High-temperature pebble-bed

FIGU RE 21.20 Fuel spheres used In a hIgh-temperature pebble-bed reactor. 

A Figure 21.20 Fuel spheres used in a high-temperature pebble-bed reactor. The image on the right is an optical microscope image of a fuel particle. 

In a high-temperature pebble-bed reactor, the fuel elements are spheres ( pebbles ) roughly the size of an orange (A Figure 21.20). The spheres are made of graphite, which acts as the moderator, and thousands of tiny fuel particles are embedded in the interior of each sphere. Each fuel particle is a kernel of fissionable material, typically... 

The low (ca 2%) yield of NO, the tendency to revert to N2 and O2 if the product stream is not quenched rapidly, the consumption of large (ca 60,000 kWh/1N2 fixed) amounts of electricity, and the concomitant expense to sustain the arc all led to the demise of this process. The related Wisconsin process for oxidising N2 at high temperatures in a pebble-bed furnace was developed in the 1950s (13). Although a plant that produced over 40 t/d of nitric acid was built, the product recovery costs were not economically competitive. 

The Arbeitsgemeinschaft Versuchsreaktor (AVR) and Thorium High-Temperature Reactor (THTR-300) were both helium-cooled reactors of the pebble-bed design [29,42,43]. The major design parameters of the AVR and THTR are shown in Table 10. Construction started on the AVR in 1961 and full power operation at 15MW(e) commenced in May 1967. The core of the AVR consisted of approximately 100,000 spherical pebble type fuel elements (see Section 5). The pebble bed was surrounded by a cylindrical graphite reflector and structural carbon... 

Several reactors are candidates for use as a high temperature heat source for the S-I cycle. Candidates include the modular helium reactor (MHR) and pebble bed modular reactor (PBMR). One of the most thoroughly investigated candidates is the PBMR. Recent work has been performed in benchmarking the THERMIX code to the PBMR-268 design (Reitsma, 2004 Seker, 2005). 

High temperature rectors were very successful in Germany as pebble bed reactors (PBR s) with the AVR-reactor in Jiilich over 20 years, 50 MW l/h, and with the THTR 300 in Hamm-Ueontrop with 300 MW, which was tested electrically for 3 years. 

In the United States, General Atomics was the main promoter of the high-temperature reactor (HTR). The company built one HTR, at Fort St. Vrain, Colorado. It had several other orders, but the program was halted in the mid 1970s. In Germany, the Nuclear Research Center at Jiilich was the focal point for development of the so-called pebble-bed HTR for both electricity production and coal gasification. A 500-megawatt reactor was expected to go on line by 1990 but never did. 

KUGELER, K., et al.. The Pebble-Bed High-Temperature Reactor as a Source of Nuclear Process Heat, Vol 4 System Considerations on Nuclear-Heated Steam Reformers, Report Jul-1116-RG, Research Center JQlich (1974). 

E. Teuchert, K.A. Haas, Features of safety and simplicity of advanced pebble bed HTR s, Proceedings of the IAEA Technical Committee Meeting on Development Status of Modular High Temperature Reactors and their Future Role, Petten, The Netherlands, 28-30 November 1994, ECN-R-95-026. 

Two kinds of indirect GT-ST cycle are investigated based on Siemens 200 MW pebble-bed modular high temperature gas cooled reactor(HTR-Module). Fig. I shows the HTR-Module and its primary loop. 

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