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The temperature fluctuations in heat-transfer systems produce thermal stresses and fatigue damage on prolonged operation. Considerable temperature fluctuations can arise in steam boilers at the start of the zone of deteriorating heat transfer on account of the alternating contact with liquid and steam [1]. The turbulent flow of the heat carrier in the presence of a considerable temperature gradient also produces temperature fluctuations which penetrate into the wall [2 ]. Finally, temperature fluctuations can also arise to some extent on account of the stochastic nature of the boiling, with random production and detachment of bubbles at the heated surface. Although there have been several studies of temperature fluctuations, it is not at present possible to estimate in advance the magnitude of the fluctuations for a particular apparatus, mainly on account of the difficulty of incorporating thermal and hydraulic characteristics of any particular design.The basic purpose of statistical experiments is to determine the sources of the pulsations, the amplitude characteristics, and the characteristic times. The measurements were made with a model of a steam boiler using two standard modules made in Czechoslovakia. The body was 159 • 7 m and length 6 m, which contained 19 tubes of diameter 8 x 3, which were fixed in double tubular assemblies. The thermal power of the testbed was 600 kW, but this did not allow us to produce normal mass flow speeds for the water in the 19-tube module. We therefore left only six working tubes, which lay at the edge of the tube bundle. The other tubes were blanked off and served for monitoring purposes. This enabled us to make measurements at flow rates in the range 400-850 kg/sec-m ~, but the sodium speed in the generator was below the nominal value by about a factor of three . The tubes were made of NT8Kh6 steel. We mounted 50 microthermocouples in stainles s-steel jackets of outside diameter 0.5 mm on one working tube at intervals of 190 mm in the 158 ~5 ~ No !

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