A brief comment on ORNL-4528

Kirk and I have been separately looking at ORNL-4528, a document that sets out ORNL thinking about a modular two fluid, graphite moderated MSR project. This concept was developed at ORNL between 1966 and 1967 and ORNL-4528 documents thinking about the concept during that brief period. This design work is of current interest because of interest in small factory build LFTRs in the Energy from Thorium community. ORNL’s interest in modular MSRs was motivated by somewhat different concerns. For ORNL scientists, the lifespan of a MSR Graphite core was am issue of major concern. The limited lifespan of the graphite core necessitated periodic reactor shutdown for core replacement. The use of small modular reactors allowed a generation plant to continue operating at 75% of capacity while one core was being replaced. The replacement of the smaller chore of the modular reactor would also have been a somewhat easier task.

The basic purpose of ORNL-4528 differed from other MSR designs between 1962 and 72. Unlike other reactor system design projects ORNL-4528 was not written to as a part of an ongoing development program. Rather it was written after the two fluid line of development it represented had been dropped in favor of a single fluid design. ORNL-4528 was one of five 1 GWe MSR designs developed between 1961 and 1971 by ORNL or by associated engineering firms. The purpose of the other 4 designs was explained by ORNL-5018:

The objectives of this activity are: (I) to develop the conceptual design for a commercial 1000 MW(e) MSBR in sufficient detail to identify the major areas im which additional technology development is required and to produce meaningful estimates of the nuclear and economic performances of this reactor type, (2) to develop the design criteria and conceptual design for a molten-salt demonstration reactor that will provide the information necessary for construction of commercial MSBRs in sufficient detail to identify additional technology development which is required for construction of the demonstration reactor and to provide improved estimates of the capital and operating costs for the demonstration reactor, (3) to develop the design criteria and conceptual design for a molten-salt test reactor in sufficient detail to identify additional technology development which is required for construction of the test reactor and to provide improved estimates of the capital and operating costa for the test reactor, and (4) to develop the design criteria and conceptual design for a molten-salt teat reactor mockup in sufficient detail to identify additional technology development which is required for construction of the test reactor mockup and to provide improved estimates of the capital and operating costs for the mckup.

An additional important objective of this activity is the examination of alternate reactor types such as molten-salt converter reactors using uranium or plutonium fuel makeup as well as uses for molten-salt reactors other than large central station electric power generation in sufficient detail to assess the likely economic importance of alternate molten-salt reactor types. Limited conceptual design work would be carried out on alternate reactor types which show promise.

Because the line of research document led by ORNL-4528, its intent was not to offer clues for future development, but to document a terminated line of research. Many ORNL scientists, including my father, were not in agreement with the decision to abandon the two fluid approach, their continued believe in the soundness of their views, may have motivated the desire to document the modular two fluid design.

At any rate the design documented by ORNL-4528 is far from mature and contains flaws. I would encourage our readers to find flaws and comment on them.

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