Question

What measures can be taken to assure subcriticality?

Operating the reactor at low power

Three diverse and redundant shut-down systems

Introducing the control elements consisting of AgInCd or B4C into the core (SCRAM)

Fast injection of boric acid into the reactor core

Answer 1

Measures that can be taken to assure subcriticality is to introduce the control elements consisting of Ag-In-Cd or B4C into the core (SCRAM).

The efficiency of these neutron absorbing materials will depend on the fuel composition, the design of the reactor core and core management. For instance, the reactivity worth of thermal neutron absorbers such as boron or Ag–In–Cd is lower for mixed oxide fuel than it is for uranium fuel. A change in the core loading scheme from ‘out-in’ to ‘in-out’ would affect the subcriticality.