Detection of frozen salt in pipes using gamma-ray spectrometry of potassium self-activity

Solar plants that use molten salts as heat transfer fluid need careful control to avoid the freezing of the salt in the pipes; if such a problem occurs, a diagnostic instrument to localize where is the frozen salt plug and to determine its length is useful. If the salt contains potassium (as is the case of the most common mixture used in solar plants, NaNO₃/KNO₃ 60/40% by weight), the gamma decay of the natural unstable isotope ⁴⁰K can be exploited to detect the frozen salt in a non-invasive way. Simulations and experimental results regarding the detectability of such plugs with different masses/lengths are presented.