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Fig. 5-3 HTTR Design Construction, and Operation Schedule

Table 5-1

Major Specifications of HTTR

item specification thermal power outlet coolant temperature inlet coolant temperature coolant pressure core structure material graphite core height core effective diameter power density fuel enrichment type of fuel element reactor pressure vessel number of main cooling loops 30 MW 850/950 degrees cent. 395 degrees cent. 4 MPa graphite 2.9 m 2.3 m 2.5 MW/m3 3 ~ 10% (mean 6%) prismatic block steel (2 1/4Cr-1Mo) 1

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Fig. 5-4 Layout of Reactor Building

Fig. 5-5a First Floor of the Reactor Building : After Concrete Construction (June 1993)

Fig. 5-5b Reactor Building : After Frame Construction (Aug. 1993)

Fig. 5-5c Spent Fuel Storage Pool : After Leak Test (Nov. 1993)

Fig. 5-5d Reactor building : Under Concrete Construction (Feb. 1994)

Fig. 5-5e First Floor of Reactor Building : Fuel Handling Floor Under Construction (Mar. 1994)

Fig. 5-5f Reactor Building : Completed (Feb. 1995)

The HTTR is now under construction. Its site area is 50,000 m2 (200 x 250 m) in the Oarai Establishment of JAERI. Its first criticality is planned for 1997.The construction schedule is shown in Fig. 5-3. The HTTR is a graphite-moderated, helium-cooled HTGR with a power rating of 30 MW. The major specifications of the HTTR are shown in Table 5-1. The cooling helium temperature is 395 degrees cent. at the inlet, 850 degrees cent. at outlet, and 950 degrees cent. at outlet when super high-temperature operation. The reactor building, 48 x 52 m, has five floors, three of which are below ground level. The arrangement of components in the reactor building is shown in Fig. 5-4. Photographs of the building's construction are shown in Fig. 5-5. Major components, such as the reactor pressure vessel, the primary cooling system components, etc., of the reactor system are now installed in the containment vessel. The utilities, laboratory building, etc., are located around the reactor building. The fuel elements of the HTTR are the pin-in-block type. They consist of a fuel rod and a hexagonal graphite block. The fuel rod, which is composed of fuel compacts and graphite sleeves, is contained within a vertical hole in graphite block. The core, which consists of a graphite moderator, helium coolant, and ceramic fuel, is stable to a very high temperature. The reactor consists of the core components, the reactor internals, and the reactor pressure vessel. The core columns are rows of prismatic hexagonal blocks stacked axially. The core is surrounded by a replaceable reflector composed of a layer of hexagonal graphite blocks. Helium gas flows through the gaps between the vertical holes in the graphite blocks and the fuel rods to cool the core components. The high- temperature helium gas flows from the reactor vessel into the concentric hot gas duct. The reactor cooling system consists of the primary cooling system, the secondary cooling system, and the vessel cooling system. The primary cooling system consists of the main and auxiliary cooling systems. Primary helium gas is transported from the reactor core to the helium-helium heat exchanger and the primary pressurized water cooler through the primary concentric hot gas duct. The auxiliary cooling system is in the standby mode during normal operation and during startup to remove residual heat in the event of reactor scram. The vessel cooling system is operated only in the event of abnormal conditions to cool the reactor vessel and the concrete shield. The intermediate heat exchanger (IHX) transfers heat from the primary helium to the secondary helium.The IHX has a double-shell structure to provide structural integrity so the high-temperature helium dose not directly contact the pressure vessel of the IHX. The high-temperature helium gas is transferred through the hot gas duct from reactor core to the IHX. The high-temperature helium gas flows in the inner duct of concentric duct. The low-temperature helium gas flows in the gap between the outer and the inner ducts in the opposite direction. The inner duct withstands the higher temperature and the outer duct maintains the high pressure of the helium gas.

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