Voltage deterioration of XLPE wires in water under gamma ray irradiation

Three types of cross-linked polyethyline (XLPE) wire were developed for insulation of internal pump motors (wet type) used in an advanced boiling water reactor. By applying gamma ray irradiation of 10 ⁴ to 10⁶ Gy and electric stress in hot water simultaneously or sequentially, the effect of gamma ray irradiation is examined. The effect of combined stresses in a large scale functional test is also described. It is proved that the gamma ray irradiation less than 10⁶ Gy does not deteriorate the properties of the insulation of the wires. In the irradiational environment of 5×10 ⁴ Gy where the internal pump motor is served, it is concluded that the wires have sufficient reliability