The High Temperature Gas cooled Reactors (HTGR) are being accepted by many countries today due to the increase interest as a future energy option. The research on HTGRs are being conducted in China and Japan, and also two new nuclear plant designs are being chased as an international project (4). These reactors are used in nuclear power plants to generate electricity and also new nuclear fuels. However, can these HTGRs be used in residential areas?
Gas-cooled nuclear reactors was originated by a professor in chemistry named Farrington Daniels at 1942 in University of Wisconsin. His report was published in 1944 with features of a direct cycle turbine, plant below grade and pebble bed cores ...view middle of the document...
In 1987, the Thorium High Temperature Reactor (THTR) was invented in Germany. It was shut down for maintenance inspection in 1988 (3). After that the plant did not restart due to financial problems.
There are also High Temperature Test Reactor (HTTR) located in Japan and China. The HTTR in Japan is at the Japanese Atomic Energy Agency campus (3). It uses the prismatic fuel type HTGR. In China, the High Temperature Test Reactor-10 (HTR-10) is situated in Tsinghua University, Beijing. It is a helium-cooled, pebble-bed reactor (3).
The High Temperature Gas cooled Reactors is a Generation IV reactor. It operates with a nuclear reactor made of graphite. It also uses fuel in the form of uranium with an outlet temperature as high as 1000oC (2). HTGRs are present in two ways, the pebble bed reactors (PBR) and prismatic block reactors (PMR). In the PMR, the graphite are hexagonal blocks shape and are packed to insert in the cylindrical shape pressure vessel meanwhile the PBR consists pebbles in fuel form (2). These pebbles are stacked together in a cylindrical pressure vessel which looks like a gum-ball machine (2).
Figure 1: Image of PBR reactor.
The HTGRs uses Brayton cycle to generate electricity and indirect cycle to produce hydrogen. It uses an intermediate heat exchanger (IHX) for these two cycles (4). During the first generation of gas-cooled reactors (GCRs), Rankine cycle was used for power generation since most of the gas turbine uses an open cycle (4). A closed cycle is required to maintain the process gas for radiological reasons.
Both the pebble bed reactors and prismatic block reactors work almost the same way. They contain a pressure vessel made from steel which can hold about 450 000 fuel spheres (4). The fuel contain low enriched uranium triple coated (triso) isotropic particle (4). Each and every coated particle comprise of a kernel of uranium dioxide which are surrounded by four coating layers (4).
Figure 2: Image of fuel sphere, TRISO coated particle and fuel kernel.
The systems are cooled by transferring heat by the helium to the power conservation system. A gas turbine is used to convert the heat transferred into electricity (4). The plant has a Reactor Pressure Vessel (RPV) and Power Conservation Unit (PCU). The perpendicular pressure vessel is 27 m high with lined 39 inch of graphite blocks in a thick layer (4). It is also 6.2 m in diameter and acts as an outer reflector and a passive heat transfer medium (4). To house the control elements, vertical holes are drilled to the graphite brick lining.
Figure 3: Image of reactor pressure vessel.
The particles which are rich in uranium dioxide are coated with silicon carbide and pyrolitic carbon and enclosed in the graphite to form the fuel sphere or pebble (4). They are approximately 6 cm in diameter, about the size of a tennis ball. Using thorium and U233 fuel cycle, the design is able towards thermal breeding (4). In both the reactors, helium is used as an energy transfer...