The train drivers' union, ASLEF, isn't involved in the current round of strikes. So, theoretically, all freight can keep moving.
However signallers who're in the RMT will be striking, meaning that managers will be trying to cover for them where possible. That will enable some lines to remain open to freight traffic, as well as to limited passenger services.
However the plans for most rail operations seem to be restricted to roughly 'office hours' on the strike days (presumably, in part, because there aren't enough managers to man the signal boxes for 24 hours), so many freight trains won't actually be able to run as they're timetabled outside of those hours.