The neutron generator for producing neutrons with 14 MeV (fusion spectrum).

Type: NSD-350-24-DT-C-W-S (type "sealed tube" largest in Europe).

Neutron Generator (LNG) Laboratory

The LNG is located in the LR-0 research reactor facility annex. LNG organizationally includes two laboratories: LNG (with a neutron generator) and LCF (with an isotopic neutron source Cf-252).

Location

The LNG is in a 10x8x7m space (m101) that is massively shielded. The thickness of the reinforced concrete walls reaches up to 150 cm, the thickness of the sandwich floor (reinforced concrete, iron, polyethylene, reinforced concrete) up to 1 m. Part of the NG operation is a shielded operator's room with control equipment and space for placing experimental apparatus.

LNG is equipped with a CISRK dosimetric control system, ensuring its safe operation.

Principle of NG function

A neutron generator is a device that produces neutrons with an energy of 14.1 MeV resulting from the fusion of light nuclei of hydrogen isotopes deuterium and tritium. Neutrons are emitted from a reaction chamber with a fusion emission zone with a volume of approx. 5 liters (ø 70 x 350 mm). During NG operation, D and T in the gaseous state are obtained by heating the reservoir to a temperature of 460 to 650 °C. The emission of 14.1 MeV neutrons is controllable by a combination of changing the high voltage, the storage temperature and the cooling rate in the range of up to approx. 1.108 neutrons/s. The accompanying emission of photons can be suppressed by placing lead rings outside the NG reaction chamber. The neutron generator can be operated in continuous or pulse mode. The thermal power loss in continuous mode at maximum emission is approx. 24 kW (currently 8-10 kW in real terms). The neutron tube itself therefore requires external cooling of adequate power. The lifetime of the D-T cartridge at maximum neutron emission is more than 10,000 hours. The operation of the NG can be operatively adapted to the needs of the experiments.

Focus of the LNG laboratory

LNG focuses on the validation of nuclear data libraries in the area of fusion research. Therefore, neutron and gamma escape spectra are measured in LNG and comparisons of calculations (Monte Carlo methods using various nuclear data libraries) with experiment (determination of the C/E ratio) are performed.

Technical details

New source of neutrons with energy of 14.1 MeV (manufacturer GRADEL Luxembourg) was installed in November 2015 in the Neutron Generator Laboratory of the Research Centre Rez in the frame of the project SUSEN. The NG is of "sealed tube" type, where the neutrons are emitted from the reaction chamber with fusion emission zone of the length of 350 mm with a volume of about 5 dm3 by D-T reaction. Deuterium and tritium with a total activity of 800 GBq at room temperature are permanently trapped in the "getter" located at the input of the reaction chamber. Deuterium and tritium released into the reaction chamber are lead to the gaseous state by heating it to a temperature of 460-560 °C. Positive ions of deuterium and tritium (D + and T +) are accelerated towards the central molybdenum cathode by potential difference up to 160 kV. The required neutrons are generated in reaction D + T → 4He + n (Q = 17.6 MeV). Beside that, also neutrons with a energy of 2.5 MeV are emitted from reaction D + D → 3He + n (Q = 3.27 MeV ). The ratio of neutrons from the reaction of D-D and D-T 1:50. Neutron emission is adjustable by combining the high voltage changes, temperature of the “getter” and current in the range of 1.108 to 1.1010 sec-1. Gamma “brems-strahlung” is reduced by using the lead cylinders with thickness about 0.5 cm slipped on NG tube. Neutron generator can be operated in continuous or pulsed mode (macro-pulses). The heat dissipation in continuous mode at maximum emission is about 24 kW, therefore the neutron tube requires an external cooling of adequate performance. Lifetime of D-T load at maximum neutron emission is declared by the manufacturer more than 10,000 hours. Operation of NG can be flexibly adapted to the needs of any type of experiments.