ORNL-5388 - the Molten Salt Energy Technologies Web Site

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Initial analyses of spectral-shift-controlled reactors were carried out in the U.S.
by M. C. Edlund in the early 1960s and an experimental verification program was performed
by Babcock & Wilcox both for LEU fuels and for HEU/Th fuels.' Edlund's studies, which
were performed for reactors designed specifically for spectral-shift control, indicated
that the inventory and consumption of fissile material could be reduced by 25 and 50%,
respectively, relative to poison control in reactors fueled with highly enriched 235U and
thorium oxide, and that a 25% reduction in uranium ore requirements could be realized with
spectral shift control using the LEU cycle.2
The spectral-shift-control concept has been demonstrated by the Vulcain reactor
experiment in the BR3 nuclear plant at Mol, Belgi~m.~ The BR3 plant after two years of
operation as a conventional PWR was modified for spectral -shift-control operation and
successfully operated with this mode of control between 1966 and 1968. The Vulcain core
operated to a core average burnup of 23,000 MWT (a peak burnup of around 50,000 MWd/T)
and achieved an average load factor and primary plant availability factor of 91.2 and
98.6, re~pectively.~ The leakage rate of primary water from the high-pressure reactor
system to the atmosphere was found to be negligible, about 30 kg of D20-H20 mixture per
year.3 AfFer the Vulcain experiment was completed, the BR3 was subsequently returned to
conventional PWR operation. In addition to demonstrating the technical feasibility of
spectral-shift control, the Vulcain experiment served to identify the potential engineering
problems inherent in converting existing plants to the spectral-shift mode of control.
At the time of the major development work on the SSCR concept, fuel resource con-
servation was not recognized as having the importance that it has today. Both uranium
ore and separative work were relatively inexpensive and the technology for D20 concen-
tration was not as fully developed as it is now. With the expectation that the plutonium-
fueled breeder reactor would be deployed in the not too distant future, there appeared to
be little incentive to pursue the spectral-shift-controlled reactor concept.
The decision to defer the commercial use of plutonium and the commercial plutonium-
fueled breeder reactor is, of course, the primary motivation for reevaluating advanced
converters, and the principal incentive for considering the spectral-shift-controlled
reactor is that the potential gains in resource utilization possible with the SSCR con-
cept may be obtainable with changes largely limited to ancillary components and subsystems
in existing PWR systems. The prospects of rapid acceptance and deployment of the SSCR
are'also enhanced by the low risk inherent in the concept. Since the SSCR can always be
operated in the conventional poison control mode, there would be a reduced risk to station
generating capacity if the SSCR were deployed, and financisi risk would be limited to the
cost of the additional equipment required to realize spectral-shift control, which is
estimated to be only a few percent of the total cost of the plant. The risk, with respect
both to capital and generating capacity, is thus much lower than for other alternate
reactor systems.
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