Fuel cycles and envisioned roles of fast neutron reactors and hybrids

M.Salvatores (CEA, Cadarache- France)

WORKSHOP ONFUSION FOR NEUTRONS AND

SUB-CRITICAL NUCLEAR FISSIONFUNFI

Villa Monastero, Varenna, ItalySeptember 12 - 15, 2011

Many of the central issues associated with nuclear power are tied primarily to the choice of fuel cycle. Resource limitations, non-proliferation, and waste management are primarily fuel cycle issues.

The fuel cycle provides the mass flow infrastructure that connects the energy resources of uranium and thorium ore through the nuclear power plants to the eventual waste management of the nuclear energy enterprise.

Natural resources include fuels (uranium and thorium), materials of construction, and renewable resources (such as water for cooling purposes). Wastes may include mill tailings, depleted uranium, spent nuclear fuel (SNF) and high level (radioactive) waste (HLW), other radioactive wastes, releases to the environment (air and water), and nonnuclear wastes.

Multiple technical facilities are deployed in the fuel cycle. In a simplified fuel cycle schematic, there are 7 major fuel cycle facilities.

Nuclear Fuel Cycles

111

2

3 4

5

6

7

The preferred choice or choices of fuel cycles and reactors depends upon the

requirements for sustainability, safety, and economics. Four generic fuel cycles span the space of feasible conversion of ore resources to energy.

• Once through. The fuel is fabricated from uranium (and/or thorium), irradiated, and stored to allow for reduction of heat, then directly disposed of as a waste. Light Water Reactors (LWRs) in the United States currently use this fuel cycle.

• Partial recycle. Some fraction of the SNF is processed, and some fraction of theactinide material is recovered from recycle, and new fuel is fabricated.The fuel is returned to the reactor one-two times

• Full fissile recycle. All SNF is processed for recovery and recycle of plutonium (and/or 233U). The SNF is repeatedly processed and recycled. Minor actinides and fission products are sent to the waste stream from the processing operation.

An example of this is the traditional Liquid Metal Fast Breeder Reactor (LMFBR) fuel cycle.

• Full-actinide recycle. All SNF is processed, and all actinides are multiply recycled.

An example of such a fuel cycle is a system of MOX-LWRs and dedicated burner reactors. The MOX-LWRs produce power and the dedicated burner reactors (e.g. ADS, Hybrid fission-fusion, critical fast reactors) are used to destroy higher actinides that would otherwise be sent to the repository.

Another example is the full TRU multiple recycle in FRs, both to extend use of resources and to reduce and stabilize wastes.

• Other fuel cycle options are envisaged according to e.g. waste management strategies

RepositoryRepository

ReprocessingReprocessing

UOX-PWRUOX-PWR

PuMulti-recycling

MOX-LWR (or

FR)

MOX-LWR (or

FR)

Fuel FabricationFuel Fabrication ReprocessingReprocessing

PuMA (+Pu)

Multi-recycling

FuelFabrication

FuelFabrication

DedicatedTransmuterDedicated

TransmuterReprocessingReprocessing

MA(+Pu)

MA

FP and TRU losses a

t

reprocessing

FP and TRU losses atreprocessing

FP and TRU losses at

reprocessing

Irradiatedfuel

Irradiated fuel

MA

(+Pu

)

Irradiatedfuel

Full-actinide recycle(So-called “Double Strata Fuel Cycle”)

RepositoryRepository

ReprocessingReprocessing

UOX-LWRUOX-LWR

Multi-recycling

Fast Reactor: homogeneous or heterogeneous recycle

Fast Reactor: homogeneous or heterogeneous recycle

Fuel/Target FabricationFuel/Target Fabrication

ReprocessingReprocessing

Pu+MAPu+MA

FP a

nd T

RU lo

sses

at

repr

oces

sing

FP and TRU losses at

reprocessing

Irradiated fuel Irradiatedfuel

Full-actinide recycle(FR only)

Fuel cycle simulation allows the calculation of the nuclei evolution under irradiation and decay outside the reactor (the Bateman equations)

Once the nuclei evolution has been performed, it is possible to evaluate all the derived quantities: nuclei mass inventories, decay heat, neutron sources, radiotoxicity, doses etc

The Uranium nuclei transmutation chain under neutron irradiation and the associated Bateman equations can be represented as follows:

where nj is the nuclide j density, σaj is the absorption cross section of isotope j, σjk is the cross section corresponding to the production of isotope j from isotope k, λj is the decay constant for isotope j, λjk is the decay constant for the decay of isotope k to isotope j and, finally, Φ is the neutron flux.

Nuclei evolution under irradiation

Bateman equations

242Cm

243Cm

244Cm

245Cm

246Cm

241Am 242Am 243Am 244Am

240Pu 241Pu 242Pu 243Pu239Pu238Pu237Pu236Pu

239Np238Np237Np236Np

239U

238U

237U

236U

235U

240Np

163d16h

17.9y26m

4.96h14.7y

7.5m2.35d2.12d87.8y

22.5h2.85y

22.5h 6.75d 23.5m

n,2n n,

EC

kjkjkk

jajjj nn

dt

dn

Application

Composition of Spent Nuclear Fuel (Standard PWR 33GW/t, 10 yr. cooling)

1 tonne of SNF contains:

955.4 kg U8,5 kg Pu

Minor Actinides (MAs)0,5 kg 237Np0,6 kg Am0,02 kg Cm

Long-Lived fission Products (LLFPs)0,2 kg 129I0,8 kg 99Tc0,7 kg 93Zr0,3 kg 135Cs

Short-Lived fission products (SLFPs)1 kg 137Cs0,7 kg 90Sr

Stable Isotopes10,1 kg Lanthanides21,8 kg other stable

Most of the hazard stems from Pu, MA and some LLFP when released into the environment, and their disposal requires isolation in stable deep geological formations.

A measure of the hazard is provided by the radiotoxicity arising from their radioactive nature.

Most of the derived quantities are of the type:

where ni is the nuclei i density and hi are coefficients, specific for each application

Example: the Radiotoxicity R of nuclei i is given by:

Ri(Sievert)= Fi(Sv/Bq)xAi(Bq)

where F is a Dose Factor (ingestion or inhalation) and A is activity in Bq

Total activity A: number of decays an object undergoes per second. Decay constant λ: the inverse of the mean lifetime.

One has:

Finally: Ri(Sievert)= Fi(Sv/Bq)xAi(Bq) =Fi xniλi

Evolution of the radiotoxic inventory, expressed in sievert per tonne of initial heavy metal (uranium) (Sv/ihmt) of UOX spent fuel unloaded at 60 GW d/t, versus time (years).

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06

Years after Spent Fuel Discharge

Rad

ioto

xic

ity

(Sv/

MT

Nat

ura

l Ura

niu

m)

Fission Products

Uranium & Decay Products

Plutonium & Decay Products

Minor Actinides & Decay Products

Total

Radiotoxicity of Natural Uranium and Decay Products

"Uranium Ore"

Derived quantities: the radiotoxicity

Derived quantities: the decay heat, one of the most demanding parameters of the fuel cycle

Fuel Cycle Modelling

Decay Heat Components

Decay heat: relative role of FPs and Actinides for standard LWR fuel

Short cooling timesLong cooling times

FP

Actinides

0.01

0.1

1

10

100

10 100 1000 10000

Time after Discharge, Years

De

ca

y H

ea

t, W

att

s/G

Wd

of

En

erg

y P

rod

uc

ed

PU238

PU239

PU240

PU241

AM241

AM243

CM242

CM243

CM244

Actinides

SR

Y

CS

BA

EU

Fission Products

Total

TotalFPTRU

Am-241

Pu-238

Decay heat: FPs and Actinides components for standard LWR fuel

The full TRU recycle, as indicated previously, allows a significant reduction of the radiotoxicity and of the decay heat of residual wastes to be sent to the repository.

This reduction can have a favorable impact in the assessment of future fuel cycles

This result is true within both scenarios for full TRU recycle indicated above.

Derived quantities and the impact of different fuel cycle scenarios

Example: Impact of the actinides management strategy on the radiotoxicity of ultimate waste

Plutonium recycling

Spent FuelDirect disposal

Uranium Ore (mine)

Time (years)

Rel

ativ

e ra

diot

oxic

ity

P&T of MA

Pu +MA +FP

MA +FP

FP

Recycle of all actinides from spent LWR fuel in fast reactors provides a significant reduction in the time required for radiotoxicity to decrease to that of the original natural uranium ore used for the LWR fuel:

From 250,000 years down to about 400 years, if 0.1% TRU loss to wastes during reprocessing.

0.1

1

10

100

1000

10000

10 100 1000 10000 100000 1000000

années

w/T

wh

éMono MOX

Recyclage Pu en REP

Recyclage Pu+Am en REP Cm au CSDV

Recyclage Pu en RNR

Recyclage Pu+Np+Am+Cm en RNR

cycle ouvert

Recyclage Pu+Am en REP Cm entreposé

One Pu recycling in PWR

Multiple Pu recycling in PWR

Pu and Am recycling in PWR – Cm disposed

Pu recycling in FNR

Pu and MA recycling in FNR

Once through cycle

Pu, Am recycling in PWR – Cm stored

MA partitioning andtransmutation

Pu recyclingno MA partitioning

years

0.1

1

10

100

1000

10000

10 100 1000 10000 100000 1000000

années

w/T

wh

éMono MOX

Recyclage Pu en REP

Recyclage Pu+Am en REP Cm au CSDV

Recyclage Pu en RNR

Recyclage Pu+Np+Am+Cm en RNR

cycle ouvert

Recyclage Pu+Am en REP Cm entreposé

One Pu recycling in PWR

Multiple Pu recycling in PWR

Pu and Am recycling in PWR – Cm disposed

Pu recycling in FNR

Pu and MA recycling in FNR

Once through cycle

Pu, Am recycling in PWR – Cm stored

MA partitioning andtransmutation

Pu recyclingno MA partitioning

0.1

1

10

100

1000

10000

10 100 1000 10000 100000 1000000

années

w/T

wh

éMono MOX

Recyclage Pu en REP

Recyclage Pu+Am en REP Cm au CSDV

Recyclage Pu en RNR

Recyclage Pu+Np+Am+Cm en RNR

cycle ouvert

Recyclage Pu+Am en REP Cm entreposé

One Pu recycling in PWR

Multiple Pu recycling in PWR

Pu and Am recycling in PWR – Cm disposed

Pu recycling in FNR

Pu and MA recycling in FNR

Once through cycle

Pu, Am recycling in PWR – Cm stored

0.1

1

10

100

1000

10000

10 100 1000 10000 100000 1000000

années

w/T

wh

éMono MOX

Recyclage Pu en REP

Recyclage Pu+Am en REP Cm au CSDV

Recyclage Pu en RNR

Recyclage Pu+Np+Am+Cm en RNR

cycle ouvert

Recyclage Pu+Am en REP Cm entreposé

One Pu recycling in PWR

Multiple Pu recycling in PWR

Pu and Am recycling in PWR – Cm disposed

Pu recycling in FNR

Pu and MA recycling in FNR

Once through cycle

Pu, Am recycling in PWR – Cm stored

MA partitioning andtransmutation

Pu recyclingno MA partitioning

years

FP MA +FP

Pu +MA +FP

Example: Impact of the actinides management strategy on the decay heat of ultimate waste

Spent fuel direct disposal

In the selected scenario study two groups of nations are In the selected scenario study two groups of nations are considered: considered:

• the first one with a stagnant or phasing-out nuclear policy the first one with a stagnant or phasing-out nuclear policy (Group A)(Group A)

• the second with an ongoing nuclear power development the second with an ongoing nuclear power development (Group B)(Group B)

An Example of Scenario StudyAn Example of Scenario Study

The final goals of the scenario areThe final goals of the scenario are::

- to reduce Group A TRU inventory down to zero till the end of the century;to reduce Group A TRU inventory down to zero till the end of the century;

- to stabilize Group B MA inventory and to save reprocessed Pu to stabilize Group B MA inventory and to save reprocessed Pu in order to allow a later introduction of fast reactors for nuclear in order to allow a later introduction of fast reactors for nuclear power generation.power generation.In the fuel cycle transmuters first use MA coming from their In the fuel cycle transmuters first use MA coming from their closed cycle closed cycle (in order to completely transmute heavy (in order to completely transmute heavy nuclides)nuclides), then those of Group A, and finally those of Group B., then those of Group A, and finally those of Group B.

Hypotheses and assumptions

-Three types of transmuters have been compared:

- The SABR fusion-fission hybrid concept is a sodium cooled sub-critical fast reactor driven by a D-T fusion neutron source;

-ADS-EFIT is Pb cooled and the external neutron source is provided by Pb-proton (800 MeV) spallation reaction on a Pb windowless target;

-LCFR is a Na cooled critical fast reactor with a conversion ratio ~0.5

-The scenario is of the “Double Strata” type, as described previuosly

Scenario Flow SheetScenario Flow Sheet

RegionalRegional (i.e. shared) (i.e. shared) facilities (i.e. facilities (i.e. transmuters, fuel transmuters, fuel fabrication, fabrication, reprocessing facilities reprocessing facilities and stocks) operation and stocks) operation start-up is assumed to start-up is assumed to be in 2045.be in 2045.

Group A:Group A: Belgium, Belgium, Czech Republic, Czech Republic, Germany, Spain, Germany, Spain, Sweden and Sweden and SwitzerlandSwitzerland Group B: Group B: FranceFrance

Required Transmuters Energy ProductionRequired Transmuters Energy Production

- - The corresponding The corresponding number of units are 13 number of units are 13 (X384 MWth) ADS-(X384 MWth) ADS-EFITs, 9 (X1000 EFITs, 9 (X1000 MWth) LCFRs, and 2 MWth) LCFRs, and 2 (X3000 MWth) SABRs(X3000 MWth) SABRs

- - Comparison is Comparison is presented per presented per energy producedenergy produced

- - As expected, more As expected, more critical low conversion critical low conversion ratio transmuters are ratio transmuters are needed since they needed since they achieve ~70% of the achieve ~70% of the max theoretical max theoretical burning rate (i.e. when burning rate (i.e. when no U in the fuel)no U in the fuel)

MA Stocks ComparisonMA Stocks Comparison

- MA stock of Group A goes to zero before the end of the century (in all cases)

- MA stock of Group B is stabilized before the end of present century (in all cases)

Fuel Fuel Cycle Cycle ImpactsImpacts

Radiotoxicity Radiotoxicity and heat load in and heat load in a repository are a repository are reduced by two reduced by two orders of orders of magnitude with magnitude with respect to the respect to the direct disposal direct disposal scenarioscenario

• Uranium and thorium mills. Uranium and thorium ores are mined and then milled to extract uranium and thorium. This process generates the highest volume waste stream in the fuel cycle: mill tailings. Also, purification and conversion facilities.

• Uranium enrichment. The uranium is isotopically separated into a stream enriched in the fissile isotope 235U and a stream depleted in the fissile isotope 235U. The enriched stream is used for fuel in most reactors. The depleted uranium may be stored for (1) further recovery of 235U in the future or (2) use in fast neutron reactors. Alternatively, it may become a waste.

• Fuel fabrication. Reactor fuel is fabricated from natural uranium, enriched uranium, plutonium reclaimed from processing discharged fuel, or uranium-233, depleted uranium, and thorium.

• Reactor. The reactor produces energy and SNF.

• Spent Nuclear Fuel Storage. The SNF is stored to allow its radioactivity and heat release rate to decrease. After storage, the SNF may be (1) considered a waste for disposal or (2) processed to recover fissile materials from the SNF for recycle back to the reactor as new fuel.

• Processing. If the SNF is recycled, the recovered fissile materials can beused to produce new fuel.

• Waste disposal. SNF direct disposal or vitrification of residues from reprocessing