Nuclear Science and Technology

Investigation of quenching phenomena during the relooding phase against the FLECHT-SEASET experiment by using RELAP5/MOD3.3

Thanh Tung Duong — 2024-09-23

The reflood model of RELAP5/MOD3.3 (patch 4) was assessed by using the FLECHT-SEASET tests. The tests were conducted to have a better understanding of the postulated loss of coolant accident in a light water reactor (LWR). The best-estimate system analysis code was used to simulate these accident scenarios, especially in Design Basic Accident such as Loss-Of-Coolant-Accident (LOCA). The primary purpose of this report was to assess the accuracy of a computer system analysis code by using RELAP5/MOD3.3 in comparison to actual test results taken from the FLECHT-SEASET tests in which the reflood model was built in. In RELAP5’s simulation cases, the various boundary and initial conditions, such as power supplied and reflooding rate were selected. As a result, the RELAP5 looked to be accurate in predicting the quenching time and rod surface temperature for this particular case. However, the RELAP5 code under-estimated the rod surface temperature in comparing with the experimental data of the FLECHT-SEASET tests. Accordingly, for this high flooding rate and particular reactor power level that the reflooding model in RELAP5 could be possible used for predicting the reflooding phenomena during the LOCA accident.

Unfolding method for surface activity density map reconstruction from ambient dose equivalent rate measurements based on solution of Fredholm equation of the 1st kind

Konstantin Chizhov — 2024-09-23

A mathematical method has been developed for determining surface activity density maps from ambient dose equivalent rate measurements on a site with buildings, taking into account the shielding effect of the buildings by using a visibility matrix. The relationship between surface activity density and ambient dose equivalent rate is described through the Fredholm equation of the 1^st kind and is numerically solved with a Tikhonov regularization. Use of the visibility matrix and raster cells made it possible to solve the Fredholm equations in barrier geometry to restore the density of the surface radionuclide contamination based on the ADER measurement. Method was used to restore locations of contamination with ¹³⁷Cs and its activities for the Andreeva Bay nuclear legacy site. The proposed method can be applied in the process of decontamination of radioactively contaminated territories, in particular during the remediation of the Andreeva Bay.

The investigation of ²³⁹⁺²⁴⁰Pu, ⁹⁰Sr and ¹³⁷Cs background radiation levels in soil samples in some provinces in the north of Vietnam

Van Khanh Nguyen — 2024-09-23

This study was carried out to investigate background levels of plutonium (^239+240Pu), strontium (⁹⁰Sr), and cesium (¹³⁷Cs) in the soil in some provinces in northern Vietnam. Thirty-one soil samples were collected from October 2020 to January 2022. These samples were analyzed by gamma spectrometry, alpha spectrometry, beta counting, and radiochemical separation procedures to quantify ¹³⁷Cs, ^239+240Pu, and ⁹⁰Sr radioactivities. The concentrations (Bq/kg dry weight) have been observed in the range of 0.768 – 2.129 for ¹³⁷Cs, 0.018 – 0.058 for ^239+240Pu, and 0.022 – 0.697 for ⁹⁰Sr, their average values are 1.393 ± 0.196, 0.039 ± 0.014 and 0.129 ± 0.011, respectively, which are relatively lower than the reported values in the neighboring country. The average recovery for radiochemical separation for ^239+240Pu and ⁹⁰Sr was 67.9 % and 60.2 %, respectively, the minimum detectable activity (MDA) (Bq/kg) for ¹³⁷Cs, ^239+240Pu, and ⁹⁰Sr are 0.012, 0.004, 0.1, respectively.

Simulation of gamma reference field at Institute for Nuclear Science and Technology using Monte Carlo method

Ky Bui Duc — 2024-09-23

This paper presents the characterization of two gamma reference fields of ¹³⁷Cs and ⁶⁰Co sources at the Institute for Nuclear Science and Technology. The characterization of the fields in terms of gamma fluence Φ, mean energy, E_Φ, kerma weighted mean energies, Eₖ, air kerma, Eair, were determined at various distances from the source center by Monte Carlo simulation using MCNP6. The air kerma results were compared with the measurements obtained by using a calibrated ionization chamber. The discrepancy between the simulated and measured air kerma was less than 4.5%. The scatterred component was also simulated and calculated. The results of both methods showed that the contribution of the scattered components to the gamma reference field is less than 3%. This contribution comply with the international standard criteria of ISO 4037 (<5%). The results confirmed that the characterization of the gamma reference field could be determined using the simulation code.

Study on the preparation of bimetallic silver-copper nanoparticles by electron beam irradiation

Ngoc Duy Nguyen — 2024-09-23

Silver and copper nanoparticles are well-known as good antimicrobial agents. In this study, we reported the preparation and characterization of bimetallic silver-copper nanoparticles (Ag-CuNPs) prepared by the electron beam (EB) irradiation method. Chitosan (CTS) was used as a stabilizer agent. The obtained Ag-CuNPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-Vis spectrophotometry. The influence of the different concentrations in the range of 100–1,000 ppm of Ag⁺ and Cu²⁺ ions at the mass ratio of [Ag⁺]:[Cu²⁺] = 1/1 on the particle size and particle size distribution of the Ag-CuNPs was investigated. The TEM results showed that the average size of the Ag-CuNPs was 11.02–13.73 nm when the total concentration of Ag⁺ and Cu²⁺ ions was 250 – 1,000 ppm, respectively. The EB-irradiation method can be applied in the production of Ag-CuNPs on a large scale.

Synthesizing high-density U₃O₈ powder from UO₂F₂ solution via AUC precipitation

Trong Hung Nguyen — 2024-09-23

Uranium trioxide octaoxide compound - U₃O₈ is a crucial nuclear material in nuclear technology. It is used as nuclear fuel for research reactors. To achieve this goal, an important characteristic that U₃O₈ powder must possess is a density ranging from 88-98% of the theoretical density (TD). This paper reports the results of an investigation of the ammonium uranyl carbonate (AUC) precipitation from uranyl fluoride (UO₂F₂) solution and optimization of sintering parameters for synthesizing high-density U₃O₈ powder, meeting the specified standards for manufacturing dispersed nuclear fuel for research reactors. The AUC precipitation was conducted using uranyl fluoride (UO₂F₂) solutions with uranium concentrations ranging from 80 to 120 gL^-1 and ammonium carbonate ((NH₄)₂CO₃) concentrations as precipitant were maintained between 200 and 400 gL^-1, while the (NH₄)₂CO₃ to U (C/U) molar ratios were kept equal to or greater than 6. The investigated parameters for sintering of the high-density U₃O₈ nuclear material derived from AUC (ex-AUC U₃O₈) are the sintering temperature and time. The experimental studies are designed by using the Response Surface Methodology (RSM) based on a Central Composite Design (CCD). As a result, a regression equation describing the dependency of U₃O₈ powder density on sintering temperature and time has been established. Based on this equation, the sintering for synthesizing high-density U₃O₈ powder has been optimized. The regression equation aids in controlling the parameters of the U₃O₈ powder sintering.