Post on 10-Apr-2018
Safety consideration in HTR-PM
Fu LI
INET, Tsinghua University, Chinalifu@tsinghua.edu.cn
VIC, Vienna, AustriaJuly 10-12,2012
IAEA Technical Meeting on Re-evaluation of Maximum Operating Temperatures and Accident Conditions for High
Temperature Reactor Fuel and Structural Materials
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Outline
1 Safety philosophy 2 Limiting conditions 3 Current implementation 4 Uncertainty analysis 5 Other topics
1 Safety philosophy
Based on current licensing framework Basically for LWR Ensure the integrity of primary circuit, or
flooding of the core With help of engineered safety features
Safety functions: Control of Power—reactivity Decay heat removal Retention of FP
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1 Safety philosophy
Basic philosophy Defense in depth - DiD
Multiple barriers First layer: TRISO --most important in HTGR Second layer: primary circuit Third layer: confinement/containment
Most important for LWR Forth layer,…: ESF, EOP,…
Large time span for accident treatment and slow development of accident is another layer
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1 Safety philosophy
Basic philosophy ALARA
As low as reasonable achievable
Safety class systems plus non-safety class systems Such as helium purification system, sub-
atmosphere ventilation system,… To reduce the radioactive release to environment
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1 Safety philosophy
Experiences Adoption of mature technology
Feedback from HTR-10 Based on steam cycle Test of systems/components before
installation Research on advanced technology
Gas turbine Hydrogen production Advanced fuel …
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2 Limiting conditions
Limiting conditions for each operation conditions Normal operation (NO) Anticipated operation occurrence (AOO) Design basis accident (DBA) Beyond design basis accident (BDBA)
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2 Limiting conditions
Types of limiting conditions Fuel temperature Component temperature
For core internal For primary circuit boundary, supporting for
RPV For structure material
CR, blower, SG tube For component in cavity
Cavity cooling system Cavity concrete
For auxiliary system 8
2 Limiting conditions
Temperature limit for fuel Normal operation: 1200C Accident: 1620 C
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2 Limiting conditions
Temperature Limit for structure
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Components Operation temp(C) Accident temp（24h）(C)
RPV 350 425
Supporting for RPV 350 425
Hot gas duct 800 1000
Hot gas duct vessel 350 600
Core barrel 375 500
Cavity concrete 70 100
2 Limiting conditions
Comments: Fuel temperature:
Safety related FP release
Large margin Long time span, small percentage of fuel
Structure temperature: Investment related?
For LWR, safety related, for the decay heat removal and fuel cooling
Based on good TRISO fuel performance Very low failure rate
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3 Current implementation
Most of safety features in HTR-PM are similar to HTR-MODUL The system arrangement, the parameters
are similar HTR-MODUL was reviewed by TUV
Most of the components are similar to those in HTR-10
Safety features of modular HTR is well recognized
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3 Current implementation
Most of the components will be tested in advance, in full scale Control rod, small absorber ball system,
fuel handling system, blower, steam generator,
More experiments are undergoing Fuel irradiation Pebble flow, pebble bed heat conduction
coefficient, graphite dust, hot gas mixture, natural circulation of cavity cooling system 13
3 Current implementation
The preliminary safety analysis report (PSAR) of HTR-PM was reviewed by NNSA, and was accepted in Sept 2009 Structure and scope: SRP Classification of operation conditions Criteria for each operation conditions Main results
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3 Current implementation
SRP: Proposed by NRC 20 chapters
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3 Current implementation
Operation conditions: NO, AOO(10-2), DBA(10-4 ,10-6), BDBA Criteria:
Operation of the unit, damage to the unit, radioactive release to the environment
NO, AOO, DBA: systems of non-safety class will not be assumed to be available
Borrowed from LWR DBDA was analyzed
Through PSA by some special topic reports
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3 Current implementation
Interested accidents: DLOFC
Most challenge for fuel temperature For capability of cavity cooling system For temperature limit for core barrel and RPV
PLOFC For capability of cavity cooling system For temperature limit for core barrel and RPV
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3 Current implementation
Interested accidents: Water ingress
For set point of primary circuit safety valve For FP release
FP deposition in SG Additional FP release from failed coated particles
Requirement for the sub-atmosphere ventilation system No requirement for safety class
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3 Current implementation
Interested accidents: ATWS (BDBA)
Time for re-criticality Requirement for the small absorber ball system No safety impact
Continuous operation of blower (BDBA) Fail to trip For the temperature of primary circuit
boundary For diversity actuation system, to trip blower
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3 Current implementation
Interested accidents: Failure of cavity cooling system (BDBA)
No effect on max fuel temperature Challenge for RPV temperature
Manual depressurization of primary circuit For concrete temperature
With/without concrete cooling system Additional supporting cooling system
Additional water supply from fire fighting system (accident management)
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3 Current implementation
Interested accidents: Air ingress accident (BDBA)
Configuration of break in primary circuit No big challenge for fuel temperature Experiment data for particle failure under air
condition (German data and Japan data) Fuel performance under normal condition and
oxidation condition Difference data from difference countries
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3 Current implementation
Interested accidents: Rod ejection accident (BDBA)
Not included in PSAR How fast of the control rod ejection Fuel temperature is not a problem Criteria for max power of kernel
250mW/Particle? More for short period
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3 Current implementation
Interested accidents: Failure of hot gas duct vessel (BDBA)
Not included in PSAR DiD
Vessel concept(basic safety) Pipe concept with LBB Movement restrain Air ingress Accident management
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3 Current implementation
Other topics Vented lower pressure containment
(VLPC) Burst release system Sub-atmosphere ventilation system Filtering system
Based on function requirement Physics protection for reactor ALARA
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3 Current implementation
Other topics Cavity cooling system
Safety class 3 redundant trains
Natural circulation Residual heat removal system? Just investment protection related?
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3 Current implementation
Other topics Non-safety sub-atmosphere ventilation
system With filtering system: for aerosol, for Iodine For normal pressure
Ventilation for small break Burst release for large break
Coincide with delayed release phenomenon of coated particles, lower failure rate of coated particles, permeation and non-condensation of helium
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3 Current implementation
Other topics Acceptance criteria
NO: AOO:
0.25mSv/reactor year DBA:
5mSv/accident 10mSv/accident
BDBA: 50mSv, 10-6/reactor year Through PSA
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3 Current implementation
Other topics For fuel temperature
Margin for normal operation AVR experience Difference for modern modular design
Requirement for cooling after reactor trip Main heat transfer system, helium purification
system, cavity cooling system Margin for accident
1620C Just few percent of fuel
Uncertainty analysis?28
3 Current implementation
Other topics For fuel temperature
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200
300
400
500
600
700
800
900
1000
0 200
400 600
800 1000
1200
温度 (℃)
轴向
坐标
(cm)
冷却剂
温度
燃料表
面温
度
燃料中
心温
度
颗粒中
心温
度
3 Current implementation
Other topics Reactor inlet /outlet temperature
IAEA TECDOC 1674 HTR-PM: 250/750C ANTARES: 400/850C GT-MHR: 490/850C GTHTR300: 587/850C HTR-MODUL: 250/700C PBMR: 500/900C
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3 Current implementation
Other topics For normal/accident fuel temperature
IAEA TECDOC 1674 HTR-PM: 930/1620C ANTARES: GT-MHR: 1320C /1600C GTHTR300/300C: 1400/1600C HTR-MODUL: 837 /1620C PBMR-400: 1080/1570C
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3 Current implementation
Other topics For normal/accident RPV temperature
IAEA TECDOC 1674 HTR-PM: SA508, 250/350C ANTARES: Mod9Cr, GT-MHR: SA508/SA533, 440C / GTHTR300/300C: SA533,140C helium/ ? HTR-MODUL: PBMR:
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3 Current implementation
Other topics Structure temperature for control rod
Under DLOFC accident INCOLOY 800 Investment protection related?
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4 Uncertainty analysis
To evaluate the max temperature of fuel and structure material under normal and accident condition Conservative assumption + conservative
analysis Best estimation + uncertainty analysis
More reasonable
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4 Uncertainty analysis
Uncertainty on Fuel temperature
For normal operation, for accident Large margin for normal accident, Less margin for accident (DLFOC accident)
Real challenge?
Structure accident For normal operation, for accident
Challenge condition: DLOFC with failure of cavity cooling system
Not real safety related?
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4 Uncertainty analysis
Uncertainty sources Nuclear cross section Other material property, correlations
Thermal conduction coefficient, pebble bed Manufacturing uncertainty Model error, numerical error
Few group, diffusion, FD, semi-equilibrium Operation history deviated from design
conditions Pebble bed movement
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4 Uncertainty analysis
Pebble bed movement Random in microscopic Random in macroscopic Error in model
Such as model in VSOP
Effect from multiple pass mode Will reduce uncertainty?
Need quantitive evaluation
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4 Uncertainty analysis
Experience from melt-wire experience in AVR Bypass Pebble flow model
2-zone fuelling Capability of code
2D- 3D Many kinds of fuel Complicated operation history
Not exact samples for modern design38
5 Other topics
Future options for V/HTR Super critical steam cycle Process heat application
Co-generation Gas turbine
Silver release
Requirements Increase of inlet temperature Increase of outlet temperature
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5 Other topics
Challenges Higher fuel temperature
For normal operation, for accident ZrC coating? UO2*?
Structure material temperature For RPV
Active cooling, 9Cr-1Mo For Component: IHX
Inconel 617? ODS?
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Conclusion remarks
HTR-PM PSAR is finished already Based on current LWR licensing
framework Maximum temperature on fuel and
structure material for normal and accident condition is very important for HTR Max fuel temperature is more important Most challenging condition is DLOFC,
plus failure of cavity cooling accident41
Comments
Assessment of AVR experiment is very important Melt-wire experiment Features of AVR, or features for all
pebble bed HTR, or features for all HTGR?
Operation on 950/1100C outlet temperature proven the robustness of pebble bed HTR?
Positive of negative lessons are learned?42
Comments
FP release, instead of fuel temperature, is the real concern For normal operation, monitoring of FP
inside primary circuit is a good indicator In helium, in graphite dust
For accident condition, qualification of fuel performance (irradiation & annealing experiment) is important
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Comments
Based on good performance of modern TRISO fuel, temperature on structure material is mainly investment protection related, not safety related. This is the fundamental difference
compared with LWR, where keeping of coolant is most important (to prevent the core melt)
This may be the key factor for future development of HTGR 44
Comments
One of important way to re-evaluate the max temperature of fuel and structure material is uncertainty analysis Uncertainty aroused from pebble flow is
an interested topic Multiple pass model will reduce the
uncertainty?
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Comments
According to basic safety function (power control, decay heat removal, FP retention), the performance of FP retention in TRISO particle is the key issue, it will relief the requirement on max temperature of fuel and structure material Based on the Defense-in-Depth and
ALARA principles, control of fuel temperature and structure temperature are also very important 46
Comments
In order to evaluate the max temperature of fuel and structure material, another methodology is risk informed analysis, probability safety analysis (PSA) Which risk? What level of probability?
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