Nuclear Science and Technology

Based on the data set about radionuclides concentration in foods and foodstuffs obtained from the implementation of the National Projects on “Investigation on radionuclides and toxic elements concentration in the main kinds of foods & foodstuffs of Vietnam” and “Assessment of Marine Environmental Radioactivity Status for two selected sites of Nuclear Power Plant in the near future at Ninh Thuan Province”, a calculation software of the International Commission for Radiological Protection (ICRP), the public committed effective doses (for adult only) caused by consumption of main foods & foodstuffs in the studied experimental region were estimated. In general, the committed effective doses for adult public caused by the daily intake of radionuclides of U, 232Th, 210Pb, 210Po, 226Ra,  40K, 90Sr, 137Cs and 239,240Pu are:  7.9´10-5, 4.1´10-6, 1.1´10-2, 1.7´10-1, 1.4´10-3, 1.2´10-1, 2.32´10-4, 1.9´10-4, 2.7´10-9 (mSv/year), respectively, and the contribution of U, Th series, 40K and artificial radionuclides are 61.3%, 38.6% and 0.1%, respectively.

Slow Positron Beam (PB) is an important device in the study of positron physics and techniques, especially in material research. For the purpose of conceptual designing a PB system, we have simulated a PB system with the parameters of an existing system – SPONSOR, using SIMION software. The simulation results have been compared with the SPONSOR published results. The effect of magnetic field in controlling beam trajectory has been investigated in the preaccelerated and accelerated stages. The simulation results of using steering coils to adjust the beam trajectory are also presented in this report.

In this work, the influences of the soil densities and the radionuclide depth distributions (RDD) on the Full Energy Peak Efficiency (FEPE) calculation of the in-situ gamma ray spectrometer using the In Situ Object Counting Systems (ISOCS) software were studied. The data of the RDDs at the sites were investigated by using laboratory HPGe gamma spectrometer. Six different RDDs of 40K, 226Ra and 232Th were found at four studied sites with radionuclide deposition moving from surface to deeper positions. The results show that FEPE values vary strongly for the different RDDs, especially for the low gamma ray energies. Use of the uniform model for calculating FEPEs can result in noticeable errors from 29% to 101% for the realistic RDD of the exponential form (surfaceradionuclide deposition), negative variations from 14% to 30% for the realistic RDD of having a radionuclide deposition at the 30 cm depth, and negligible variations of less than 5 % for the realistic RDD of quasi uniform form in the range of gamma ray energies of interest.

This paper presents an application of a genetic algorithm (GA) to the fuel reload optimization for a research reactor. In this work, a model of the problem and a new coding procedure for the GA to automatically search for optimal fuel loading patterns most suitable for the research reactor is proposed. The objective function maximizes the effective multiplication factor and minimizes the power peaking factor. The GA works with an elitist selection based on the elitism strategy and the roulette wheel spin method, a modified one-point crossover and a simple mutation.  Results from illustrative calculations for the Dalat research reactor show that the GA can successfully search for the optimal loading patterns, which can be employed in a practical refueling operation.

It is known that secondary cosmic rays are high energetic particles which are products of shower particles, when primary cosmic rays from outer space hit the atmosphere molecules. Many studies of cosmic rays show that cosmic flux depends on the depth of atmosphere. At ground level, most secondary cosmic rays are muons, a type of charged particle, and have angular dependence. The purpose of this article was to develop the telescope with the use of two plastic scintillation detectors, to investigate the angular distribution of cosmic rays at ground level. Measurements were carried out for vertical, 45-degree oblique and horizontal directions with respect to earth surface, approximately from North to South. Electronic readout system was built from a Flash Analog Digital Converter (Flash-ADC) of 8 bits-250Ms/sec, and Embedded Field Programmable Gate Array (FPGA)-based trigger. A computer interface was written on LabVIEWTM Platform for controlling system’s trigger and taking data. For each direction measurement, the energy spectrum in each scintillator detector was obtained. The interest of cosmic-ray events was analyzed for counting. Angular distribution was obtained quantitatively. The experiment has been done at University of Science-HCMC.

The particle identification (PID) method based on TOF-Bρ-ΔE measurement at RIKEN are discussed, and its application for Z = 25 – 28 neutron-rich nuclei from SEASTAR (Shell Evolution And Search for Two-plus energy At RIBF) experimental data are presented. The results including the PID for beam and residual nucleus at BigRIPS and ZeroDegree, respectively, demonstrate that the reactions of interest are well separated. This ensures the precision in the data analysis later on.

To acquire the existence of natural and artificial radionuclides in the main kinds of foods & foodstuffs samples is a necessary task for assessing the environment impact. For this reason, the Ministry of Science and Technology had approved a project on “Investigation on radionuclides and toxic elements concentration in the main kinds of foods & foodstuffs of Vietnam”. The paper focused on: Concentration of 40K, 210Pb, 210Po, 226Ra, U, Th, 90Sr, 137Cs, 239, 240Pu radionuclides in foods & foodstuffs samples collected from the Southern of Vietnam (Lam Dong, Ninh Thuan, Tien Giang, Can Tho and Tra Vinh Provinces and Ho Chi Minh City). About 1250 data of above mentioned radionuclides concentrations in 140 the samples collected at 6 selected sites are summarized and presented in this paper. In general, the levels of radionuclides in the samples are much lower as compared with the ICRP's Guidline levels.

Degradation of chitosan in swollen state with hydrogen peroxide solution (5% w/v) by γ-irradiation was investigated. Molecular weight (Mw) of irradiated chitosan was determined by gel permeation chromatography (GPC). Fourier transform infrared (FT-IR) and ultraviolet-visible (UVvis) spectrawere analyzed to study the structure changes of degraded chitosan. The results showed that the chitosan of low Mw ~30-45 kDawas efficiently prepared by γ-irradiation of chitosan swollen in hydrogen peroxide solution at low dose less than 20kGy. The main structure as well as the degree of deacetylation of the degraded chitosan was almost no significant change. Furthermore, the radiationdegradation yield (Gs) was remarkably enhanced by the presence of H2O2. The obtained low Mw chitosan revealed high antimicrobial activity for E. colithat can be used for food preservation and other purposes as well.

Radioactivities of some natural (Ra-226, Th-232, U-238, Po-210) and artificial (Cs-137, Sr-90 and Pu-239,240) radionuclides in coastal seawater at monitoring points of Ninh Thuan, Ba Ria - Vung Tau and Ca Mau provinces were analyzed quarterly in the year of 2018. Radioactivities of Ra-226, Th-232, U-238, and Cs-137 had been determined by simultaneous precipitation method and measured on low-level background gamma spectrometer; the radioactivities of Po-210 and Pu- 239,240 had been analyzed by radiochemical separation method and measured on alpha spectrometer; the radioactivity of Sr-90 had been analyzed by radiochemical separation method and measured on low-level background beta counting system. The ranges of radioactivities of Ra-226, Th-232, U-238, Po-210, Cs-137, Sr-90, and Pu-239,240 were 2.71 ÷ 15.91, 3.45 ÷ 35.93, 3.02 ÷ 21.47, 1.51÷ 6.74, 0.88 ÷ 1.68, 1.08 ÷ 1.86 and 0.0026 ÷ 0.0062 mBq/L, with the average values of 6.37, 12.67, 8.34, 3.29, 1.36, 1.46 and 0.0043 mBq/L, respectively. The results shown that the radioactivities of the above-mentioned radionuclides varied between the seawaters at Ninh Thuan, Ba Ria - Vung Tau and Ca Mau seawater. Additionally, physicochemical parameters in seawater were also surveyed to assess their impact on the fluctuations of the above radionuclides.

Sodium void worth and the Doppler coefficient, which are very important safety parameters in safety analysis of the KALIMER-600 TRU burner, should be carefully evaluated. A perturbation analysis for the TRU burner has thus been performed using the perturbation method, not only to make sure the reactivity feedbacks meet the predetermined design targets but also to obtain insight into the actual physical processes in response to severe coolant voiding accidents. The more detailedinformation on the actual physical phenomena that can be achieved, the more helpful it can be to the safety design and analysis of the TRU burner. Hence, a perturbation code, PERT-K, has been developed by the Korea Atomic Energy Research Institute based on the diffusion code, DIF3D,to allow reactivity effect breakdown calculations for fast reactor analysis. This paper presents recent updates on a perturbation analysis of the KALIMER-600 TRU burner using DIF3D and PERT-K. The currently developed isotope-wise reactivity module of PERT-K is described along with an analysis of the scenarios of whole core voiding and fuel temperature change in the TRU burner. The perturbation results are believed to be useful for further optimization of the passive safety characteristics of theTRU burner.