Abstracts and Available Papers Presented at the
1996 International RERTR Meeting

MEASUREMENT OF THERMAL AND FAST NEUTRON FLUX DISTRIBUTION FOR THE INITIAL CORE OF HANARO

Byung Chul Lee, Hark Rho Kim, Byung Jin Jun and Ji Bok Lee

HANARO Center, Korea Atomic Energy Research Institute
P.O. Box 105, Yusong, Taejon, 305-600, Korea


ABSTRACT

It is very important to measure the thermal and fast neutron flux distribution in a new research reactor, because the measured neutron flux is very helpful to calibrate the reactor power at low power level and it can be used to not only validate the accuracy of the reactor design tool but also verify the research reactor performance as a neutron source.

To measure the thermal neutron flux in HANARO, gold wires are irradiated for 10 hours at 1.5 kW. On the while, nickel wires are activated for 17 hours at 150 kW to measure the fast neutron flux. The activities of the irradiated wires are measures every 2 cm using NaI(Tl) detector to formulate the axial distribution.

The measured reaction rates from which we can infer the neutron flux distributions are compared with the ones calculated by adopting the fully explicit 3-dimensional MCNP reactor model with ENDF/B-V library.

The fractional standard deviation of the calculated thermal and epithermal neutron flux in 2 cm segment of Au wire is lower than 10%, but that of fast neutron flux in Ni wire is within 15%. The measured axial flux distributions are in good agreement with the calculated ones. The relative ratios of the calculated to measured flux over the whole core are 1.114 for thermal flux and 1.078 for fast flux, respectively. This can give us a power calibration factor at the low power level. The relative errors in normalized reaction rate distribution are presumed as the errors of local flux estimation by the design tool. The measurement flux levels at the irradiation holes confirm the HANARO design performance as a neutron source.

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