Design of an advanced fork system for assembly burnup measurement

An Advanced Fork System has been designed to add gamma-ray collimation and spectroscopy capability to the Fork measurement system, which has been used for burnup verification at pressurized water reactors (PWR). The Advanced Fork System measures the neutron and gamma-ray yields and the energy spectnum of gamma-rays from spent fuel assemblies. A cadmium-zinc-telluride (CZT) crystal permits the identification of the radioactive isotopes of cesium (134 and 137). The cesium isotope concentrations, with proper calibration can be used to determine the assembly burnup independent of reactor records, and to provide a measure of minimum cooling time. Tungsten gamma-ray collimators are used to define the spatial resolution of the gamma-ray detectors along the axis of the assembly. The capability to rapidly perform a burnup distribution scan using the collimated ion chamber may be important to the verification of burnup for boiling water reactors (BWR)