The spent fuel coincident counter (SFCC) is an underwater neutron coincident counter for the verification of operator declared plutonium content in canned fast breeder reactor spent fuel. A single ionization chamber measures the γ ray dose from the spent fuel to determine the appropriate operational parameters to avoid γ ray pile effects in the 3 He tubes. The plutonium isotopics are calculated based on a validated burnup chains code. Specially developed iterative software in combination with Monte Carlo N particle transport code (MCNP) modelling converts the measured single and double neutron count rates to plutonium mass. The SFCC easily distinguishes irradiated fuel from non-fuel items which are loaded into the reactor to replace discharged assemblies.

(Source: IAEA Safeguards Techniques and Equipment)