Assessment of the Reliability of Thermal-Hydraulic and Neutronics Parameters of Ghana Research Reactor-1 Control Systems

ABSTRACT

The thermal–hydraulics and neutronics parameters of GHARR-1 control systems were assessed for its reliability after 18 years of operation using the Micro-Computer Closed Loop System (MCCLS) and original Control Console (CC). The MCCLS and some components that control the sensitivity and the reading mechanism of the meters on the control systems have been replaced with new ones over the years, due to ageing, repairs and obsolescence. The results show that when reactor is operated at the different power levels the preset neutron fluxes at the control systems is 1.6 times the Neutron fluxes obtained using a flux monitor at the inner irradiation site two of the reactor. The average percentage of deviation of fluxes from the actual preset was 36.5% which compares very well with the reactivity decrease of 36.3% after operating the reactor at critical neutron flux of 1.0 x 109n/cm2s. The reactivity regulators were adjusted to increase the core reactivity to 4 mk and the reactor operated at 15 kW. The preset neutron flux at the control systems reduced to 1.07 times the Neutron fluxes obtained using a flux monitor at the inner irradiation site 2 of the reactor. The performance of the current micro – amplifiers in the two independent control instrumentations was assessed at an input current of 10 µA. The results showed that the flux registered on both the CC and MCCLS varied by a factor of 1.2. The correlation between neutron flux and power, as well as temperature and power at transient state produced almost the same thermal power at about 20% above the rating power of 30 kW but deviated at lower and higher power ratings. The dynamic test through positive reactivity insertion, demonstrate or confirm the inherent safety of the reactor.