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Conference Article: Boiler referruling on the Hartlepool and Heysham 1 advanced gas-cooled reactors

Abstract

The Hartlepool and Heysham I reactors each use eight cylindrical boilers having nineteen rows of helical tubes. The advantages of this design are partially offset by the relatively poor radial gas mixing. Some rows of tubing may have an imbalance between heat input from the gas and the flow of feedwater. causing a temperature profile at the upper transition joints. The thermal/hydraulic behaviour meant that the metallurgical constraints limited output. Analysis of the behaviour of these boilers required a new two-dimensional mathematical model, known as PODMIX. This describes the thermal hydraulics in each of the rows of tubing and also in the gas between the rows. Not all of the parameters for the model can be determined from first principles. However, two out of the thirty two pods have thermocouples at some of the upper transition joints and these made back calculation possible. In order to translate this model to other boiler pods, a novel thermocouple rake system was designed for sampling superheated steam temperatures in selected tubes. A result of this analysis was to show that different, individual ferrule patterns were needed for each pod. The characteristics could, in general, best be met using twin orifice ferrules. Unfortunately, the installed system did not permit the replacement of orifices, so that a completely new system had to be developed. In the course of designing this, the opportunity was taken to over come susceptibilities to erosion/corrosion and crevice corrosion. Removal of the old ferrules and replacement with the new ones necessitated the development of high precision, programmable machines to operate under difficult site conditions. These carried out drilling, boring, grinding and polishing operations as well as making face welds and tube bore welds. Modifications have already achieved substantial improvements in performance and output, but an extended, iterative programme still lies ahead.

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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:188-194