Neutron dose near spent nuclear fuel and HAW after the 2007 ICRP recommendations

The ICRP has published in its 2007 recommendations new radiation weighting factors for neutrons to replace the values of the ICRP Publication 60 of 1990. Whereas the function of the neutron weighting factor does not change for energies above 1 MeV it decreases to about half of the former values for lower energies. In the present paper changes in the effective doses in mixed neutron gamma radiation fields near spent fuel assemblies and vitrified high level radio active waste (HAW) due to the new neutron weighting factors will be presented. These results are based on calculations of the radiation fields and of the effective doses in the vicinity of the mentioned radiation sources under free air conditions as well as outside of German transport and storage casks of CASTOR type loaded with these sources. The calculations have been made by means of the Monte Carlo Code MCNP for high and intermediate burn up of UO2-spent fuel, for MOX-spent fuel and for vitrified high active waste versus distance. The generation of neutrons was considered from spontaneous fission and from alpha capture and the gamma generation was considered from prompt emission and from neutron capture reactions. The results show that for practical applications the effective neutron dose decreases in the range of about 5 to 15 %. Taking into account the dominating contribution of the gamma dose compared to the neutron dose the influence of the new radiation weighting factors for neutrons to the total effective dose will be rather low. (author)