fuel cycle subcommittee: overview and status fusion-fission hybrid workshop gaithersburg, md...

Fuel Cycle Subcommittee:Overview and Status

Fusion-Fission Hybrid WorkshopGaithersburg, MDSeptember 30, 2009

Robert N. HillDepartment Head – Nuclear Systems AnalysisNuclear Engineering DivisionArgonne National Laboratory

Work sponsored by U.S. Department of Energy Office of Nuclear Energy, Science & Technology

2Fusion Hybrid Workshop, September 30, 2009

Overview

A wide variety of hybrid concepts are proposed

– Different fuel cycle missions are postulated

Thus, it is important to provide a systematic and well defined framework to categorize

– Goals of different fuel cycle approaches

– Strategies employed to meet the fuel cycle goals

This is a prerequisite for valid comparisons

– (e.g., a breeder compared to a minor actinide burner should have vastly different performance)


Outline of Fuel Cycle Chapter

3.1 Fission Fuel Cycles

3.2 Fusion Fuel Cycles

3.3 Proposed Hybrid Fuel Cycles

– Limited input on 3.3 before workshop!

Given that fusion-fission hybrids primarily conceived to deal with fission fuel cycle issues, the focus of this presentation will be on 3.1


3.1 Fission Fuel Cycles

Nuclear energy is a significant contributor to U.S. and international electricity production– 16% world, 20% U.S., 78% France

Given the concern over carbon emissions, there may be significant growth worldwide

In the U.S., a once-through fuel cycle has been employed to-date– Large quantities of spent fuel stored at reactor sites– Final waste disposal is not secured

With nuclear expansion, this is not a sustainable approach; thus, advanced fuel cycles being explored – two key goals– Waste Management– Resource Utilization


AFCI is considering a variety of fuel cycle options: Closed fuel cycle with actinide management

Spent nuclear fuel will be separated into re- useable and waste materials

Residual waste will go to a geological repository

Uranium recycled for resource extension

Fuel fabricated from recycled actinides used in recycle reactor

Fuel cycle closure with repeated use in recycle reactor

Energy Production Reactor

Recycle Reactor

Recycle FuelFabrication

Recycle Used Uranium

Extend Uranium Resources


Reduction in the volume of HLW that must be disposed in a deep geologic disposal facility as compared to the direct disposal of spent nuclear fuel

– Factor of 2-5 reduction in volume as compared to spent nuclear fuel

– Intermediate-level (GTCC) and low-level volumes could be large and disposal pathways would have to be developed

Reduction in the amount of long-lived radioactive material (e.g., minor actinides) that must be isolated in a geologic disposal facility (reduction of source term)

– Potential for re-design of engineered barriers

– Advanced waste forms could result in improved performance and reduced uncertainty over the very long time periods

Reduction in decay heat allowing for increased thermal management flexibility, potentially increasing emplacement density

– Increased loading density - better utilization of valuable repository space

Advanced Nuclear Fuel Cycle – Potential Benefits


Radiotoxicity reflects the hazard of the source materials

– transuranics dominate after about a 100 years. The fission products contribution to the radiotoxicity is small after 100 years

Radiotoxicity alone does not provide any indication of how a geologic repository may perform

– Engineered and natural barriers serve to isolate the wastes or control the release of radionuclides

0.001

0.01

0.1

1

10

100

1000

10000

10 100 1000 10000 100000 1000000 10000000

Time after Discharge (year)

No

rma

lize

d R

ad

ioto

xic

ity

UOX SNF - Total

UOX SNF - FP w/o Tc & I

UOX SNF - Tc & I

UOX SNF - Np

UOX SNF - Actinide w/o Np

226Ra242Pu 237Np99Tc 129I239Pu 226Ra242Pu 237Np99Tc 129I239Pu

Waste Hazard and Risk Measures


Transmutation for Improved Waste Management

Long-term heat, radiotoxicity, and peak dose are all dominated by the Pu-241 to Am-241 to Np-237 decay chain

Thus, destruction of the transuranics (neptunium, plutonium, americium, and curium) is targeted to eliminate all problematic isotopes

Some form of reprocessing is necessary to extract transuranic elements for consumption elsewhere

The transuranic (TRU) inventory is reduced by fission

– Commonly referred to as ‘actinide burning’

– Transmutation by neutron irradiation

– Additional fission products are produced This requires the development of transmutation fuel forms

– Robust fast reactor fuel form – high reliability

– Partial destruction each recycle – high burnup goal In the interim, the TRU inventory is contained in the transmutation fuel cycle


Reactor Types for Transmutation System:Minimization of Waste

Conventional LWRs using LEU fuels produce TRU

– At current 50 GWd/MT burnup, 1.3% TRU content at discharge

– This corresponds to ~250 kg/year for each GWe power For any fission energy system, 1 gram of actinides destroyed produces

roughly 1 MWt-day of energy

– This implies 1.3%/5% = 25% of the original LWR energy production is created in the destruction of the TRU content (significant capacity)

– Thus, efficient use of this energy is a key to both system economics and resource utilization

However for uranium-based fuel, TRUs are also being produced

– This behavior is quantified by the conversion ratio (CR)

ratendestructioTRU

rateproductionTRURatioConversion

– Dictated primarily by the recycle fuel composition (U content)

– Fast system can be designed with CR ranging from >1 (breeders) to <<1 (burners); for thermal reactors CR < 0.7 is achievable with MOX


Reactor Types for Transmutation System:Minimization of Waste (cont.)

To assure no TRUs remain in waste, the LWR production rate must be balanced by destruction in the actinide burners (AB)

1000

*/)1(

/50

*013. ABMWdgCR

MTGWd

LWR

– For pure burner (CR=0), 1 burner for every four LWRs

– For CR=0.25, 1 burner for every three LWRs

– For CR=1, all recycle reactors If only the minor actinides are to be consumed in the burner reactor, the

initial production rate by LWRs is only 10% of the TRU content

– However, the plutonium must be consumed elsewhere

– Additional minor actinides are produced as the plutonium is consumed, particularly if a thermal spectrum is utilized

LWR

AB

CR

1

26.0


Reactor Types for Transmutation System:Maximization of Energy

The opposite trend is observed when the goal is to maximize the energy production for a fixed amount of resource materials

)1(

/*

CR

gMWtdfissileInitialproducedEnergy

– For a given quantity of recovered TRU, the energy can be extended by recycling the material in a high CR system

Thus, net resource utilization is vastly improved at high CR

– For once-through cycle, 7MT of uranium ore required to produce 1 MT of fuel to 5% burnup -- .05/7 = 0.7% of the energy content

– With TRU recovery and recycle, burnup extended to .05 + .013/(1-CR)• Roughly 1% of energy content at low conversion ratio• Limit of 100% utilization at CR=1 where a make-up feed (e.g.,

depleted uranium or thorium) that contains fertile material is required


3.2 Fusion Fuel Cycles

Tritium needs to be produced to sustain the fusion cycle– 14 MeV neutrons can be used to breed– Typically employ Li-6 capture in fusion blanket

For hybrid, fusion blanket must also be utilized– Wide variety of technology options– Homogeneous or heterogeneous with fission blanket– Neutron balance is enhanced through subcritical

multiplication in the fission blanket


3.x.4 Proliferation Issues

The proliferation risks associated with spent fuel reprocessing and recycle continue to be hotly debated– At least partial separation is required

• Fission products are waste, actinides recycled• This reduces the radiation barrier

– Safeguards employed for material accounting– Physical protection provides additional barriers– Technology misuse is another concern– Enrichment technology may be an easier pathway

Any neutron source can produce fissile material– Fertile targets installed to capture neutrons– This became an issue for ADS concepts


3.3 Hybrid Fuel Cycles

Waste management role– Lack of criticality constraint allows operation on very

low reactivity fuels and potentially very high burnup– However, practical operation (e.g., large power swings)

and material (e.g., radiation damage) challenges exist Some proposals:

– Burn the entire TRU inventory– Target a smaller fleet of minor actinide burners– Sustain “support” of LWR power production or nuclear

close-out scenarios (like ADS) Resource extension role proposals:

– Breed fuel for use in fission fuel cycle– Perform an extended in-situ breed and burn– Similar challenges to the burner mode noted above


Backup Slides


Fast and Thermal Reactor Energy Spectra

In LWR, most fissions occur in the 0.1 eV thermal “peak” In SFR, moderation is avoided – no thermal neutrons

0.00

0.05

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0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

Energy (eV)

No

rma

lize

d F

lux

/Le

tha

rgy

LWR (EPRI NP-3787)

SFR (ufg MC2 -2 metal)


Impact of Energy Spectrum on Fuel Cycle (Transmutation) Performance

Fissile isotopes are likely to fission in both thermal/fast spectrum

– Fission fraction is higher in fast spectrum Significant (up to 50%) fission of fertile isotopes in fast spectrum

Net result is more excess neutrons and less higher actinide generation in FR

0.000.100.20

0.300.400.500.600.70

0.800.901.00

Fis

sion/A

bso

rption

PWR

SFR


Equilibrium Composition in Fast and Thermal Spectra

Equilibrium higher actinide content much lower in fast spectrum system Generation of Pu-241 (key waste decay chain) is suppressed However, if starting from once-through LWR composition (e.g., burner reactor)

the higher actinide content will be higher than the U-238 equilibrium

Isotope Once-

Through Fast

U-238 Thermal

U-238 Np237 0.048 0.008 0.002 Pu238 0.024 0.014 0.046 Pu239 0.476 0.666 0.388 Pu240 0.225 0.243 0.197 Pu241 0.106 0.021 0.111 Pu242 0.066 0.018 0.085 Am241 0.034 0.021 0.019

Am242m 0.000 0.001 0.001 Am243 0.015 0.005 0.033 Cm242 0.000 0.000 0.002 Cm244 0.005 0.002 0.055 Cm245 0.000 0.000 0.018 Cm246 0 0.000 0.031 Cm247 0 0.000 0.004 Cm248 0 0.000 0.006


Fuel Cycle Implications

The physics distinctions facilitate different fuel cycle strategies Thermal reactors are typically configured for once-through (open) fuel cycle

– They can operate on low enriched uranium (LEU)

– They require an external fissile feed (neutron balance)

– Higher actinides must be managed to allow recycle• Separation of higher elements – still a disposal issue• Extended cooling time for curium decay

Fast reactors are typically intended for closed fuel cycle with uranium conversion and resource extension

– Higher actinide generation is suppressed

– Neutron balance is favorable for recycled TRU• No external fissile material is required• Can enhance U-238 conversion for traditional breeding• Can limit U-238 conversion for burning


Advanced Nuclear Fuel Cycle – Potential Benefits

Cs/Sr (and decay products), Cm, and Pu dominate “early” decay heat Am dominates “later” decay heat Removal of decay heat producers would allow for increased utilization of

repository space


Aqueous Processing Potential Waste Streams and Waste Forms

Chopping Cladding: ZircaloyHardware: SS

Volox

Dissolu-tion

Gases: I, HTO, Kr, Xe, CO2

UREX

UDS: Pd, Ru, Rh, Mo, Tc, Zr, O

Ion Exchange

Tc

U

TRUEX

TALSPEAK

FPEX Cs/Sr: Cs, Sr, Ba, Rb

TMFP: Fe, S, Ru, Pd, Rh, Mo, Zr

LNFP: Ce, Ln, Pr, Nd, Y

TRU: Pu, Am, Cm, Np

Metal Waste Form

Specialized Waste Forms

Metal Waste Form

Metal Waste Form

Metal Waste Form

Decay Storage Waste Form (glass or ceramic)

Glass Waste FormLosses


Advanced Nuclear Fuel Cycle – Waste Form Development

Glass Bonded Sodalite

Metallic Waste Form from Electro-Chemical Processing

Cs/Sr Glass

Lanthanide Borosilicate Glass


Waste management is an important factor in developing and implementing an advanced closed nuclear fuel cycle

– The waste management system is broader than disposal (processing, storage, transportation, disposal)

– Deep geologic disposal will still be required

– Disposal of low level and intermediate level (GTCC) wastes will be required

• Volumes potentially larger than once-through An advanced closed nuclear fuel cycle would allow for a re-optimization of

the back-end of the current once-through fuel cycle, taking advantage of:

– Minor actinide separation/transmutation

– Heat producing fission product (Cs/Sr) management (i.e., decay storage)

Decisions must consider this entire system

– Regulatory, economic, risk/safety, environmental, other considerations

Advanced Nuclear Fuel Cycle - Waste Management


AFCI Integrated Waste Management Strategy establishes the framework for analyzing and optimizing the waste management system– Emphasizes recycle and reuse, but based on economic recovery

evaluation factoring in value of material and cost avoidance of disposal– Considers need for industry to have a reliable system to routinely

transport nuclear materials and dispose wastes– Considers disposal options based on the risk of the waste streams and

waste forms • Rather than requiring all waste be disposed as HLW in a geologic

repository• Requires change to existing waste classification system embodied in

current regulatory framework– A key aspect is the inclusion of managed storage facilities where

isotopic concentrations, and heat, are allowed to decay prior to storage

Evaluation of alternatives and options are being performed under the context of the IWMS

Waste Management System for Advanced Fuel Cycle


Integrated Waste Management Strategy – Logic Diagram

fuel cycle subcommittee: overview and status fusion-fission hybrid workshop gaithersburg, md...

Documents

fuel cycle goals

fusion fuel cycles

fuel fabrication

closed fuel cycle

fuel cycle subcommittee

nuclear fuel factor

advanced fuel cycles

reactor fuel cycle closure