I am doing a project in which I fill a cylinder with a volume of $636cm^2$ (made of stainless steel) with molten salt: 60% Sodium Nitrate ($NaNO_3$) and 40% Potassium Nitrate($KNO_3$).
The container might reach (worst case scenario) -35 degrees Celsius in a cold winter night and in the summer (with ideal conditions) up to 700 degrees Celsius.
I'm trying to find out if I should add a relief valve (like in old water boilers) or just seal it tight. This of course depends o how much the pressure increases between those 2 states.
I know that molten salt melts at 221 degrees Celcius and starts freezing when it reaches 238 degrees Celcius.
I can't find any relevant data, so I don't know how I could find the result for this. Any ideas or suggestions?
EDIT: My worry is that it would blow up due to pressure or the lid would blow open...