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Conference Article: The internal instrumentation of the THTR steam generator

Fricker, H.W. (Sulzer Brothers Ltd., Winterthur (Switzerland))

Abstract

The THTR steam generator contains several highly loaded components. Is is also the first nuclear steam generator employing downhill boiling. It is therefore very important to know the internal temperatures of both gas and water at some critical locations and to compare them with predictions. Since all six steam generators are of identical design it was decided to instrument one module only. A total of 71 thermocouples were introduced. 21 thermocouples measure the gas temperature around the tubes and 50 thermocouples the water/steam temperature inside the tube. The thermocouples are of the sheathed design with electrically insulated tip. In order to measure the correct temperature the design and execution of the attachment is of utmost importance. The type of attachment will be described and the predicted measuring deviations given. The location of the thermocouples is such that the temperature distribution along some selected tubes can be determined. The results will, therefore, give information not only about the precision of the thermal sizing but also on flow distribution, boundary effects and flow stability. The installation of the thermocouples had to go parallel with the manufacture of the steam generator subassemblies. This had to be considered very carefully in the design and in the planning of the manufacturing sequences. When assembling the subassemblies the thermocouple leads had to be joined together or to the penetration in a pressure and temperature resistant gas tight manner, without interfering with the electrical properties. All manufacturing steps were closely followed and supervised by quality control actions, and the results were recorded. The performance of all 71 thermocouples in the commissioning stage of the reactor has been faultless.

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key words: Gas Cooled Reactor, Nuclear Technology
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:107-111