For advanced reactors with homogeneous fuel designs, such as Molten Salt Reactors (MSRs), the ability to: (1) remove samples of fuel salt from the reactor for analysis, (2) add fissile material to the reactor to increase/maintain reactivity, and (3) add chemistry control species to minimize corrosion and the formation of undesirable chemical compounds is critical to its long-term safety and operability. In the Molten Salt Reactor Experiment (MSRE), a homogeneous fuel test reactor operated at Oak Ridge National Laboratory between 1965 and 1969, these functions were performed by the Sampler-Enricher system.
The MSRE Sampler-Enricher was a mechanical system, in which a manipulator, a cable-pulley system, and a series of isolation valves were used to transport sample capsules in and out of the MSRE pump bowl while maintaining appropriate barriers to containment Robertson (1965). According to the MSRE staff Gallagher (1971), the Sampler-Enricher displayed adequate functionality; however, review of detailed operational logs revealed that Sampler-Enricher operational upsets were frequent and resulted in the need for regular system corrective and preventive maintenance, including diagnostics, repairs or replacements, design or procedural changes, etc. On two occasions, Sampler-Enricher operational occurrences resulted in the shutdown of the MSRE.
The attractiveness of advanced reactors, particularly MSRs, as a potential carbon-free energy source has contributed to the re-evaluation and modernization of historical advanced test reactor system designs, such as the MSRE Sampler-Enricher. Insights gained from a systematic performance analysis of the Sampler-Enricher can provide essential information on the constraints and design requirements that would apply to an updated system for sampling molten salt and adding fissile and potentially other materials to the fuel salt loop of a MSR.
The Systems Theoretic Accident Model and Process (STAMP) is a systems engineering-based accident analysis methodology that can be used to identify the design and operating constraints that were violated to bring about an accident or an operational upset Leveson (2004). STAMP reflects that the safety of a system is dependent on the way a system interacts with its environment, not solely on component-level interactions. STAMP was used in conjunction with historical Sampler-Enricher operational records to identify contributors to the operational upsets suffered by the Sampler-Enricher that can be used to inform the design of a modernized Sampler-Enricher.