  Here we present an improved algorithm to model the serpentinization process
in planetesimals in the early Solar system. Although it is hypothesized that
serpentinization-like reactions played an important role in the thermal
evolution of planetesimals, few and restricted models are available in this
topic. These processes may be important as the materials involved were abundant
in these objects. Our model is based on the model by (Gobi & Kereszturi 2017),
and contains improvements in the consideration of heat capacities and
lithospheric pressure, and in the calculation of the amount of interfacial
water. Comparison of our results with previous calculations shows that there
are significant differences in the e.g. the serpentinization time -- the time
necessary to consume most of the reactants at specific initial conditions -- or
the amount of heat produced by this process. In a simple application we show
that in icy bodies, under some realistic conditions, below the melting point of
water ice, serpentinization reaction using interfacial water may be able to
proceed and eventually push the local temperature above the melting point to
start a 'runaway' serpentinization. According to our calculations in objects
with radii R $\gtrsim$ 200 km serpentinization might have quickly reformed
nearly the whole interior of these bodies in the early Solar system.
