NET.01.2012.505 PHYSICS OF AMERICIUM TRANSMUTATION

PHYSICS OF AMERICIUM TRANSMUTATION

JANNE WALLENIUSReactor physics, KTH, AlbaNova University CentreS-10691 Stockholm, Sweden*Corresponding author. E-mail : [email protected]

Invited March 23, 2011Received February 06, 2012Accepted for Publication February 20, 2012

1. INTRODUCTION

Separation and transmutation of americium and curium,in addition to plutonium, would permit a reduction of highlevel waste inventories by more than a factor of 100. Thetime needed to store the residual waste would consequentlyshrink dramatically and the capacity of geologicalrepositories would increase significantly. Conducting therecycle of americium and curium in light water reactorswould however lead to a very high inventory of neutronemitting 252Cf in fuel cycle facilities, requiring expensiveinvestments in shielding. Hence, these elements shouldbe directed to fast spectrum systems, which would reducethe inventory of 252Cf by more than a factor of 100 [1].

The safety problems appearing when introducingminor actinides into the fuel are however still prevalentin a fast neutron spectrum, and in certain cases they areeven more problematic than in a light water reactor.Compared to a “standard” breeder reactor with (U, Pu)O2

fuel, the presence of americium will lead to:A reduction in Doppler feedbackAn increase in coolant temperature coefficientA smaller effective delayed neutron fraction.

The combination of these three phenomena will leadto a reduced safety margin during transients, which mustbe compensated for by reducing the power density of thefuel. It would be a serious mistake to underestimate thesignificance of these safety issues. In this paper we willinvestigate the physics of americium transmutation,explaining in detail the detrimental effects on the

aforementioned safety parameters, before discussinginnovative Gen-IV solutions permitting to conduct recyclingwith a minimum cost penalty.

2. DOPPLER FEEDBACK

Doppler broadening of capture resonances in evenneutron number actinides is the most important safetymechanism in breeder reactors with oxide fuels. Thebroadening occurs in the laboratory system as a result ofincreasing amplitude of thermal oscillations of actinideatoms in the crystal lattice of the fuel. The magnitude ofthe broadening is of the order of the increase in thermalenergy, which for ∆T = 1000 Kelvin is kB∆T ≈ 0.1 eV.Hence, Doppler feedback is more effective for resonanceslocated at lower neutron energies. Consequentially, themagnitude of the Doppler coefficient is smaller in fastreactors than in light water reactors. Figure 1 shows thecontribution of neutron captures in 238U resonances asfunction of energy, when going from cold (T = 600 K) tohot (Tfuel = 1800 K) state in a sodium cooled core with(U0.8, Pu0.2)O2 fuel. The Doppler feedback deriving fromcaptures taking place above 100 keV is negligible. It isremarkable that captures below 3 keV provide 60% ofthe feedback, while constituting only 15% of the totalcapture rate!

In order for Doppler feedback to be of significance forcore stability, the total magnitude needs to be comparableto typical positive reactivity insertions. As we will see,

Using fast neutron Generation IV reactors, recycling of americium and curium may become feasible. The detrimentalimpact of americium on safety parameters has recently been quantified in terms of a power penalty for surviving a given set oftransients in sodium fast reactors. In the present paper, a review of the physical reasons for the adverse effect of americium isprovided, and different Gen-IV technologies are assessed with respect to their capability of hosting americium in the fuel.

KEYWORDS : Transmutation, Americium, Fast Reactors

199NUCLEAR ENGINEERING AND TECHNOLOGY, VOL.44 NO.2 MARCH 2012

http://dx.doi.org/10.5516/NET.01.2012.505

rising coolant temperatures and control rod expulsion maylead to reactivity increases of the order of a few hundredpcm. Loss of coolant, due to boiling or gas bubble formationmay introduce more than 1000 pcm. In metal fuel cores,axial expansion of the fuel may help in terminating suchreactivity transients gracefully, but in reactors with ceramicfuel, Doppler is essential.

Table 1 displays Doppler constants, in units of pcm,for large oxide fuel cores when uranium is substituted withamericium. The most striking effect is how the additionof americium to the fuel suppresses Doppler feedback.The more americium we have in the core, the weaker thedefence against fast reactivity insertions will become.Note however that fertile plutonium isotopes may yield astrong Doppler feedback in a fuel where neither uraniumor americium is present.

The physical reason for the unpleasant behaviour of

americium turns out to be its high cross section for captureof neutrons with energies above 30 keV [2]. Figure 2compares the cross section of 241Am and 238U. The capturecross section of americium is about 10 times larger thanthat of uranium in this region. Therefore, in an americiumbearing fuel, the probability for capture in uranium isreduced much more than what the decrease in uraniumconcentration would indicate. Substituting the standard fastbreeder reactor (FBR) (U0.8, Pu0.2)O2 fuel with (U0.5, Pu0.2,Am0.3)O2, the fraction of neutron captures in 238U dropsfrom 65% to 18%. In addition, fewer neutrons are able toreach capture resonances below 30 keV, which providethe bulk of Doppler feedback.

The distribution of captures over energy in theamericium bearing fuel is shown in Table 2. The fractionof captures taking place below 1 keV is reduced by afactor of five, comparing to the fraction for (U, Pu)O2

obtained from Figure2 above. These facts will be veryimportant when selecting an americium transmutationstrategy involving fast neutron reactors.

200 NUCLEAR ENGINEERING AND TECHNOLOGY, VOL.44 NO.2 MARCH 2012

JANNE WALLENIUS Physics of Americium Transmutation

Fig. 1.Relative Contribution of Neutrons in a Given EnergyInterval to Total Capture Rate and to the Total Increase in

Capture Rate by Doppler Broadening.Fig. 2. Capture Cross Sections of 241Am and 238U.

(U0.8, Pu0.2)O2

(U0.7, Pu0.2, Am0.1)O2

(U0.6, Pu0.2, Am0.2)O2

(U0.5, Pu0.2, Am0.3)O2

(Pu0.2, Am0.3, Zr0.5)O2

(Pu0.1, Zr0.9)O2

Fuel

570 20

230 20

60 10

25 10

5 10

420 10

KD[pcm]

Table 1. Doppler Constants for Large Oxide Cores withVarying Content of Uranium and Americium.

0-1 keV

1-10 keV

10-100 keV

0.1-1 MeV

1-10 MeV

Energy

0.01

0.11

0.50

0.34

0.05

238U

0.01

0.11

0.53

0.33

0.02

241Am

Table 2. Capture Distribution in (U0.5, Pu0.2, Am0.3)O2 Fuel.



3. COOLANT TEMPERATURE COEFFICIENT

The combination of a fast neutron spectrum with a largeconcentration of fertile nuclides in the fuel leads to apositive coolant temperature coefficient. Figure 3 illustratesthe energy dependence of the fission probability for 238U and241Am. As can be seen, americium is much more sensitiveto changes in the magnitude of the neutron flux in theenergy region between 0.2 and 0.8 MeV. Since fission ofhigher actinides produces more neutrons than fission ofuranium and plutonium, a hardening of the spectrum willincrease the average value of ν. The combination of thesetwo effects lead to a higher coolant temperature coefficientin reactors dedicated to transmutation than in classicalbreeder reactors.

The integral (core averaged) temperature coefficientis a balance between the positive contribution fromhardening of the neutron spectrum and negative contributionsfrom increase in leakage and reduction of capture in thecoolant. The leakage effect is particularly important forcores with large surface to volume ratio. The relativefraction of plutonium (or fissile to fertile ratio) in the fuelalso plays an important role. The fission probability isclose to unity for fissile nuclides in a fast spectrum. Achange in spectrum therefore will not have a significantimpact on reactivity. Since small cores usually require ahigher plutonium fraction to achieve criticality, they willexhibit a lower, and possibly even negative coolanttemperature coefficient. Other ways to increase the leakagecomponent is to reduce the height to diameter ratio (H/D),or to introduce heterogeneities in the core design [3].

Table 3 compares sodium temperature coefficientscalculated at T=690K for different oxide fuels in a mediumsized core with pin pitch to diameter ratio (P/D) equal to

1.24, a steel radial reflector and a power of 1500 MWth.The substitution of uranium with americium leads to anincrease in the sodium temperature coefficient which issignificant already for a few percent Am in the fuel. Thepure plutonium fuel, on the other hand, comes with anegative coolant temperature coefficient (αNa), even thoughthe core size is identical.

We may compare the magnitude of the core averagedtemperature coefficient with the Doppler feedback, byassuming an average operating temperature of the fuel. Foroxide fuels, 1500 Kelvin may be considered as a typicalvalue, giving αD= –0.2 pcm/K in the case of a fuel containing10% americium (see Table 1). A small increase in coolanttemperature would thus lead to a prompt increase inreactivity for such a fuel, even after Doppler feedback istaken into account.

4. EFFECTIVE DELAYED NEUTRON FRACTION

Delayed neutrons are emitted by certain decayingfission products up to one minute after the original fission.The most important precursors for delayed neutrons arebromine, rubidium and iodine. The yield of these elementsis different for each actinide. In particular the averagemass of the light fission product varies with the mass ofthe mother nuclide, since it to a lesser extent is pinned bythe presence of doubly magic nuclei. One therefore findsthat the yield of bromine isotopes falls by a factor of fivewhen going from 235U to 245Cm, as illustrated in Figure 4.

The relative fraction of delayed neutrons produced bya fission is denoted β. In general, β decreases with atomicnumber, but increases with number of neutrons. Thehighest β value is thus found for 232Th, and the lowest for241Am and 244Cm. Table 4 compares β for the two latternuclides with those of 238U and 239Pu, explaining why theaverage β value is reduced for uranium free fuels.

Delayed neutrons are born with a neutron spectrumthat differs qualitatively from that of the prompt fission

Fig. 3. Fission Probabilities of 241Am and 238U.

(U0.8, Pu0.2)O2

(U0.7, Pu0.2, Am0.1)O2

(U0.6, Pu0.2, Am0.2)O2

(U0.5, Pu0.2, Am0.3)O2

(Pu0.2, Am0.3, Zr0.5)O2

(Pu0.1, Zr0.9)O2

Fuel

+0.17

+0.34

+0.47

+0.58

+0.53

-0.35

αNa

Table 3. Sodium Temperature Coefficient for a 1500 MWth core,in Units of pcm/K.

neutrons, as illustrated in Figure 5. For instance, the mediandelayed neutron energy is about 0.5 MeV, which may becompared to the median prompt neutron energy of 1.6 MeV.An important consequence of this fact is that delayedneutrons do not induce fission with the same probabilityas do prompt neutrons. In a fast neutron spectrum, delayedneutrons are less likely to fission even neutron numbernuclides. When calculating the growth rate of the neutronpopulation one should therefore use the effective delayedneutron fraction βeff, defined as the fraction of fissioninducing neutrons that were born as delayed neutrons. Ina fast spectrum system we have βeff < β. For standard (U,Pu)O2 fuels, one typically has βeff ≈ 0.85β.

Considering transmutation, americium once again turnsout to be the villain. Its very high capture cross section atenergies below 0.5 MeV reduces the efficiency of thedelayed neutrons in americium bearing fuels even further.Table 5 displays values for β and βeff in the simplifiedcore model previously used to calculate Doppler constants.With 30% Am in the fuel, βef ≈ 0.61β, leading to values

of βeff smaller than 230 pcm even when uranium is present.The sensitivity to reactivity perturbations thus increases.As we have seen, the magnitude of such perturbationsalso increases with americium in the basket.

5. IMPACT ON TRANSIENT BEHAVIOUR

Until recently, no proper study on the transientperformance of fast reactors had been conducted as functionof americium concentration in the fuel. A few studieshave stated that a given fixed concentration of about 2%is acceptable in large sodium cooled fast reactors (SFRs)with oxide fuel [4,5], albeit without a proper transientanalysis to back up the claim.

Wallenius and Zhang therefore developed a consistentmethodology to investigate the influence of americiumon the behaviour of liquid metal cooled reactors during aset of representative design basis conditions, such as



Fig. 5. Spectrum of Delayed and Prompt Neutrons fromFission of 239Pu.

Fig. 4. Fission Product mass Distribution of 235U and 245Cm.

(U0.8, Pu0.2)O2

(U0.6, Pu0.2, Am0.2)O2

(U0.5, Pu0.2, Am0.3)O2

(Pu0.2, Am0.3, Zr0.5)O2

(Pu0.1, Zr0.9)O2

Fuel

390/460

270/390

220/350

160/260

290/310

βeff /β

Table 5. Delayed and Effective Delayed Neutron Fraction (in Unitsof pcm) for Large Oxide Cores with Varying AmericiumContent.

238U

239Pu

241Am

244Cm

Nuclide

2.53

3.02

3.37

3.42

νtot

1.89%

0.22%

0.13%

0.13%

νd/νtot

Table 4. Fission Neutron yield and Delayed Neutron Fractionfor 1.0 MeV Neutrons.

unprotected transient overpower (UTOP) and unprotectedloss of flow (ULOF) [6]. The approach consists of designinga reference core with a uranium-plutonium fuel to have acertain temperature margin to failure during the above setof transients. Then, by gradually increasing the americiumfraction, the reduction in power density required to maintainthe same margin to failure becomes a measure of the penaltyresulting from the presence of americium in the fuel.

Figure 6 shows how the maximum temperature in theMOX fuel of a medium sized sodium fast reactor increasesas function of americium content, following a UTOPresulting from a reactivity insertion of one dollar with arate of 0.05$ per second [6]. For this accident, Dopplerbroadening is the most important negative feedbackmechanism. As the Doppler constant is reduced, a higherasymptotic temperature is required to balance the positivereactivity insertion with negative temperature feedbackfrom the fuel, the temperature of which increases with 50K for every additional percent americium. In order tomaintain the same margin to melting, the nominal powerdensity of the SFR would have to be reduced by six percentper percent americium.

The equilibrium fraction of americium in the fuel in atypical fast spectrum system is 1%. Hence, in order forthe reactor to function as an americium burner, the fuelhas to contain more than 1% Am at beginning of life (BOL).With 20% plutonium in the fuel, the burning rate of Amis roughly 1.7 kg per TWh for every additional percent ofamericium. In order to achieve a burning rate of 7 kg Amper TWh (the production rate of higher actinides in lightwater reactors), it is thus required to load the fuel with 5%

americium, leading to a power penalty of 25%. Since capitalcosts remain the same, this power penalty will lead to anincrease in the cost for SFR electricity of a similar magnitude.

The relatively large cost penalty for conductingamericium transmutation in MOX fuelled SFRs is hencean incentive to investigate alternative design choices.

6. HETEROGENEOUS RECYCLING IN MOX CORES.

The softer spectrum and the higher importance ofleakage in the periphery of the core permit largerconcentrations of americium in this region. Placingseparated americium only in dedicated assemblieslocated at the periphery of a standard (U, Pu)O2 core,therefore allowing improved safety perameters andincreased burning rates for Am and Cm [7]. A coreaveraged net burning rate of 6-7 kg higher actinides perTWhe is possible to achieve in such configurations,meaning that the higher actinide inventory may bestabilised with about 50% fast reactors in the power park.

In the most straightforward option, americium isreplacing depleted uranium in the dedicated assemblies.Concentrating the americium in 40% of the assemblies ofthe core leads to a decrease in the sodium void worth offive percent and an increase of the Doppler constant of13 percent [8].

In the so called “target” concept, the uranium issubstituted with an inert matrix, such as MgO. In thiscase, the small fission probability of americium leads to alarge variation in the power density in target assemblies,



Fig. 6. Fuel Temperature During a UTOP, for Americium Content Ranging from 1 to 5% in the MOX Fuel of a Sodium FastReactor.



as plutonium is built up through the decay of 242Cm. AtBOL, the targets thus contribute negatively to the neutronbalance of the core.

One may also consider the possibility of moderatingthe fast neutrons leaking out of the standard core, in orderto decrease the radiation damage dose to the cladding tubesin the target assemblies. Calculations indicate that a burnupof 90% would be possible to achieve in an assembly whereAmO2-MgO target pins are mixed with ZrH moderator pins[9]. This result is however dependent on the assumptionthat the clad may withstand a dose of 200 dpa. The thresholdfor swelling of cladding tube steels is dependent on doserate, and a material surviving up to 200 dpa in a high fluxfast neutron spectrum does not necessarily do so in amoderated spectrum with lower dose rate.

With heterogeneous recycling of higher actinides inMOX fuelled SFRs, one thus maximises the transmutationcapability in reactor concepts proven on industrial scale.Fuel cycle facilities for target fabrication and reprocessingcould be designed for smaller mass flows, which is a clearbenefit when dealing with highly active elements. From atechnical viewpoint the large production of helium in thetarget pins (mainly being a result of the decay of 242Cm)will require tall gas plenums to be introduced [10], withconsequences for the core design in general.

7. METAL ALLOY FUEL

In the Unites States, metal alloy fuel has been developedas an alternative fuel for fast breeder/burner reactorswithin the Integral Fast Reactor (IFR) programme [11].By mixing uranium and plutonium with zirconium, aradiation resistant alloy with improved thermal propertiesis obtained. The high swelling rate of metallic fuels canbe accommodated by introducing a large gap between thefuel slug and the clad, which then is filled with liquidsodium to keep fuel temperatures below the melting pointof the alloy. Starting with a smear density of 75%, themetal fuel initially swells rapidly until fission gas releaseoccurs. The fuel then becomes sponge-like, which meansthat fuel-clad mechanical interaction is less severe. Burnupsof about 20% have been achieved in test irradiations.

An important advantage of metallic fuels in the contextof transmutation is the high thermal expansion coefficientof the actinide based alloy. In standard fast reactorconfigurations, the axial expansion of the fuel slug, whichacts on a time scale of milli-seconds, compensates for thedegraded Doppler feedback of the metallic fuel. This isparticularly important for the performance under UTOPaccidents. Since axial expansion is not significantly affectedby the introduction of americium in the fuel, the powerpenalty of metallic fuelled cores is only 3% per percentamericium in the fuel [12]. This is about half the penaltypertaining to the MOX fuelled SFR. Moreover, the harderspectrum and the higher actinide density of the metallic

fuel permit a smaller fraction of plutonium in the fuel toachieve a conversion ratio equal to unity. The equilibriumconcentration of Pu is about 12%, which may be comparedto 16% for MOX fuelled SFRs. Hence, the productionrate of americium is smaller in the metal core, leading toa better net consumption of higher actinides.

The fraction of power required to be produced in fastneutron reactors, in order to stabilise higher actinideinventories, thus may be reduced.

Manufacturing methods for americium bearing metalfuels are still not suitable for large-scale production. Anadditional drawback is the need for sodium bonded fuelpins. Consequently, aqueous methods cannot be used forreprocessing of this fuel type. Pyroprocesses, where thefuel is dissolved in a molten salt, could be applied, buthave so far not enabled to recover more than 99% of theactinide mass when operated on a pilot scale. Losses ofthe order of one percent in every reprocessing cycle areclearly incompatible with the objective of reducingradiotoxic inventories by more than a factor of 100.

8. NITRIDE FUEL

Nitride fuels have the advantage of combining a highmelting temperature with a high thermal conductivity.The margin to fuel failure therefore is larger than for oxideand metallic fuels. In simulation of unprotected transients,one therefore finds that the fuel will not constitute thelimiting factor. Rather, it will be the cladding which failsfirst. As nitride fuels yield a harder spectrum than oxidefuels, the Doppler constant will be smaller than for oxides.Thanks to the lower operational temperature of the fuel,the Doppler coefficient in nitride and oxide cores willstill be of similar magnitude, leading to similar responsesto unprotected loss of flow accidents. In comparison tometallic alloy fuels, the axial expansion feedback will besomewhat smaller. Hence, a sodium cooled reactor withnitride fuel is slightly more sensitive to ULOF accidentsthan its metal fuel counterpart.

9. LEAD COOLANT

Lead has a melting temperature of 603 K and is apotential coolant for fast neutron reactors. Besides beinginert with respect to water it has the advantages of a highboiling temperature (2024 K) and in absolute numbers,large thermal expansion. These features make coolantvoiding less likely and permits a significant amount ofheat removal by natural circulation[13]. Lead cooling istherefore of special interest in the context of minor actinidetransmutation, where void worths and decay heating ratesare high. In particular it will be easier to design the primarysystem to survive unprotected loss of flow accidents.

A major problem related to application of lead and

lead alloys is corrosion of clad and structural materials inthe reactor. Eutectic lead-bismuth, which has a meltingtemperature of 398 K, has already been used in Russiansubmarine reactors in the early sixties. However, blockageof fuel assemblies due to accumulation of corrosionproducts caused a core melt in the first operational sub-marine. Methods for controlling the oxygen content in themolten metal were subsequently developed which allowedfor successful operation of eight so called “alpha”-classsubmarines for a total of 80 reactor years. Bismuth ishowever a relatively scarce metal. Further, neutron captureduring irradiation leads to the production of the highlyradio-toxic nuclide 210Po. For commercial application, itis therefore considered that pure lead should be used.

Oxygen control technology, novel steel compositionsand surface alloying techniques have since been developedthat appear to proved adequate corrosion protection overextended exposure times in temperature ranges typicalfor the operation of lead fast reactors, that is 670 - 820 K.

A power reactor design based on lead cooling andnitride fuel was developed in Russia under the acronymBREST [14]. This particular combination of fuel andcoolant makes the design highly resistant to both UTOPand ULOF accidents, which will permit loading of ahigher fraction of minor actinides and hence maximisetransmutation rates.

The ELSY design of a lead-cooled fast reactor withmixed oxide fuel made by a European collaboration [15]has an exceptionally good performance under loss of flowaccidents. The margin to melt for the fuel is however nobetter than for the corresponding SFRs, resulting in asimilar power penalty when introducing americium intothe core [16].

10. SUMMARY AND CONCLUSIONS

Plutonium is easily recycled in fast reactors, whichmay act as either Pu breeders or burners. Multirecyclingof americium and curium in a fast neutron system reducesthe production of californium by two orders of magnitude,as compared to recycling in a PWR. Fast reactors henceare the preferred choice for higher actinide management.

Introduction of americium into the fuel however reducesDoppler feedback, increases the coolant temperaturecoefficient and reduces the effective delayed neutronfraction.

In order to maintain a sufficient margin to fuel andclad failure during unprotected transients, the linear powerdensity of the core must be reduced as the americiumconcentration increases. For homogeneous recycling inSFRs with MOX cores, the reduction of linear power densityhas been estimated to six percent per percent americium.

Development of innovative fuels and/or coolants couldreduce this power penalty down to a value of three percentper percent americium. This would enable to stabilise the

minor actinide inventory in a nuclear power park where25% of all energy is produced in Generation-IV fastneutron reactors.

ACKNOWLEDGEMENTSFinancial support from SKB (The Swedish Nuclear

Fuel and Waste Management Company) and KNS(Korean Nuclear Society) is gratefully acknowledged.

REFERENCES_______________________________[ 1 ] M. Salvatores et al., “Intercomparison of systems for TRU

recycling at equilibrium,” Proc. Int. Conf. Nuclear EnergySystems for Future Generation and Global Sustainability(GLOBAL05), Tsukuba, Japan, 2005, AESJ (2005).

[ 2 ] J. Wallenius and M. Eriksson, “Neutronic design of minoractinide burning accelerator-driven systems with ceramicfuel,” Nucl. Technol., 152, 367 (2005).

[ 3 ] H.S. Khalil and R.N. Hill, “Evaluation of liquid metal reactordesign options for reduction of sodium void worth,” Nucl.Sci. Eng., 109, 221 (1991).

[ 4 ] J. Tommasi et al., “Long-lived waste transmutation inreactors,” Nucl. Technol. , 111, 133 (1995).

[ 5 ] T. Wakabayashi, S. Ohki and T. Ikegami, “Feasibilitystudies of an optimised reactor core for MA and FPtransmutation,” Proc. Int. Conf. Evaluation of EmergingNuclear Fuel Cycle Systems (GLOBAL95), Versailles,France, 1995, ANS (1995).

[ 6 ] Y. Zhang, J. Wallenius and A. Fokau, “Transmutation ofamericium in a medium sized sodium cooled fast reactordesign,” Ann. Nucl. Energy, 37, 629 (2010).

[ 7 ] D. Verrier et al., “Heterogeneous recycling of americiumin (Am, Pu)O2 target subassemblies in a fast reactor core,”Proc. Int. Conf. Evaluation of Emerging Nuclear FuelCycle Systems (GLOBAL95), Versailles, France, 1995,ANS (1995).

[ 8 ] P. Fernandez, “Transmutation of minor actinides in asodium cooled fast reactor,” MSc thesis TRITA-FYS2009:38, KTH, Sweden (2009).

[ 9 ] C. De Saint Jean et al., “Americium and curium heterogeneoustransmutation in moderated S/A in the framework of CNEscenarios studies,” Proc. Int. Conf. Back-End of the FuelCycle: From Research to Solutions (GLOBAL01), Paris,France, 2001, ANS (2001).

[ 10 ] H. Beaumont et al., “Heterogeneous minor actiniderecycling in the CAPRA high burnup-core with target sub-assemblies,” Proc. Int. Conf. Future Nuclear Systems(GLOBAL99), Jackson Hole, Wyoming, 1999, ANS(1999).

[ 11 ] D.C. Wade and R.N. Hill, “The design rationale of the IFR,”Prog. Nucl. Energy, 31, 13 (1997).

[ 12 ] Y. Zhang and J. Wallenius, “Upper limits to americiumconcentration in large sized sodium fast reactors loadedwith metallic fuel,” submitted to Nucl. Sci. Eng., 2011.

[ 13 ] Ser Gi Hong, Ehud Greenspan, Yeong Il Kim, “Theencapsulated nuclear heat source (ENHS) reactor coredesign,” Nucl. Technol., 149, 22 (2005).

[ 14 ] E.O. Adamov et al., ”The Next Generation of Fast Reactors,”Nucl. Eng. Des., 173, 143 (1997).

[ 15 ] L. Cinotti et al., ”The potential of the LFR and the ELSYproject,” Proc. Int. Congress on Advances in Nuclear



Power Plants (ICAPP 2007), Nice, France, May 13–18,2007 (2007).

[ 16 ] M. Tesinsky, Y. Zhang and J. Wallenius, “The impact of

americium on the ULOF and UTOP transients of theEuropean Lead Cooled System ELSY,” submitted to Ann.Nucl. Energy, 2011.



Documents

NET.01.2012.505 PHYSICS OF AMERICIUM TRANSMUTATION