NUREG-1537, Part 2 - NRC

4.2.2 Control Rods
Areas of Revew
REAC DESaRIPTON
The control rods in a non-power reactor are designed to change reactivity by
changing the amount of neutron absorber (or fuel) in or near the reactor core.
Depending on their function, control rods can be designated as regulating, safety,
shim, or transient rods. To scram'the reactor, the negative reactivity' of the control
rods is usually'added passively and quickly when the rods drop into the core,
although gravity can be assisted byspring action. In the case of control rods
fabricated completely of fuel, the rods fall out of the bottom of the core. Because
the control rods serve a dual function (control and safety), control and safety
systems for non-power reactors are usually not completely separable. In nonpower
reactors, a scram does not challenge the safety of the reactor or cause any
undue strain on any systems or components associated with the reactor.
The areas of review are discussed in this section of the format and content guide.
Acceptance Criteria
The acceptance criteria for the information on control rods include the following:
The control rods, blades, followers (if used), and support'systems should
bedesigned consevativelytowithstand-all anticipated stresses and'
challenges from mechanical, hydraulic, and thermal forces and the effects of
their chemical and radiation environment.
* The control rods should be sufficient in number and reactivity worth to
comply with the 'single stuck rod' criterion; that is, it should be possible to
shut down the reactor and comply with the requirement of minimum
shutdown margin with the highest worth scrammable control rod stuck out
of the core., The control rods should also be sufficient to control the
- reactor in all designed operating modes and to shut down the reactor safely
from any operational condition. The design based for redundancy and
diversity should ensure these functions.
* The control rods should be designed for rapid, fail-safe shutdown of the
reactor from any operting condition. The discussion should address
* conditions under which normal electrical power is lost.-:
* The control rods should be designed so that scramming them 'does not
challenge their integrity or operation or the integrity or operation of other
* reactor systems.
STANnD REVIEW PLAN
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