Regional Basic Professional Training Course in Korea

4.2.6.2.3 Reactor Systems
❙ 295 ❙
4. DESIGN OF NUCLEAR REACTORS
The primary coolant enters the inlet plenum and flows upward through fuel channels for
cooling. The coolant is gathered in the chimney, and then exits through two outlet
.nozzles. Each of the two loops has a 400hp pump, a 14 MW plate‐type heat exchanger,
and a check valve which is designed to close with a reverse flow. The two loops combine
at a returning line into the core. 10% of the returning flow (bypass flow) is branched to
the bottom of the reactor pool. A hot water layer is formed at the pool surface for the
safety of workers around the pool surface. For the removal of decay heat, two natural
circulation modes are available; loop and pool natural circulation. When the density
driving force is not enough for the loop natural circulation, the core is cooled by pool
natural circulation through two flap valves. The secondary coolant is cooled by a cooling
tower with 4 cooling fans. The reflector tank surrounding the reactor core is made of
zircaloy 4 and filled with heavy water which is pumped around in a closed circuit. It
accommodates various vertical and horizontal experimental holes. Four CARs are
connected to the driver through a magnetic clutch and driven by four independent
stepping motors. The reactor regulating system is controlled by a multi‐loop controller in
which the control algorithm is embedded. The reactor protection system is of a safety
class system. The reactor is tripped by dropping four SORs. The SORs drop once the
solenoid valves, which are attached to the hydraulic circuit of the shutdown mechanism,
are opened.