Crud formation on low duty PWR fuel in the Halden reactor

A previous paper summarised observations on the effects of water chemistry and thermal-hydraulic conditions on crud formation on PWR fuel in the Halden reactor. These observations led to the conclusion that a critical degree of fuel duty (which can be expressed as degree of coolant sub-cooled boiling, void fraction or mass evaporation rate) was required for the formation of tenacious crud deposits. Recent measurements of the oxide layers on low duty PWR fuel have revealed the formation of tenacious crud deposits. This paper describes the operating history of the fuel rods, including water chemistry and thermal-hydraulic conditions, and suggests reasons for the sudden appearance of the crud deposits. (author)