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3.1. ESTIMATED U CONCENTRATIONS IN DENATURED U FUELS
D. T. Ingersoll
Oak Ridge National Laboratory
Although it is mandatory that’the concentrations of 232U at each stage of the fuel
cycle be predictable for the various reactors operating on thorium-based fuels, little
information on the subject is available at this time. This is attributable to the fact
that the interest in thorium fuel cycles is relatively recent and therefore the nuclear
data required for calculating the production of 232U have not been adequately developed.
Of primary importance are the (n,y) cross sections of 23’Pa, 230Th, and 232Th and the
(n,Zn) cross sections of 233U and 232Th, all of which are intermediate interactions that
can lead to the formation of 232U as is illustrated by the reaction chain given in Fig.
3.1-1.
These cross sections are under current evaluation’ and should appear in the Version
V release of the Evaluated Nuclear Data File (ENDF/B-V).
I
232
9oTh
I
h2n)
t
E h l
Fig. 3.1-1 Important Reaction Chains
Leading to the Production of 232U.
3.1.1. Light-water Reactor Fuels
In spite of the nuclear data deficien-
cies, some results for 2321) concentrations
are available from calculations for denatured
fuels in light-water reactors (LWRs) and in
fast breeder reactors (FBRs) . A1 though no
results for denatured high-temperature gas-
cooled reactors (HTGRs) are currently available,
232U concentrations can be roughly inferred
from existing HTGR fuel data. Moreover, the
analysis of 232U concentrations in standard
HTGR designs (HEU/Th) serves as an upper
bound for the denatured systems.
tion of the available results is given below.
The current state of the related 232U nuclear
data is amply reflected in the large variances
of the calculated concentrations.
A compila-
Existing data on 232U concentrations in denatured LWR fuels are primarily from cal-
culations based on the Combustion Engineering System 80TM reactor design.2 Results from t ’
CE3 for a denatured 235U cycle (20% 235U-enriched uranium in 78% thorium) show the 232U L
concentration after the zeroth generation to be 146 ppm 232U in uranium, while after
five generations of recycle uranium, the concentration is increased to 251 ppm.
levels are in good agreement with ORNL calculation^,^ which indicate 130 ppm 232U in
uranium for the zeroth generation. The discharge uranium isotopics are summarized in
Table 3.1-1.
These
Also shown are the results from an ORNL calculation for a denatured 233U cycle
L
L; h