Nuclear Science and Technology

Fundamental investigation of natural convection induced by vertical heated rod using ultrasound velocity profiler

2024-05-14T16:11:29+07:00

Natural convection is a fundamental phenomenon observed in various industrial, nuclear energy, power generation, and electronics cooling applications. In nuclear reactors, natural convection plays a crucial role in residual decay heat removal following reactor shutdown incidents or accidents. The design of fuel elements and fuel assemblies significantly influences flow rates, impacting natural circulation. Understanding natural convection requires analysis of the spatiotemporal velocity profile, which provides valuable insights into flow behavior. Therefore, the Ultrasonic Velocity Profiler (UVP) emerges as a suitable tool for observing natural convection flow behavior. However, since sound velocity in a fluid is temperature-dependent, it might affect the accuracy of velocity measurements. Hence, confirming the applicability of UVP becomes essential. In this study, a vertical heated rod with a diameter of 12 mm and a length of 225 mm is immersed at the center of a vertical acrylic pipe with a diameter of 144 mm and a height of 500 mm. The ultrasonic transducer is positioned outside the pipe to enable long-term flow behavior measurement. Utilizing the UVP technique, one-dimensional velocity profile behavior inside the pipe is measured and validated using Particle Image Velocimetry (PIV). Consequently, the spatiotemporal velocity profile is depicted in color scale to comprehend the natural flow behavior induced by a single heater rod.

Thickness measurement of 10b and 11b targets using the alpha transmission method

2024-08-27T16:43:23+07:00

Experiments were performed to measure the thickness of ¹⁰B and ¹¹B targets using the α-transmission method. These targets were prepared at INFN. A ²⁴¹Am source provided α particles of 5.486 MeV energy. The results were compared with the supplier’s values, showing a good agreement in thickness for the ¹¹B target, while the results for the ¹⁰B target were reasonable within the uncertainty range.

Research and development of the algorithms to determine the operational personal quantities for photon using photoluminescent dosimeter

2024-04-19T10:18:39+07:00

Objective: This study presents the results of investigating the dosimetric characteristics of Inlight Al₂O₃:C dosimeters to develop algorithms for determining effective dose, equivalent doses for lens and skin organs by evaluating the operational personal dose equivalent Hp(10) and the ICRU 95 operational personal doses. These quantities are the best approximate values to evaluate the dose limits specified in Circular 19/2012/TT-BKHCN on occupational radiation exposure control. These quantities are calibrated with the ISO 4037 standard dose fields. Research object and method: Investigating dosimetric characteristics of optically stimulated luminescent dosimeter (OSLD) – Inlight type, and applying them in the development of the personal dosimetry algorithms for radiation workers working in the radiation field of gamma and X-ray, using the method of comparing values calculated by both recently developed algorithms and Landauer's algorithm with the reference values for assessing uncertainty. Result: Initially, the algorithms have been developed to evaluate the effective energy of radiation beams using the multi-filter technique, to determine the energy of incident beam air Kerma and conversion coefficients from air Kerma to operational personal dose equivalents Hp(d), and the ICRU 95 new operational quantities. The NTTU-OSLD algorithm has shown a great improvement in energy estimation. This will be useful for other applications such as lens dose measurement by nanodot. Conclusion: The algorithms allow the evaluation of the energy of the incident beam, air Kerma, effective dose, lens and skin equivalent doses through the measurement of the quantities Hp(10), Hp(3), and Hp(0.07) as well as Hp, D_p,_lens, and D_{p, local}_skin according to ICRU 95.

A study on the RIMPUFF module (ARGOS) and simulation of radiation dispersion from a hypothetical floating nuclear power plant accident in the East Sea

2024-02-19T09:13:13+07:00

In this study, the RIMPUFF module (ARGOS) was used to simulate the Fukushima-Daiichi nuclear power plant accident (FNPPA), thereby assessing the research team’s capability in using the program. The FNPPA simulation results showed good agreement in trend and intensity with the environmental monitoring data and other simulation models. Based on these results, our research team used RIMPUFF to simulate the atmospheric dispersion from the hypothetical accident of a floating nuclear power plant operating in the East Sea (Phu Lam Island, the Paracel Islands, Da Nang Province, Vietnam), through which we analyzed the accident’s impacts on the Vietnamese mainland territory. Depending on weather conditions and specific locations, the impact area of the accident varies. Under conservative conditions, the wind blowed from the East Sea at a speed of 7.5 m/s, the radioactive cloud would reach the mainland territory (Quang Tri and Quang Binh provinces) approximately 15 hours after the accident. Subsequently, the accident created an area of hundreds of square kilometers, with dose rate greater than 1 µSv/h; I-131 and Cs-137 deposition on the ground would exceed 10 kBq/m² and 2 kBq/m², respectively. According to the regulation on preparedness and responses to nuclear and radiological emergencies, people in the affected areas must immediately stop consuming local food and milk until the result of sample examination is available. The study results demonstrate the ARGOS usability and its value in supporting decision-making in the nuclear accident emergencies.

Testing convergence of the solution of the continuum discretized coupled channels method for deuteron-induced reactions

2024-05-14T16:18:52+07:00

We briefly introduced the formalism of the CDCC method in which reactions involving weakly bound nuclei are treated as a three-body system and took into account the contribution of breakup states. Numerically examined results were done for the elastic scattering of two typical d + ¹²C and d + ⁵⁸Ni systems. Truncations of E_max, l_max, and R_match for model spaces in CDCC calculations were established. A description of realistic elastic d + ¹²C and d + ⁵⁸Ni scattering data at 80 MeV was made to see the valuable CDCC method and the vital role of deuteron breakup effects.

Preliminary analysis of structural defects in thin BiVO4 layer using the slow-positron-beam based facilities at JINR, Dubna

2024-07-08T14:32:48+07:00

The present paper introduces the slow-positron beam system at the Joint Institute for Nuclear Research (JINR). Preliminarily studies on thin films using the combined analyses of the variable energy Doppler broadening (VEDB) and variable-energy electron-momentum distribution (VEEMD) measurements at JINR are also reported. These studies provide a unique tool for the in-depth investigations of the structural defects in nanomaterial as thin films, from material’s surface to various depths (in the range from a few nm ups to 1 µm). Application of that method to BiVO4 thin film implanted with P+ ions (200 keV) reveals that the structural defects in the thin film achieve the highest concentration in the depth range of 40 – 200 nm (VEDB analysis), whereas the introduction of P+ ions into the thin film should reduce the positron annihilation probability with high-momentum core electrons. These results open the possibility to use advanced analytical techniques for in-depth study of nanomaterial in JINR, performed, in particular, by Vietnamese scientists.