Evaluation method for metal material for fuel assembly

Protons generated by reacting neutrons formed by fission reaction in the reactor core and hydrogen in reactor water are reacted with predetermined elements in metal material to be evaluated, to form inherent radioactive nuclides, and the reactor water containing the inherent radioactive nuclides is separated chemically. Then, radiation measurement is conducted to quantitatively determine the inherent radioactive nuclides, and the integrity of the metal material to be evaluated is evaluated based on the change of the quantitatively determined value. That is, radioactive niobium generated by Zr(p · n)Nb reaction with zirconium at the surface of the cladding tube is partially transferred into the reactor water. The integrity on the surface of the cladding tube is evaluated by measuring the Nb concentration in the reactor water. According to this method, the reaction on the surface of the metal material in the reactor can be recognized rapidly, and symptoms of the rupture of the fuel assembly in the reactor can be previously evaluated, thereby enabling to conduct continuous control. (T.M.)