  Based on our recent MHD simulations, first, a concept of the successive
merging of plasmoids and fragmentation in the current sheet in the standard
flare model is presented. Then, using a 2.5-D electromagnetic particle-in-cell
model with free boundary conditions, these processes were modelled on the
kinetic level of plasma description. We recognized the plasmoids which mutually
interacted and finally merged into one large plasmoid. Between interacting
plasmoids further plasmoids and current sheets on smaller and smaller spatial
scales were formed in agreement with the fragmentation found in MHD
simulations. During interactions (merging - coalescences) of the plasmoids the
electrons were very efficiently accelerated and heated. We found that after a
series of such merging processes the electrons in some regions reached the
energies relevant for the emission in the hard X-ray range. Considering these
energetic electrons and assuming the plasma density 10^9-10^10 cm^{-3} and the
source volume as in the December 31, 2007 flare (Krucker at al. 2010, ApJ 714,
1108), we computed the X-ray spectra as produced by the bremsstrahlung emission
process. Comparing these spectra with observations, we think that these
processes can explain the observed above-the-loop-top hard X-ray sources.
Furthermore, we show that the process of a fragmentation between two merging
plasmoids can generate the narrowband dm-spikes. Formulas for schematic fractal
reconnection structures were derived. Finally, the results were discussed.
