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[en] Work executed: In the present phase, work is being concentrated on the points of emphasis associated with the reactor pressure vessel, in particular the prestressed concrete vessel concept with ''hot'' liner and the sequence of erection. The work was carried out by the firms B 4- G, GS and HRB. Below an outline is given of the state of the techniques before the work commenced, the present state reached and the objectives up to mid-1977. The work performed has been based on two main results of the HTR development: first the licencing procedure for the prestressed concrete pressure vessel of the HTR 1 160 plant, in which the pod boiler design together with the calculation procedures, material data, and design regulations were assured; secondly the calculations and tests carried out in Phase IA for the HHT vessel of the three-loop configuration.
[en] When we submitted our last status report to you in Jülich in 1975, 2 V2 years of Phase I of our project laid behind us and we reported to you on the reference design. We hat the impression at that time that you were not particularily keen on it, and we believe that development since then have proved that you were right. It has taught us that technically elegant solutions alone cannot prepare the way for a new nuclear power plant concept: much more important are the premises on which new developments are initiated. Before reporting on the present state I would like to recall briefly the situation as it was at that time, and to sketch what has happened in the meantime, and why our present results can be better. In preparing the reference design we had proceeded on the assumption that the HTR double-circuit system was about to invade the market and to secure a due share of it. Accordingly our calculations were based on a successful advance of the double-circuit configuration with a series of plants (Fig. 1-1). As a consequence of this we wanted to adopt as much as possible from the double-circuit design. Another limiting factor was the desire to complete a first HHT plant as soon as possible. To accelerate this the simpliest concept possible was aimed at, forgoing all extras unless these were absolutely essential. In addition a joint concept was to be established with GAC.
[en] The aim in phase IA of the HHT project was first to recognise and then to solve step-by-step the problems which might arise from the use of standard commercial components for the main recooling system of an HHT plant. This aim was achieved especially by successfully progressing so far with the design of the cooling components, research into the corrosion behaviour of the individual components, and a technical and economic comparison of cooling tower bodies that even the computer programs for optimum costing of dry cooling towers for an HHT plant could be drawn up and used. In order to be able fully to exploit the advantages of the gas-cooled high-temperature reactor, the design of the heat rejection system of the plant must be optimised and care must be taken to ensure that the combination of the primary and recooling circuits is economical. The entire recooling system was laid out in conjunction with BBC Mannheim. The following statements deal only with the dry cooling tower because this component is least known and perhaps therefore always a subject for discussion. In the latest layout (see fig. 6-1), the cooling water enters the dry cooling tower at a temperature of about 70 °C and must be cooled to about 14 °C. In a first approximation, a small cooling tower was to be used for this relatively large temperature difference.
[en] Alternative concepts: Before presenting the chosen concept the selection process shall first be described briefly. On the basis of the analysis made in the fall of 1975, the choice was narrowed to the following three concepts (see Fig. 2-1): — a gas turbine cycle with intercooling and turbine circuit integrated in the reactor pressure vessel, hereinafter called INT, — the same with non-integrated layout, abbreviated NINT, and — a gas turbine cycle without intercooling with steam cycle in series, as combined cycle KD; here the primary circuit is integrated in the reactor pressure vessel analogous to the INT, but the steam circuit is located outside the reactor safety building in conventional manner. Fig. 2-2 shows the measures by which the target figures ought to be achieved with these variants. The first column contains the three superordinated criteria: economy, licencibility, and operational aspects.
[en] In this section the machine concept is discussed first, followed by a closer look at some of its major components. In accordance with the cycle data and limit conditions mentioned in the previous sections (e.g. integration in the reactor pressure vessel), the helium turbine for the 1,200 MWel INT plant has been designed as a two-casing three-bearing machine, above all on account of the high output. Fig. 4-1 shows a longitudinal section through the turbine tunnel with the machine installed. The tunnel diameter is 5.7 m, while the diameter of the biggest casing is 4.4 m. The high-pressure compressor and the turbine are housed in a common casing, while the low-pressure compressor has its own casing. Distances between bearings are 11 and 12 m respectively. The generator is driven from the turbine end. The axial thrust bearing is arranged on the free shaft end of the low-pressure compressor. On account of the large flow and in order to equalize the nozzle forces, all turbine inlets and outlets have two branches arranged opposite, with the exception of the high-pressure compressor outlet. Here the helium flows into the turbine cavern through openings around the entire casing circumference close to the diffuser, and thence coaxially to the two turbine inlet ducts to the heat exchangers. The casing is thus surrounded by high-pressure gas on the outside, which facilitates dimensioning from the strength aspect, which is particularly beneficial in conjunction with the connecting nozzles arranged in the plane of the horizontal dividing flange. The nozzles are joined to the gas ducts in the reactor pressure vessel by displaceable remote-controllable intermediate pipes.
[en] Under the HHT development program, the high-temperature helium test plant (HHV) was set up on the site of the Jülich Nuclear Research Institute (KFA). This plant, which was erected using public funds supplied by the Federal Republic of Germany, the State of North-Rhine-Westphalia, and the Swiss Confederation, is intended to demonstrate the operational suitability and reliability of the HHV turbo-machine in addition to testing circuit components. It is the largest and one of the most important test plants in the HHT project, since only there it is possible to obtain process data like pressure, temperature, and total helium flow directly comparable with data on a large HHT plant. The decision to build in 1972 was preceded by various design studies made by the industrial and research establishments participating in the HHT project and the Colleges of Advanced Technology in Aachen and Hannover. Here, it was decided not to proceed with the immediately obvious procedure of building a fossil-fuel-fired closed gas turbine circuit with test loop and a power of about 150 MW, because of the special very high material loads occuring in the heater, which would have necessitated the use of little-known materials with the concomitant heavy costs and risks.
[en] Problem and state of the art: Heat exchangers for closed gas turbine installations using fossil fuels have been built for decades. In addition, a modern tradition has already grown up in the construction of large heat exchangers, namely steam generators for gas-cooled reactors. The earliest CO2-cooled plants have already been in operation for 20 years, and helium-cooled reactors for more than 10. I now propose to try to put the heat exchanger designs for high-temperature-helium-turbine circuits in the context of experience in building the aforementioned heat exchanger components. Here, I should like to show that the proposed ideas in no way break new ground which cannot be trodden with safety using already available industrial experience. The performance, temperature, and pressure of the main heat exchangers for an HHT plant, i.e. the recuperator, precooler, and intercooler, have no stricter requirements to satisfy than in existing and operating equipment. What is new is the combination of the various parameters, especially the requirement for compact construction and adaptation to the shape of the pods in the prestressed concrete reactor vessel (PCRV) at relatively high volume flows and the technological problems arising from the use of helium. The first figures show how the HHT heat exchangers fit in the field of heat exchangers built so far.