26.08.2015   Modern Power Station Practice

Temperature measurements

2.3.1 Basic requirements

Many of the requirements are associated with fuel element temperature assessment but a large number of measurements are made of the temperatures of reactor graphite, the pressure vessel and parts of the boiler in addition to measurements of auxiliary plant operation.

Another set of temperature measurements is re­quired for connection to the temperature trip units in the reactor safety circuit discussed in Section 5.4 of this chapter.

The measurements are normally made using indus­trial-type, metal-sheathed, mineral-insulated thermo­couples manufactured generally to BSl041:l943, with batch accuracies of ±4°C up to 500°C. The thermo-

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couples are supplied in accordance with the CEGB specification for reactor instrumentation, and illus­trated in Fig 2.55; further details are given in Volume F, Chapter 4. Stainless steel sheathed chromel/alumel, Type К thermocouples are used mainly in the reactor and on the reactor vessel structure, iron/constantan Type J thermocouples being used in the concrete biological shield. In a power reactor there may be several thousand thermocouples.