Abstract
The anti-neutrino source properties of a fission reactor are governed by the production and beta decay of the radionuclides present and the summation of their individual anti-neutrino spectra. The fission product radionuclide production changes during reactor operation and different fissioning species give rise to different product distributions. It is thus possible to determine some details of reactor operation, such as power, from the anti-neutrino emission to confirm safeguards records. Also according to some published calculations, it may be feasible to observe different anti-neutrino spectra depending on the fissile contents of the reactor fuel and thus determine the reactor's fissile material inventory during operation which could considerable improve safeguards. In mid-2014 the University of Liverpool deployed a prototype anti-neutrino detector at the Wylfa R1 station in Anglesey, United Kingdom based upon plastic scintillator technology developed for the T2K project. The deployment was used to develop the detector electronics and software until the reactor was finally shutdown in December 2015. To support the development of this detector technology for reactor monitoring and to understand its capabilities, the National Nuclear Laboratory modelled this graphite moderated and natural uranium fuelled reactor with existing codes used to support Magnox reactor operations and waste management. The 3D multi-physics code PANTHER was used to determine the individual powers of each fuel element (8×6152) during the year and a half period of monitoring based upon reactor records. The WIMS/TRAIL/FISPIN code route was then used to determine the radionuclide inventory of each nuclide on a daily basis in each element. These nuclide inventories were then used with the BTSPEC code to determine the anti-neutrino spectra and source strength using JEFF-3.1.1 data. Finally the anti-neutrino source from the reactor for each day during the year and a half of monitored reactor operation was calculated. The results of the preliminary calculations are shown and limitations in the methods and data discussed.
Highlights
THE anti-neutrinos emission from fission has been suggested as a way to monitor nuclear reactors for some time as they have extremely low rates of interaction with matter and are considered impossible to shield their emission from reactors
The experiment to calculation ratios for 235U, 238U, 239Pu and 241Pu are shown in figure 4. These results show quite good agreement with measured values for 235U and 239Pu above 3 MeV being within the one standard deviation uncertainties on the anti-neutrino spectra calculated from the fission product yield uncertainties
The initial result of this work has suggested that the FISPIN calculations used to generate inventories for all 49248 rods in the core during each day of reactor operation with irradiation/cooling history should give an estimate of the antineutrino flux and spectra to within 20%
Summary
THE anti-neutrinos emission from fission has been suggested as a way to monitor nuclear reactors for some time as they have extremely low rates of interaction with matter and are considered impossible to shield their emission from reactors. This extremely low interaction rate makes the detection of anti-neutrinos very difficult. Nuclear Safety on such sites requires that any equipment must not introduce risks to the reactor or its staff. The equipment should not introduce extra chemical, physical, fire or radiation risks, nor should it need to be incorporated into existing safety systems or have significant power requirements. To ensure that the equipment is useful it must be demonstrated that the detector can function on a nuclear site and that the reported information obtained from the detector be verified against plant records by carrying out experiments on well characterized reactors
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