Hoai-Nam Tran

Characterization of a neutron calibration field with 241Am−Be source using Bonner sphere spectrometer

This paper presents the characterization of a neutron calibration field of a 241Am-Be source using Bonner sphere spectrometer. The characterization of the neutron field in terms of neutron ambient dose equivalent, H*(10), rates and neutron flux spectra was performed using generalized-fit and semi-empirical fit methods together with an unfolding technique using the MAXED code. Monte Carlo simulations using MCNP5 have also been conducted to qualify the characterization process. Comparison of the neutron fluxes and the H*(10) rates obtained from the various methods shows that the components of the neutron fluxes are in good agreement with a discrepancy of about 2% while the discrepancy of the direct H*(10) rates is within 3%. This good agreement among the methods indicates the reliability of the characterization process for practical calibration of neutron measuring devices. The results also suggest that the calibration should be conducted at a distance less than 200cm to ensure the contribution of the scattered component in the reading of the device less than that of the direct component by 40%.

Enhancing neutron spectral results based on the combination of genetic algorithm and activation method

AbstractThe generated neutron spectrum from KIRAMS MC-50 cyclotron has been adjusted and enhanced by the combination of the genetic algorithm (GA) and activation foil methods. The activation rates were derived from the measurements of Shieldwerx activation foil using the ORTEC HPGe spectroscopy system and applying the GA method to return the adjusted spectral information. It is worth mentioning here that the result, which was successfully validated with the unfolding spectrum from STAY’SL PNNL code, is significant as it will be a referenced neutron spectrum for the experiments of the MC-50 cyclotron.

Evaluation of Gamma Contribution in a Neutron Calibration Field of 241Am−Be Source

The paper presents the evaluation of gamma contribution in a neutron calibration field of a 241Am-Be source. The characterization of gamma flux spectra and gamma ambient dose equivalent rates has been performed using a portable NaI(Tl) gamma spectrometer. For obtaining the gamma ambient dose equivalent rates from the measured spectra, two approaches were applied based on the applications of the G(E) function and the ICRP 74 conversion factors, respectively. Comparison of the gamma ambient dose equivalent rates obtained from the two approaches shows an agreement within 5%. The gamma contribution in the neutron calibration field is evaluated about 2.3-3.3% of the total neutron ambient dose equivalent rate in the distance range of 100-250cm.

Comparative Analysis of the Dalat Nuclear Research Reactor with HEU Fuel Using SRAC and MCNP5

Neutronics analysis has been performed for the 500 kW Dalat Nuclear Research Reactor loaded with highly enriched uranium fuel using the SRAC code system. The effective multiplication factors, keff, were analyzed for the core at criticality conditions and in two cases corresponding to the complete withdrawal and the full insertion of control rods. MCNP5 calculations were also conducted and compared to that obtained with the SRAC code. The results show that the difference of the keff values between the codes is within 55 pcm. Compared to the criticality conditions established in the experiments, the maximum differences of the keff values obtained from the SRAC and MCNP5 calculations are 119 pcm and 64 pcm, respectively. The radial and axial power peaking factors are 1.334 and 1.710, respectively, in the case of no control rod insertion. At the criticality condition these values become 1.445 and 1.832 when the control rods are partially inserted. Compared to MCNP5 calculations, the deviation of the relative power densities is less than 4% at the fuel bundles in the middle of the core, while the maximum deviation is about 7% appearing at some peripheral bundles. This agreement indicates the verification of the analysis models.