Moon Sung Cho

A STRESS ANALYSIS FOR A COATED FUEL PARTICLE OF A HTGR USING A FINITE ELEMENT METHOD

A finite element method utilizing the Galerkin form of the weighted residuals procedure was developed to estimate the mechanical behavior for a coated fuel particle (CFP) of a high temperature gas-cooled reactor (HTGR). Through a weak formulation, finite element equations for multiple layers were set up to calculate the displacements and stresses in a CFP. The finite element method was applied to the stress analyses for three coating layers of a tri-isotropic coated fuel particle (TRISO) of a HTGR. The stresses calculated by the finite element method were in good agreement with those from a previously developed computer code and depicted the typical stress behavior of the coating layers very well. The newly developed finite element method performs a stress analysis for multiple bonded layers in a CFP by changing the material properties at any position in the layers during irradiation.

IRRADIATION DEVICE FOR IRRADIATION TESTING OF COATED PARTICLE FUEL AT HANARO

The Korean Nuclear-Hydrogen Technology Development (NHTD) Plan will be performing irradiation testing of coated particle fuel at HANARO to support the development of VHTR in Korea. This testing will be carried out to demonstrate and qualify TRISO-coated particle fuel for use in VHTR. The testing will be irradiated in an inert gas atmosphere without on-line temperature monitoring and control combined with on-line fission product monitoring of the sweep gas. The irradiation device contains two test rods, one has nine fuel compacts and the other five compacts and eight graphite specimens. Each compact contains about 260 TRISO-coated particles. The irradiation device is being loaded and irradiated into the OR5 hole of the in HANARO core from August 2013. The device will be operated for about 150 effective full-power days at a peak temperature of about 1030°C in BOC (Beginning of Cycle) during irradiation testing. After a peak burn-up of about 4 atomic percentage and a peak fast neutron fluence of about 1.7×10 21 n/cm 2 , PIE (Post-Irradiation Examination) of the irradiated coated particle fuel will be performed at IMEF (Irradiated Material Examination Facility). This paper reviews the design of test rod and irradiation device for coated particle fuel, and discusses the technical results for irradiation testing at HANARO.

Development of the Fission Product Release Analysis Code COPA-FPREL

The COPA-FPREL computer code has been developed to estimate the releases of gaseous and metallic fission products (FPs) from high-temperature gas-cooled reactor (HTGR) fuel into coolant. The COPA-FPREL code treats FP release from a coated fuel particle (CFP), diffusion in a fuel element, and leakage into the coolant considering the temperature distribution within a CFP and a fuel element. The code uses a finite difference method to calculate FP migration and heat transfer. In the finite difference method, the kernel, buffer, and coating layers of a CFP and the fuel element are divided into small finite difference intervals. A steady-state heat transfer equation and the Fickian diffusion equation are applied to these intervals. A relatively high diffusion coefficient is assigned to the buffer and the broken coating layers to describe fast diffusion in those regions. Sorption equilibrium is set up between the concentration at the fuel element surface facing the coolant and the vapor pressure at the graphite side of the boundary layer that forms on the fuel element surface. Mass transfer occurs through the boundary layer into the bulk coolant. In a prismatic HTGR, sorption equilibrium is assumed to form between the concentrations at the compact and structural graphite surfaces and the vapor pressure in the gap between the compact and the structural graphite. For 137Cs, 90Sr, 110mAg, and 85Kr isotopes, the fractional releases from a CFP, a pebble, and a fuel block during simulated heating processes and reactor operations were calculated using COPA-FPREL.

Effects of Thermal Treatment Conditions on the Powder Characteristics of Uranium Oxide in HTGR Fuel Preparation

The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for kernel preparation. In this study, ADU compound particles were calcined to particles in air and Ar atmospheres, and these particles were reduced and sintered in 4%-/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to phases at . At , the phase appeared together with . After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric . As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of and .

Spherical UO 3 Gel Preparation Using the External Gelation Method

HTGR (High Temperature Gas-cooled Reactor) is spotlighted to next generation nuclear power plant for producing the clean hydrogen gas and the electricity. In this study, the spherical UO₃ gel particles were prepared by the external gelation process, and the characteristics of these particles were analyzed the particle shape, composition of precipitate, and thermal decomposition characteristics with the Streoscope, FT-IR, and X-ray diffractometer. Raw material of the ADUN (Acid Deficient Uranyl Nitrate) solution, which has [NO₃]/[U] mole ratio = 1.75, was obtained from dissolution of the U₃O 8 powder with concentrated HNO₃, and its concentration is 3.5 M-U/l. The broth solution is prepared with the ADUN, urea, PVA, and THFA solution. The droplets of the broth solution was made through a nozzle system. From this study, we obtained the following results; 1) an externel chemical gelation process is a suitable method in the spherical UO₃ particle production, 2) the particle shape are changed by an urea mixing time, THFA volume, and the viscosity of the broth solution, 3) the amorphous UO₃ particles obtained from these experiments was converted to U₃O 8 and then UO₂ by heat treatment in hydrogen atmosphere at 600℃.

Characteristics of the Ammonium Diuranate Powders Prepared with Different Experimental Apparatus in Sol-gel Process

This paper describes the spherical ammonium diuranate gel particles which are the intermediated material of the microsphere for an VHTR(very high temperature reactor) nuclear fuel. The characteristics of the intermediate-ADU gel particles prepared by AWD(ageing, washing, and drying) and FB(fluidized-bed) apparatus were examined and compared in a sol-gel fabrication process. The electrical conductivity of washing filtrate from the FB treating and the surface area of dried-ADU gel particles were higher than those of AWD treating. Also, an internal pore volume in dried-ADU gel particles showed a more decrease in AWD treatment than FB treatment because of decomposition of PVA affected by the washing time. However, the internal microstructures of ADU gel particles were similar regardless of the process variation.