Kyung-Chai Jeong

겔침전과 화학증착법에 의한 구형 UO₂ 입자와 TRISO 피복입자 제조

HTGR using a TRISO coated particles as nuclear raw fuel material can be used to produce clean hydrogen gas and process heat for a next-generation energy source. For these purposes, a TRISO coated particle was prepared with 3 pyro-carbon (buffer, IPyC, and OPyC) layers and 1 silicone carbide (SiC) layer using a CVD technique on a spherical UO₂ kernel surface as a fissile material. In this study, a spherical UO₂ particle was prepared using a modified sol-gel method with a vibrating nozzle system, and TRISO coating fabrication was carried out using a fluidized bed reactor with coating gases, such as acetylene, propylene, and methyltrichlorosilane (MTS). As the results of this study, a spherical UO₂ kernel with a sphericity of 1+0.06 was obtained, and the main process parameters in the UO₂ kernel preparation were the well-formed nature of the spherical ADU liquid droplets and the suitable temperature control in the thermal treatment of intermediate compounds in the ADU, UO₃, and UO₂ conversions. Also, the important parameters for the TRISO coating procedure were the coating temperature and feed rate of the feeding gas in the PyC layer coating, the coating temperature, and the volume fraction of the reactant and inert gases in the SiC deposition.

Preparation of an Intermediate and Particle Characteristics for HTGR Nuclear Fuel

In this study, first the ADU gel particle, an intermediate for final UO₂ kernel of a HTGR nuclear fuel, was prepared from sol-gel method using the broth solution which was made by mixing of the uranyl nitrate, poly vinyl alcohol and tetra-hydrofurfuryl alcohol. The prepared dried-ADU gel particles were converted to the UO₂ via UO₃ from thermal treatment with the 4% H₂ atmosphere. The sizes of the spherical liquid droplets appeared 1900~2100 ㎛, and the harmony between the flow rate of the broth solution and the frequency and the amplitude of a vibrating system are important factors for the spherical ADU gel particles via the mono size spherical droplets. From the XRD and FT-IR analyses, the prepared ADU gel particles were judged to be a UO₃ㆍxNH₃ㆍyH₂O form, and the most important factor during the thermal treatment of the dried-ADU gel particle must be avoided a rapidly heating rate in the range of 180~400℃, and the heating rate should be kept below 5℃/min.

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.

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 .

Study on an Intermediate Compound Preparation for a HTGR Nuclear Fuel

In this study the preparation method of the spherical ADU droplets, intermediate compound of a HTGR nuclear fuel, was detailed reviewed and then, the characteristics on an ageing and a washing steps among the wet process and the thermal treatment process on the died-ADU→UO₃ conversion with the high temperature furnaces were studied. The key parameters for spherical droplets forming are a precise control of feed rate and a suitable viscosity value selection of a broth solution. Also, a harmony of vibrating frequency and amplitude of a vibration dropping system are important factor. In our case, an uranium concentration is 0.5~0.7 mol/l, viscosity is 50~80 centi-Poise, vibration frequency is about 100 Hz. In thermal treatment for no crack spherical UO₃ particle, the heating rate in the calcination must be operated below 2℃/min, in air atmosphere.

고온가스로용 핵연료 UO₂ Kernel 입자제조

The broth solution was prepared by the mixing of an uranyl nitrate, THFA, PVA, and water. The uranium concentration of the broth solution was 0.5~0.8 mole-U/L and the viscosity of it was 30~80 cSt. The droplets of this broth solution were formed in air and a㎜onia by the vibrating nozzle with the frequency of 100 ㎐ at the amplitude of 100~130 V. The diameter of the droplet was about 1900 ㎛ from using the nozzle diameter of 1 ㎜. The diameter of the aged gel was about 1400 ㎛ after aging in a㎜onia solution at 60~80℃, and the dried gel with the diameter of about 900 ㎛ was obtained after drying at room temperature or partially vacuum condition. The diameter of the calcined UO₃ microsphere after calcination at 600℃ appeared about 800 ㎛ in air atmosphere. Although the droplets of the same sizes were formed, the calcined microspheres of different sizes were manufactured in the case of the broth solutions of the different uranium concentration. The droplets of the desired diameters were obtained by the change of the nozzle diameters and the broth flow rates.

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.

HTGR Nuclear Fuel Microsphere Preparation Using the Modified Sol-Gel Method

UO₂ microsphere particles, core material of HTGR(High Temperature Gas Reactor) nuclear fuel, were prepared using by the GSP(Gel Supported Precipitation) method which is a modified-method of the wet sol-gel process. The spherical shape of initial liquid ADU droplets from the vibration nozzle system was continuously kept till the conversion to the final UO₂ microsphere. But the size of a final UO₂ microsphere was shrunken to about 25% of an initial ADU droplet size. Also, we found that the composition of dried-ADU gel particles was constituted of the very complicated phases, coexisted the U=O, C-H, N-H, N-O, and O-H functional groups by FT-IR. The important factors for obtain the no-crack UO₂ microsphere during the thermal treatment processes must perfectly wash out the remained-NH₄NO₃ within the ADU gel particle in washing process and the selections of an appropriate heating rate at a suitable gas atmosphere, during the calcining of ADU gel particles, the reducing of UO₃ particles, and the sintering of UO₂ particles, respectively.

Effects of Process Parameters on the Powder Characteristics of Uranium Oxide Kernel Prepared by Sol-gel Process

In this study, we investigated the unit process parameters in spherical UO 2 kernel preparation. Nearly perfect spherical UO 3 microspheres were obtained from the 0.6M of U-concentration in the broth solution, and the microstructure of the UO 2 kernel appeared the good results in the calcining, reducing, and sintering processes. For good sphericity, high density, suitable microstructure, and no-crack final UO 2 microspheres, the temperature control range in calcination process was 300~450C, and the microstructure, the pore structure, and the density of UO 2 kernel could be controlled in this temperature range. Also, the concentration changes of the ageing solution in aging step were not effective factor in the gelation of the liquid droplets, but the temperature change of the ageing solution was very sensitive for the final ADU gel particles.