Calibration of CFUL01 fission chambers in the standard neutron fields of the BR1 reactor at SCK CEN

Recent subcritical VENUS-F experiments showed that fission chambers with a threshold deposit like U-238 can essentially improve the on-line sub-criticality measurments with the beam interruption method, which is currently supposed to be the main method for the ADS MYRRHA. To suppress the uncertainty caused by fissions in the U-235 impurities, the fraction of U-235 in the U deposit should be accurately known. Three PHOTONIS CFUL01 type fission chambers with U-238 deposit were purchased for sub-critical experiments in the VENUS-F reactor. To verify the purity of their deposits, the effective U-235 masses were measured in the empty cavity of the BR1 reactor with a well-known thermal neutron spectrum. It turned out that the measured effective U-235 mass in two fission chambers is lower than the declared mass (as it should be), but this is not the case for the third fission chamber. Then, the effective U-238 mass in these FCs was measured in the well-known fast spectrum of the MARK-III convertor in the BR1 reactor. Finally, the isotopic composition was obtained and it was found that the purity of two CFUL01 FCs is in agreement with the values declared in the certificates but it is not the case for the third fission chamber. As the length of the deposit is bigger than the length of the MARK-III convertor, necessary corrections were calculated with MCNP. The developed procedure using the BR1 standard irradiation fields can be applied for calibration and impurity determination of large fission chambers.

Measurement of temperature-dependent thermal neutron spectrum in CaH2 moderator material for space reactor

In order to accurately design a CaH2 moderated small high-temperature reactor, it is necessary to experimentally confirm the temperature-dependent thermal neutron spectrum in the CaH2 moderator material. To obtain the temperature-dependent thermal neutron spectrum in the CaH2, we have carried out the neutron scattering experiment using the TOF method at the Kyoto University Institute for Integrated Radiation and Nuclear Science - Linear Accelerator (KURNS-LINAC). In present experiment, we raised the temperature of the CaH2 from a room temperature 294 k to 392 K and 565 K, and obtained the change of the thermal neutron TOF spectrum for the increase of temperature. The obtained thermal neutron TOF spectra in the CaH2 are compared with the calculated results using the Monte-Carlo simulation code MCNP-6.2.

Development of a Setup for Material Identification Based on Laser-Driven Neutron Resonance Spectroscopy

With the phasing out of many research reactors over the upcoming years, a shortcoming of small and medium sized neutron sources is to be expected. Laser-driven neutron sources have the potential to fill this void, with enormous progress being made in laser technology over the past years. Upcoming petawatt lasers with high repetition rates up to 10 Hz promise a tremendous increase in neutron flux. In this paper, a setup is developed and optimized to conduct neutron resonance spectroscopy at a laser-driven neutron source. This setup is then evaluated at an experimental campaign at the PHELIX laser system. Laser intensities up to 1021 W/cm² with a ns pre-pulse contrast of 10-7 were used for ion acceleration, resulting in (1.8±0.7)×108 N/sr per pulse corresponding to (2.3±1.0)×109 N in a 4 π equivalent. These pulses were moderated, collimated and investigated via the time of flight method in order to characterize the thermal neutron spectrum as well as the signal to noise ratio.

Nuclear instrumentation in VENUS-F

VENUS-F is a fast zero power reactor with 30 wt% U fuel and Pb/Bi as a coolant simulator. Depending on the experimental configuration, various neutron spectra (fast, epithermal, and thermal islands) are present. This paper gives a review of the nuclear instrumentation that is applied for reactor control and in a large variety of physics experiments. Activation foils and fission chambers are used to measure spatial neutron flux profiles, spectrum indices, reactivity effects (with positive period and compensation method or the MSM method) and kinetic parameters (with the Rossi-alpha method). Fission chamber calibrations are performed in the standard irradiation fields of the BR1 reactor (prompt fission neutron spectrum and Maxwellian thermal neutron spectrum).

Reactor Thermal Neutron Spectrum Measurement with Time of Flight Method

The basic principle of neutron spectrum measured with time of flight method was simply introduced. The design of the experimental system for the time of flight spectrum detected in the thermal column of the reactor was offered. The most probable neutron energy of the measured thermal neutron was about 0.0248±0.0007eV, and the spectrum average energy was 0.042±0.001eV. The results showed that the measured spectrum was softer than thermal Maxwellian theory spectrum.