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Tobin, Stephen Joseph

Publications and source records attributed to Tobin, Stephen Joseph.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Conceptual Design of Passive Neutron Albedo Reactivity and Active Neutron Albedo Reactivity Instruments for Various Arrangements of Pebble Bed Reactor Pebbles

MCNP6 simulations were performed to assess the anticipated capability of the Passive Neutron Albedo Reactivity technique for nuclear safeguards measurements of irradiated pebble/pebbles. Two physical setups were examined. One with a single pebble of three different burnups and one with 27 pebbles in a cube. For all cases the sensitivity to removing all the fissile material was examined. For both of the physical setups, 4 assay cases were examined: (a) singles count rates for which the only source neutrons were the inherent neutrons in the fuel, (b) singles count rates again except this time two relatively weak AmLi sources were placed above and below the top central pebble and the combined effect of both neutron source terms were examined, (c) doubles count rates for which the only source neutrons were the inherent neutrons in the fuel, and (d) doubles count rates again except this time two relatively weak AmLi sources were placed above and below the top central pebble and the combined effect of both neutron source terms were examined. Finally, a few parameters such as Cd near the 3 He tubes were perturbed to see if the results could be improved.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Passive methods for spent fuel characterisation at the Finnish geological repository

Development of the Passive Gamma Emission Tomography (PGET) and Passive Neutron Albedo Reactivity (PNAR) methods in the context of the Finnish geological repository for spent nuclear fuel has shown that they provide, for BWR fuel assemblies, the comprehensive verification needed to meet the nuclear safeguards objectives of the repository. The principles of the PGET and PNAR methods and the design and operation of the respective instruments are presented. A few results from measurements at the spent fuel storage pools at the Finnish nuclear power plants are discussed. The directions of ongoing and future developments are indicated.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2021

Reduction of bright exciton lifetimes by radiation-induced disorder

Quantum-radiative decay is a fundamental process in many optoelectronic systems such as laser diodes and solar cells. The bright exciton lifetime is a critical factor in determining the performance of these systems. Motivated by the ever-increasing need for laser systems in space and nuclear applications, we develop a many-particle approach to predict the radiative lifetime under harsh radiation environments. Here, using GaAs as a model system, we find that radiation-induced band tailing reduces the bright exciton lifetime. This result shows that the efficiency of radiative recombination, in addition to nonradiative recombination, can be affected by ionization radiation. Our approach enables a detailed understanding of the interplay between correlation, localization, and radiation that affect the performance of gain media.

36 MATERIALS SCIENCE↗
DOE OSTI2019

PNAR Measurement Report

STUK performed an NDA inspection at the spent fuel interim storage facility at Olkiluoto NPP during 22.7-26.7.2019. The inspection was also attended by experts from US DOELANL, Helsinki Institute of Physics, Euratom and IAEA and was made possible by the operators from TVO. The inspection included fuel verification with STUK’s new PNAR instrument and IAEA’s PGET. Simultaneous measurements were made possible with a support quadropod common for both instruments. The inspection and the results of the PGET verification are described in separate memorandums. This report focuses on the results of the PNAR verification. The inspection was the very first one performed with STUK’s PNAR instrument. Thus, the main goal of the inspection from the PNAR point-of-view was to demonstrate that the PNAR method works in practice, identify possible improvements and assess if PNAR can be utilized in SNF verification. Furthermore, the measurement campaign was an initial step in exploring the fuel parameter range where PNAR could be used and an initial investigation into quantifying the uncertainties of the system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗