the ion exchangers of the reactor water cleanup system with a decontamination factor of about 100. As far as it is known, cesium in the reactor water is present as the Cs ion, whereas large proportions of most of the polyvalent fission products and of the actinides are attached to the corrosion product particles suspended in the water as yet, there is no detailed knowledge on the chemical state of these elements (i. e., adsorbed to the surfaces or incorporated into the Fe203 lattice). It was reported that the strontium isotopes as well as Np appear in the reactor water in the dissolved cationic state, while Tc was found in the reactor water as a dissolved anionic species, most likely Tc04 (Lin and Holloway, 1972). According to James (1988), discrete fuel particles were not detected in the BWR reactor water. 

Of the a-emitting nuclides, Cm represents more than 95% of the total a activity, with the combined plutonium isotopes 238, 239 and 240 accounting for the remainder. The relative activity proportions of these nuclides in the water as well as those of other insoluble fission products such as Zr, Ce and ° Ru are the same as in the fuel. 

The threshold reaction contributions to the total fission rate can be assumed small for the AGN-201 reactor, since its moderator-to-uranium volume ratio is appreciable and its fuel is enriched with the isotope. Very fast fission is normally accounted for in the four-factor formula by the factor e, the number of neutrons produced by all fissions divided by the number produced by thermal fission. In the AGN-201, nonthermal fission is predominately resonance fission, since has finite fission cross sections at all energies. The amount of epithermal fission can be determined by a simple cadmium-ratio measurement of AGN-201-type fuel. The fission product activity of a bare and cadmium-covered fuel sample can be counted on a proportional counter after two similar irradiations in the reactor core. Their ratio will yield the amount of nonthermal fission to total fission after proper corrections for differences of sample weight, irradiation times, and, power level have been made. The final expression for power level then becomes, . . f... 

Working with gold, Sachtler and Fahrenfort (23) studied the distributions of the hydrogen isotopes in the decomposition products of HCOOD in mixtures with HCOOH. At 150°C and at different HCOOH/ HCOOD ratios, the three molecular hydrogen isotopes are formed in their equilibrium proportions. As under the same conditions HCOOH did not exchange with D2, and no H2 - D2 exchange occurred, the authors concluded that the equilibrium mixture is formed as a primary product. This means that the equilibrium must be reached while the hydrogen is still in the atomic form on the metal surface, which points to an independent fission of the H atoms from the molecule. 

It is convenient to consider the production rate of Xe by the various routes, and scale the yield of the other Kr and Xe fissiogenic isotopes to this product (Table 7). Xe production by spontaneous fission in the crust is directly proportional to the concentration. has a branched decay mode, producing " Th by a-decay with Xa = (Steiger and Jager 1977), and spontaneous fission producing amongst... 

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