relative to infinite-dilution cross sections is introduced. The MA transmutation rates
are burn-up properties. Thus, the sensitivity calculation method for burn-up-dependent properties is derived. Finally, we investigate how many energy groups are
required in sensitivity calculations. Calculated MA transmutation rates have large
uncertainties resulting from the large uncertainties in MA cross sections. To reduce
these uncertainties in MA transmutation rates, we introduce a new method to reduce
prediction uncertainties of MA transmutation rates in Chap. 5. In this method, we
eliminate bias factors included in experiments and calculations by using ratios of
the calculation to the experiment of core performance parameters. After removing
the bias factors, the cross section is adjusted using measured data. The conclusions
are shown in Chap. 6.
17.2 MA Transmutation Core Concept
MA transmutation core concepts are developed by considering the amount of MA
loading and the safety-related core parameters. Increase of MA loading in the core
of a SFR makes the amount of MA transmutation large, which may decrease longterm radiotoxicity and decay heat of MA. On the other hand, loading a large amount
of MA into the core of a SFR increases the sodium void reactivity. Therefore,
harmonization of MA transmutation and sodium void reactivity is a key issue in
designing the core concepts. As an example, Fig. 17.1 shows the relationship of MA
content and sodium void reactivity; when the MA content is about 10 %, the sodium
void reactivity increases by about 1$.
A homogeneous MA-loaded core of 750 MWe was designed in the FaCT project
[1, 2] (Fig. 17.2). The configuration of this core is a conventional homogeneous
core and homogeneous MA loading into the core fuel increases sodium void
reactivity. Therefore, MA content in the core fuel assembly is limited to less than
about 5 wt%. On the other hand, the safety issue has become more and more
important since the Fukushima Daiichi NPP accident. Further, low void reactivity
SFR designing has been pursued in Russia and France [5]. In this study, the
coexistence of enhanced MA transmutation and zero void reactivity, that is, the
harmonization of MA transmutation and core safety, is set as an objective.
Hitachi proposed an axially heterogeneous core (AHC) concept with sodium
plenum [6, 7]. It was clarified that an increase of flux level at the top of the core fuel
caused by the presence of the internal blanket and decrease of the height of the inner
core fuel greatly decreased sodium void reactivity. In the core concept, sodium void
reactivity can be extremely reduced without disrupting core performance for
normal operation. The difference in core configurations between the Hitachi AHC
with sodium plenum proposed in FR ‘91 [6] and the ASTRID ACV [5], which has
been recently studied in France, is that absorber material is loaded in the upper
shield for the ASTRID ACV.
We are going to optimize the specifications of the core shown in Fig. 17.3 to
realize the high MA transmutation and zero sodium void reactivity. Figure 17.4
17 Method Development for Calculating Minor Actinide Transmutation in a Fast. . .
181
are burn-up properties. Thus, the sensitivity calculation method for burn-up-dependent properties is derived. Finally, we investigate how many energy groups are
required in sensitivity calculations. Calculated MA transmutation rates have large
uncertainties resulting from the large uncertainties in MA cross sections. To reduce
these uncertainties in MA transmutation rates, we introduce a new method to reduce
prediction uncertainties of MA transmutation rates in Chap. 5. In this method, we
eliminate bias factors included in experiments and calculations by using ratios of
the calculation to the experiment of core performance parameters. After removing
the bias factors, the cross section is adjusted using measured data. The conclusions
are shown in Chap. 6.
17.2 MA Transmutation Core Concept
MA transmutation core concepts are developed by considering the amount of MA
loading and the safety-related core parameters. Increase of MA loading in the core
of a SFR makes the amount of MA transmutation large, which may decrease longterm radiotoxicity and decay heat of MA. On the other hand, loading a large amount
of MA into the core of a SFR increases the sodium void reactivity. Therefore,
harmonization of MA transmutation and sodium void reactivity is a key issue in
designing the core concepts. As an example, Fig. 17.1 shows the relationship of MA
content and sodium void reactivity; when the MA content is about 10 %, the sodium
void reactivity increases by about 1$.
A homogeneous MA-loaded core of 750 MWe was designed in the FaCT project
[1, 2] (Fig. 17.2). The configuration of this core is a conventional homogeneous
core and homogeneous MA loading into the core fuel increases sodium void
reactivity. Therefore, MA content in the core fuel assembly is limited to less than
about 5 wt%. On the other hand, the safety issue has become more and more
important since the Fukushima Daiichi NPP accident. Further, low void reactivity
SFR designing has been pursued in Russia and France [5]. In this study, the
coexistence of enhanced MA transmutation and zero void reactivity, that is, the
harmonization of MA transmutation and core safety, is set as an objective.
Hitachi proposed an axially heterogeneous core (AHC) concept with sodium
plenum [6, 7]. It was clarified that an increase of flux level at the top of the core fuel
caused by the presence of the internal blanket and decrease of the height of the inner
core fuel greatly decreased sodium void reactivity. In the core concept, sodium void
reactivity can be extremely reduced without disrupting core performance for
normal operation. The difference in core configurations between the Hitachi AHC
with sodium plenum proposed in FR ‘91 [6] and the ASTRID ACV [5], which has
been recently studied in France, is that absorber material is loaded in the upper
shield for the ASTRID ACV.
We are going to optimize the specifications of the core shown in Fig. 17.3 to
realize the high MA transmutation and zero sodium void reactivity. Figure 17.4
17 Method Development for Calculating Minor Actinide Transmutation in a Fast. . .
181