
@lillymunster , in analogy to what I wrote about #RCIC weaknesses ( brainmindinst.blogspot.com ), #HPCI pumps are run with turbines driven by reactor steam. The valves controlling the steam, called governors, have a notorious breakdown record. They are fickle and need knowledgable, constant maintenance and adjustment. In the US, the manufacturer had to teach refresher courses on proper maintenance and calibration.
Improper maintenance could be one source of the vibrations the operator noticed. The other source could be that the quake damaged the piping for the steam fed into the turbines causing fluctuations in steam pressure that the governor overcompensated, perhaps leading up to a resonance catastrophe. That prospect may have frightened the operator. Above is an example of such turbine by Dresser Rand (source www.dresser-rand.com ). i1214.photobucket.com

Early Tepco records on Unit 3 from Mar. 11 ( www.tepco.co.jp ). i1214.photobucket.com
On of the highest readings I've seen.
Have a Very Merry Christmas Everyone!