tained in the form of TN03 and T 2 0 vapors. These should react relatively slightly with oxidized walls, so little escape is indicated by permeation of corrosion hydrogen through the metal. The gaseous T 2 0 or TN03 in the system would occupy the fulI volume (-IO5 liters) of the heat transfer system, which thereby would have appreciable capacitance before processing was required. (The -2400 Ci/day of total tritium production is 0.04 moles/day, most of which should not even penetrate into this system.) Processing to remove such tritium as enters the nitrogen dioxide system could probably be accomplished by various schemes, batchwise or on side streams: adsorption, freezing, or distillation suggest themselves. Addition and removal of H 2 0 could readily provide an isotope dilution effect if desired. Thus the major modes of escape of tritium from the power system which remain are by leakage, either through turbine seals or into the condenser water. It would appear necessary to prevent leakage of NOz and such burden as it has of tritium into condenser water, and to contain or recover any leakage past turbine seals. This appears required in corresponding steam systems also, but tritium is thought to enter the steam systems considerably more readily. In either system the diversion of tritium from the power system implies a requirement that it be recovered from the primary circuits. Recovery from the primary system is not discussed here. In summary, possible advantages of a nitrogen dioxide power system thus include:
1. The ability to block a major tritium path to the environment.
2. The recovery of such tritium as may enter the system in a concentrated form. 3. The lower equipment costs because of improved thermal transport properties. 4. Improved thermodynamic efficiency.
5. Less restriction on properties of intermediate coolant salt, since vapor generation can be accomplished with possibly greater ease.
Hazards and uncertainties include: 1 . Routine handling of toxic or noxious gases under pressure. 2. The question of the irreversible decomposition of
nitrogen oxides into the elements. 3. The relation between chemical reaction rates, heat transfer, and flow rates when all rates are high. 4. The effectiveness of the oxide films in preventing
tritium passage has not been evaluated.
5. Recovery methods for recovery of such tritium as enters the system are undefined. 6. Cost comparisons with other systems (steam) have not been made.
On balance the use of nitrogen dioxide as a dissociating-gas thermal fluid for a Molten-Salt Breeder Reactor appears to merit further consideration.