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Poster excerpt 17: Detecting Geoneutrinos and reactor antineutrinos in the world

March 5, 2015

(The following text has been submitted by M.Baldoncini)

In this study we estimate the reactor antineutrino signal all over the world, based on official reactor operational records published by the Power Reactor Information System (PRIS) of the International Atomic Energy Agency (IAEA). The website  www.fe.infn.it/antineutrino  collects all the information necessary for the evaluation of the expected reactor signal over the last 10 years in every location in the world. A database containing official operational data of commercial nuclear power plants is compiled separately for each year starting from 2003 up to now, and can be freely downloaded together with the worldwide numerical and image signal maps.

Neutrino experiments are investigating neutrino properties at different wavelengths according to different reactor-detector baselines, as well as shedding light on the Earth’s interior via the detection of geoneutrinos. For a  better discrimination among different compositional models of the Bulk Silicate Earth, new measurements of geoneutrino fluxes are highly awaited from experiments entering operation (SNO+), under construction (JUNO) and proposed to the scientific community (RENO-50, LENA, Hanohano, Homestake). As the reactor antineutrino energy spectrum extends beyond the endpoint of the geoneutrino one, nuclear power plants emerge as the most severe background sources in geoneutrino measurements.

A Monte Carlo based approach provides a combined 1s uncertainty of approximately 3% in the entire reactor spectrum energy region and of approximately 4% in the geoneutrino energy window. A comparison of the reactor signals obtained using different reactor spectra reveals that the uncertainty related to the antineutrino spectrum is as critical as the combined uncertainty of the other input quantities.

A 2.4% systematic enhancement of the unoscillated inverse beta decay event rate in the  geoneutrino energy window is estimated to be caused on average by the spent nuclear fuels. Research reactors, accounting for total thermal power of 2.2 GW, contribute less than 0.2% to the commercial reactor signal in the investigated sites.

Figure 1 illustrates the reactor signal at Borexino and KamLAND over a time lapse of 10 years. Borexino exhibits a periodic seasonal signal variation as it is relatively insensitive to the operational conditions of single cores, while the KamLAND signal time profile is governed by the Japanese nuclear industry operational status, which makes the shutdown of nuclear power plants concomitant to strong earthquakes manifestly visible.

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Figure 1:Reactor signals in the entire energy spectrum  for the KamLAND experiment (blue panel) and for the Borexino experiment (red panel), calculated from January 2003 to December 2013 on a monthly timeline. The vertical dashed lines indicate the data taking start of the experiments (March 2003 for KamLAND and May 2007 for Borexino).

Figure 2 represents the location map, produced according to the 2013 reactor operational status, illustrating the percentage contributions to the signal given by the close-by reactors for the three long baseline experiments KamLAND, Borexino and SNO+ and for the proposed medium baseline experiments JUNO and RENO-50.

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Figure 2:Location map of the percentage contributions to the reactor signal given by the close-by reactors for the three long baseline experiments KamLAND, Borexino and SNO+ and for the proposed medium baseline experiments Juno and RENO-50. The map is produced with 2013 reactor operational data.

This study refers to the paper http://arxiv.org/pdf/1411.6475v2 , currently accepted for publication in Physical Review D.

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