<p>Neutrino emission from nuclear reactors provides real-time insights into reactor power and fuel evolution, with potential applications in monitoring and nuclear safeguards. Following reactor shutdown, a low-intensity flux of “residual neutrinos” persists due to the decay of long-lived fission isotopes in the partially burnt fuel remaining within the reactor cores and in spent nuclear fuel stored in nearby cooling pools. The Double Chooz experiment at the Chooz B nuclear power plant in France achieved the first quantitative measurement of this residual flux based on 17.2 days of reactor-off data. In the energy range where the residual signal is most pronounced, the neutrino detector located 400 m from the cores recorded <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>106</mn><mo>±</mo><mn>18</mn></math> neutrino candidate events (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>5.9</mn><mi>σ</mi></mrow></math> significance). This measurement is in excellent agreement with the predicted value of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>88</mn><mo>±</mo><mn>7</mn></math> events derived from detailed reactor simulations modeling the decay activities of fission products and incorporating the best-available models of neutrino spectra.</p>

Brazil

T. Abrahão

Germany

H. Almazan

J.C. dos Anjos

S. Appel

France

J.C. Barriere

I. Bekman

T.J.C. Bezerra

L. Bezrukov

United States

E. Blucher

C. Bourgeois

C. Buck

J. Busenitz

A. Cabrera

Spain

M. Cerrada

E. Chauveau

P. Chimenti

O. Corpace

J.V. Dawson

J.F. Du

Z. Djurcic

A. Etenko

Japan

H. Furuta

I. Gil-Botella

A. Givaudan

H. Gomez

M.C. Goodman

T. Hara

J. Haser

D. Hellwig

A. Hourlier

M. Ishitsuka

J. Jochum

C. Jollet

K. Kale

M. Kaneda

M. Karakac

T. Kawasaki

E. Kemp

D. Kryn

M. Kuze

T. Lachenmaier

C.E. Lane

T. Lasserre

D. Lhuillier

H.P. Lima

M. Lindner

J.M. LoSecco

B. Lubsandorzhiev

J. Maeda

C. Mariani

J. Maricic

J. Martino

T. Matsubara

G. Mention

A. Meregaglia

T. Miletic

R. Milincic

A. Minotti

X. Mougeot

D. Navas-Nicolás

Y. Nikitenko

P. Novella

L. Oberauer

M. Obolensky

A. Onillon

A. Oralbaev

C. Palomares

I.M. Pepe

L. Perisse

G. Pronost

J. Reichenbacher

S. Schönert

S. Schoppmann

L. Scola

R. Sharankova

V. Sibille

V. Sinev

M. Skorokhvatov

P. Soldin

A. Stahl

I. Stancu

M.R. Stock

L.F.F. Stokes

F. Suekane

S. Sukhotin

T. Sumiyoshi

C. Veyssiere

B. Viaud

M. Vivier

S. Wagner

C. Wiebusch

G. Yang

F. Yermia

First Measurement of Neutrino Emissions from Spent Nuclear Fuel by the Double Chooz Experiment

The oscillation results published by the Double Chooz Collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle θ13 by including 7.53 days of reactor-off data. A global fit of the observed antineutrino rates for different reactor power conditions is performed, yielding a measurement of both θ13 and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields sin2(2θ13)=0.102±0.028(stat.)±0.033(syst.) . The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of θ13 that does not depend on a background model.