EFFECT OF HOOP-STRESS ON CORROSION OF ZIRCALOY-4 CLADDING TUBE

Corrosion of Zircaloy-4 cladding tube has been investigated either wit h or without hoop stress in steam at 400 degrees C as well as in a LiO H solution of 2200 ppm Li at 350 degrees C, respectively. Corrosion en hancement is observed under hoop stress in the highly lithiated soluti on of 2200 ppm Li. The applied hoop stress was found to cause hydrides to redistribute non-uniformly, resulting in the concentration of hydr ides near the oxide/metal interface and furthermore the formation of s ome radial hydrides near the surface. However, this stress effect does not occur when Zircaloy-4 cladding is corroded in steam at 400 degree s C for up to 150 d because of lower hydrogen pickup. It is concluded that the corrosion is accelerated by the hydrides concentrated near th e oxide/metal interface, and the corrosion enhancement by hydrides is likely to be due to faster corrosion of hydrides. Consequently, the en hanced corrosion of Zircaloy-4 cladding tube at high burnup in PWRs is suggested to be associated with the concentration of hydrides near th e surface which takes place at high burnup.