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• A new novel-1-step shutdown dose rate technique is described, and its features documented. • N1S method has been benchmarked against the FNG ITER shutdown dose rate experiment. • Results from the N1S method have been compared against other SDDR codes using the ITER code cross-comparison. • Future developments of the method are discussed. A new method for the calculation of Shutdown Dose Rates (SDDR) has been developed, the Novel-1-Step (N1S) method. The new method retains the benefits of only requiring a single radiation transport calculation, as in the use of the direct-1-step (D1S) method, while removing the need for pre-calculations to determine dominant nuclides and time correction factors. The N1S method uses a time dependent source and decay data for all nuclides. When reactions in the transport occur leading to unstable daughter nuclide, the correct contribution of photon radiation from all the decay products of a nuclide are calculated with no need for additional external activation calculations. Weights of these decay photons are calculated for each decay time of interest and are analytically determined based on the solutions to the Bateman equations. The N1S method has been implemented into MCNP and preliminary verification calculations performed. These calculations included the FNG ITER shutdown dose rate benchmark and the ITER SDDR cross comparison. For the FNG ITER SDDR benchmark the N1S method showed good agreement, within experimental error, for the first campaign apart from the first decay time where a C/E value of 1.34 was obtained. This overestimation was shown to be due to the decay of 64 Cu inside the copper cup of the neutron generator. For the second campaign the N1S method showed an under prediction of up to 20% at short decay times and an over prediction up to 20% at longer decay times. These times are dominated by 56 Mn and 58 Co respectively and it is likely the difference is due to under and over predictions in the reaction rates leading to these nuclides. The ITER cross comparison showed good agreement between the N1S method and MCR2S (and by association other D1S and R2S codes). Differences seen in the results were shown to be due to difference in the calculated reaction rates using EAF2010, TENDL2019 and FENDL3.2. [ABSTRACT FROM AUTHOR]

Fast neutron time-of-flight (ToF) has been used to characterise the location of a source of a mixed radiation field. Two EJ-309 organic scintillators and a fast, digital, data acquisition system have been used in a variety of positions to identify the location of a 252Cf neutron source inside a steel, water-filled tank. A methodology for extracting the distance between the neutron source and the neutron detector has been developed and verified with MCNP simulations. A reconstruction algorithm using the ToF data has been developed. The location of the neutron source has been estimated on this basis to be within 20 cm of its known location with a spatial resolution of ± 7.8 cm. p-values extracted from the null test hypothesis have been estimated to be 0.975 and 0.996 for experimental and simulation data, respectively. By correctly identifying the location of the source, the potential for the system to discern between scattered and unscattered neutrons is demonstrated. • Fast neutron time-of-flight data, derived from the separation of γ rays and neutrons emitted in spontaneous fission in 252Cf, have been used to identify the position of a 252Cf source. • Experimental data, derived with two organic scintillation detectors, have been compared with data from a parallel simulation-based study and are observed to converge with one another. • The technique appears to be resistant to perturbations by neutrons scattered by the surroundings. • The position of the source determined by time-of-flight agrees within uncertainties with the known source location. [ABSTRACT FROM AUTHOR]