Abstract
The assessment of fissile material mass is a key requirement to enhance radioactive waste management and to ensure a high level of safety in the nuclear industry. The assessment of plutonium fissile mass by passive coincidence measurements is usually obtained by detecting the neutrons generated by the spontaneous fissions of Pu isotopes. The detection and the quantification of a fissile mass in the radioactive waste can also be carried out using active neutron interrogation with a pulsed D-T neutron generator. The 14-MeV neutrons are moderated to induce fissions in the uranium and plutonium-contaminated waste. The emitted neutron signal can be analyzed by considering their detection time after the generator pulse. Data are measured according to the principles of the neutron measurement techniques. As proportional counters filled with 3He gas display high neutron detection efficiency and good gamma-ray immunity, they are the reference detector for passive neutron coincidence counting. A charge preamplifier or a current amplifier, depending on applications, collects the electric pulse produced by neutron interaction in the 3He gas, and a threshold discriminator produces a logic pulse used for neutron counting. This article describes the performance assessment of different commercially-available electronics from Mirion Technologies, Precision Data Technology (PDT), Mesytec, as well as MONACO electronics originally developed by CEA LIST for fission chamber measurements in experimental reactors. Comparative passive neutron measurements are carried out with these electronics at CEA/DEN Nuclear Measurement Laboratory in Cadarache. Overall, PDT and Mesytec electronics show similar detection efficiency as the ACH-NA98 charge amplifier, which is commonly used in our laboratory for such applications. However, MONACO electronics have a lower detection efficiency, similar to the Mirion 7820 current amplifier used in specific high-count rate applications. An optimization of MONACO settings would probably be necessary to adapt to 3He counters instead of fission chambers.
Highlights
The knowledge of the fissile material mass is a key challenge to enhance radioactive waste management and to ensure a high level of safety in nuclear industry.Proportional counters filled with 3He gas display high neutron detection efficiency and good gamma-ray discrimination
In the field of a technology survey, five electronics have been tested for passive neutron counting with 3He gas proportional counters and compared to 7820 current amplifier and ACHNA98 charge amplifier, both from Mirion technologies, which are commonly used at Nuclear Measurement Laboratory of CEA, DEN, Cadarache
The Precision Data Technology (PDT) and Mesytech devices lead to an equivalent detection efficiency to that of ACH-NA98 charge amplifier, which allows the best signal-to-noise ratio
Summary
The knowledge of the fissile material mass is a key challenge to enhance radioactive waste management and to ensure a high level of safety in nuclear industry. Proportional counters filled with 3He gas display high neutron detection efficiency and good gamma-ray discrimination. They are an obvious choice for neutron detection, especially for radioactive waste characterization [1]. Technologies, which have been widely qualified at the Nuclear Measurement Laboratory (LMN) of CEA/DEN in Cadarache , are used as reference electronics. The ACH-NA98 module allows the best performances in terms of detection efficiency, while 7820 amplifier is more robust in case of high-count rate and high gamma radiation level. The PDT10A and PDT10M+PDT12S modules from Precision Data Technology, as well as MRS2000-1 and MRS2000-2 amplifiers from Mesytec, have been compar]ed to our reference electronics. The first section describes the experimental setup, the detection system, and the electronics. The detector efficiency and dieaway time are determined for each configuration
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