Study into the dependence of the Co-60 and Lu-177g production efficiency on the energy structure of neutron flux density

At present, the existing approaches to production of artificial isotopes are mostly based on the development experience from previous years. This work aims to develop an algorithm for selecting the most effective irradiation modes for target materials. The study is based on sequential modeling of irradiation of target isotopes by neutrons of different ‘single-group’ fluxes at the same neutron flux density within each energy group (BNAB-93). In this study, a flux density equal to 2×1015 n/(cm2×s) was used for each energy group. This approach will help ‘designing’ and selecting the actual neutron spectrum that has the highest efficiency compared to alternatives. The study modelled Co-60 and Lu-177g production for each energy group. The kinetics was analyzed in the most efficient groups in terms of specific activity. The maximum specific activity for Co-60 is reached in group 17 and is equal to 1 kCi/g. For the scheme of Lu-177g production through Lu-176 the maximum specific activity is reached in group 26 and is equal to 58.5 kCi/g. For the scheme of Lu-177g production through Yb-176, the maximum specific activity is reached in group 17 and is equal to 260 Ci/g, advantageous for production are groups 15–17 and 26

Assessment of the neutron flux stability in a high power BN-type reactor in terms of modal spatial kinetics

The article discusses the neutron flux stability in the core of a high-power sodium-cooled fast reactor (of the BN-type) without feedbacks. The importance of this problem for high-power BN-type reactors is associated with the specific features of the layout of their cores, including a large diameter and height/diameter ratio about 5. The technique used to substantiate the stability of neutron fields is based on the analysis of the spectrum of the matrix of the system of spatial kinetics equations describing the core of a high-power BN-type reactor without feedbacks. A computational model of the spatial kinetics of a high-power BN-type reactor has been developed in the modal approximation based on the representation of an unsteady flux as a sum of orthogonal functions multiplied by time-dependent amplitudes. The eigenfunctions of the conditionally critical problem are used in the diffusion approximation, which in the discrete case form a complete system. The spectrum of the matrix of the system of ordinary differential equations describing the spatial kinetics of the reactor has been calculated. It is shown that the neutron flux in the core of a high-power BN-type reactor without feedbacks is stable. Test calculations have illustrated the damping of perturbations of the power distribution for a reactor in a critical state

Reactivity Coefficients in BN-600 Core with Minor Actinides

International audienceIn 1999, the IAEA has initiated a Coordinated Research Project on ‘‘Updated Codes and Methods toReduce the Calculational Uncertainties of the LMFR Reactivity Effects.’’ Three benchmark modelsrepresenting different modifications of the BN-600 fast reactor have been sequentially established andanalyzed, including a hybrid core with highly enriched uranium oxide and MOX fuel, a full MOX corewith weapons-grade plutonium, and a MOX core with plutonium and minor actinides coming from spentnuclear fuel. The paper describes studies for the latter MOX core model. The benchmark results includecore criticality at the beginning and end of the equilibrium fuel cycle, kinetics parameters, spatialdistributions of power, and reactivity coefficients obtained by employing different computation toolsand nuclear data. Sensitivity studies were performed to better understand in particular the influence ofvariations in different nuclear data libraries on the computed results. Transient simulations were done toinvestigate the consequences of employing a few different sets of power and reactivity coefficientdistributions on the system behavior. The obtained results are analyzed in the paper