actinide burning in reactors: options and...
TRANSCRIPT
Actinide Burning in Reactors:Options and Outcomes
Mujid S. KazimiTEPCO Professor of Nuclear Engineering
Director, Center for Advanced Nuclear Energy SystemsMassachusetts Institute of Technology
In Memory of Manson Benedict:A plenary session on the Nuclear Fuel Cycle
at the ANS Meeting in Boston June 26, 2007
Scope of Talk Is there a need for actinide burning and recycling?
Resource extension, Waste management, Stockpile Reduction
Approaches to reduction of transuranic actinides in the fuel cycle
Reduce TRU in LWR uranium fuel cycle
Transmute the TRU actinides through recycling (involvesactinide separation form UO2, fuel manufacturing, irradiation incore and recycling)
Effect of actinide burning technology choice on
U needs, TRU accumulation, potential costs.
Implications for the repository, using quantification from the AFCIwork at ANL.
Transuranic Element Buildup Production of Pu and minor actinides is a byproduct of using U as nuclear
fuel Roughly 2000 (8000) tons of spent fuel are discharged annually in the
US (world) About 50,000 (130,000) tons have been discharged in the US (world) Mostly uranium (about 95%, at 0.5 to 0.8% 235U) with:
1% plutonium, 0.1% minor actinides, 3-5 % fission products. Pu and higher actinides are accumulating in spent fuel storage or
reprocessing output storage. In the US, and some countries like Sweden, S. Korea, Spain and
Finland, spent fuel is currently stored at the reactor sites, but destinedfor a repository.
In France, Japan and other countries one recycle of Pu in LWRs asmixed oxide (MOX) is planned, then fuel is stored until it is needed forfuture fast reactors.
Add to that discarded weapons Pu, about 10% of civilian Pu to date, or 150tons, with more potentially coming
LWRs as a Source of Actinides Once-Through Uranium Cycle
HEU avoids Pu and higher actinide in LWR spent fuel, butproliferation concerns limit enrichment below 20%
LEU cycle is more efficient in U utilization and SWU utilization
LWR spectrum maximizes Pu-238 content in Pu
High burnup reduces Pu production per unit energy derived
Discharged Pu is proportional to B0.5
Discharged 238 Pu is proportional to B2.2
High burnup reduces spent fuel volume per unit energy
High burnup reduces decay heat production in most of theimportant periods of up to 10 years and from 100 to 10,000 year
Fuel cycle cost is not sensitive to burnup given a fixed 18 monthcycle. A shallow optimum around 70 MWd/kg.
Decay Thermal Energy per GW-yr(e)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100 1000 10000 100000 1000000
Decay time after discharge (year)
Re
lative
th
erm
al e
ne
rgy (
33
MW
d/k
g a
s b
ase
)
50 MWd/kg
70 MWd/kg
100 MWd/kg
120 MWd/kg
150 MWd/kg
Decay time after discharge (year)
Rel
ativ
e th
erm
al e
nerg
y (3
3 M
Wd/
kg a
s ba
se)
Fuel Cycle Economics
*Fixed 18-month cycle, PWRDischarge burnup (MWd/kg)
Nuc
lear
Fue
l Cyc
le (m
ills/
kWhr
-e)
Closed Cycle with Transuranic Burning
Many options to burn (transmute) Pu and higher actinides havebeen proposed and a few have been thoroughly considered:
- LWR, most widely deployed reactors- Gas cooled HTRs- Heavy water cooled CANDU reactors- Fast reactors (with various conversion ratios)- Accelerator Driven Systems
Choices include uranium, thorium, or inert material as a host of theactinide. Only uranium has a wide industrial base.
Choices also involve the higher actinide content besides Pu (Np,Am, Cm, etc)
Metallic, Oxide, nitride or carbide forms , Oxide and metal havesome industrial base.
LWRs as Actinide BurnersIt is possible to recycle TRUs in LWRs such that there would be netTRU reduction. Designs include CORAIL and CONFU
A CONFU fuel assembly composed of 80% of U fuel pins and20% TRU in non-fertile host pins would preserve power peakingand safety characteristics of current reactors. CONFU approach is superior to MOX recycling (limiting Puand MA production), and limiting the heavy metal throughput inrecycling plants. This approach is better than thorium based TRU burning sinceit avoids U232/U233 issues. Handling of high content of Am and Cm is an issue that needsfurther evaluation. Longer cooling time after discharge shouldlimit the neutron sources to only a few times the level of MOXrecycling.
The CONFU Assembly Concept
UO2 Pins
4.2% Enrichment
GuideTubes Fertile Free Pins:
70 v/o – Zr/Mg oxide
18 v/o – YSZ oxide
12 v/o – (TRU) oxide
Total 13.2 kg of TRU/assembly
Combined Non-Fertile and UO2 Assembly
• Multi-recycling of all transuranics (TRU) in fertile free pins leads to zero net TRUgeneration
• Preserves the cycle length, neutronic control and safety features of all uranium cores
Shwageraus, Hejzlar and Kazimi, Nuclear Technology, 2005
CONFU Strategy
LWR Separation
Reprocessing
6-yearStorage
CONFU
UO2 pins UO2 pins
18-yearStorage
2nd and subsequentRecycle FFF pins
New FFF pins
6-yearStorage
1st RecycleFFF pins
Reprocessed FFF pins
UO2 pins
CONFU: TRU net generation rate
-2.50
-2.00
-1.50
-1.00
-0.50
0.00
1 2 3 4 5 6
Recycle Stage
Net
TRU
Genera
tion,
kg/assem
bly
7 Years to recycling
10 Years to recycling
20 Years to recycling
Shwageraus, Hejzlar and Kazimi, Nuclear Technology, 2005
Practical Issues for Repeated TRU Recycle• Repeated recycle can be
achieved– Based on physical
considerations (reactivitybalance and coefficients)
• Repository goals are met• TRU content gradually
increase with recycle• High minor actinide
content complicates fuelhandling and usage– Number of recycles may be
limited in practice - 2 to 3From AFCI presentation to Blue Ribbon committee by Philip Finck, 2004
CONFU: Spent fuel SFS After Multiple Cycles
0.0E+00
5.0E+09
1.0E+10
1.5E+10
2.0E+10
2.5E+10
3.0E+10
3.5E+10
4.0E+10
4.5E+10
1 2 3 4 5 UO2
(10Y)
MOX-Pu
(10Y)Recycle stage
neutr
ons
/ s
ec /
fuel ass
em
bly
Total Neutron Source, #/sec (7Y decay)
Total Neutron Source, #/sec (20Y decay)
Recycle Stage
neut
rons
/ se
c / f
uel a
ssem
bly
6/26/07 14
Advanced Fuel Cycles AssessmentCAFCA is a nuclear fuel cycle systems model :
Tracks nuclear fuel materials in the various components of a fuel cycle.
Estimates the cost of various fuel cycle strategy and technology choices.
Simulates deployment of advanced technology in the context of a growing nuclearenergy demand.
Helps study impact of choices of fuel cycle strategies on: TRU inventories,demand for recycling facilities and advanced reactors, and fuel cycle cost.
Actinide Fueled Reactor Choices
• CONFU: Recycling of TRU LWRs, using COmbined Non-Fertile and UO2fuel assemblies technology starting 2027
• ABR: Recycling TRU in fast spectrum cores of Actinide Burner Reactors(TRU in Fertile Free Fuel); starting either early in 2047 or late in 2067
• GFR: Recycling TRU and U in self-sustaining (conversion ratio of one)Gas-cooled Fast Reactors, starting either early in 2047 or late in 2067
6/26/07 15
Simulation Parameters & Recycling Industrial Capacity
50 MT/Yr/YrFFF reprocessing plant industrial capacity
500 MT/Yr/YrUO2 separation plant industrial capacity
1,000 MT/YrU/TRU RP nominal capacity
50 MT/YrFFF reprocessing plant nominal capacity
1,000 MT/YrUO2 separation plant nominal capacity
2.4 %Annual growth rate
100 YearsSimulation period
LWRs lifetime 60 YearsFast reactors lifetime 60 YearsFuel facilities lifetime 40 Years
Initial LWR fleet The U.S. fleetIndustrial capacity doubling date 2047 yearThe U.S. spent fuel “legacy” 50,000 MT
6/26/07 16
Uranium Demand for Various Options
• Little difference in U consumption will result from TRU burning in lowconversion ratio reactors.
• GFR technology requires less uranium resources due to U recycling andnear unity conversion ratio.
• In a non-breeding fuel system (CR=1), there is Increased consumption ofU after 75 years due to lack of TRU.
From R. Busquim eSilva, P. Hejzlar and M. Kazimi, ANS, Boston, 2007
8 M
6 M
4 M
2 M
0
2007 2017 2027 2037 2047 2057 2067 2077 2087 2097 2107
Years
MT
Cumulative
210,000
157,500
105,000
52,500
0
2007 2017 2027 2037 2047 2057 2067 2077 2087 2097 2107
Years
MT/Year
Annual
6/26/07 17
TRU Inventory in Interim Storage
• CONFU is the best option to deplete the current TRU inventory, and toconsume the TRU generated from LWRs fleet every year.
• Earlier introduction of ABRs or GFRs will have a small impact on TRUinventory in interim storage.
• The time for depletion of TRU in interim storage is little affected by theburner vs breeder reactor choice.
12,500
9,375
6,250
3,125
0
2007 2017 2027 2037 2047 2057 2067 2077 2087 2097 2107
Years
MT
6/26/07 18
Fuel Recycling Facilities
• Earlier recycling in LWRs will require fewer separation plants for the firsthalf of this century to minimize TRU in interim storage.
• Delayed introduction of advanced actinide burning technology will end uprequiring a faster buildup of these facilities to burn down the interim TRUinventory.
UO2 Separation Plants
24
18
12
6
0
2007 2027 2047 2067 2087 2107
Years
Plants
FFF Reprocessing Plants
15
12
9
6
3
0
2007 2027 2047 2067 2087 2107
Years
Plants
TRU Mass Balances until 2100(Scenario C: continued growth at 2.1%)
CONFU ABR
Note: CONFU incinerates more TRU than fertile-free ABR
2000 2020 2040 2060 2080 21000
0.5
1
1.5
2
2.5x 10
4
Year
Mass [MT]
TRU Balance
TRU in SF:Once-throughIncinerated TRUTRU in FFF StorageTRU in ReactorsTRU in SF storageTRU in RepositoryTRU in FFF Fab. Plant
2000 2020 2040 2060 2080 21000
0.5
1
1.5
2
2.5x 10
4
Year
Mass [MT]
TRU Balance
TRU in SF:Once-throughIncinerated TRUTRU in FFF StorageTRU in ReactorsTRU in SF storageTRU in RepositoryTRU in FFF Fab. Plant
Sourcel MIT paper by Boscher et al, Nuclear Technology, September issue, 2006
TRU inventories : CONFU vs ABR(same year of deployment)
CONFU ABR
2000 2020 2040 2060 2080 21000
0.5
1
1.5
2
2.5x 10
4
Year
Mass [MT]
TRU Balance
TRU in SF:Once-throughIncinerated TRUTRU in FFF StorageTRU in ReactorsTRU in SF storageTRU in RepositoryTRU in FFF Fab. Plant
2000 2020 2040 2060 2080 21000
0.5
1
1.5
2
2.5x 10
4
Year
Mass [MT]
TRU Balance
TRU in SF:Once-throughIncinerated TRUTRU in FFF StorageTRU in ReactorsTRU in SF storageTRU in RepositoryTRU in FFF Fab. Plant
•CONFU still incinerates more TRU•Limited by TRU availability from reprocessing plants•ABR has higher thermal efficiency than CONFU (45% vs 33%)
Nuclear Electricity Cost $/MWhr
CONFU ABR
Once ThroughAll strategies meanbuilding new units whichwill increase cost: OT : CONF: ABRPeak: 37 : 40 : 41 in 2048
2000 2010 2020 2030 2040 20500
5
10
15
20
25
30
35
40
45
Year
Electricity Cost [mills/kWhe]
Detailed Once-Through Costs
Fuel CycleO&MCapital
2000 2010 2020 2030 2040 20500
5
10
15
20
25
30
35
40
45
Year
Electricity Cost [mills/kWhe]
CONFU/LWR Strategy
Fuel CycleO&MCapital
2000 2010 2020 2030 2040 20500
5
10
15
20
25
30
35
40
45
Year
Electricity Cost [mills/kWhe]
ABR/LWR Strategy
Fuel CycleO&MCapital
Radiotoxicity of wastes from Once-Through andRecycle (transmutation) Options
From AFCI report to congress 2005
Importance of Processing Loss Fraction
Radiotoxicity of process high-level waste decreases to less thanthat of natural uranium ore from which the original fuel was derivedin less than 1,000 years if the loss fraction can be held below 0.2%
From Jim Laidler’s talk at MIT Symposium “Rethinking The Nuclear Fuel Cycle”, October 2006
Geologic Disposal of Hazardous Nuclear Waste
• In the United States, geologic disposal of spent nuclear fuel and high-level waste is planned for at the Yucca Mountain repository
• Disposal of nuclear wastes at a single location may be constrained byat least three major factors– Peak dose rate for repository releases to satisfy regulatory limits– Temperature limits for parts of the repository system to provide
greater assurance of long-term performance predictions– Volume of the waste materials
• For direct spent fuel disposal, the loading of the Yucca Mountainrepository is constrained by the temperature limits due to the highdecay heat– Estimates of peak dose rate have been calculated, and they meet
EPA guidelines. But there are no regulations (from NRC) in placeat this time for acceptability of the planned waste disposal
– Space between the waste packages is applied to limit the linearheat load in the emplacement drifts (tunnels), so waste packagevolume is not an issue
From Roald Wigeland talk at MIT Symposium “Rethinking the Nuclear Fuel Cycle”, October 2006
Current Yucca Mountain Thermal Limitations• Current temperature limits for the repository design include:
– Peak temperature below the local boiling point (96 oC) at all times midwaybetween adjacent drifts
• To ensure adequate drainage of water at all times– Peak temperature of the drift wall below 200 oC at all time
• Structural integrity of the repository– Limits are still evolving, in response to concerns related to the long-term
performance of the repository
Potential Increase in Utilization of Repository Space
• Pu, Am, Cs, Sr, & Cm arethe dominant elements– The recovered
elements must betreated
– separate storage ofCs & Sr for 200-300years
• Recycling of Pu, Am, & Cmfor transmutation andfission– Irradiation in reactors
• No direct disposal of anyspent fuel
• With the processing of spent PWR fuel to remove the elements responsible forthe decay heat that cause temperature limits to be reached, large gains inutilization of repository space are possible– The amount of gain is related to separation efficiency– Only considering thermal performance, not dose rate
10.1
0.010.001
10.1
0.010.001
225.0
94.0
10.5
1.0
175.0
91.0
10.3
1.0
54.0
44.0
10.0
1.0
5.75.5
4.4
1.0
Fraction Pu, Am, & Cm
in WasteFraction Cs & Sr
in Waste
Limited by 200 ºC Drift Wall
Temp. at EmplacementLimited by 96 ºC
Mid-Drift Temp.
>1600 yrs Limited by 200 ºC Drift
Wall Temp. at Closure
Assumptions
Burnup: 50 GWd/MT
Separation: 25 years
Emplacement: 25 years
Closure: 100 years
From Jim Laidler’s talk at MIT Symposium “Rethinking the Nuclear Fuel Cycle”, October 2006
Can we afford recycling?• The closed fuel cycle is beneficial to waste handling, but at a higher cost than
the open cycle unless U prices stay high. The French Pu recyclingtechnology, after much learning, is estimated to be economic when the U priceis above $300/kg.
• Cost of new processes is not certain, since the engineering scale tests haveyet to be performed.
• If the waste fee fund is allowed to cover reprocessing cost, our studies showeconomic parity with direct fuel disposal after 25 years of cooling period inwhich the fee is accumulating interest.
• Other cost reduction routes:– High plant capacity factor– Increased plant throughput capacity - after learning at a smaller scale - will bring
cost down– Innovative process and process equipment design
• Voloxidation head-end step for tritium removal and capture• Use of centrifugal contactors to minimize floor space and overhead clearance
requirements for chemical separations segments• Minimization of liquid wastes
Time after discharge from reprocessing (years)
Inge
stion
haz
ard
inde
x (m
3 per
MT
of h
eavy
met
al)
Reducing the Waste Burden:A Worthwhile Goal That Need Not be Hurried
Sensible Fuel Cycle Steps:
Once-Through• High burnup fuel• Central storage facility• Repository that allowsretrievability for a long time
Closed Cycle• Advanced separationresearch• Develop Non-fertile fuelfor actinide burning• System simulation toassess impact of themultiple options