Nuclear Safety Research        
     

16

Depressurization action byrelief valve (RV) operationPressurizer
stuck-open
PORV(TMI type)
LLevelmeter

Steamgenerator(SG)

Primary Pressure (MPa)

Depressurization action in caseof HPI failure and AIS gas inflow
AM start
945s (SP3),941s (SP4)

128

SP3,
Core heat-up
start, 8573s

SlowdropGas inflow〜1.5MPa

4RapiddropVessel topbreak
PipebreakSP3 : Constant (-55K/h)
SP4 : Rapid (RV fully opened)

Gas inflow〜1.5MPa

00

2000

4000

6000

8000

10000

Time after Break (s)        




GasVessel bottom
instrument tube break

Accumulator injection
system (AIS) (P<4.5MPa)

1.2

Low pressure injection(LPI) (P<1.2MPa)

1.0High pressure injection(HPI)    
Various LOCA tests were conducted at LSTF, the world’s
largest plant simulator with the same height and 1/48 volumeof a 3423 MWt PWR, to examine the effectiveness of accident
management (AM) measures if there is severe loss of coolant.
In case of HPI total failure, it is important for operators todepressurize the primary coolant system by opening SG relief
valves (RVs) to activate the AIS and LPI system. The tests
verified the effectiveness of this AM measure even in a LOCA
caused by vessel bottom break which is the worst breaklocation. A code analysis also confirmed the effectiveness.

                                              

Coolant Retention (MR/M0)

PWR

LPI
1.24MPa

Initial stateRapid
drop

0.8

0.6
Slow
drop0.4

Core overheat
before LPI (SP3)0.002

Critical coreheat-up level
MR/M0=0.25

Temporaryheat-up

0.2

4SP3 : Core overheat
SP4 : Core cooled

1068
Primary Pressure (MPa)121416 
    








This shows the difference in retained coolant in two tests ofdifferent AM actions (SP4 achieved the goal).

                                                            


82 JAEA R&D Review 2006

AIS
4.5MPaAM start

SafeGoal 