RRFM 2009 Transactions - European Nuclear Society

BENCHMARK OF HEAT DEPOSITION MEASUREMENT TECHNIQUES
IN THE SAFARI-1 REACTOR USING MCNP5
B.M. MAKGOPA, M.BELAL
Radiation and Reactor Theory, South African Nuclear Energy
P.O Box 582, Pretoria – South Africa
ABSTRACT
In-core calorimetry is a valuable experimental technique for measurement of total
nuclear heating rates. This technique is adopted in an experiment performed in the
South African First Atomic Reactor Installation (SAFARI-1 reactor). The objective
of the experiment is to provide experimental data of nuclear heating for materials:
molybdenum and stainless steel (SS 304). The experiment was conducted in core
channel B6 at low reactor power, 5 MW.
This paper presents results of a Monte Carlo simulation of this experiment by
comparison of the calculated (C) to experimental (E) nuclear heating values.
Calculations were performed using a Monte Carlo N-Particle (MCNP5) code
version 1.4. The amount of heat deposited in core channel B6 using the track
length estimate of energy deposition in a cell (F6) in a neutron-photon coupled
mode (mode n p) and as well using the pulsed height tally (*F8) which gives the
energy distribution of pulses created in a detector. Below the core centreline,
relative errors in nuclear heating values for stainless steel range from 11% to 16%
compared to a range of 1% to 6% in molybdenum. Above the core centreline,
stainless steel exhibits relative errors, from 1% to 19% whereas the relative errors
in molybdenum range from 5% to 34%.
1. Introduction
For the purpose of material and fuel irradiations in a nuclear reactor core, it is essential to
acquire very accurate knowledge of the neutron flux spectrum and the power distribution in
the whole core, as well in the target core irradiation position. This work presents a
benchmark of the in-core calorimeter experiment performed in SAFARI-1 reactor. This
technique has been used to measure the amount of heat deposition along the axial length of
the core in channel B6. The experiment was done at beginning of cycle (BoC) 0704-1, at low
reactor power (5 MW) to facilitate instantaneous measurements.
For benchmark purposes, the Monte Carlo N-Particle (MCNP5) code is used to simulate the
experiment. The track length estimate of heat deposition (F6) tally in a coupled neutronphoton
mode and the pulsed height tally (*F8), which gives the energy distribution of pulses
created in a detector are calculated. This work presents a comparison of the experimental
and calculational results.
2. The SAFARI-1 Reactor
The SAFARI-1 reactor is a tank-in-pool type material testing reactor (MTR). The reactor is
light water cooled and moderated. The standard core configuration as depicted in Figure 1
below is configured in an 8×9 matrix. The core consists of twenty six fuel elements, six
control elements, in-core and ex-core irradiation positions as well as reflector elements. This
water cooled and moderated reactor is mainly used for production of medical isotopes and
material irradiations.
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