Report of the Fluid Fuel Reactors Task Force to the Division of Reactor Development (TID-8507)
This report was prepared by a task force composed of fifteen highly qualified engineers and scientists from the Atomic E=nergy Commission, its national laboratory and contractor organizations, and representatives of the architect-engineering and utility industry, The task force was named the Fluid Fuel Reactors Task Force and was organized and convened by the Evaluation and Planning Branch of the Office of Civilian Reactors to perform a critical evaluation of the three fluid fuel reactor concepts (aqueous homogeneous – AHR, molten salt – MSR, and liquid metal fuel -LMFR) under development.
The Task Force met continuously during January and February of 1959 and evaluated information presented by the national, laboratories and industrial contractors developing the concepts. This document is the report of the Fhuid Fuel Reactors Tcsk Force to the Division of Reactor Development and represents the group evaluation and judgment of the three fluid fuel reactor concepts.
Present State of Development and Technical Feasibility
The molten salt reactor has the highest probability of achieving technical feasibility. This is largely due to the use of a solution fuel (as contrasted to a slurry fuel in the LMFR and the AHR), and the availability of a suitable container material (INOR-8).
Summaries of the relative comparisons of the three concepts follow:
1. The technical feasibility of fuels and materials is a critical factor. At the present state of technology, the MSR has the best possibility of obtaining a satisfactory fuel, if indeed
it does not already have a satisfactory fuel. Slurries, as used by the LMFR and AHR require a greater amount of development effort to establish feasibility. The FER also offers the best possibility for achieving a satisfactory container material since the LMFR and the AHR have difficult materials problems at the present stage of technology. However, the compatibility of molten salt fuel with graphite which is contemplated for use for the internal construction of a reactor still remains to be demonstrated and the problem is judged to be more severe than in the LMFR.
2. The achievement of satisfactory primary and auxiliary systems and components depends largely on matters of engineering ingenuity and is believed to be technically feasible; however,
these systems will be complicated and hence expensive. In comparing the molten salt with the liquid metal fuel reactor, no significance has been placed on the difficulties arising from the molten salt solution’s higher melting point (975°F vs. 525°F) and higher top operating temperature (1225°F VS. 1050°F). Difficulties in designing caused by the higher temperatures are offset by the fact that the MSR primary system will be smaller than the LMFR system because of the high volumetric heat capacity of the salt,
3. From the standpoint of operation, it is anticipated that all three reactor concepts can be designed to meet load changes, and it is assumed that they will be able to operate for extended periods of time. However, t h i s has not yet been demonstrated. When considered from the standpoint of reliability for extended periods of time, the AHR is at a disadvantage because of its more extensive and complex auxiliary systems.
4. Maintenance is the most important factor influencing the practicability of any of the three concepts. At present the feasibility of maintaining a large, fluid-fuel reactor power station is doubtful because of the need for circulating a high-level radio- active, fluid fuel stream. While experience with the HRX-2 has shown that it can be maintained by the use of wet maintenance, it is not known if these techniques can be applied to large plants. The use of remote dry maintenance for any of the plants is unproven. The feasibility of any maintenance scheme can only be established by a comprehensive design study backed up by extensive full-scale mockup testing under conditions simulating actual requirements.
5. The AHR is easily controlled, as has been indicated by reactor experience. Analytical studies show that the PER and LEIFR can be controlled, but this requires experimental verification.
Both may require shim rods.
6. The AHR is potentially the most hazardous because of its high pressure system, radiolytic gas explosion hazard, and the potential instability of the fuel. However, HRE-2 has operated for a long period of time under very disadvantageous circumstances without serious release of radioactivity. The PIS2 and LMFR are similar to each other in their safety characteristics,
7. With the exception of the AHR, chemical reprocessing for the reference designs has received little attention.