Experiments are being planned at Research Centre Rež (RC Rež) to use the FLiBe (2 7LiF-BeF2) salt from the Molten Salt Reactor Experiment (MSRE) to perform reactor physics measurements in the LR-0 low power nuclear reactor. These experiments are intended to inform on neutron spectral effects and nuclear data uncertainties for advanced reactor systems utilizing FLiBe salt in a thermal neutron energy spectrum. Oak Ridge National Laboratory (ORNL) is performing sensitivity/uncertainty (S/U) analysis of these planned experiments as part of the ongoing collaboration between the United States and the Czech Republic on civilian nuclear energy research and development. The objective of these analyses is to produce the sensitivity of neutron multiplication to cross section data on an energy-dependent basis for specific nuclides. This report provides a status update on the S/U analyses of critical experiments at the LR-0 Reactor relevant to fluoride salt-cooled high temperature reactor (FHR) and liquid-fueled molten salt reactor (MSR) concepts. The S/U analyses will be used to inform design of FLiBe-based experiments using the salt from MSRE.

Written to assist individuals in academia and industry and in relevant regulatory and policy roles, this publication provides a summary of the current knowledge on the status of research, technological developments, reactor designs and experiments in the area of advanced reactors that are fueled or cooled by a molten salt. Identification of challenges and areas where research and development are still required in preparation for commercial deployment gives context to current and planned work. The aim of this publication is to share information on programs and projects on molten salt reactors in Member States which will shape future collaborative efforts.

With the recent interest in advanced nuclear reactors, the need for developing nuclear material accounting strategies arise. Especially in liquid-fueled molten salt reactors, which preclude the ability to count fixed amount of material in a discrete way, as opposed to the traditional counting method widely used in the current nuclear fleet. Usually, these reactor concepts involve online fuel processing where fuel and its products flow within many streams along the plant. In computational modeling, this feature requires high fidelity depletion schemes, including the addition of feed and removal capabilities that can simulate their regular operation. Estimating isotopic inventory under regular and diversion scenarios would provide an insight on which reactor parameters could be tracked to timely detect diversion of special nuclear material. To achieve this, a depletion model was developed for the Molten Salt Demonstration Reactor (with minor adaptations) in Serpent 2 and SCALE. Feed and removal capabilities were implemented in the Serpent latest release and is under testing in SCALE 6.3 beta versions. Plutonium diversion scenarios are modeled and their impact on regular operation of the reactor is analyzed. The SCALE module Sampler is used to estimate nuclear data uncertainties propagated along the depletion interval. Several isotopes presented changes in their concentrations given a 10SQ plutonium diversion protracted scenario. Some examples are fission products such as 89Sr (1.06% change and 0.58% uncertainty), 91Y (1.92% change and 0.43% uncertainty), 113Cd (-5.00% change and 3.31% uncertainty), 151Eu (-3.84% change and 2.70% uncertainty) and also actinides like 241Am (-6.88% change and 2.23% uncertainty), 242mAm (-6.22% change and 4.88% uncertainty) and 242Cm (-4.50% change and 3.84% uncertainty). Preliminary sensitivity analyses were performed using TSUNAMI and Sampler. Results revealed that 238U(n,[gamma]) plays an important role in contributing to the uncertainty in parameters (e.g., k-inf) and nuclide concentrations (e.g., 239Pu and 241Pu). Future work includes the full analyses of scenarios - including abrupt ones, which are already modeled, and a comprehensive sensitivity study on nuclide concentrations - including fission products and higher actinides. Moreover, methods to improve nuclear covariance data - guided by the sensitivity study - will also be pursued using Bayesian methods and machine learning techniques.

Written to assist individuals in academia and industry and in relevant regulatory and policy roles, this publication provides a summary of the current knowledge on the status of research, technological developments, reactor designs and experiments in the area of advanced reactors that are fuelled or cooled by a molten salt. Identification of challenges and areas where research and development are still required in preparation for commercial deployment gives context to current and planned work. The aim of this publication is to share information on programmes and projects on molten salt reactors in Member States which will shape future collaborative efforts.

Sensitivity analysis, as applied to both nuclear design and data uncertainty, has developed into a valuable tool for fusion reactor nuclear analysis. Several such studies have been undertaken with the LASL sensitivity system LASS, which includes as its principal modules SENSIT-1D, ONETRAN, and ALVIN. These modules function in a multigroup environment using standard flux and data interface files for communication. The input multigroup cross-section data and uncertainties are obtained primarily from ENDF/B using the NJOY processing system. In particular cases, the input library can be modified by the ALVIN module to improve consistency with available integral experiments. The primary output from LASS is the uncertainty (or change) in important reactor parameters, as calculated in the SENSIT-1D module. Applications of LASS and its component parts have been made to the Tokamak Fusion Test Reactor (TFTR), the Reference Theta-Pinch Reactor (RTPR), and to an Experimental Power Reactor (EPR). This paper emphasizes the initial assessment of cross-section sensitivity for an EPR design. Nucleonic responses examined include neutron and gamma-ray kerma in the toroidal field coils and Mylar superinsulation, displacement damage and transmutation in the copper of the toroidal field coils, and activation of the outboard dewar. These sensitivities are now being used to narrow the range of uncertainty analyses required to quantitatively assess cross-section adequacy for EPR design calculations. Acceptable target uncertainties in nucleonic design parameters are simultaneously being formulated. Experience at LASL with sensitivity and uncertainty analysis techniques incorporated in LASS has provided convincing evidence of their value for fusion reactor studies. Many of these studies are of a shielding nature; e.g., deep penetrations of high-energy neutrons through steel, lead, boron carbide, and graphite, with responses such as activation and kerma.