Continued from the report (III), transient phenomena of iodine concentrations in primary coolant which appeared after sudden opening of hair crack on fuel cladding under constant power state are all analyzed.
From these analyses it is understood that the information on every state of cladding defect are given by observed iodine concentrations ¹³¹I and ¹³³I. But the direct ejection of fuel uranium by fission fragments and knock-out phenomena to primary coolant which may occur under the most unfavorable condition, are all excluded from this paper.
Observations of iodine concentrations in primary coolant in every 12h or 24h, or even every 48h under power state are very convenient to catch information of cladding defects.