On the Stability of Uranium Carbide in Aqueous Solution—Effects of HCO₃^– and H₂O₂

Abstract

Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H 2 O 2 . In this work, we have studied the dissolution of uranium upon exposure of UC powder to aqueous solutions containing HCO 3 − and H 2 O 2 , separately and in combination. The experiments show that UC dissolves quite readily in aqueous solution containing 10 mM HCO 3 − and that the presence of H 2 O 2 increases the dissolution further. UC also dissolves in pure water after the addition of H 2 O 2 , but more slowly than in solutions containing both HCO 3 − and H 2 O 2 . The experimental results are discussed in view of possible mechanisms.

Route to Stabilization of Nanotechnetium in an Amorphous Carbon Matrix: Preparative Methods, XAFS Evidence, and Electrochemical Studies

“…Materials containing technetium–carbon bonds in an amorphous carbon matrix could be more suitable for making radioactive waste storage matrices than metallic technetium. Because irradiated nuclear fuel is radioactive, oxidizers can be produced as products of water radiolysis . The impact of the oxidizing environment on technetium carbide under conditions of underground corrosion will lead to the formation of a protective layer of technetium oxides at its surface, which impedes its corrosion.…”

“…Because irradiated nuclear fuel is radioactive, oxidizers can be produced as products of water radiolysis. 15 The impact of the oxidizing environment on technetium carbide under conditions of underground corrosion will lead to the formation of a protective layer of technetium oxides at its surface, which impedes its corrosion. In addition, if the outer protective barriers fall, then the nanosized amorphous carbon forms an additional chemical and mechanical barrier against oxidation by oxygen dissolved in the penetrating water.…”