On the development of nuclear data for LFR

The Lead-cooled Fast Reactor (LFR) is one of the three technologies selected by the Sustainable Nuclear Energy Technology Platform that can meet future European energy needs. To achieve the requested level of safety for this reactor technology and to minimize the increase in the costs due to additional safety measures, accurate and reliable nuclear data are necessary.

A precise knowledge of nuclear data uncertainties allows not only determining the design margins that are needed for safe and economical operation of new reactor systems. It also allows insuring sub-criticality, which is essential whenever fissile materials are manufactured and handled, transported, processed, or stored outside of a reactor core; as well as accurately assessing the isotopic content and decay power of spent nuclear fuel for its safe management, transport and disposal. Furthermore, other applications outside reactor physics, such as medial applications (e.g., radiotherapy for cancer treatment), also benefit from an accurate knowledge of nuclear data. Better nuclear data entail an increase in the predictive capability of simulation tools and, consequently, a reduction in the safety margins needed and in the associated costs.

The aim of this article is to present the analyses and work performed to improve the nuclear data required for the development, safety assessment, licensing and operation of LFRs, reducing the uncertainties in the criticality safety parameters due to the uncertainties in nuclear data, in order to reach the target accuracies defined by researchers, industry and regulators.

To that end, the SUMMON and DAWN codes have been developed to perform sensitivity and uncertainty analyses and data assimilation of the most relevant criticality safety parameters of detailed complex reactor designs from the neutronic point of view, i.e., keff, ßeff, Λeff  and reactivity coefficients, using state-of-the-art nuclear data libraries and covariances.

Exhaustive analyses of the latest version of the European nuclear data library for isotopes relevant to the criticality safety of LFRs have been performed. Problems have been found in the resolved resonance region of JEFF-3.3T1 bismuth and lead evaluations and recommendations have been given to the JEFF project, which have been adopted in the release version of the library, JEFF-3.3. Furthermore, sensitivity and uncertainty analyses have been carried out and nuclear data have been consistently adjusted to reduce the uncertainties of integral safety-related parameters due to neutron induced nuclear data.

As a result of this work, nuclear data needs for advanced LFRs have been identified, improvements of existing nuclear data libraries have been suggested, recommendations for consistent data assimilation have been given and new measurements of energy dependent neutron induced data and integral parameters have been proposed. Moreover, it has been proven that SUMMON and DAWN codes allow calculating and reducing the uncertainties due to nuclear data, making possible to accurately determine the criticality safety parameters of nuclear reactors and reducing the associated costs due to additional safety measures.

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