On Using Code Emulators and Monte Carlo Estimation to Predict Assembly Attributes of Spent Fuel Assemblies for Safeguards Applications

Cadmium Subtraction Method for the Active Albedo Neutron Interrogation of Uranium

“…The difference between the detected neutron events for these two measurement conditions corresponds to the additional neutron events from fission induced by the thermal neutron albedo. The ability to use the LAWCC in a new mode using AANI has the field implementation benefit of enabling a Cd subtraction calibration curve to be determined for uranium mass, without the use of AmLi sources and with a counter of modest efficiency, i.e., without having to use an instrument with greater 3 He requirements or an overly complex instrument. In the experimental configuration as applied, collected data can also be used as a future extension of the ORNL-developed Direct Multiplication Measurement (DMM) technique [2].…”

“…Menlove and Beddingfield [1] were the first proponents of the method for safeguards neutron coincidence counting. Since then, the principle of a re-entrant neutron flux has been applied to safeguards neutron counting measurements, both total and correlated neutron counting, for two safeguards applications (spent nuclear fuel verification and UF 6 cylinder assay for mass and enrichment verification) and in three resulting safeguards technology NDA measurement systems supported by NGSI: Passive Neutron Albedo Reactivity with Fission Chambers (PNAR-FC) [3]; PNAR with 3 He gas-filled proportional counters (PNAR-3 He) (supported in the past but succeeded by Differential Die-away Self-Interrogation, or DDSI) [4,5]; and the Passive Neutron Enrichment Meter (PNEM) [6]. These techniques, with the exception of DDSI, all feature neutron measurements performed with and without Cd.…”

“…This principle can be applied for criticality safety and is used when safely storing multiplying items in close proximity, such as when storing spent nuclear fuel assemblies in poisoned racks under boronated water. The idea of using passive (or self, from Pu spontaneous fission (SF), Cm SF or, e.g., F(α,n) depending on the circumstances) neutron interrogation, or an external neutron driver, together with a change in the environment as a means to determine information of safeguards significance about an object has been discussed for a number of years [1,3,4,5,7,8]. One of the simplest ways to change the environment is to insert a slow (thermal and epi-thermal) neutron absorber, such as Cd, to block returning neutrons degraded in energy.…”

“…The LAWCC is the highest efficiency neutron well counter currently available at ORNL with a total neutron detection efficiency ~29% to a 252 Cf neutron energy spectrum, and die-away time of 70.6 µs [2]. This neutron detection efficiency is achieved by a total of 48 3 He gas-filled proportional tubes in the counter body (24 3 He tubes in the inner detector ring and 24 3 He tubes in the outer detector ring), each with a 1in. diameter and 4 atm fill-gas pressure.…”

Integration of facility modeling capabilities for nuclear nonproliferation analysis

“…This facilitates decision analysis and needs-based experimental planning. As an important aside, if the forward model is expensive or slow to run, then code emulation (Conlin et al, 2011) provides an effective shortcut that substitutes model approximations via the emulator for actual code runs inside the MCMC loop.…”