  Inertial confinement fusion hotspots and cluster Coulomb explosion plasmas
may develop a positive net electric charge. The Coulomb barrier penetrability
and the rate of nuclear fusion reactions at ultra-low energies ($\lesssim 10$
keV) are altered by such an environment. These effects are here studied via the
screening potential approach. Approximate analytical results are developed by
evaluating the average screening potential for some scenarios of interest. It
is found that fusion is hindered for reactions between thermal fuel nuclei,
while an enhancement is expected for secondary and "beam-target" reactions.
Depending on the plasma conditions, the variations can be relevant even for
relatively small net charges (several % difference or more in the fusion rate
for an average net charge per nucleus of $10^{-5}$ proton charges).
