Feasibility study on Cherenkov radiation-based crack detection for reactor vessel monitoring in sodium-cooled fast reactors

초록

Structural health monitoring of reactor vessels in sodium-cooled fast reactors (SFRs) is challenging due to high temperatures, intense gamma fields, and the optical opacity of liquid sodium. This study proposes a crack detection methodology utilizing Cherenkov radiation generated within optical fiber sensors deployed in the annular space between the reactor vessel and guard vessel. The detection principle exploits spatial variation in gamma-ray transmission through the vessel wall, where structural defects produce localized enhancements in Cherenkov photon yield due to reduced material attenuation. Experimental validation was performed using a60Co source at approximately 1 kGy/h with lead crack phantoms containing precision slits of 2–10 mm widths. A sensor array of high-OH silica fibers coupled to silicon photomultipliers resolved slit widths of 3–10 mm above the 3σ detection criterion (SNR ≥3.0), while the 2 mm slit produced a visually discernible peak (SNR = 1.84) approaching the formal minimum detectable limit of 2.355 mm. A preliminary width calibration yielded R2 = 0.9987, and stable optical transmission was confirmed up to 450 °C. This passive approach, requiring no external source and offering intrinsic electromagnetic immunity, represents a promising alternative for in-service inspection of SFR structural components.

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