Neutron-gamma flux and dose calculations for feasibility study of DISCOMS instrumentation in case of severe accident in a GEN 3 reactor

Mariya Brovchenko,Isabelle Duhamel,Benjamin Dechenaux

doi:10.1051/epjconf/201715307030

Mariya Brovchenko, Isabelle Duhamel + Show 1 more

Open Access

https://doi.org/10.1051/epjconf/201715307030

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Abstract

The present paper presents the study carried out in the frame of the DISCOMS project, which stands for “DIstributed Sensing for COrium Monitoring and Safety”. This study concerns the calculation of the neutron and gamma radiations received by the considered instrumentation during the normal reactor operation as well as in case of a severe accident for the EPR reactor, outside the reactor pressure vessel and in the containment basemat. This paper summarizes the methods and hypotheses used for the particle transport simulation outside the vessel during normal reactor operation. The results of the simulations are then presented including the responses for distributed Optical Fiber Sensors (OFS), such as the gamma dose and the fast neutron fluence, and for Self Powered Neutron Detectors (SPNDs), namely the neutron and gamma spectra. Same responses are also evaluated for severe accident situations in order to design the SPNDs being sensitive to the both types of received neutron-gamma radiation. By contrast, fibers, involved as transducers in distributed OFS have to resist to the total radiation gamma dose and neutron fluence received during normal operation and the severe accident.

Highlights

At Fukushima Daiichi, the loss of electricity power supplies has quickly led most of instrumentation to be inoperative and the operator (TEPCO) with no way to monitor the status and the progress of the accident
To overcome these important drawbacks, the DISCOMS project [1], which stands for “DIstributed Sensing for COrium Monitoring and Safety”, considers taking advantage of the potential of distributed sensing technologies based on both “Optical Fiber Sensors” (Raman, Brillouin, and Rayleigh Reflectometry) and long-length “Self Powered Neutron Detectors” (SPNDs)
The radiation was characterized for a state during normal reactor operation and severe accident situation

Summary

Introduction

At Fukushima Daiichi, the loss of electricity power supplies has quickly led most of instrumentation to be inoperative and the operator (TEPCO) with no way to monitor the status and the progress of the accident To overcome these important drawbacks, the DISCOMS project [1], which stands for “DIstributed Sensing for COrium Monitoring and Safety”, considers taking advantage of the potential of distributed sensing technologies based on both “Optical Fiber Sensors” (Raman, Brillouin, and Rayleigh Reflectometry) and long-length “Self Powered Neutron Detectors” (SPNDs). The goal consists in inquiring about the status of the third barrier of confinement and to define possible mitigation strategies in case of severe accident, namely: i) reactor pressure vessel breakthrough and corium relocation outside the vessel, ii) concrete floor erosion and iii) corium cooling Such monitoring should consist in “sensing cables” inserted in basemat below the reactor vessel and interrogated from a rear base, where operators can work safely. The SPNDs need a sufficient level of radiation to generate a signal, and could be placed on the surface of the reactor pit

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