Analysis of radioactive waste streams via neutron monitoring techniques

Neutron monitoring techniques can be used for analyzing a variety of problems in high-radiation areas in reprocessing plants. (1) Hafnium monitors. Hafnium sieve plates are used in pulsed extraction columns in the Purex process in reprocessing plants to accomplish a thorough mixing of the aqueous and organic phases and simultaneously as heterogeneous neutron absorbers to prevent the solutions from becoming inadvertently critical. In such a high radiation area the presence and intactness of these hafnium plates can be easily monitored by neutron-transmission measurements. (2) Accumulation monitor. Pu-accumulations on the sieve plates of a pulsed extraction column have to be continuously monitored in order to avoid any criticality problems. This monitoring can be accomplished by passive neutron measurements of spontaneous fission neutrons originating from ( ,n) nuclear reactions. (3) Concentration monitor for fissile material in solutions. Since a distinct correlation exists between the epithermal neutron flux multiplication factor and the concentration of fissile material even in the presence of neutron poisons the measurement of the former parameter allows the determination of the amount of fissile material present. Details of the techniques, their applicability, advantages and disadvantages are discussed