A SENSITIVITY EVALUATION OF GAS-LIFT PROBE INCLUDED INTO CLADDING FAILURE DETECTION SYSTEM BY THE MODEL OF GASEOUS FISSION PRODUCT SOLUTION/DEGASSING INTO LEAD COOLANT

Gas-lift probe is an element of cladding failure detection system of perspective lead cooled reactor. Its function is local measurement of gaseous fission product activity in the coolant and the most defected fuel assembly localization. In the coolant leaving the defected fuel assembly the specific activity of gaseous fission products is higher than the average one in the primary circuit. In the barbotage channel of gas-lift probe gaseous fission products diffuse through the bubble interface surface into the volume of the bubbles. The bubbles deliver gaseous fission product to interface surface in the separation volume. The gas enriched with radioactive gaseous fission product goes to measurement volume of the probe. The more significant the damage and the closer the defective fuel assembly is located to the probe input, the more gaseous fission product activity will be registered. The paper presents a model of gaseous activity transfer from cladding defect to probe measuring volume. The gaseous activity transfer is described on the basis of the inert gases dissolution/degassing processes in lead. The gas-lift probe sensitivity was estimated as the ratio of the entry velocity of gaseous activity into the measurement volume to the exit one into the coolant through fuel assemblies cladding defects. A gas-lift probe sensitivity for exposed fuel surface calculated as an example. Gaseous fission products with significant gamma radiation are considered. The calculation results are presented in the article.