[en] High-Level radioactive liquid waste is being reduced to a liquid slurry by an evaporation and crystallization process and stored in the existing single-shell tanks. Continuous pumping of the waste storage tank will reduce the present 30 to 50% moisture to the minimum possible. The reduced waste is a relatively immobile salt cake consisting predominantly of sodium nitrate (NaNO₃) with lesser amounts of sodium nitrite (NaNO₂), sodium metaaluminate (NaAlO₂), and sodium hydroxide (NaOH). Trace amounts of fission products, transuranics, and a broad spectrum of organic materials in small but unknown amounts are also present. A program was initiated in 1973 to determine whether or not conditions exist which could lead to an exothermic reaction in the salt cake. Results of the latest series of tests conducted to determine the effects of mass and pressure are summarized. Hanford salt cake, as stored, cannot support combustion, and does not ignite when covered with a burning volatile hydrocarbon