RELEVANT SBWR PHENOMENA

MSLB & LOFW

SBWR

Nodalization of SBWR plant for the integrated FUMO code

SBWR Decay heat is removed at different locations:
PCCS or IC: decay heat transferred outside
structures: decay heat remains inside
vent pool surfaces: energy transfer from DW to PSP, which heat-up leads to WW pressure increase & to overall pressurisation

 

Higher PSP temperature à higher overall pressure
vs.
For PSP vent water à lower condensation on surface
decreasing overall pressure for the reduced DW to PSP energy transfer

 

Significant phenomena to be evaluated in safety analysis:
PSP stratification, affecting both the capability to store energy coming from condensation & steam partial pressure above the pool surface
PCCS & IC efficiency, considering non-condensable gas effects

 

MSLB Sensitivity studies by Integrated FUMO

condensation on vent water evaluated assuming the PSP superficial temperature equal to average one (maximum credible)
condensation on vent water neglected
condensation evaluated taking into account pool side thermal resistance

A great condensation on vent water decreases the steam condensation in PCCS and is responsible for storing energy in PSP
This, in turn, determines the long term containment pressure increase


DW pressure


PCCS power

 

  LOFW

Down-comer Level & Core Temperatures show
effects of different assumptions for the containment pressure
on GDCS injection time & on core cooling conditions

Stand-alone: containment pressure set to constant values from previous separate containment analysis
FUMO: actual containment pressurisation simulated à different core cooling behaviour


LOFW - Down-comer level


LOFW - Core rod temperature

Containment behaviour

Feedback of containment pressurisation on DPV flow rate à different DW & WW pressure histories
Pressure equalisation is predicted earlier in integrated FUMO than in separate calculations


LOFW - DW and WW pressures (integrated code)


LOFW- DW and WW pressures (stand alone data)

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