  Chondrules in primitive meteorites likely formed by recrystallisation of dust
aggregates that were flash-heated to nearly complete melting. Chondrules may
represent the building blocks of rocky planetesimals and protoplanets in the
inner regions of protoplanetary discs, but the source of ubiquitous thermal
processing of their dust aggregate precursors remains elusive. Here we
demonstrate that escape of positrons released in the decay of the short-lived
radionuclide $^{26}$Al leads to a large-scale charging of dense pebble
structures, resulting in neutralisation by lightning discharge and
flash-heating of dust and pebbles. This charging mechanism is similar to a
nuclear battery where a radioactive source charges a capacitor. We show that
the nuclear battery effect operates in circumplanetesimal pebble discs. The
extremely high pebble densities in such discs are consistent with conditions
during chondrule heating inferred from the high abundance of sodium within
chondrules. The sedimented mid-plane layer of the protoplanetary disc may also
be prone to charging by the emission of positrons, if the mass density of small
dust there is at least an order of magnitude above the gas density. Our results
imply that the decay energy of $^{26}$Al can be harvested to drive intense
lightning activity in protoplanetary discs. The total energy stored in positron
emission is comparable to the energy needed to melt all solids in the
protoplanetary disc. The efficiency of transferring the positron energy to the
electric field nevertheless depends on the relatively unknown distribution and
scale-dependence of pebble density gradients in circumplanetesimal pebble discs
and in the protoplanetary disc mid-plane layer.
