Fuel Defect Root Cause Investigation at Wolsong-1

Abstract

Wolsong Unit 1 had experienced a number of fuel failures from September 1995 until August 1996. There was a rapid increase in the primary heat transport system (PHTS) activity during that period. I-131 and Xe-133 levels of up to 290 and 80,000 uCi/kg, respectively, were recorded. The investigation concluded that the root cause was high hydrogen content within the fuel elements resulting from insufficient baking of the CANLUB graphite coatings. After the manufacturing process and hydrogen analyses procedures were improved, the total amount of hydrogen within a fuel element now remains below 0.6 mg. Fuel manufactured with the improved process is performing well and the coolant activity levels have slowly returned to normal as the defects were discharged from the core.