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Inadvertent Opening of a SG Relief Valve

IC8 was created for hot zero power of RC pressure near 2200 psia and Tavg 560ºF.  By opening the left side single ADV and lock it open, a flow rate about 500 lb/s is discharged from loop A.  It overcools the RCS.  As a result, moderator temperature reactivity causes return to criticality and a power surge.  PCTRAN’s result (about 20% peak) is greater than the MHI prediction of 5%.   Depressurization in the RCS initiates HSPI and its boron reactivity suppresses the total reactivity back to sub-critical.

 

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Apparently MHI’s analysis has assumed that all MSIV’s were closed so the intact side not affected by the ADV opening.  We assumed that they were still open so both decreased
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