The behavior of U(IV) in pulsed columns during off-standard operation is studied. The effects of disturbances on the behavior of U(IV) and U(VI) are tested using extraction equipment. The experimental results show that disturbances induce a marked accumulation of U(IV). Furthermore, simulations are carried out with the DYNAC numerical calculation model. For U(VI) and nitric acid concentration, the simulated values are in good agreement with experimental values. There is, however, a tendency to underestimate the concentration of U(IV) in the organic phase when U(IV) distribution correlations based on available data are used. Temperature profiles are also predicted, and the estimated values agree well with the measured values. Therefore, it is confirmed that DYNAC is applicable to heat balance calculation.