| Summary: | Current regulations specify the minimum number of operators required per nuclear power plant.
However, these requirements are based on the operation of large nuclear power plants, which
are not inherent safe and can result in a meltdown. For newly developed small nuclear
reactors, the current number of operators seems to be excessive causing the technology to be
less competitive. Before the number of required operators can be optimised, it should be
demonstrated that human errors will not endanger or cause risk to the plant or public.
For this study, a small pebble bed High Temperature Reactor (HTR) Nuclear Power Plant
(NPP), the Th-100, was evaluated. The inherent safety features of this type of nuclear reactor
include independent barriers for fission product capture and passive heat dissipation during a
loss of coolant. The control and instrumentation architecture include two independent
protection systems. The Control and Limitation System is the first protection system to react if
the reactor parameters exceed those of the normal operational safe zone. If the Control and
Limitation System fail to maintain the reactor within the safe zone, the Reactor Protection
System would at that time operate and force the reactor to a safe state. Both these automated
protection systems are installed in a control room local to the reactor building, protected from
adverse conditions. In addition, it is connected to a semi-remote control room, anticipated as a
multi-unit control room to include the monitoring and control of the auxiliary systems.
Probable case studies of human error associated with multi-unit control rooms were evaluated
against the logic of the Control and Limitation System. Fault Tree Analysis was used to
investigate all possible failures. The evaluation determined the reliability of the Control and
Limitation System and highlighted areas which design engineers should take into account if a
higher reliability is required. The scenario was expanded, applying the same methods, to
include the large release of fission products in order to verify the reliability calculations. The
probability of a large release of fission products compared with studies done on other nuclear
installations revealed to be much less for the evaluated HTR as was expected.
As the study has proved that human error cannot have a negative influence on the safety of the
reactor, it can be concluded that the first step has been met which is required, when applying for
a waiver to utilise a multi-unit control room for the small pebble bed HTR NPP. Also, from the
study, it is recommended that a practical approach be applied for the evaluation of operator
duties on a live plant, to optimise the number of operators required. This in turn will position the
inherent safe HTR competitively over other power stations. === MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015
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