Characterization Of Ghana Research Reactor-1 Low Enriched Uranium Core Irradiation Sites Using A Theoretical Method

ABSTRACT

The GHARR-1 is in the final stages of converting its HEU (90.2 %) fuel to LEU (13 %)

fuel. Due to the differences if the LEU core design as compared to that of the HEU;

fuel density, dummy arrnagement, number of fuel elements, this study was carried out

characterize the neutron spectrum at the irradiation sites of GHARR-1 to ascertain the

impact of the conversion on the neutron spectrum. This was done theoretically using the

MCNP5 code. The neutron spectrum parameters (a and f ), neutron fluxes and their axial

variation were determined. Average results of a for the LEU (inner sites, -0.096; outer sites,

-0.031) as compared to the HEU (inner sites, -0.103; outer sites, -0.034) indicate a further

deviation from the ideal 1/E epithermal spectrum distribution for the HEU as compared to

the LEU. Results of f for the HEU (inner sites, 18.76; outer sites, 48.75) and LEU (inner

sites, 17.77; outer sites, 45.08) indicate some levels of neutron flux trade off in the LEU

as compared to the HEU. This is attributed to the increased inventory of 238U in the LEU

as compared to the HEU. The neutron flux distribution showed high levels of uniformity

at the irradiation sites (2 % to 10 % variation), with the thermal neutron flux showing the

highest level of uniformity. The flux distribution for GHARR-1 with HEU and LEU both

followed similar patterns.

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