A Preliminary Comparison of MCNP6 Delayed Neutron Emission from

A Description of the Experiment The DNC system at RMCC uses the SLOWPOKE-2 reactor [2] as a source of neutrons. Samples containing 235 U were prepared as acidified aqueous solutions from certified reference standards (natural U standard CRM 4321C, NIST, Gaithersburg, MD, and depleted U standard CRM U005A 0.5064 ± 0.0003 atom% U, New Brunswick Laboratory, Argonne, IL). Each solution was contained in heat sealed small polyethylene (PE) vials (LA Packaging, Yorba Linda, CA) with a nominal solution of 1 mL. To minimize the potential of solution leakage into the pneumatic tubing of the system, secondary containment was achieved using heat sealed 7 mL polyethylene vials (LA Packaging). By irradiating the inner and outer polyethylene vials without any fissile sample, the vials have been found to contain no impurities that contribute to the overall neutron count rate recorded by the DNC system [3]. Samples containing the fissile content were sent to an irradiation site inside the SLOWPOKE-2 beryllium reflector where they were exposed to a predominately thermal neutron spectrum of 5.6e11 cm -2 s -1 (±5%) for durations up to 60 s. After the samples were irradiated they were automatically sent, via pneumatic transfer system, to the neutron counting arrangement. This consisted of six 304 Stainless Steel (S.S.); Reuter Stokes 3 He detectors (RSP4-1613-202, GE Energy, Twinsburg, OH) embedded in a paraffin moderator. Samples were located at the center of the hexagonal detector array. A delay time of 3 s was employed to account for sample travel time from the irradiation site and the commencement of the delayed neutron count. Delayed neutrons were recorded as a function of time, in 0.5 s intervals.