Resistivity monitor to indicate oxide content of sodium

The electrical resistivity of sodium or sodium-potassium is continuously measured whilst flowing at operating temperature in a pipe, to provide an indication of impurity level, particularly oxygen, and thus to enable progress of clean-up in liquid-metal loops to be followed and to give assurance that high purity is achieved and maintained. The meter is designed to be sensitive to a change of one part in 106 in oxygen level, corresponding to a change in resistivity of about one part in 104. A change in liquid-metal temperature of only 0.04° C will also produce this effect, and hence temperature compensation and achieving high stability are the chief problems of the design. Two types of resistivity meter are described, both of which have been installed in the Dounreay fast reactor. Tests indicate that the design objective has been achieved and the value of the meter as an impurity monitor has been proved.