Phenomena identification and ranking table exercise for thorium based molten salt reactor-solid fuel design
Xiaojing LIU1(), Qi WANG1, Zhaozhong HE2, Kun CHEN2, Xu CHENG1
1. School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
Thorium based molten salt reactor-solid fuel (TMSR-SF) design is an innovative reactor concept that uses high-temperature tristructural-isotropic (TRISO) fuel with a low-pressure liquid salt coolant. In anticipation of getting licensed applications for TMSR-SF in the future, it is necessary to fully understand the significant features and phenomena of TMSR-SF design, as well as its transient behavior during accidents. In this paper, the safety-relevant phenomena, importance, and knowledge base were assessed for the selected events and the transient of TMSR-SF during station blackout scenario is simulated based on RELAP/SCDAPSIM Mod 4.0.
The phenomena having significant impact but with limited knowledge of their history are core coolant bypass flows, outlet plenum flow distribution, and intermediate heat exchanger (IHX) over/under cooling transients. Some thermal hydraulic parameters during the station blackout scenario are also discussed.
Primary side of molten salt-to-molten salt heat exchanger
Intermediate loop
Secondary-loop molten salt pump
Secondary-loop pipeline
Secondary side of molten salt-to-molten salt heat exchanger
Operating condition heat removal air-molten salt heat exchanger
Residual heat removal air-molten salt heat exchanger
Passive residual heat removal system (PRHS)
Air heat exchanger
Tab.3
Importance rank
Definition
L
Small influence on primary evaluation criterion
M
Moderate influence on primary evaluation criterion
H
High influence on primary evaluation criterion
Tab.4
Knowledge level
Definition
H
Known: approximately 70%–100% of complete knowledge and understanding
M
Partially known: 30%–70% of complete knowledge and understanding
L
Unknown: 0%–30% of complete knowledge and understanding
Tab.5
Phenomena/process
Normal operation
Protected transient of over power (PTOP)
ATWS
Station blackout
LOHS
LOFC
Overcooling
Small loss of coolant accident (LOCA)
Thermal conductivity of carbonaceous material
HM
HM
HM
HM
HM
HM
HM
Specific heat capacity of carbonaceous material
MM
MM
MM
MM
MM
MM
MM
Thermal conductivity of fuel kernel
HM
HM
HM
HM
HM
Specific heat capacity of fuel kernel
MM
MM
MM
MM
MM
MM
Coolant bypass flow
HL
HL
HL
HL
ML
Coolant flow distribution due to temperature gradient
MM
MM
Coolant flow distribution due to graphite irradiation
ML
ML
Viscosity/friction of FLiBe
HM
HM
HM
HM
HM
MM
Thermal conductivity of FLiBe
HM
HM
HM
HM
HM
Subchannel flow
HM
HM
HM
Coolant mixing in lower plenum
MM
MM
Upper plenum mixing
HL
HH
HH
Thermal conductivity of graphite
LM
MH
MH
MH
MH
Specific heat capacity of graphite
MH
HH
HH
HH
HH
Thermal conductivity of vessel
LM
MM
MM
LH
LM
Reactor vessel specific heat capacity
MH
MH
MH
MH
MH
Heat transfer to vessel upper flange
MM
Heat radiation from upper plenum to top support plate
HM
HM
HM
HM
Molten salt freezing and melt
HL
HL
Heat transfer across vessel to gas space
MM
MM
MM
MM
MM
Heat transfer across gas space to heat insulation
MM
MM
MM
MM
MM
Concrete thermal conductivity
HM
HM
Reactivity insertion due to overcooling transient
LH
First loop piping heat loss
LH
Secondary-loop piping heat loss
MM
MM
MM
MM
MM
Heat transfer across penetration piece of PRHS to concrete
MM
MM
MM
MM
MM
Passive heat removal system (PHRS) piping heat loss
HM
HM
HM
Heat transfer across heat transfer area of PHRS to gas space
MM
MM
MM
Tab.6
Parameter
Value
Core power level/MWt
10
Core inlet coolant temperature/°C
600
Core outlet coolant temperature/°C
650
Core mass flow rate/(kg?s–1)
84
Secondary-loop mass flow/(kg?s–1)
166
Environment temperature/°C
40
Tab.7
Fig.2
Parameter
Value
Station blackout occurring/s
30000
All the pumps switch off/s
30001
Loss of primary coolant flow/s
30000
PRHR system fully operation/s
30060
Tab.8
Fig.3
Fig.4
Fig.5
Fig.6
Fig.7
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