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Frontiers in Energy

ISSN 2095-1701

ISSN 2095-1698(Online)

CN 11-6017/TK

Postal Subscription Code 80-972

2018 Impact Factor: 1.701

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Front. Energy    2019, Vol. 13 Issue (4) : 707-714    https://doi.org/10.1007/s11708-019-0616-0
RESEARCH ARTICLE
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
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Abstract

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.
Keywords phenomena identification and ranking table (PIRT)      thorium based molten salt reactor-solid fuel (TMSR-SF)      safety analysis      RELAP/SCDAPSIM     
Corresponding Author(s): Xiaojing LIU   
Online First Date: 12 March 2019    Issue Date: 26 December 2019
 Cite this article:   
Xiaojing LIU,Qi WANG,Zhaozhong HE, et al. Phenomena identification and ranking table exercise for thorium based molten salt reactor-solid fuel design[J]. Front. Energy, 2019, 13(4): 707-714.
 URL:  
https://academic.hep.com.cn/fie/EN/10.1007/s11708-019-0616-0
https://academic.hep.com.cn/fie/EN/Y2019/V13/I4/707
Fig.1  Schematic of the TMSR-SF and the fuel
Design parameter Value
Thermal power/MW 10
Fuel type TRISO
Height of reactor core/cm 190.31
Diameter/height of reactor core cylinder/cm 135/180
First loop coolant FLiBe
Secondary-loop coolant FLiNaK
Inlet temperature/(100% FP, °C) 600
Outlet temperature/(100% FP, °C) 650
Mass flow rate/(100% FP, kg/s) 84
U-235 enrichment/% 17.08
Maximum pressure in vessel/MPa <0.5
Tab.1  Main design parameters for TMSR-SF1
Step Process
Step 1 Issue
Step 2 PIRT objective
Step 3 Hardware-scenario
Step 4 Figure of merit (FoMs)
Step 5 Data base
Step 6 Identify phenomena
Step 7 Importance ranking
Step 8 Knowledge level
Step 9 Document PIRT
Tab.2  Nine step process of PIRT
Systems Subsystem
Reactor Pebble fuel
Primary coolant flow
In-vessel component—graphite reflector
In-vessel component—compaction device
Reactor vessel Top support plate
Upper plenum
Downcomer
Lower plenum
Reactivity control Backup reactivity control system
Passive reactivity control
First loop First loop molten salt pump
First loop pipeline
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  Summary and description of systems and subsystems for TMSR-SF
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  Scale of phenomena importance
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  Scale of knowledge level
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  PIRT summary for TMSR-SF
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  Initial condition for simulation
Fig.2  Overview of RELAP5-MOD 4.0 model of TMSR-SF
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  Transient for station blackout simulation
Fig.3  Inlet and outlet coolant temperature
Fig.4  Coolant temperature distribution in hot channel
Fig.5  Air mass flow rate of PRHS
Fig.6  Inlet and outlet air temperature of PRHS
Fig.7  Transient response of TMSR-SF coolant temperature in hot channel at various elevations
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