  The performance of a muon radiography system designed to image the inner
structure of a nuclear plant located at a distance of 64 m was evaluated. We
concluded absence of the fuel in the pressure vessel during the measurement
period and succeeded in profiling the fuel material placed in the storage pool.
The obtained data also demonstrated the sensitivity of the system to water
level changes in the reactor well and the dryer-separator pool. It is expected
that the system could reconstruct a 2 m cubic fuel object easily. By operating
multiple systems, typically four identical systems, viewing the reactor from
different directions simultaneously, detection of a 1 m cubic object should
also be achievable within a few month period.
