By Valerii Hnidyi KHARKIV, Ukraine (Reuters) – The head of a nuclear research facility in the northeastern Ukrainian city of Kharkiv said on Friday that the grounds of the institute had been struck by Russian shells during recent fighting, but the core housing nuclear fuel remains intact. He warned, however, that any future damage to equipment in the core could pose a danger. “The facility, in working condition, doesn’t present any danger whatsoever,” said Mykola Shulga, director general of the National Science Centre Kharkiv Institute of Physics and Technology. “However, if there is physical …