Some British nuclear reactor cores contain serious cracks that could limit their continued operation and potentially lead to radioactive releases, according to newly released documents from the government's own nuclear inspectorate. The documents, which had been withheld from the public, were obtained by a group seeking to close one of the most controversial reactors, Hinkley Point B. That reactor has cracks at its graphite core that the owner, British Energy, has little information about and cannot further investigate without shutting down Hinkley and perhaps other similar reactors.