Regular Article

MODENA project: decay heat prediction using non-destructive assay

¹ Uppsala University, Uppsala, Sweden
² National Cooperative for the Disposal of Radioactive Waste (Nagra), Wettingen, Switzerland

^* e-mail: virginie.solans@nagra.ch

Received: 21 March 2025
Received in final form: 21 March 2025
Accepted: 8 July 2025
Published online: 3 September 2025

Abstract

The long-term safety of nuclear waste disposal is a major challenge for countries with nuclear energy programs. Across Europe, (deep) geological repositories have been identified as the best solution for the permanent isolation of spent nuclear fuel (SNF) and high-level radioactive waste. These repositories use multi-barrier systems, including both engineered and geological barriers, to ensure that radioactive materials are isolated from the biosphere for thousands of years. A critical factor for the safety of geological repositories is managing the decay heat, which is the thermal energy produced by radioactive decay in SNFs. Although heat generation decreases over time, significant amounts are emitted for many years after the SNF is removed from a reactor. Improper management of decay heat can compromise the integrity of the repository barriers. Calorimetric measurements can directly measure the decay heat, but they are time-consuming and resource-intensive. To address this, the MODENA project is focused on developing a fast method to estimate decay heat that relies on measurements that will be performed on every SNF before its encapsulation to verify calculated fuel properties to fulfil international safeguards regulations. These measurements are non-destructive gamma and neutron measurements. The model uses only key radionuclides such as Cs-137 and Eu-154, along with neutron emissions, which allows the prediction of decay heat without the need for additional measurements. The strength of the methodology developed in the MODENA project is its flexibility. The model is based on measurement data from radionuclides that are expected to be measurable at encapsulation and can be adapted to well-known measurement instruments, which makes it easy to apply this model in different countries. Improving decay heat prediction could lead to a more efficient use of available resources, ultimately ensuring optimized sustainability of the repository.