Nuclear Fusion Research and Development

4-4

Accuracy Validation of Nuclear Data for Fusion Reactor Design－ Toward More Accurate Fusion Reactor Design －(unit: cm)

Ironassembly

100φDT
NeutronSource2095

Neutron flux
(n/cm2/lethargy/source neutron): Measuring pointExpt.
Calculation with JENDL-3.3
Calculation with JENDL-4.0

10-510-610-710-610-510-410-310-2-1

10100101

Neutron energy (MeV)

Fig.4-8 Layout sketch of iron experiment (vertical crosssection)
Data for neutrons and gammas were measured inside aniron assembly 100 cm in diameter and 95 cm in thickness.

Fig.4-9 Neutron energy spectra at depth of 31 cm in ironassembly
The measured data are plotted as black circles, and thevalues calculated using the JENDL are shown by coloredlines.

Various studies toward the practical use of fusion reactors
as a future energy source have been proceeding step by step.
Fusion power plants produce 14 MeV neutrons through thereactions of deuterium and tritium in high-temperature plasma.
Nuclear reactions of these neutrons with surrounding materials
generate thermal energy (nuclear heating) and tritium (tritiumproduction), which is used as fuel in the plants. For safety, theneutrons have to be shielded so that they do not leak outside
the fusion power plants (shielding).
The 14 MeV neutrons initiate various nuclear reactions
with all the materials surrounding the plasma. Fusion reactor
designs estimate the nuclear heating, tritium production,shielding, and so on by considering all the nuclear reactions
using a radiation transport code and database (nuclear datalibrary) of nuclear reaction cross sections (nuclear data)
to characterize the probability that a nuclear reaction willoccur. The typical radiation transport code is the Monte
Carlo code MCNP, which is used worldwide because of its
few calculation approximations. On the other hand, there areseveral nuclear data libraries; the Japanese Evaluated Nuclear

Data Library (JENDL) in Japan, ENDF/B in the US, and JEFF
in Europe. Nuclear data libraries are one of the most important
databases that determine the calculation accuracy of fusion
reactor design results. It is necessary to examine and improve
the accuracy of nuclear data libraries experimentally.
The Fusion Neutronics Source facility in the Japan Atomic
Energy Agency (JAEA) can produce the same 14 MeV neutrons
as those generated in fusion reactors with an accelerator. We
inject these neutrons into various assemblies, as shown inFig.4-8, and measure the data for neutrons and gammas inside
the assemblies. We simulate these experiments with MCNP
and the nuclear data libraries and validate the accuracy of thelibraries. Fig.4-9 shows a typical example (iron experiment).
The calculated neutron spectrum below 0.01 MeV with theprevious version, JENDL-3.3, is about 30% larger than themeasured one, but the discrepancy between the calculated andmeasured results decreases to about 15% in the calculation
result with the latest version, JENDL-4.0 (some of the crosssection data for 57Fe were dramatically modified on the basisof our study).

Reference
Konno, C. et al., Detailed Benchmark Test of JENDL-4.0 Iron Data for Fusion Applications, Fusion Engineering and Design, vol.86, issues 9-11, 2011,
p.2682-2685.
JAEA R&D Review 201353