The visit saw Mrs Gradden and Steve Cottam, head of strategy and technical for the legacy ponds, give a presentation to the Boardman family.
They were also shown the Thorp viewing gallery, National Nuclear Laboratory and the underwater test facility.
Samuel, who lives in North Wales, described himself as a ‘nuclear physics expert’ in his letter to Sellafield.
Adrian Bull MBE, director of external relations for the National Nuclear Laboratory, said: “We are always keen to encourage bright, young people to make a contribution to society by suggesting ways things could be improved – whether through the development of new technology or through the creative application of existing techniques.
“Samuel has shown tremendous talent and enthusiasm through sharing his suggestions with the industry and I was delighted the he was able to visit NNL’s facilities on the Sellafield sire to see for himself some of the work we are doing.”