The facilities that involve the presence of neutron fields get the materials activated. That means a radioactive inventory that emits decay photons everywhere in the facility. Depending on the location in the facility, the decay photons field might be challenging to the survivability of the electronics, or tot he human intervention. It has a strong impact on the economics. The understanding of the decay photon field to minimize it and mitigate its effect is key to ensure the viability of those facilities.

However, the accurate determination of the decay photon field and its effects is one of the most complex activities in the field of the nuclear analysis nowdays. It involves sophiscated algorithms, the coupling of computational codes and the use of High Performance Computing (HPC) infraestructures. The correct analysis of the phenomenon requires an advanced understanding of nuclear engineering and physics.

In the last two decades, two modern computational methods to determine the decay photon field have been developed as an international joint effort: the mesh-based Rigorours-two Steps (R2S) and the Direct-one Step (D1S). They represent a step change as they allow full 3D resolution.

TECFIR / UNED developed in 2012 the tool called R2S-UNED. It is an implementation of the R2S method making use of MCNP5 for the radiation transport and ACAB for the determination of the radioactive inventory. It present the main advantage of ensuring a full and correct treatment of the radioactive inventory, and it is one of the most advanced implementation of the R2S method, enabling unique features.

R2S-UNED is recommended for the initial exploration of the decay photon field features in a given facility and/or for facilities with the presence of intense neutron fields. For more information about R2S-UNED, see the following paper:


P. Sauvan, J. P. Catalán, F. Ogando, R. Juárez and J. Sanz. “Development of the R2SUNED Code System for Shutdown Dose Rate Calculations”, IEEE Transactions on Nuclear Science, Volume 63 (2016), Pages 375-384