  Intermediate level nuclear waste must be stored until it is safe for
permanent disposal. Temperature monitoring of waste packages is important to
the nuclear decommissioning industry to support management of each package.
Phosphor thermometry and thermal imaging have been used to monitor the
temperature of intermediate level waste containers within the expected range of
environmental storage conditions at the Sellafield Ltd site: temperatures from
10 {\deg}C to 25 {\deg}C and relative humidities from 60 %rh to 90 %rh. The
feasibility of determining internal temperature from external surface
temperature measurement in the required range of environmental conditions has
been demonstrated.
