Abstract: The reaction heats released by the reaction between nitrous acid and hydrazine and hydroxylamine were respectively investigated using micro calorimeter C80. The results show that the reaction heat per mole of nitrous acid with hydrazine depends on their proportions. While the concentration of nitrous acid is two times higher than that of hydrazine, the reaction heat per mole of hydrazine(ΔE₁) is 284.4 kJ/mol. The reaction heat per mole of nitrous acid(ΔE₂) is 166.7 kJ/mol when the concentration ratio of nitrous acid to hydrazine is less than 1. Additionally, when the concentration ratio is between 1 and 2, the reaction heat per mole of hydrazine is between ΔE₁ and ΔE₂. The reaction heat per mole of nitrous acid depends on nitrous acid/hydroxylamine proportions. When the concentration of nitrous acid is more than that of hydroxylamine, the reaction heat per mole of hydroxylamine ΔE₄ is 200.0 kJ/mol; whereas the concentration of nitrous acid is less than that of hydroxylamine, the reaction heat per mole of nitrous acid ΔE₅ is 194.9 kJ/mol. The temperature increment of feed adjustment for 1 BP in the spent fuel reprocessing process is also discussed and tested.