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1. Introduction<br />

Due to its excellent physic-chemical and nuclear characteristics, lead-bismuth has been proposed<br />

both as a coolant and a spallation target for hybrid systems, so called accelerator driven systems<br />

(ADS) [1]. However, heavy liquid metals, and particularly lead-bismuth, present a high corrosivity to<br />

most of structural materials.<br />

Austenitic steels may be used in a hybrid system in contact with liquid lead-bismuth if the operating<br />

temperature is not beyond 400ºC. For higher temperatures, martensitic steels are recommended [2].<br />

However, with long operation times, the interaction between the structural material and the eutectic<br />

leads to the solution of some elements of the steel (Ni, Cr and Fe, mainly) in the liquid metal. In a nonisothermal<br />

lead bismuth loop, the material dissolution takes place at the hot leg of the loop and, due to<br />

mass transfer, deposition occurs at the cold leg. The available experience, proceeding from the Former<br />

Soviet Union, shows that one of the possible ways to improve the performance of structural materials<br />

in lead-bismuth is the formation and maintenance of a protective oxide layer, which would constitute a<br />

barrier between the liquid metal and the steel.<br />

2. Experimental<br />

Tests have been performed in a small thermal convection loop built of austenitic stainless steel<br />

type 316, containing a lead-bismuth volume of 1.2L. A scheme of the loop is shown in Figure 1. The<br />

maximum temperature is of 550ºC with a temperature gradient between 50 and 100ºC. Thermocouples<br />

placed in several points of the loop, embedded in the lead-bismuth, were used to control the loop<br />

temperatures. The eutectic and the gas for controlling the atmosphere were introduced into the loop<br />

from an expansion tank placed on top of it.<br />

Figure 1. Thermal convection loop<br />

Pb-Bi<br />

Ar + O 2<br />

Cold leg<br />

Corrosion<br />

specimens<br />

Cold leg<br />

Hot leg<br />

Hot leg<br />

Drain tank<br />

Cylindrical specimens (10 mm length and 7 mm of diameter) of martensitic steel F82Hmod. and<br />

low alloy steel 2¼ Cr-Mo, named P22, have been tested. The materials composition is shown in<br />

398

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