Studi Pengaruh Fraksi Coated Fuel Particle pada Desain Pebble Bed Reactor 40 MWt Berbahan Bakar Uranium

Coated Fuel Particle (CFP) adalah tipe elemen bakar mikro berdiameter lebih kecil dari 1 mm, yang di dalamnya terdapat material fisil yang dilapisi oleh beberapa lapisan karbon. Pebble Bed Reactor (PBR) menggunakan konsep CFP untuk elemen bakarnya. CFP dimasukan ke dalam bola elemen bakar berukuran 6 cm dan disebar di dalam zona elemen bakar. Tujuan penelitian ini adalah untuk mempelajari pengaruh dari fraksi CFP terhadap beberapa parameter neutronik penting seperti faktor multiplikasi efektif, spektrum energi neutron, perubahan densitas material fisil dan fertil, serta tingkat utilisasi material fisil. Analisa dilakukan untuk pada sistem PBR berdaya 40 MWt dengan menggunakan kode Monte Carlo MVP/MVP-BURN, dengan fraksi CFP yang dianalisa berkisar antara 5-60%. Dari penelitian ini didapatkan bahwa fraksi CFP sebesar 10% memberikan nilai optimal untuk beberapa parameter neutronik terkait dan dapat dijadikan acuan untuk desain Pebble Bed Reactor berdaya 40 MWt dengan elemen bakar uranium.

The Effects of the Number of Coated Fuel Particles on the Neutronic Aspects of 25 MWt Pebble Bed Reactor with Thorium Fuel

High-Temperature Gas Reactor (HTGR) is a type of reactor that continues to be developed because of its advantages in terms of economic aspects, proliferation resistance, and safety aspects. One of the safety aspect improvements is due to the use of the Coated Fuel Particle (CFP). A coated fuel particle is a fuel with a diameter smaller than 1 mm and is protected by several carbon layers. In the Pebble Bed Reactor (PBR) type of HTGR design, the CFP is placed in a 6 cm fuel ball. How much CFP is put into the fuel ball will determine the neutronic characteristics of the reactor. In this study, the effect of the amount of CFP in the fuel ball on the 25 MWt PBR design using Thorium fuel and its impact on several important neutronic aspects, such as the effective multiplication factor, the amount of fuel enrichment, the utilization of fissile material, and the density of the fissile material formed. The calculation was performed by the Monte Carlo MVP / MVP-BURN code. This study found that the coated fuel particle fraction of 15% was the optimum value for the studied neutronic parameters.

Resonance Self-Shielding Treatment for Fully Ceramic Micro-Encapsulated Fuels With the Embedded Self-Shielding Method

Fully ceramic micro-encapsulated (FCM) fuels generate double heterogeneity (DH) challenging greatly for classical resonance self-shielding calculation method. New methodologies have been proposed and verified in this research. The target of this study is to provide homogeneous multi-group cross sections reflecting the effect of DH. Embedded Self-Shielding Method (ESSM) [1] was selected to perform resonance self-shielding calculation. Therefore, Monte Carlo code MVP [2] which is capable of well modeling the stochastic dispersed tri-structural isotropic (TRISO) coated fuel particle throughout carbide matrix and method of characteristics (MOC) were chosen to develop the heterogeneous resonance integral (RI) tables for DH problems. Benchmark problems from reference [3] were provided to verify the new methodologies. The results show that ESSM with RI tables from MVP and MOC could well address the resonance calculation for DH problems.

Improved Lumped Models for Transient Combined Convective and Radiative Cooling of Multilayer Spherical Media

In this work, we studied the transient combined convection and radiation of multilayer spherical media with volumetric heat generation, extending the previous work on the particular case of a spherical body subjected to radiative cooling. The proposed lumped models were obtained through two-point Hermite approximations for the average temperature and heat flux in each layer. For the average temperature, the plain trapezoidal rule (H0,0 approximation) was employed in all layers, except for the innermost layer, where the second-order two-side corrected trapezoidal rule (H2,1 approximation) was utilized. For the heat flux, the plain trapezoidal rule (H0,0 approximation) was employed for all the layers. The transient heat conduction in a TRISO-coated fuel particle being composed of five layers (namely, fuel kernel, buffer of porous carbon, inner pyrocarbon, silicon carbide, and outer pyrocarbon) was analyzed using the proposed lumped models, the results of which were verified by comparison with the finite difference solution of the original distributed parameter model. Parametric studies were conducted to examine the effects of the dimensionless heat generation rate, the radiation-conduction parameter, and the Biot number on the temporal variations of the average temperatures.

Effect of PyC Thermal Behavior on the Stress of TRISO-Coated Fuel Particles

TRISO coated fuel particle is the most important component in HTR fuel, the silicon carbide (SiC) coating layer is regarded as the pressure vessel to contain the fission products. During reactor operation, the inner pressure resulting from fission products and pyrocarbon (PyC) thermal effect will contribute to the failure of TRISO-coated particles. The higher temperature will result in the increasing of inner pressure and PyC thermal expansion, which will then change the stress of SiC layer. Considering the effects of temperature on inner-pressure expansion and elastic strain into the pressure vessel failure model, thermal effects on the stress of TRISO-coated particles were studied with analytical solution. The results indicated that the effects of inner pressure on the particle stresses were increasingly highlighted at the late stage of irradiation. And the increasing temperature caused a slight effect on PyC elastic modulus while elastic strain is unaffected greatly, either. Therefore, CFP stresses remain unchanged basically.

Comparative Study of Coated Particle Stresses With Different Coating Layer Performance

Tristructural-isotropic coated fuel particle is an important fuel design for high-temperature gas-cooled reactor. Irradiation-induced pyrocarbon (PyC) shrinkage and creep behavior will affect greatly the stresses of a TRISO-coated particle. In this study, 5 cases under different conditions by analytical solution were studied to calculate the particle stresses with different fuel behavior. These cases varied in particle geometries, the mount of gas pressure or fuel behavior. A comparison between the results and other benchmarking studies among different codes was made. The results indicated that the calculated results in this study were in good agreement with other codes.

Fission Products Distribution in TRISO Coated Fuel Particles Irradiated to 3.22 X 1021 n/cm2 Fast Fluence at 1092°C

Mechanisms by which fission products (especially silver [Ag]) migrate across the coating layers of tristructural isotropic (TRISO) coated fuel particles designed for next generation nuclear reactors have been the subject of a variety of research activities due to the complex nature of the migration mechanisms. This paper presents results obtained from the electron microscopic examination of selected irradiated TRISO coated particles from fuel compact 1-3-1 irradiated in the first Advanced Gas Reactor experiment (AGR-1) that was performed as part of the Next Generation Nuclear Plant (NGNP) project. It is of specific interest to study particles of this compact as they were fabricated using a different carrier gas composition ratio for the SiC layer deposition compared with the baseline coated fuel particles reported on previously. Basic scanning electron microscopy (SEM) and SEM montage investigations of the particles indicate a correlation between the distribution of fission product precipitates and the proximity of the inner pyrolytic carbon (IPyC)-silicon carbide (SiC) interface to the fuel kernel. Transmission electron microscopy (TEM) samples were sectioned by focused ion beam (FIB) technique from the IPyC layer, the SiC layer and the IPyC-SiC interlayer of the coated fuel particle. Detailed TEM and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDS) were performed to identify fission products and characterize their distribution across the IPyC and SiC layers in the areas examined. Results indicate the presence of palladium-silicon-uranium (Pd-Si-U), Pd-Si, Pd-U, Pd, U, U-Si precipitates in the SiC layer and the presence of Pd-Si-U, Pd-Si, U-Si, U precipitates in the IPyC layer. No Ag-containing precipitates are evident in the IPyC or SiC layers. With increased distance from the IPyC-SiC interface, there are less U-containing precipitates, however, such precipitates are present across nearly the entire SiC layer.