Fine motion control rod drives
Fine Motion Control Rod Drives (FMCRD) are being introduced in the ABWR. Day to
day operation is performed with an electric stepping motor which moves the drive
in 0.75" increments (compared to the Locking Piston Drive which had 3" incremen
ts, hence the name "fine motion"). The control rods are scrammed hydraulically
but can also scrammed by the electric motor as a backup. The FMCRD is so
reliable that it is not necessary to inspect all of them during the
lifetime of the plant. Therefore, only 3 drives will be removed for
inspection during the outage which is a huge savings in time.
Typically, 30 Locking Piston Drives are remeoved
every outage. The FMCRDs have continuous clean water purge to keep radiation
to very low levels.
Special Features of ABWR