  As it was shown by many authors, a slow decrease in X-rays observed during
the decay phase of long duration flares (LDE) can be explained only by a
magnetic reconnection and energy release ceaselessly ongoing in the coronal
part of a flare. Using RHESSI data we try to answer two following questions.
How effective are these processes at the LDEs decay phase and how can precisely
the energy release rate be calculated based on these data? To answer the
questions images of the selected LDEs during their decay phase were
reconstructed. Physical parameters of flare coronal sources obtained from image
spectral analysis allowed us to study the efficiency of the energy release
process. We also examined terms included in the energy equation to find out
what is the accuracy of determination of each term.
