Keywords Burn-up • KUR-LINAC • MOX pellet • Nondestructive assay • Numerical validation • Resonance • Self-indication method
4.1 Introduction
To perform decommissioning of the Fukushima Daiichi NPP safely, it is very
important to measure the components of the fuel debris. Therefore, a new nondestructive assay to identify and quantify a target nuclide in the fuel debris using a
pulsed-neutron source is under development in Kyoto University Research Reactor
Institute.
We use the self-indication method for the nondestructive assay. This method is a
neutron transmission method. The neutron transmission method is focused on
resonance reactions (i.e., capture, fission) at the target nuclide. In the conventional
neutron transmission method, a sample is irradiated by a pulsed-neutron beam and
the energy distribution of transmitted neutrons from the sample is measured by the
time-of-flight technique. Then, the target nuclide in the sample is identified and
quantified by using the transmitted neutrons in the resonance energy region. This is
a remarkably effective method to identify and quantify the target nuclide. However,
if the energy spectrum of the transmitted neutron has many dips caused by resonance reactions of other nuclides, it is difficult to identify and quantify the target
nuclide in the sample.
In the self-indication method, the transmitted neutrons from the sample are
injected into an indicator, which consists of a high-purity target nuclide. The
transmitted neutrons are obtained via resonance reactions in the indicator. The
self-indication method has a high signal-to-noise (S/N) ratio compared to the
conventional method.
In this chapter, numerical validation for application of the self-indication
method is carried out. A calculational model and conditions are shown in
Sect. 4.2 and the numerical results are shown in Sect. 4.3. From these results,
some conclusions are drawn in Sect. 4.4.
4.2 Calculational Model and Condition
In this chapter, applicability of the self-indication method to identify and quantify
nuclides in a BWR-MOX pellet is evaluated. The burnup of the MOX pellet is
0 GWd/t, 20 GWd/t, and 30 GWd/t. A plutonium vector in the fresh MOX pellet is
employed as the OECD/NEA BWR MOX benchmark (Pu4) (
235 U, 0.2 w/o; total
Pu, 6.71 w/o;
238 Pu, 2.2 %;
239 Pu, 46.2 %;
240 Pu, 29.4 %;
241 Pu, 8.8 %) [1]. The
burn-up calculations of the BWR-MOX pellet are carried out by using deterministic
neutronics code SARC 2006 [2] with JENDL-4.0 [3]. The numerical validations are
performed by using the MVP2.0 [4] with the JENDL-4.0. The MVP2.0 is a
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T. Sano et al.
4.1 Introduction
To perform decommissioning of the Fukushima Daiichi NPP safely, it is very
important to measure the components of the fuel debris. Therefore, a new nondestructive assay to identify and quantify a target nuclide in the fuel debris using a
pulsed-neutron source is under development in Kyoto University Research Reactor
Institute.
We use the self-indication method for the nondestructive assay. This method is a
neutron transmission method. The neutron transmission method is focused on
resonance reactions (i.e., capture, fission) at the target nuclide. In the conventional
neutron transmission method, a sample is irradiated by a pulsed-neutron beam and
the energy distribution of transmitted neutrons from the sample is measured by the
time-of-flight technique. Then, the target nuclide in the sample is identified and
quantified by using the transmitted neutrons in the resonance energy region. This is
a remarkably effective method to identify and quantify the target nuclide. However,
if the energy spectrum of the transmitted neutron has many dips caused by resonance reactions of other nuclides, it is difficult to identify and quantify the target
nuclide in the sample.
In the self-indication method, the transmitted neutrons from the sample are
injected into an indicator, which consists of a high-purity target nuclide. The
transmitted neutrons are obtained via resonance reactions in the indicator. The
self-indication method has a high signal-to-noise (S/N) ratio compared to the
conventional method.
In this chapter, numerical validation for application of the self-indication
method is carried out. A calculational model and conditions are shown in
Sect. 4.2 and the numerical results are shown in Sect. 4.3. From these results,
some conclusions are drawn in Sect. 4.4.
4.2 Calculational Model and Condition
In this chapter, applicability of the self-indication method to identify and quantify
nuclides in a BWR-MOX pellet is evaluated. The burnup of the MOX pellet is
0 GWd/t, 20 GWd/t, and 30 GWd/t. A plutonium vector in the fresh MOX pellet is
employed as the OECD/NEA BWR MOX benchmark (Pu4) (
235 U, 0.2 w/o; total
Pu, 6.71 w/o;
238 Pu, 2.2 %;
239 Pu, 46.2 %;
240 Pu, 29.4 %;
241 Pu, 8.8 %) [1]. The
burn-up calculations of the BWR-MOX pellet are carried out by using deterministic
neutronics code SARC 2006 [2] with JENDL-4.0 [3]. The numerical validations are
performed by using the MVP2.0 [4] with the JENDL-4.0. The MVP2.0 is a
32
T. Sano et al.