Regional Basic Professional Training Course in Korea

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4. DESIGN OF NUCLEAR REACTORS
in a severe accident situation involving meltdown of a part of the fuel in the core. It is
intended to study the release of fission products and their subsequent behavior in the
primary coolant system and the containment.
Furthermore, the intense neutron flux from research reactors can be used to carry out
irradiation experiments in a shorter time than in power reactors and under better
conditions, because of the flexibility of the research reactors and the associated risks that
are generally not as high.
4.2.4.1. Risks associated with research and test reactors
In low‐power research reactors (under 100 kW) the risk of irradiation mainly concerns the
operating staff. The design of the installations and observance of radiological protection
procedures are intended to prevent this risk. In the case of homogeneous reactors, there is
also a critically accident risk if the fissile solution is transferred into a chamber of
unknown geometry.
Open‐core pool‐type reactors such as OSIRIS and ISIS have easily accessible cores with
configurations that are simple to modify. The probability of a reactivity accident that
could lead to meltdown of the fuel is therefore greater for open‐core pool‐type reactors
than for other types. An accident of this nature can be prevented by observing procedures
and instructions governing handling operations in the core.
The experimental devices in the OSIRIS reactor and the test loops associated with
CABRI and PHEBUS (FP program) reactors constitute hazard for the reactor itself. For
example the following risks are present: explosion of an irradiation loop under pressure,
interaction between the water in the pool and the NaK contained in some of the
irradiation devices or interaction between the molten experimental fuel and the water in
the cooling system of the PHEBUS‐FP test devices.