Combining Thorium with Burnable Poison for Reactivity Control of a Very Long Cycle BWR
Name
NFC-064.pdf
Description
NFC-064.pdf
Size
1.04 MB
Format
Adobe PDF
Checksum (MD5)
9a7010bbb540a754f9edc48c60d48d6b
Author(s)
Inoue, Y.
Pilat, Edward E.
Xu, Z.
Kazimi, Mujid S.
Date Issued
June 2004
Publisher
Massachusetts Institute of Technology. Center for Advanced Nuclear Energy Systems. Nuclear Fuel Cycle Program
Series/Report no.
MIT-NFC;TR-64
Abstract
The effect of utilizing thorium together with gadolinium, erbium, or boron
burnable absorber in BWR fuel assemblies for very long cycle is investigated. Nuclear
characteristics such as reactivity and power distributions are evaluated using CASMO-4.
Without thorium, the results show that gadolinium enriched in Gd-157 has the lowest
reactivity swing throughout the cycle. However, the local peaking factor (LPF) in the
assembly at beginning-of-life (BOL) is high. The erbium case shows more reactivity
swing but the LPF is lowest of all three cases. B4C case has the highest reactivity at
BOL which would have to be suppressed by control rods. The most important
advantage of B4C over others is the saving of uranium inventory needed to achieve the
target exposure of 15 effective full power years (EFPY). Further analysis for transient
conditions must be performed to ensure meeting all transient limits.
Use of thorium in place of some burnable poison makes it possible to save
some uranium enrichment while achieving equivalent discharge burnup to the case
without thorium, but only by about 1 %. The benefit is small because almost the same
amount of burnable poison is always required for suppressing excess reactivity
throughout the cycle. Since Th-232 functions more like U-238 than burnable poison,
this limits the allowed thorium to extend discharge burnup.
Since all fuel assembly designs in this study have the same target exposure of
15EFPY, the economic performance of each design can be compared based on the
amount and enrichment of both uranium and burnable absorbers for each fuel design.
The B4C-Al fuel is most economical in overall cost even with large uncertainties. The
overall cost of gadolinium and erbium cases are concluded to be about the same when
large uncertainties are considered.
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