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Conference Article: The THTR steam generator: design, manufacture and installation

Abstract

In the THTR 300 MWe nuclear power station six steam generator units produce live and reheat steam of conventional pressure and temperature: HP: 185 bar / 550 deg. C. LP: 50 bar / 535 deg. C. The steam generator units are identical and arranged around the thermal shield inside the prestressed concrete pressure vessel. Water/steam inlet and outlet pipes penetrate the pressure vessel through a primary and a secondary closure at the top. The heat exchanging surface is of the helical type. The individual tubes are carried in support plates. Each unit consists of two high pressure and one low pressure bundle. In the HP section, which works on the once-through (monotube) principle, 80 parallel tubes are used. A particularity is the principle of the so-called down-hill boiling: the feedwater enters at the top, steam leaves at the bottom. This arrangement was chosen because it permitted a simple gas flow. Because of the gas flow in the reactor core the hot gas enters the steam generator at the bottom. The simplest arrangement is thus to have an upward gas and a downward steam flow in the steam generator. The steam generator units were fabricated in a special workshop. Each unit is 2000 mm in diameter, 18000 mm long and weighs 65 tons. Transport to the site was by rail on a normal rail wagon with special transport attachments. Unloading and erection on site made use of the existing lifting equipment on site and was carried out in a short time without any surprises. After fitting the units into the PCRV the external piping to the main headers were mounted. Because the safety requirements for this piping system were changed after the original design and planning stage, extensive redesign and changes became necessary. Existing space limitations made it extremely difficult to fulfill all functional and safety requirements. However, the new concept was completed in time for reactor operation.

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Reference:

Specialists' meeting on technology of steam generators for gas-cooled reactors Winterthur (Switzerland) 9-12 Mar 1987

International Atomic Energy Agency, International Working Group on Gas-Cooled Reactors, Vienna (Austria)

IWGGCR--15, pp:77-86