Reference worldwide model for antineutrinos from reactors

Antineutrinos produced at nuclear reactors constitute a severe source of background for the detection of geoneutrinos, which bring to the Earth’s surface information about natural radioactivity in the whole planet. In this framework, we provide a reference worldwide model for antineutrinos from reactors, in view of reactors operational records yearly published by the International Atomic Energy Agency. We evaluate the expected signal from commercial reactors for ongoing (KamLAND and Borexino), planned ($\mathrm{SNO}+$), and proposed (Juno, RENO-50, LENA, and Hanohano) experimental sites. Uncertainties related to reactor antineutrino production, propagation, and detection processes are estimated using a Monte Carlo-based approach, which provides an overall site-dependent uncertainty on the signal in the geoneutrino energy window on the order of 3%. We also implement the off-equilibrium correction to the reference reactor spectra associated with the long-lived isotopes, and we estimate a 2.4% increase of the unoscillated event rate in the geoneutrino energy window due to the storage of spent nuclear fuels in the cooling pools. We predict that the research reactors contribute to less than 0.2% to the commercial reactor signal in the investigated 14 sites. We perform a multitemporal analysis of the expected reactor signal over a time lapse of ten years using reactor operational records collected in a comprehensive database published at www.fe.infn.it/antineutrino.

Figure 1

A sketch of the expected reactor signal in the LER and in the HER. The reactor signal in the HER is crucial for modeling the reactor contribution in the LER and therefore for extracting information on geoneutrinos. The reactor contribution to the signal changes according to the different reactor operational conditions, while the geoneutrino component is time independent.

Figure 2

Map of the worldwide predicted antineutrino signals from nuclear power plants in the LER, expressed in TNUs. The map has a spatial resolution of $1^{\circ }\times 1^{\circ }$, and it is produced with 2013 operational data on nuclear power plants.

Figure 3

Reactor signals in the FER for the KL experiment (blue panel) and for the BX 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 KL and May 2007 for BX).

Figure 4

Reactor antineutrino spectra above the IBD threshold for the KL experiment (upper panel) and for the BX experiment (lower panel) calculated over different data-taking periods. KL spectra are evaluated over three peculiar time intervals, corresponding to a maximum, an average, and a minimum expected reactor signal (October 2005, December 2007, and April 2012, respectively). BX spectra are calculated in correspondence to a winter and a summer seasonal signal variation (January 2011 and June 2012). All the spectra are normalized to the signal corresponding to the specific month.

Figure 5

Cumulative percentage contribution to the total expected reactor signal as a function of the distance of the reactors from the experimental site for KL, BX, and $\mathrm{SNO}+$. Data refer to the 2013 reactor operational period.

Figure 6

Location map of the percentage contributions to the reactor signal given by the close-by reactors for the three long-baseline experiments KL, BX, and $\mathrm{SNO}+$ and for the proposed medium-baseline experiments Juno and RENO-50. The map is produced with 2013 reactor operational data.