TRISO-coated particle fuel

The GTHTR300 reactor system has been designed based on the technologies and design codes developed and validated on the test reactor H lT R shown in Figure 9 and with further technical base for high bumup fuel [6] to allow specification of a modified TRISO coated particle fuel to meet commercial system objectives [7]. 

Updated neutronics analyses were performed at SNL to better match the reference AHTR geometry and fliel/coolant fractions. As before, the fuel type was TRISO-coated particle fuel with a particle packing fraction of 30% in the fuel compacts. All of the calculations were performed with 1200 K neutron cross-sections, and the thermal scattering function, S(a,P), was also used at 1200 K for the carbon in the fuel compacts and prismatic matrix. 

Concerning the fuel cladding contairunent barrier, special mention must be made of the high-temperature ceramic cladding used with TRISO coated-particle fuel diat provides excellent containment behaviour in hi temperature gas cooled reactors, even though fuel based on this principle is not presently plicable to PWRs. A similar subdivision of the fuel cladding containment is found in die CARAMEL-type [7] fuel plates used in certain French research reactors. 

TRISO-coated particle fuel temperature capability. 

The standard fuel cycle option for the CHTR would depend upon the technology development for reprocessing of TRISO coated particle fuel and fuel compacts. In case of the development of a reprocessing technology, a closed nuclear fuel cycle option would be adopted. Fresh fuel for the reactor would be made from and Th recovered from the spent fuel. Alternately, it would be a once though fuel cycle without reprocessing. The objective then would be to achieve the highest possible fuel bum-up. 

Research for reprocessing of TRISO coated particle fuel in the fuel compacts is in early stages. The process would include operations for the extraction of fuel compacts from the fuel tube, dismantling fuel compacts to free fuel particles and mechanical and thermo-chemical treatment of these particles to extract spent fuel. 

A large margin between the normal operating temperature of the fuel (around 1373 K) and the leak tightness limit of the TRISO coated particle fuel (1873 K) to retain fission products and gases ... 

Excellent high temperature (up to 1873 K) performance of TRISO coated particle fuel, ensuring that the probability of the release of fission products and gases is very low. 

A number of inherent and passive safety features in the design of the CHTR prevent the TRISO coated particle fuel from exceeding the limiting temperatures in postulated accidents or abnormal events, among them ... 

A highly negative Doppler coefficient of fuel ensures that the average fuel temperature does not exceed 1373 K in case of a power transient the acceptable maximum temperature of the TRISO coated particle fuel is 1873 K. 

The reprocessing of the TRISO coated particle fuel is not available as a commercial technology. 

The CHTR is a high temperature reactor with a coolant outlet temperature of 1273 K. It uses based fuel in the TRISO coated particle fuel form and is cooled by Pb-Bi eutectic coolant. It employs many passive safety features and passive reactor core heat removal... 

GT-MHR spent fuel elements, with their TRISO-coated particle fuel, achieve these qualities to a much greater degree than other waste forms, including spent zircalloy-clad fuel rods irradiated in the LWR. GT-MHR spent whole elements are an excellent waste form for permanent disposal. 

A proven radiological cleanness of TRISO coated particle fuel, resulting from the proven perfect confinement capability of such fuel at high temperatures. 

An option to use thorium fuel (GT-MHR) and an option to operate in a closed fuel cycle with the reprocessing of the TRISO coated particle fuel (GT-MHR, GTHTR300, HTR-PM) for the GTHTR300 it is indicated that the feasibility of TRISO fuel reprocessing has already been investigated. 

FIG. XV-12. TRISO coated particle fuel temperature capability. 

The technical basis for VHTR is the TRI-ISOtropic (TRISO)-coated particle fuel. The VHTR has potential for inherent safety, high thermal efficiency, process heat application capability, low operation and maintenance costs, and modular construction. 

The VHTR has two typical reactor configurations, namely the pebble bed type and the prismatic block type. Although the shape of the fuel element for two configurations are different, the technical basis for both configuration is same, such as the TRISO-coated particle fuel in the graphite matrix, foil ceramic (graphite) core structure, helium coolant, and low power density, in order to achieve high outlet temperature and the retention of fission production inside the coated particle under normal operation condition and accident condition. The VHTR can support alternative fuel cycles such as U—Pu, Pu, mixed oxide (MOX), and U—thorium (Th). 

Pebble bed and prismatic reactor are the two major design variants. Both are in use today. In either case, the basic fuel construction is the TRISO-coated particle fuel. Uranium, thorium, and plutonium fuel cycle options have been investigated and some have been operated in the reactors. Spent fuel may be direct disposed or recycled. The unique constmction and high bumup potential of the TRISO fuel enhances proliferation resistance. 

Kim, B.G., et al., October 27—31, 2014. Irradiation testing of TRISO-coated particle fuel in Korea. In Proceedings of the HTR 2014, Weihai, China. 

An IHTR is a pebble-bed molten salt-cooled reactor. Pebbles consist of TRISO-coated particle fuel, and the coolant is driven through natural circulation. The reactor core is a long right circular cylinder with an annular core that consists of fuel pebbles and molten salt coolant. Fig. 15.13 shows a schematic of a 600-MWth IHTR. There are graphite neutron reflectors in the center and on the top, bottom, and outside of this fuel annulus. Vertical bores in the central and outer reflectors are provided for the reactivity control elements. R D activities being pursued include a molten salt natural circulation loop, as shown in Fig. 15.14, which has been set up to perform thermal... 

Fuel and Th02 based high bum-up TRISO-coated particle fuel... 

India is developing two concepts of molten salt reactors. One of the concepts has a pebble-bed configuration with molten salt being used as the coolant. The pebbles are made of TRISO-coated particle fuel. This is explained in Section 13.3.8. The other configuration is the fluid-fueled MSBR. This portion of the chapter will describe Indian R D efforts for the development of the IMSBR. 

---