Review of the Property Differences of Hydrogen and Deuterium for the Accident Consequences in CANDU Reactors

The CANDU reactors are moderated and cooled by D2O. Therefore, it is natural that any accidents resulting in unmitigated degradation in fuel cooling can only be expected to involve D2O interactions with hot metals in degraded channel behavior and not H2O interactions. This paper compiles published information on deuterium gas properties and compares it to that for the lighter isotope of hydrogen. Differences in production rates by oxidation and other phenomena, such as radiolysis, energy release during these processes, transport phenomena, burns, flame acceleration, transition from burns to detonation and recombination rates are just some of the important aspects of the combustible gas phenomena that need to be reconsidered. Potential effect of a failure to consider D2 in safety evaluations on various aspects of computations undertaken in support of risk assessments is discussed. Literature survey indicates that the differences in production, combustion and transport properties of the two gases are significant. It demonstrated that deuterium and tritium differ from common hydrogen in a number of fundamental ways. Significant progress has been made in developing a data base of deuterium properties and deuterium behaviour in combustion and recombination. We have identified the issue of singularity of D2 properties and the errors made in depending upon systems for H2 detection, measurement and control at locations where H2 may not exist. Further work is necessary in updating the safety reports and in updating station instrumentation calibration to reduce any residual risk.