The pressure exerted by sunlight (radiation pressure force) would not be significant for the comet, but only act on the dust escaping from the surface. That is why the dust tails curve away from the gas tails in comets. At perihelion the solar energy arriving at the surface would be greater and so raise the surface temperature. This could have the effect of increasing the sublimation rate of ices, and along with the water vapour gas dust particles could also escape.
However, my view is that the extra solar heat conducted into regions tens of metres deep would lead to warm lakes containing biology, and biological replication with gas production (methane, CO2) would rupture the surface and produce geysers carrying microbes with the gas.
Nuclear energy sources (radioactive decay of Al-26, for example) would be confined to the early history of comets in the solar system.
Does this answer your question?
Chandra: Yes, the tidal forces are totally negligible.
Prof. Chandra Wickramasinghe
Dear C, thanks. Perfect answer. I assume as you do not mention gravity, that the sun’s gravitational attraction , max at the perihelion, is not contorting the comet? Sent from my Windows Phone