In the event of a far-reaching nuclear disarmament, nuclear weapon states would cease pro-duction of fissile materials for nuclear weapons, and also place their pre-existing plutonium andhigh enriched uranium (HEU) under international inspection. In this case, it can be anticipated that sizes of stockpiles are declared, with detailed records on how they were produced. Forexample, if the core geometry and operational history of a military reactor would be declaredby the owner state, the plutonium production of the core can be reconstructed using reactorphysics codes, which can provide confidence in the declared plutonium stockpiles.Challenges include that any data on fuel cycle operations provided by the state cannot beassumed to be truthful. This leads to the additional need to verify the declared operationalhistory by consistency checks within records and when possible with inspections. A further complication is that a long time might have passed since the fissile material production tookplace, and records can therefore be expected to be incomplete or inaccurate, and the responsiblepersonnel may be retired or even deceased. In this case, there may be a need to be able toreconstruct lost information on fuel cycle operations.
We consider a test and training case of the Swedish pressurised heavy water reactor (PHWR) in Ågesta, which was in operation between 1963 and 1974. In this case study, we explore available archive material in order to obtain information such as the core loadings of the reactor, its operational history and the fuel designs used. Primarily we explore the use of records from the tritium monitoring for consistency checks with operational data records. Tritium production occurs via neutron capture in deuterium; a main component of heavy water, and since heavy water is an expensive asset, the consumption of it is closely monitored, for example by measuring tritium release. Moreover, the tritium production is proportional to the neutron flux in thereactor which is also a crucial component for calculating plutonium production