In PWRs they are inserted from above, with the control rod drive mechanisms mounted on the reactor pressure vessel head.
2.
The flaw was near the nozzle for a control rod drive mechanism and attributed to primary water stress corrosion cracking, though no actual leakage was detected.
3.
Many of the failure modes that caused a stuck rod during tests ( like bearing and clutch wear ) would only apply to a movement performed by the control rod drive mechanism.
4.
IRIS is a smaller-scale design for a Pressurized water reactor ( PWR ) with an integral reactor coolant system layout, meaning the steam generators, pressurizer, control rod drive mechanisms, and reactor coolant pumps are all located within the reactor pressure vessel.
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