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Bacteria found to reduce uranium mobility in clay
Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) research laboratory in Germany have investigated a microorganism capable of transforming water-soluble hexavalent uranium [U(VI)] to the less-mobile tetravalent uranium [U(IV)]. The researchers found that the sulfate-reducing bacterium Desulfosporosinus hippei, a relative of naturally occurring microorganisms present in clay rock and bentonite, showed a relatively fast removal of uranium from clay pore water.
Taro Ueki
Nuclear Science and Engineering | Volume 141 | Number 2 | June 2002 | Pages 101-110
Technical Paper | doi.org/10.13182/NSE141-101
Articles are hosted by Taylor and Francis Online.
This paper investigates intergenerational correlation in the Monte Carlo k-eigenvalue calculation of a neutron effective multiplicative factor. To this end, the exponential transform for path stretching has been applied to large fissionable media with localized highly multiplying regions because in such media an exponentially decaying shape is a rough representation of the importance of source particles. The numerical results show that the difference between real and apparent variances virtually vanishes for an appropriate value of the exponential transform parameter. This indicates that the intergenerational correlation of k-eigenvalue samples could be eliminated by the adjoint biasing of particle transport. The relation between the biasing of particle transport and the intergenerational correlation is therefore investigated in the framework of collision estimators, and the following conclusion has been obtained: Within the leading order approximation with respect to the number of histories per generation, the intergenerational correlation vanishes when immediate importance is constant, and the immediate importance under simulation can be made constant by the biasing of particle transport with a function adjoint to the source neutron's distribution, i.e., the importance over all future generations.