Clad failure detection system based on Delayed Neutron Detection without photoneutron noise for Sodium-cooled fast reactors

E. Rohée (1) , R. Coulon (1) , C. Jammes (2) , S. Normand (1) , F. Carrel (1) , F. Laine (1) , H. Hamrita (1) , P. Filliatre (2)

1 LCAE (CEA, LIST) - Laboratoire Capteurs et Architectures Electroniques (CEA, LIST)
2 LDCI - Laboratoire de Dosimétrie, de Contrôle-commande et Instrumentation

In the context of failed fuel detection in Sodium-cooled Fast Reactors (SFR), Delayed Neutrons Detection (DND) systems are implemented. This study deals with the design optimization of such a system by Monte-Carlo particle transport simulation (MCNP). During a clad failure, neutron precursor fission products (mainly halogen ones: 137 I, 87 Br, 88 Br) escape into the primary coolant. The detection of these precursors through their delayed neutrons ensures a diagnosis on clad failures events. In DND systems, 3 He proportional counters are chosen as the best available technology for neutron detection purposes. Associated with 3 He counters, polyethylene blankets are required in order to thermalize neutrons. Feedbacks from past SFR have shown an important noise coming from photoneutrons mitigating the signal-to-noise ratio. These photoneutrons originate from the 2 D(γ,n) reaction in polyethylene (in natural abundance) and is due to the 24 Na activity. Another material avoiding photoneutrons production is considered in this paper as moderator. Indeed, the graphite appears as a good candidate, sufficiently light for neutron thermalization and with a C(γ,n) reaction threshold higher than energies considered here. The first simulations run with MCNPX code provide satisfactory results for a low-noise DND system based on graphite thermalizing.

Mots clés: Fast reactor; Sodium; Fission products; fission reactor fuel claddings; fission reactor instrumentation; liquid metal fast breeder reactors; Monte Carlo methods; sodium-cooled fast reactor; delayed neutron detection; photoneutron noise; clad failure detection system; SFR; DND; Monte-Carlo particle transport simulation; MCNP; clad failure; neutron precursor; fission product; 3He proportional counter; polyethylene blankets; neutron detection; signal-to-noise ratio; 2D(gamma; n); neutron thermalization; MCNPX code; low-noise DND system; graphite thermalization; fuel detection

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Applications [stat.AP]; Instrumentations et Détecteurs [physics.ins-det]; Radiochimie

E. Rohée, R. Coulon, C. Jammes, S. Normand, F. Carrel, et al.. Clad failure detection system based on Delayed Neutron Detection without photoneutron noise for Sodium-cooled fast reactors. 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), Nov 2014, Seattle, United States. pp.7431098, ⟨10.1109/NSSMIC.2014.7431098⟩. ⟨cea-01887897⟩