Reconsideration of Hydrogen Source Term in CANDUs to include Oxidation of Steel

The technical basis of the argument is in the parametric analyses presented in the paper. This is consistent with the methodology used in the safety report where a stylized steam flow is used to arrive at a 'hydrogen' source term However, as this paper is to urge reconsideration of hydrogen source term in CANDUs from oxidation of steel, the actual analyses of (LOCA+LOECC) will be undertaken afterwards with concrete integrated codes like CAISER or ROSHN1 which model every fuel channel with consideration of its feeder flow resistant characteristics in relation to each other. In the PHWR licensing analyse.. fuel thermal analyses are conducted by single channel models that assume a constant critical flow rate of steam into the channel that mayinn7as oxidation potential of the fuel sting. The analyses are typically carried out for a simulation period of an hour during which the 'hydrogen' source tam is calculated for a number of representative channels. These source term predictions are based on only fuel channel modeling ming computer codes such as CHAN-II or CATHENA. These coda, however. does not by to model oxidation by steam and air of other reactor components. especially carbon steel feeders and main heat transport system Piping as well as stainless steel end fittings. The hydrogen mitigating measures such as igniters and PAIL, in Wolsong are designed to avoid hydrogen explosions for both LCD and SCD which finally lead off-site sauce terms to be bounded within regulatory limits. In doing this, the hydrogen source terns; at CANDU could have remained under-estimated if oxidation of low carbon. low chrome feeders that are susceptible to high rates of oxidation in steam and air is not considered. All high temperature steam interaction phenomena, including exothermic oxidation of carbon steel feeders etc., needs to be studied. Also, the actual source term for combustible deuterium may be different from that of previously assumed hydrogen species. Hydrogen mitigation measures. such as ignites and recombiners have been sized according to the predicted source term that does not include hydrogen source term from steel oxidation. Carbon steel oxidation by steam at the inside surfaces and air at the external surfaces (exposed to containment atmosphere after the insulation in the feeder cabinet buns off) have to be considered together. Furthermore. the feeders are known to be mat during normal operation from moisture and their oxidation after the core damage accident associated with a (LOCA-i-LOECC) must consider oxidation with consideration of water vapor presence. Increase of oxidation rates for almost all metals in presence of steam is easily expected.