Probing the inner structure of a blast furnace by cosmic-ray muon radiography

The visualization of the inner state of a blast furnace was investigated by exploiting the feature of cosmic-ray Muon that attenuates according to the density and the thickness of the object through which it penetrates. The distribution of the cosmic-rayMuon accumulated in an object in a blast furnace during a certain period has been determined by a probing system provided with two sets of a pair of panels with plastic scintillation counters segmented in parallel along each direction of both sides. Measurement was performed in the furnace hearth structure that had been taken out after the shutdown of Oita No.2 blast furnace repaired in 2004. The solid angle distribution of the amount of Muon penetration during a certain period was determined by the probing system located on a slant upward from the furnace bottom brick and the remaining iron in the furnace hearth structure. The average density of the object material in each azimuth was calculated on the basis of the accumulation ratio obtained from the relation between the intensity coming from the blast furnace side and that coming from the symmetrically opposite free space side. It was thus confirmed that the calculated average density was distributed according to that of the actual remaining brick and iron. Next, another measurement was performed in the same manner in the renewed furnace hearth of Oita No.2 blast furnace which had just started working after its repairs. The density of the material at the iron-rich portion inside the hearth was estimated fromthe accumulation ratio obtained from the relation between the intensity of theMuon channel passing through the iron-rich part in the hearth and that passing through its opposite channel symmetric to the coordinate origin. Then, the level of the furnace bottom brick, meaning its eroded thickness, was estimated from those accumulation ratios in relation to each channel crossing both the iron-rich part and the furnace bottom brick. The possibility of the density distribution of the material inside a blast furnace and the remaining thickness of bricks being estimated by this measurement method was identified.