overview and status of the advanced gas reactor fuel … · · 2015-12-14advanced gas reactor...
TRANSCRIPT
ww
w.in
l.g
ov
Overview and Status of the Advanced Gas Reactor Fuel
Development and Qualification Program
David Petti Co-National Technical Director, Advanced Reactor Technologies Program
Fuel Element
TRISO fuel is a key part of the “Functional Containment” strategy for licensing modular HTGRs • Functional Containment is the collection of design selections that,
taken together, ensure that:
– Radionuclides are retained within multiple barriers, with emphasis on retention at their source in the fuel
– Regulatory requirements and plant design goals for release of radionuclides are met at the Exclusion Area Boundary
2
• Fuel Kernel
• Fuel Particle Coatings
• Matrix/Graphite
• Helium Pressure Boundary
• Reactor Building
TRISO Fuel is at the heart of the safety case for modular HTGRs
• Fabrication of high-quality low-defect fuel is achievable at industrial scale.
– Defect fractions on the order of 10-5
– Process produces narrow distributions of fuel attributes (standard deviation of thicknesses and densities are small)
– Process is stable and repeatable at industrial scale (batch to batch variation is very small)
• Robust irradiation performance inside design service envelope
– Designer assumes incremental failure fraction of 2x10-4
– Performance is better than designer assumption
• Robust accident performance inside design service envelope
– Designer assumes incremental failure fraction of 6x10-4
– Performance is better than designer assumption
Results in low activity of fission products in helium coolant
For the small level of defective particles, significant retention in fuel kernel, fuel matrix and graphite
Results in low incremental release of fission products to the helium coolants
Significant retention of metallic fission products in graphite and fuel matrix
Results in low incremental release of fission products under accident conditions
Lo
w S
ou
rce T
erm
3
Coated Particle Failure Mechanisms
4
Coated Particle Failure Mechanism Control • Structural/mechanical mechanisms
– Excessive PyC irradiation induced shrinkage leading to SiC cracking
– Pressure vessel failure
• Thermochemical mechanisms
– Kernel migration
– Corrosion of SiC
– Thermal decomposition of SiC
• Control of failure mechanism
– Coated particle design
– Fuel specifications
– Product upgrading (sieving, tabling)
– Qualified characterization and acceptance procedures
– Limits on service conditions (burnup, fluence, temperature, temperature gradients)
5
UCO Fuel being Qualified as Improved Fuel
• UCO (UCxOy) is UO2 with UC and UC2 added
• UCO designed to provide superior fuel performance at high burnup
– Kernel migration suppressed (most important for prismatic designs because of larger thermal gradients)
– Eliminates CO formation; internal gas pressure reduced
– Fission products still immobilized as oxides
– Allows longer, more economical fuel cycle
• Reference fuel for NGNP prismatic reactor designs
• Potential higher burnup alternative for pebble bed HTGRs
6
TRISO Particle Fabrication
Overcoating
Furnaces
dry-calcine-sinter
200 – 800 – 1600°C 235U <20% U3O8 Ammonia
Donor
Dissolution
Carbon for UCO
Water-Wash
Gel-Sphere
Kernel
Gelation
TRISO Particle
Matrix + particles
Compaction
Compact
Furnaces
carbonize – heat treat
800 – 1800°C
Insulation
Fluid-Bed Coater
(1300-1500°C) Pyrocarbon, SiC Layers
7
Scaling Up Kernel Production, Coating, Overcoating, and Compacting Processes to Create a Pilot Line
Prepare
Matrix
Overcoat
and Dry Sieve Table
Riffle Compact Carbonize Heat Treat
Granurex Overcoat
and Dry
Dry Mix
and Jet Mill
Matrix
Hot Press
Compact
Carbonize +
Heat Treat in
one Sequential
Process
Lab Scale
Engineering Scale
Lab Scale 2-inch CVD
Coating (60 g charge)
Industrial Scale 6-
inch CVD Coating
(2 kg charge)
Sol-Gel Kernel Production
Kernel Forming
and Drying
8
Fuel Fabrication Evolution
Kernels Coatings Compacts
AGR-1 Engineering scale Lab Scale Lab Scale
AGR-2 Engineering Scale Engineering scale Lab Scale
AGR-5/6/7 Engineering Scale Engineering Scale Engineering Scale
9
AGR TRISO Fuel Fabrication Process Improvements • Removed human interactions in the process
– Eliminated tabling with 3D sieving of coated particles
– Replaced multi-step matrix production (resin solvation, matrix mixing, kneading, drying and crushing) with dry mixing and jet milling of matrix
– Replaced rotary overcoater and upgraded to an automated fluidized bed overcoater that produces highly spherical, uniformly overcoated particles
– Automated die filling and punch travel to form compacts
• Kernel fabrication – Internal gelation to improve sphericity
– Method of carbon addition modified to improve distribution of oxide and carbide phases
• Improved chemical vapor deposition process control – Argon dilution during SiC coating
– Coater “chalice” and multiport nozzle to improve yields (>95%)
– Mass flow controllers to control gas flows during deposition of each coating layer
– Improved MTS vaporizer (leveraging computer chip industry) to evaporate MTS and make SiC layer
• Improved measurement science – Computer measurements of thicknesses
– Greatly improved anisotropy measurements
– Improved density measurements using better density column materials
10
AGR Fabrication Results
• Good tight distributions of particle populations
• Have trouble sometime meeting U.S. prismatic specification on HM
contamination
• Can probably meet German specification of 6E-05
• X-energy can probably have a higher specification here because of low
power level and hence low source term 11
Fuel Fabrication Accomplishments
• Re-established capability to fabricate and characterize TRISO-coated particle fuel in the U.S. after a 10-15 year hiatus
• Developed a significantly improved understanding of how to fabricate high-performing TRISO fuel providing the technical basis for co-location of NGNP in industrial complexes
• Currently fabricating high-quality, low-defect TRISO-coated fuel particles in industry (BWXT). Can meet physical specifications and are almost meeting all defect specifications at 95% confidence. With larger sample sizes and a mature process, should meet the defect specifications in production mode
• Vastly improved quality, reproducibility, process control, and characterization of TRISO fuel. Better control of the process, removal of high variability human interactions in the process, and better measurement technologies all contribute to better quality TRISO fuel
• Establishing a domestic vendor and associated fundamental understanding of key fuel fabrication parameters establishes credibility that the historical industrial experience from Germany in the 1980s is repeatable and has a sound technical basis
• All technologies needed to establish a pilot line are in industrial hands. Qualification fuel for AGR-5/6/7 is being fabricated now
12
Performance Envelope for US AGR TRISO Fuel Program is More Aggressive than Previous German and Japanese Fuel Qualification Efforts
Radar plot of five key parameters of fuel performance
Packing Fraction
50
30
10
Time-averaged
Temperature (°C)
Fast Fluence (x1025 n/m2) Burnup (% FIMA)
Power
Density
(W/cc) 1250
1100 2
10
10 25 3 5
NGNP
German
Japan
13
Overview of AGR Program Activities
Moisture and air ingress effects are part of AGR-5/6 PIE
Early Lab Scale Fuel
Capsule Shakedown
Coating Variants German
Type Coatings
Large Scale Fuel
Performance
Demonstration
Failed Fuel to Determine
Retention Behavior
Fuel Qualification
Proof Tests
Fuel and Fission
Product Validation
Fuel Product
Transport/Retention
AGR-1
AGR-2
AGR-3/4
AGR-5/6/7
AGR-8
Lab Tests
AGR-1
AGR-2
AGR-3/4
AGR-5/6/7
AGR-8
Integral Loop
Validation
Update Fuel
Performance and
Fission Product
Transport Models
Validate Fuel
Performance and
Fission Product
Transport Models
Purpose Irradiation Safety Tests
and PIE
Models
14
AGR Program Irradiation Experiments and PIE
AGR-1 AGR-2
AGR-3/4
AGR-5/6/7
AGR-1
AGR-2
AGR-3/4
AGR-5/6/7
Early test of lab-scale fuel
performance; shakedown
of test train design.
Fuel qualification proof tests.
Engineering scale particles and
compacts.
Irradiation
(in ATR)
PIE
(INL and ORNL)
Failed fuel to assess
fission product retention
and transport in reactor
graphite and fuel matrix.
Engineering scale particles in lab-
scale compacts. Includes UCO
and UO2 fuel.
15
Capsules
In-core
He Ne He-3
Silver
Zeolite
Particulate
Filters
H-3
Getter
Grab Sample
FPMS
Vessel Wall
Individual capsule assembly
with fuel compacts Completed test train Insertion into INL ATR FPMS system 16
Fuel Irradiations (AGR-1, AGR-2 and AGR-3/4)
TRISO Fuel Irradiation Qualification Accomplishments • Completed most successful U.S. irradiation of
TRISO-coated particle fuel (AGR-1). 300,000
particles tested to peak burnup of 19.6% FIMA, a
peak fast fluence of 4.3×1025 n/m2 and peak
time-average peak temperatures of <1200°C –
peak MHTGR service conditions – with no
failures
– The expected superior irradiation performance
of UCO at high burnup has been confirmed -
no kernel migration, no evidence of CO attack
of SiC, and no indication of SiC attack by
lanthanides
17
• AGR-1 95% confidence failure fraction is <1E-5, a factor of 20 better than the design in-
service failure fraction of 2E-4. The more severe AGR-1 irradiation conditions compared to
the vast majority of historic modular HTGR designs suggest substantial fuel performance
margin
• Irradiation of AGR-2 is complete. PIE is underway. No full TRISO failures based on PIE to
date. With 114,000 UCO TRISO particles in the irradiation this corresponds to a failure
fraction of 2.6E-05 at 95% confidence
• Irradiation of AGR-3/4 to study release/retention of fission products from failed TRISO fuel
completed in April 2014. This experiment will provide data needed for source term
evaluations for UCO TRISO fuel and new matrix and graphite. PIE is underway.
1.0E-10
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
Kr-
85
m R
/B U.S. TRISO/BISO
U.S. WAR TRISO/BISO
U.S. TRISO/TRISO
U.S. TRISO-P
German (Th,U)O2 TRISO
German UO2 TRISO
AGR-1
AGR-2
U. S. Fuel German Fuel
U.S. German
Irradiation temperature ( C) 930 - 1350 800 - 1320
Burnup (%FIMA) 6.3 - 80 7.5 - 15.6
Fast fluence (1025 n/m2 ) 2.0 - 10.2 0.1 - 8.5
Rp AGR-3/4 & AGR-2 Comparable with Historical Data
Combined fit of AGR-3/4 and AGR-2 data
18
AGR-5/6/7 details
Desired Fraction of Particles
per Temperature Range
Minimum Number of Particles
Based on 500,000 total
30% <900C 150,000
30% 900C - 1050C 150,000
30% 1050C - 1250C 150,000
10% 1250C - 1350C 50,000
Total 500,000
Temperature Range Minimum Number of Particles
1350C - 1500C 50,000
AGR-5/6
AGR-7
19
Post-Irradiation Examination (PIE) and Safety Testing of TRISO Fuel
• Examine fuel performance:
– Fission product retention:
• during irradiation
• during high temperature accident scenarios (safety testing)
– Fuel kernel and coating microstructure evolution and causes of coating failures
20
Key AGR PIE Accomplishments and Results
• Re-established coated particle fuel PIE and safety testing capabilities at both INL and Oak Ridge National Laboratory
• Developed numerous new tools and approaches for analyzing irradiated particle fuel
• Advanced PIE methods are enabling an unprecedented level of understanding of coated particle fuel behavior
21
Studying failed particles greatly improves ability to characterize and understand fuel performance
AGR-1 Test Train
Vertical Section
Fuel
Compacts
Plenum
between
Capsules
300,000
particles
in AGR-1
irradiation
Gamma scan
tomography to
identify cesium hot
spot and compact
location
Deconsolidation to
obtain 4,000 particles
from compact
X-ray tomography to
nondestructively locate
defects/fractures
0.15
0.36
0.25
0.00
0.00
0.12
0.00
0.64
1.04
0.51
0.72
0.89
0.49 0.61 0.34 0.19 0.33 0.00 0.24 0.61 0.20 0.31 0.62 0.31
5-2-1 5-2-3
5-2-2
IMGA to find
particles with low
cesium retention
Advanced
microscopy to
study
microstructure
in detail
Capsule
disassembly
22
TRISO Fuel Post-irradiation Examination Accomplishments • Post-irradiation examination is revealing
new understanding of fuel performance and fission product transport
– Characterization of kernel and coating behaviors to better understand performance and potential failure modes
– More complete mass balance of key fission products (Ag, Cs, Sr, Eu, Ce, Pd)
• Very low releases of safety important fission products
• Models overpredict releases
– Lack of significant fission product/SiC interactions
• Gross overprediction by computer models
– Have observed 4 SiC failures out of 300,000 particles corresponding to a SiC failure fraction of 3.1E-05 at 95% confidence
23
Deconsolidated
AGR-1 particles
and matrix
Particle handling and
inspection
Capsule Disassembly
and Non-contact
metrology
Advanced-IMGA
AGR-2 PIE Progress (1/2)
• Disassembly of irradiation capsules complete
• Dimensional measurements of fuel and capsule components complete
• Gamma scanning of compacts and graphite holders from US capsules complete
– Measured burnup of compacts for comparison with physics calculations
– Determined inventory of fission products in compacts; compare Ag-110m inventory with predictions to estimate silver release in-pile
– Map fission products in the graphite fuel holders; determine which compacts may have contained particles with failed SiC based on cesium hot-spots in the graphite
• Analysis of fission product inventory on capsule components is in progress; used to determine total fission product release from fuel compacts
AGR-2 PIE Progress (2/2)
• Destructive analysis of as-irradiated compacts:
– Deconsolidation of two UCO compacts and particle analysis in progress (locate and analyze particles with failed SiC)
– Cross-section analysis of four compacts in progress
• High temperature safety testing
– Completed safety tests on two UO2 compacts (1600°C); post-test analysis in progress, including locating particles with failed SiC
– Completed safety tests on two UCO compacts (1600°C); post-test analysis in progress, including locating particles with failed SiC
– Preliminary results indicate excellent performance of UCO fuel at 1600°C; UO2 exhibits higher cesium release relative to UCO
Results of AGR-2 compact gamma scanning
• Good agreement between burnup measured by gamma spectrometry and burnup determined by physics predictions
6
7
8
9
10
11
12
13
14
15
-30 -20 -10 0 10 20 30 40 50 60
Bu
rnu
p (
%F
IMA
)
Distance from Core Centerline (cm)
Measured Burnup (Cs-134/Cs-137)
Burnup Cs-137 Activity
Predicted Burnup
Capsule 2 Capsule 3 Capsule 5 Capsule 6
0%
20%
40%
60%
80%
100%
120%
950 1050 1150 1250
Re
tain
ed
Ag-
11
0m
Fra
ctio
n
TAVA Temperatture (°C)
Capsule 2
Capsule 3
Capsule 5
Capsule 6
• Ag-110m inventory measured in fuel compacts
as a function of time-average, volume-average
(TAVA) irradiation temperature
Gamma scanning of graphite holders for fission products
• Empty graphite holders gamma-scanned to map the location of fission productts
• Based on areas of elevated cesium activity, a total of 5 compacts have been identified as potentially containing particles with failed SiC
• Compacts are being destructively examined to explore the nature of the SiC failures
Stack 1 Stack 2
Stack 3
Cs-134 activity intensity map of one
level in the AGR-2 Capsule 5 graphite
holder, showing elevated activity near
the location of Compact 5-2-3
AGR-3/4 PIE Progress
• Capsule disassembly completed
• Dimensional measurements of fuel compacts and capsule components completed
• Gamma scanning of graphite and matrix rings to map fission product distributions is in progress
AGR-3/4 ring analysis
• Matrix and graphite rings are gamma-scanned to map the distribution of fission products
• Fission product distributions are compared to model predictions for fission product transport
Co-60
Cs-134 Cs-137
Eu-154
Activity intensity maps of a cross-section of the inner
matrix ring from AGR-3/4 capsule 7
TRISO Fuel Safety Testing
30
INL Furnace ORNL Furnace
AGR-1 Safety Testing Results Highlights
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
-50 50 150 250 350 450
13
4C
s r
ele
as
e f
rac
tio
n
Time at temperature (h)
'3-3-2 '3-2-2 '4-1-2'4-3-3 '5-3-3 '6-2-1'6-4-1 '6-4-3 '3-3-1'4-4-3 '4-3-2 '4-4-1'5-1-3 3-2-3
1800°C 1700°C
1600°C
Level of one particle
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
-50 50 150 250 350
85K
r re
leas
e f
rac
tio
n
Time at temperature (h)
'4-3-3 '5-3-3'6-2-1 '6-4-1'3-3-1 '4-3-2'4-4-1 '5-1-33-2-3 1800°C
1700°C
1600°C
• Fuel compacts were heated to 1600 – 1800°C for 300 h while measuring release of fission products
• No TRISO failures at 1600 and 1700°C; only two failures in a single compact at 1800°C
• Cs release used as indication of SiC layer failure; fuel compacts with SiC failures processed to identify failed particles and characterize the coatings
• Specific mechanism of SiC failure was identified (IPyC failure followed by Pd attack of SiC)
• High temperature fuel performance generally considered very good
31
Eu and Sr Results
32
Safety Behavior Summary
• Accident performance of UCO TRISO is very robust (300 hours at 1600, 1700 and 1800°C). Releases of safety significant fission products are very low at 1600 and 1700°C.
• No full particles failures observed in testing to date at 1600 or 1700°C (10 compacts = ~41,000 particles). This implies a 95% failure fraction of ~ 7.3E-05, a factor of 8 margin relative to the prismatic reactor specification. We expect the margin to be 10× when all testing is complete.
• Recall that only 2-3% of reactor core sees 1600°C in conduction cooldown scenario
• Release from intact particles at 1600 and 1700°C is hard to discern. Release appears to be coming from material that diffused into the matrix under irradiation
• No SiC degradation noted at 1800°C as was seen in German UO2 TRISO
– Releases imply very different physics/chemistry. Lack of CO production in UCO is believed to be the cause
• Cesium releases above the level of one particle are seen infrequently and are related to SiC failures that occurred during heating. Have observed 3 SiC failures out of 33,000 at 1600°C corresponding to a SiC failure rate of 2.4E-04 at 95% confidence.
• Specific mechanism of SiC failure was identified (IPyC failure followed by Pd attack of SiC)
33
Comparison of Key Results to Fuel Performance Design Assumptions (all at 95% confidence)
MHTGR
Prismatic
HTR MODUL
Pebble
AGR Results
Manufacturing Defect Level
Heavy Metal Contamination 2 x 10-5
6 x 10-5
2 to 5 x 10-5
(depending on batch)
SiC Defects
1 x 10-4 3 to 6 x 10-5
(depending on batch)
In-service Performance Requirements
Incremental Full TRISO Failures
Normal Operation
Incremental SiC Failures Normal
Operation
2 x 10-4
-----
1.6 x 10-4
-----
< 1 x 10-5 (AGR-1)
2.6 x 10-5 (AGR-2)
2.6 x 10-5
Incremental Full TRISO Failures
Accidents
Incremental SiC Failures Accidents
6 x 10-4
-------
6.6 x 10-4
------
7.3 x 10-5
2.4 x 10-4
34
Impact of UCO TRISO Fuel as key part of Functional Containment Concept for modular HTGR Licensing
• UCO TRISO fuel is being fabricated at industrial scale (BWXT) to the high quality low defect level required by designer to support the HTGR safety case
– This contributes substantially to the very low source term under normal operation
• The irradiation performance of UCO TRISO is excellent up to 20% FIMA and 1250°C
– The failure rate is 20x below the designer requirement (substantial margin)
– Releases of key safety-relevant fission products (e.g. Cs and Sr) are very low (high degree of fission product retention)
• The safety performance of UCO TRISO fuel is excellent
– Fuel is robust after 300 hours at 1600, 1700 and 1800°C
– Failure rate at 1600°C is 8-10x below designer requirement (substantial margin)
– Releases of key safety-relevant fission products are very low (high degree of fission product retention) at 1600 and 1700°C
35
Future Fuel Activities (next 3 years)
• Complete PIE and safety testing of AGR-2 industrially produced TRISO particles
• Complete PIE and safety testing of AGR-3/4
– This fuel contains designed to fail particles and provides crucial information about fission product release from failed/defective UCO TRISO fuel which is needed to support VHTR source term analysis
• Complete fabrication of final qualification fuel at BWXT for AGR-5/6/7 campaign
• Complete design of AGR-5/6/7 irradiation test train and initiate irradiation of qualification fuel
• Beyond 2017, complete AGR-5/6/7 irradiation, complete PIE and safety testing including moisture and air ingress effects
36