Measurement of Release Rate of lodine-131 Released from Artificially Pin-Holed Fuel Rod into Primary Coolant of In-Pile Water Loop

Abstract

To pursue amounts and movements of iodine-131 released from the UO₂ pellet to outside and from the pin-holes of fuel rod clad into the primary coolant water of loop, the fission products release experiment was performed by using an artificially pin-holed fuel rod at the in-pile water loop. The specifications of an artificially pin-holed fuel rod were as the following: UO₂ pellet-weight 13.331₅g, content of ²³⁵U0.32 g, diameter 10.63₂mm, height 14.6 6mm; Zircaloy-2 clad-total length 84.9₅ mm, outer diameter 12.21₈mm, thickness 0.69₈mm; Pin-holes located at plenum part, hole diameters 20 μm and 200 μm. An artificially pin-holed fuel rod was irradiated at the JMTR OWL-1. The representative coolant water conditions at the test section in reactor core, in boiling water mode operation, were as follows: coolant water pressure 71kg/cm2 G, coolant water temperature 288°C, steam quality 6∼8%, coolant water flow rate 25 kg/min. The irradiation period of fuel rod at the estimated linear heat rate of 340 Wicm was as long as 21.2 days. The amounts of iodine-131 in the coolant water were determined by gamma ray spectrometry with chemical separation after sampling.
At the end of irradiation, total amounts of iodine-131 released from the artif icially pin-holed fuel rod into the primary loop coolant water came out to be 1.9 Ci. Through the irradiation period, the averaged release rate of iodine-131 was 2.5, μCi/s. A radiochemical m ethod for irradiation examination for nuclear fuel safety was developed by measurement of ¹³¹I released into the coolant water from an artificially pin-holed fuel rod at in-pile water loop. L