Lead does not block Gamma radiation, cosmic rays, but will block other radiation as will the metal shell of a freezer. My experience has been that the faster the film the more prone to fogging as it ages. Tmax 400 and new version TriX have thinner emulsions with less silver and seem to fare better than the old Trix. I bought a bulk roll of an unnamed film made in England expired in 1972, ASA 50 but on different base than PanF, it was fine still shot at ASA 50, no fog. Bought a camera that came with a roll of GAF 500 expired 1976. The camera had been in Alaska the film was totally fogged.