Development of a real-time detection strategy for process monitoring during nuclear fuel reprocessing using the UREX+3a method

Reprocessing nuclear fuel is becoming more viable in the United States due to the anticipated increase in construction of nuclear power plants, the growing stockpile of existing used nuclear fuel, and a public desire to reduce the amount of this fuel. A new reprocessing facility will likely have state of the art controls and monitoring methods to safeguard special nuclear materials, as well as to provide real-time monitoring for process control. The focus of this research was to create a proof of concept to enable the development of a detection strategy that uses well established gamma and neutron measurement methods to characterize samples from the Uranium Extraction Plus 3a (UREX+3a) reprocessing method using a variety of detector types and measurement times.A facility that implemented real-time gamma detection equipment could improve product quality control and provide additional benefits, such as waste volume reduction. In addition to the spectral analyses, it was determined by Monte Carlo N Particle (MCNP) simulations that there is no noticeable self-shielding for internal pipe diameters less than 5.08 cm, indicating that no self-shielding correction factors are needed. Further, it was determined that High Purity Germanium (HPGe) N-type detectors have the high gamma ray energy resolution and neutron damage resistance that would be required in a reprocessing facility. Finally, the gamma ray spectra for the measured samples were simulated using MCNP and then the model was extended to predict the responses from an actual reprocessing scenario from UREX+3a applied to fuel that had a decay time of 3 years. The 3-year decayed fuel was more representative of commercially reprocessed fuel than the acquired UREX+3a samples. It was determined that the 3-year decayed fuel is easier to apply real-time process monitoring due to an increased number of short lived detectable isotopes. This research found that real-time gamma ray detection for process monitoring would be beneficial to a reprocessing facility and that commercially available detectors may be adequate for the neutron environment.

Research highlights▶ HPGe detectors are suitable for UREX+3a real-time spectroscopy. ▶ HPGe N-type detectors may be suitable for a reprocessing facility. ▶ Gamma ray self-shielding does not occur for pipe diameters less than 2 in.