If the sodium is sprayed out into an atmosphere that contains oxygen, then again the possibility of a fire is present. The sodium spray may arise from the failure of a primary sodium pipe under pressure or a similar cir­cumstance, although it is a little unlikely in an actual plant. Pipe leaks form­ing pools are more probable if a leak occurs.

When fine particles of sodium are sprayed into the air, the sodium may ignite at room temperature if it is in the form of a mist, although it may not ignite until the temperature is about 250°F if the sodium is in the form of droplets. The burning rate increases as the oxygen concentration is increased, up to 5%. It also increases if the moisture content of the atmosphere is increased, although there is no significant effect following an increase in the spraying pressure (55). Experiments have produced burning rates that are as rapid as the ejection rates themselves.

Heat from the spray fire is lost to the oxide particles, to the unburned sodium, to nitrogen in the air, and to the containment walls by radiation. Modeling of a spray fire must therefore take all these modes of heat transfer into account.

Due to the motion of the particle, the fire is less likely to be extinguished by oxide blanketing. Safety features that could be employed to protect against the consequences of spray fires include baffles to accumulate the spray volume thus reducing the heat transfer area and allowing the fire to be blanketed. A better safeguard is to provide inert gases only in proximity with sodium.