GB1072745A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

1,072,745. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. March 7, 1966 [March 15, 1965], No. 10939/65. Heading G6C. A gas-cooled nuclear reactor has at least some of the surfaces in contact with the coolant of Ni or a Ni-Cu alloy and the coolant comprising CO 2 and a quantity of CO to reduce the oxygen potential of the coolant. In a reactor where the fuel is provided with metallic sheaths, these should be of Ni or a Ni-Cu alloy. At a temperature of 600‹ C., the minimum concentration of CO to give complete inhibition of oxidation is about 0À17% of the volume of CO 2 + CO whilst at 1000‹ C., inhibition is obtained with an addition of about 1À3% CO. With a lower CO content, e.g. 0À8 to 1À0%, some oxidation of the sheaths would occur at 1000‹ C. but the oxidation rate might be sufficiently low to be acceptable. However, other surfaces in contact with the coolant, e.g. in the coolant ducts and heat exchangers, although at a lower temperature than the fuel element sheaths, might also be subject to oxidation and since renewal of these surfaces will not normally be possible, it is desirable to prevent completely the oxidation of these surfaces. These surfaces should also be of Ni or a Ni-Cu alloy. Preferably, to ensure that there is no oxidation, the CO concentration should slightly exceed the minimum required to give complete oxidation inhibition. The strength of the Ni used for the fuel element sheaths may be increased by incorporating oxide dispersions. ThO 2 is most commonly used for this purpose but may not be suitable for nuclear purposes, in which case an oxide, e.g. Al 2 O 3 , of a non-nuclear metal having a low neutron captive cross-section would be preferred.