JAEA-Conf 2011-002 - 日本原子力研究開発機構

JENDL-3.3 showed better applicability to the HTTR criticality calculations than the other
libraries as mentioned above, but still overestimated the keff values by 0.5-1.1%k.
Overestimating the keff values, the calculation result of the loaded number of the fuel columns
achieving the first criticality did not agree with the experimental results. These problems has
not been resolved until today, despite our efforts of the refinement such as the description of the
core geometry and the concentration of the components. Meanwhile, the neutron capture cross
section of carbon at 0.0253eV stored in each nuclear data library had not been revised for a long
time. Thus we proposed this cross section should be revised based on the latest measurement
data, and also predicted that the problem of overestimating the keff values will be resolved by
revising the cross section to be about 10% larger than that of JENDL-3.3.
In May 2010, the latest JENDL: JENDL-4.0[2], was released by JAEA. In JENDL-4.0, our
proposal and prediction were applied, and the neutron capture cross section of carbon at
0.0253eV was revised based on the latest measurement data[3]. Accordingly the problem of
overestimating the keff values in the HTTR criticality calculations was expected to be improved.
This paper describes the investigation of the applicability of JENDL-4.0 to the HTTR criticality
calculations.
2. Calculations for HTTR critical approach with JENDL-4.0
2.1 Objective and method
The objective of this study is to investigate the applicability of JENDL-4.0 to the HTTR
criticality calculations. The investigation was performed by comparing (a)The loaded number of
fuel columns achieving the first criticality, and (b)Excess reactivity of the fully loaded core,
between the experimental results and the calculation results with several nuclear data libraries,
which are JENDL-4.0, previous JENDL: JENDL-3.3, the latest ENDF: ENDF/B-VII.0, and the
latest JEFF: JEFF-3.1. Additionally, identification of nuclides which have large effects on the
difference of the following issues among the libraries was studied.
2.2 HTTR critical approach
JAEA-Conf 2011-002
(1) HTTR
The HTTR is a graphite-moderated and helium gas-cooled block-type HTGR, situated at
JAEA-Oarai Resarch and Development Center. It has 30MW thermal power and its outlet
coolant temperature, which can be used for nuclear heat utilization, is 850C in rated power
operation. Additionally, the HTTR can also be operated in high temperature test operation
mode, with which its outlet coolant temperature is 950C.
Figure 1 shows radial and bird-eye views of the HTTR core. The core is constructed by
stacking four kinds of hexagonal blocks, which are fuel blocks, control rod guide blocks,
replaceable reflector blocks and irradiation blocks (for irradiation test), and is surrounded by
permanent reflectors made of graphite. All these hexagonal blocks are made of high-purity
graphite, and are the same in across flats (36cm) and height (58cm). Fuel region in the core is
composed of 30 fuel columns, in which five fuel blocks are stacked.