Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
Reactor shutdown : The reactor is shut down if it is subcritical by at least 1 dollar both in
the reference core condition and for all allowed ambient conditions with the reactivity
worth of all installed experiments included.
Reference core condition is the reactivity condition of the core when it is at 20 'C and the
reactivity worth of xenon is zero (i.e., cold, clean, & critical).
Shutdown margin is the minimum shutdown reactivity necessary to provide confidence
that the reactor can be made subcritical by means of the control and safety systems
starting from any permissible operating condition. It should be assumed that the most
reactive scrammable rods and all non‐scrammable rods are in their most reactive position
and that the reactor will remain subcritical without further operator action.
Shutdown reactivity is the value of the reactivity of the reactor with all control rods in
their least reactive positions (e.g., inserted). The value of shutdown reactivity includes the
reactivity value of all installed experiments and is determined with the reactor at ambient
conditions.
Secured shutdown is achieved when the reactor meets the requirements of the definition
of "reactor secured" and the facility administrative requirements for leaving the facility
with no licensed reactor operators present.
Reactor Secured : A reactor is secured when
(1) Either there is insufficient moderator available in the reactor to attain criticality or
there is insufficient fissile material present in the reactor to attain criticality under
optimum available conditions of moderation and reflection;
(2) Or the following conditions exist:
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