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the LMFBR on its reference cycle are currently being revised, and a study of L.e denatured
fast breeder fuel cycle, which includes fast transmuters and denatured breeders, is included
as part of the INFCE program (International Nuclear Fuel Cycle Evaluation).
from the INFCE study should be available in the near future.
5.1.1. Light-Water Reactors
The results
Preliminary evaluations of design and safety-related considerations for LWRs operat-
ing on the conventional thorium cycle indicate thorium-based fuels can be employed in LWRs
with little or no modification.
Consequently, the R&D costs given here have been estimated
under the assumption that denatured fuel will be employed in LWRs of essentially present
design. This assumption is not meant to exclude minor changes to reactor design (for
example, changes in the number of control drives, shim loadings, or fuel management, etc.)
but rather reflects our current belief that design changes necessitated by DUTH fuels will
be sufficiently straightforward so as to be accommodated within the engineering design
typically performed for new plants.
As has been described in the discussion above, the first phase of such fuel-cyclerelated
research consists of the development of a data base from which safety-related
parameters and fuel performance can be predicted in subsequent core physics design and
safety analysis programs. First, existing thorium materials and fuel performance information
should be thoroughly reviewed, and a preliminary evaluation of safety and licensing
issues should be made in order to identify missing information and guide the subsequent
development program. Although this initial phase is required to fully define the required
data base R&D, it is possible to anticipate in advance the need to establish information
in the areas of physics verification and safety-related fuel performance.
As shown in Table 5.1-1, the physics verification program under data base development
is estimated to cost %$lo million. This program should be designed both to provide
the information required to predict important safety-related physics parameters and to
demonstrate the accuracy of such predictions as part of the safety analysis. Improved
values must be obtained for cross sections of thorium and of isotopes in the thorium
depletion chains, such as 233U and protactinium, all of which have been largely neglected
in the past. Resonance integral measurements should also be performed for denatured fuels
both at room temperature and at elevated temperatures, such experiments being very important
for accurately calculating safety-related physics characteristics and also for
establishing the quanti ties of plutonium produced during irradiation. Finally, an LWR
physics verification program should include a series of critical experiments, preferably
both at room temperature and at elevated moderator temperatures, for each of the fuel
types under consideration (i .e. , for thorium-based fuels utilizing denatured 23sU, denatured
233U, or plutonium). These experiments would serve as a basis for demonstrating the adequacy
of the cross-section data sets and of the ability of analytical models to predict such
safety-related parameters as reactivity, power distributions, moderator temperature
reactivity coefficients, boron worth, and control rod worth.