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Fusion Engineering and Design 83 (2008) 948–953

Contents lists available at ScienceDirect

Fusion Engineering and Design

journa l homepage: www.e lsev ier .com/ locate / fusengdes

usion–fission hybrids for nuclear waste transmutation: A synergistic stepetween Gen-IV fission and fusion reactors

.A. Mehlhorn ∗, B.B. Cipiti, C.L. Olson, G.E. Rochauandia National Laboratories, P.O. Box 5800, MS 1181, Albuquerque, NM 87185-1181, USA

r t i c l e i n f o

rticle history:eceived 4 September 2007eceived in revised form 2 April 2008ccepted 13 May 2008vailable online 26 June 2008

eywords:uclear waste transmutation

a b s t r a c t

Energy demand and GDP per capita are strongly correlated, while public concern over the role of energyin climate change is growing. Nuclear power plants produce 16% of world electricity demands withoutgreenhouse gases. Generation-IV advanced nuclear energy systems are being designed to be safe andeconomical. Minimizing the handling and storage of nuclear waste is important. NIF and ITER are bring-ing sustainable fusion energy closer, but a significant gap in fusion technology development remains.Fusion–fission hybrids could be a synergistic step to a pure fusion economy and act as a technologybridge. We discuss how a pulsed power-driven Z-pinch hybrid system producing only 20 MW of fusion

usion energyusion reactor materials

yield can drive a sub-critical transuranic blanket that transmutes 1280 kg of actinide wastes per year andproduces 3000 MW. These results are applicable to other inertial and magnetic fusion energy systems. Ahybrid system could be introduced somewhat sooner because of the modest fusion yield requirementsand can provide both a safe alternative to fast reactors for nuclear waste transmutation and a maturationpath for fusion technology. The development and demonstration of advanced materials that withstandhigh-temperature, high-irradiation environments is a fundamental technology issue that is common to

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. Introduction

Nuclear power, both fission and fusion, will likely grow in impor-ance in meeting world energy demand. Presently, the developmentf Generation-IV fission reactors and fusion research are largelyeparate activities. However, as we now enter a transition fromusion physics experiments into large devices such as ITER andIF, and consider the next step to a Demo fusion device, the com-onalities in technology between fission and fusion become more

pparent. Therefore, it is timely to ask what research and devel-pment synergies can be exploited to accelerate the contributionsf both fission and fusion to the global energy economy. In thisaper we first briefly overview the development of the nuclearnd fusion programs, then offer a new concept for an inertialusion–fission hybrid that might serve as a bridging technologyhat could benefit both fission and fusion concepts. Finally, we offerome ideas on how a synergistic advanced materials development

rogram could help advance all fission and fusion programs, andow a hybrid reactor could both benefit from, and contribute tohis effort.

∗ Corresponding author. Tel.: +1 505 845 7266; fax: +1 505 845 7685.E-mail address: tamehlh@sandia.gov (T.A. Mehlhorn).

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920-3796/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.fusengdes.2008.05.003

Generation-IV reactors.© 2008 Elsevier B.V. All rights reserved.

. Energy, Gen-IV reactors and fusion

A 1997 study of sixty countries [1] showed a strong correlationetween the United Nations’ Human Development Index (HDI) andnnual per-capita electricity consumption. Significantly, no countryith an annual electricity consumption below 4000 kilowatt hours

kWh) per capita had an HDI of 0.9 or greater. Although there arearious reasons for differences in energy intensity across regionalnd national economies, studies generally confirm the correlationf Gross Domestic Product (GDP) with total primary energy use perapita (see, e.g. the website of the Energy Information Adminis-ration of the U.S. Department of Energy at www.eia.doe.gov). Athe same time, the correlation between atmospheric CO2 levelsnd climate change is increasingly well accepted and is bringingn increased public impetus to reduce the emission of greenhouseases in all energy sectors (electricity, heating, transportation, etc.).he DOE reports that nuclear energy supplies over 20% of U.S.nd 16% of world demand for electricity [2]. In 2002, the 103perating U.S. nuclear power plants generated 790 billion kWh oflectricity at a cost of 1.68 cents/kWh valued at $50 billion. Since

970, use of nuclear power, rather than fossil fuels, has reducedotal U.S. CO2 emissions by over 3 billion tons. However, pub-ic concerns over safety, nuclear waste, and proliferation haveimited the contributions of nuclear power to the global energyconomy.

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The goal of the DOE Generation-IV (Gen-IV) Program is toevelop and demonstrate advanced nuclear energy systems thateet future needs for safe, sustainable, environmentally respon-

ible, economical, proliferation-resistant, and physically securenergy systems. Within the Gen-IV Program, the Advanced Fuelycle Initiative (AFCI) has been created to achieve a sustainablerowth of nuclear energy through the recycling of nuclear mate-ials in the fuel cycle, with the additional goal of minimizing theandling and storage of nuclear waste. Building upon the provenechnology of the first three generations of nuclear power, Gen-IVeactors must play an important role in the global energy economy.uclear fusion has an even greater potential to meet all of thesenergy requirements, and to do so without the possibility of a crit-cality accident or the production of more than Class C commercialadioactive waste (i.e. qualified to be buried in a low-level wasteisposal facility per 10 CFR 61).

The near completion of the NIF in the U.S. and the inter-ational agreement to begin building ITER in France hold theromise of significant burning plasmas that will demonstrateome critical technologies and increase public interest in fusionnergy. However, a tremendous gap in the development of theechnology required for fusion power plants will still remain.usion–fission hybrids could provide a technology bridge, as wells be a synergistic step towards a future pure fusion economy,hile reducing the nuclear waste inventory of the fission power

ndustry.The fusion hybrid concept has a substantial history. For exam-

le, in 1978, Bethe [3] proposed the use of a uranium or thoriumlanket to multiply the energy of a magnetic fusion device, whilet the same time producing fissile fuel (Pu239 and U233) from theertile isotopes (U238 and Th232). Manheimer [4] attributes the ideao Andrei Sakharov as early as 1950. Many of the early papers focusn magnetic-confinement devices as the fusion neutron source,ith energy multiplication and the breeding of nuclear fuels as

he main goals. These references reflect the international domi-ance of magnetic systems (primarily Tokamaks and Stellerators),articularly in Europe and Asia, coupled with the concern overhe limited supply of fissile fuels for the nuclear power indus-ry.

More recently, the handling and storage of radioactive wasterom light water reactors has become an issue of increasing con-ern and it is often cited as an impediment to the expansion of theuclear power industry. This has led to the development of manyifferent proposals for reducing the magnitude of the waste streamrom reactor fuels. The Gen-IV plan calls for the use of fast reactors2]. A modular helium reactor [5] using the “Deep Burn” conceptas been proposed by General Atomics. Accelerator driven systemsADS) have been favored in Europe and also considered by the U.S.nd Japan (cf. [6–8]). Fusion hybrids based on magnetic confine-ent fusion systems have also been evaluated by the Fusion Energy

ciences Advisory Committee (FESAC) [9] and have been studiedn China [10]. Manheimer [4] has written several articles on thepplication of ITER technology to fusion hybrids, and has recentlyncluded the idea of combining the Inertial Fusion Energy (IFE) con-ept being studied in the High Average Power Laser (HAPL) programith the concept of a fusion hybrid. In this paper we describe a

cenario for transmuting actinides from light water reactors intossion products using fusion neutrons from a Z-pinch-driven ICFource.

. A pulsed-power-driven Z-pinch transmuter

Sandia National Laboratories has completed an initial three-ear study into the use of a Z-pinch fusion driver we call theIn-Zinerator” for transmuting waste [11]. The technical details of

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and Design 83 (2008) 948–953 949

he In-Zinerator study can be found in Ref. [11], and only the out-ine of this work can be discussed in this overview paper. The keyonclusion of this study is that relatively modest fusion require-ents on the order of 20 MW can be used to drive a sub-critical

ransuranic blanket that transmutes 1280 kg/year of actinides androduces a blanket power of 3000 MW through the fissioning ofhe actinides. In this study MCNP 5.0 was used for a majorityf the neutronic calculations including determining keff, multi-lication, heating rates, dpa calculations, tritium breeding ratio,ulse modeling, and neutron spectrum analysis. The MCise simula-ion model was used to calculate transmutation rates and fissionroduct production rates. The ORIGEN code was used to calcu-

ate activities and heat loads of the products along with helpingo verify the transmutation results. The study included an initialvaluation of the sensitivity of the results to the use of JENDL,NDF/B-VI and JEF libraries; especially for the minor actinides.he 63-group CINDER90 nuclear data library was used for bothransmutation reactions and fission reactions with fission productields.

This hybrid Z-pinch-driven transmuter is a new addition to thereviously published Z-IFE roadmap [12] and is based on repetitiveulsed power and the recyclable transmission line (RTL) concept.ig. 1 shows a conceptual layout of an In-Zinerator Power Plant. Aagnetically insulated transmission line from a linear transformer

river system delivers the electrical pulse for the fusion target. Theusion output destroys the bottom portion of the transmission line,hich is designed so that the fragments can be captured and reused.

he RTL geometry uses two nested thin-walled cones, which min-mizes the inductance. The RTL and target debris will be removedrom the chamber after each shot.

The chamber is 5 m in height and cylindrically symmetric, with2 m standoff from the target to the wall. The first wall, which sep-rates the Z-pinch driver from the blanket and coolant, sees the4 MeV neutron flux from the fusion target. The chamber materialust be able to withstand high temperatures, and the most likely

andidate is Hastelloy-N based on the published data on Hastel-oy alloys used for the Molten Salt Breeder Reactor (MSBR) at Oakidge National Laboratory [13]. The chamber, in this study, con-ains ∼1300 Pa of argon for attenuation of X-rays and has liquid

etal sprays or aerosols to absorb energy, prevent excessive firstall heating, and minimize the required chamber radius. A lowelting temperature metal like tin will likely be used for both the

TL and sprays for easy collection after the shot. However, issuesf corrosion with molten metals such as tin and lead still need beddressed.

The 20 MW to drive the blanket is achieved using a fusion targetaving a yield of around 200 MJ at a repetition rate of once every teneconds. The fusion neutrons drive a sub-critical blanket containinghe actinides in a fluid form within a hexagonal array of pipes usingLiF eutectic, (LiF)2–AnF3. A lead coolant circulates through the

hamber to remove the energy from the fissioning of the actinides.he thick lead coolant region outside of the actinide array is simi-ar to pool-type reactors designs. An intermediate heat exchangeremoves energy from the lead to power a Rankine or Brayton cycle.he coolant operating temperature in this preliminary study was50 K.

The actinide mixture is slowly circulated to allow for removal ofssion products and tritium. The rate of circulation is such thathe entire actinide mixture volume is processed once per day.etailed neutronic calculations of the blanket show that tritium

s bred from the lithium in sufficient quantity to sustain the fusioneaction. The fission products will be continuously removed andither converted to a waste form, or converted to a form suit-ble for shipment back to a reprocessing plant. The criticality (keff)f the blanket design in this report is 0.97 which results in an

950 T.A. Mehlhorn et al. / Fusion Engineering and Design 83 (2008) 948–953

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nergy multiplication of 150 through fissioning of the actinidesixture.The actinides being in a fluid form eliminates the need for expen-

ive fuel fabrication and allows for continuous refueling, removal ofssion products, and tritium breeding to sustain the fusion driver.he continuous refueling also eliminates the need for fueling shut-owns. Detailed neutronic and isotope tracking calculations showhat the reactor has the capability of burning 1280 kg of actinideser year while at the same time producing a significant amount ofower. There are two key advantages of burning actinides in a fluid,ub-critical blanket. The first is that there is no need to have fertileuel (like 238U) in the blanket. This means that the blanket containsnly transuranics (e.g. Np, Am, and Cm), so it burns waste withhe maximum efficiency. The second advantage is that the blan-et can be fueled with virtually any transuranic mix depending onhe fuel cycle of the future. Therefore it has much more flexibilityhan a fast reactor and the sub-critical configuration allows uniquectinide mixtures to be burned safely without the need to worrybout reactor control issues or the possibility of a prompt-criticalxcursion.

The detailed design parameters of the In-Zinerator Power Plantre found in Table 3-1 of Ref. [11]. As compared to the baseline Z-IFEesign of a pure fusion reactor, the engineering advantages of mov-

ng towards the In-Zinerator concept are that (1) only one chambers required, (2) the fusion yield requirement is an order of magni-ude lower, and (3) the associated tritium fueling requirements areignificantly lower. The presence of actinides in the blanket resultsn considerable changes to the chamber design. A first wall sep-rates the fusion chamber from the actinide and coolant region,hich may make the RTL insertion and recovery system simpler.e note that the blanket region is dominated by neutrons with an

nergy spectrum that is similar to a fast reactor. The In-Zinerator

esign parameters may provide cost savings and reduce the engi-eering challenges of generating power from the Z-pinch target.he destruction of transuranic waste along with energy productionives the concept another saleable service, so the economics maye better as compared to a pure fusion energy plant.

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. Fusion–fission hybrids compared to alternative wasteransmuters

Looking at the nuclear fuel cycle, in our studies of the In-inerator concept we have found that the most logical approacho waste reduction is to burn Pu in existing light water reactors,hile building one fusion transmutation reactor to burn only theinor actinides Np/Am/Cm. After a few decades, when the limit

f Pu recycle in light water reactors is reached, additional trans-uters can be built to take care of the spent Pu fuel. This strategy

ltimately requires fewer fast transmutation systems to be builthile at the same time achieving the same waste reduction goals.fusion-driven sub-critical transmutation reactor has the flexi-

ility to utilize this fuel cycle, which is an advantage over fasteactors since it is not possible to control a fast reactor that usesnly Np/Am/Cm fuel. This application provides fusion with a use-ul application and provides valuable experience in the design ofusion reactor systems, so that one day we can achieve the ultimaten nuclear waste reduction: pure fusion energy.

In our design study, we find that the In-Zinerator can effectivelyonvert actinides into fission products. We have tracked the effec-iveness of transmuting actinides for 50 years in terms of the totaleat production from 64 metric tons of actinides as compared tohe heat production from the sum of the all the fission productsroduced as a result of fissioning the 64 metric tons of actinides.e find that after 10 years of cooling the heat load is decreased byfactor of 10, and after 50 years the heat load is reduced by a factorf 500. The Yucca Mountain nuclear waste repository capacity isurrently limited by heat load, so the reduction of heat productiony transmuting actinides into fission products could lead to muchore effective use of repository space. The ultimate goal of trans-utation technologies (along with reprocessing) is to obviate the

eed for additional costly repositories for a couple hundred years.An advantage of the In-Zinerator concept is that it can oper-

te with the lowest possible support ratio. The support ratio is theatio of transmutation reactors to light water reactors required tourn up the transuranic actinides as fast as the current light water

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eactor fleet produces them. The In-Zinerator does not require anyertile material, like U238, which would otherwise breed additionalctinides. This allows the In-Zinerator concept to reach a muchower support ratio than fast reactors (FRs). Specifically, the In-inerator support ratio in the fuel cycle is 1:5, meaning that onen-Zinerator will be required for every five light water reactorsn order to burn up the transuranic actinides as fast as the lightater reactor fleet produces them. The current fleet of light water

eactors would then require about twenty In-Zinerators, each pro-ucing 1000 MWe to stabilize transuranic levels. If, on the otherand, the plutonium were first recycled to light water reactors,he In-Zinerator support ratio would increase to1:10 because of theecrease in volume of the leftover Pu isotopes remaining with thep/Am/Cm.

Although it is too early to estimate the cost of the In-Zinerator,ur study included an economic analysis to allow a cost comparisonor actinide transmutation using a fleet of fast reactors compared tofleet of In-Zinerators. Due to the better support ratio offered by the

n-Zinerator, we estimate that this concept can cost up to 25% morehan a FR and still be competitive. Whether FRs or In-Zineratorsre used, reprocessing and transmutation are likely to add at least.0 million/kWh to the cost of nuclear power across the entire fleet.ompared to other fusion designs, the In-Zinerator may offer theost compact fusion source due to the unique power delivery sys-

em. The solid transmission lines come in from the top of the reactor,hich means that the sides and bottom are left clear for installa-

ion of a blanket. Unique shock mitigating techniques using aerosolsill be possible since the chamber atmosphere does not need to be

lean for the driver to function. An extensive life-cycle comparisonf all nuclear reactor, accelerator-driven, and fusion (both ICF andFE) systems for actinide burning was beyond the scope of this

reliminary study.In general, a fusion hybrid operating as a nuclear waste trans-

uter should provide valuable operating experience for a fusionystem, which could provide a path to a pure fusion power plantn the future. The energy multiplication in the actinide blanketecreases the demands on fusion output, and opens opportunitiesor earlier introduction of hybrid systems. In addition to provid-ng electrical power, the transmuter has the additional economicalue of decreasing the radioactive waste stream from the LWReet, thereby extending the lifetime of the Yucca Mountain repos-

tory. The combination of lower required fusion powers, electricalower production via blanket multiplication, and economic valueerived from extending nuclear waste repository capacity shouldake the economics of hybrid systems more favorable than early

ure fusion power plants.Another advantage for hybrid reactors could be related to the

bility to produce abundant tritium to fuel the hybrid, as well asther fusion power plants. A recent analysis of the tritium fuel cyclef controlled thermonuclear reactors [14] asserts that the need forn, 2n) reactions to maintain a favorable neutron balance makeshe availability of beryllium the limiting factor in the expansionf a pure fusion power economy. As expected, in our neutronicesign studies we found that the tritium breeding ratio (TBR) was

n competition with the actinide destruction rate. For an isolatedn-Zinerator system our target TBR was conservatively set at 1.2.owever, the neutron multiplication in a hybrid blanket could allowhigher TBR if required to help provide fuel for additional pure

usion reactors.

. Technical challenges and synergy in system technology

As described in the previous two sections, the In-Zinerator hashe potential to extract latent energy from the actinides in reactoraste and transmute them into isotopes that have shorter decay

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and Design 83 (2008) 948–953 951

alf-lives. However, there are many technical risks and challengeshat will require intensive R&D before such a device could be for-

ally proposed. In particular, the pulsed power ICF and technologyrograms at Sandia [15] must first demonstrate significant fusionutput from a Z-pinch target as well as a rep-rated pulsed powerapability. Current planning activities place a 5–10 years horizonor these efforts. In parallel we propose to begin studying the pow-rplant technologies and reactor materials that will be requiredor this hybrid system. There are many challenges in these areas,ncluding the processing of the liquid actinide waste stream, theower extraction from the blanket, and many materials compati-ility issues. With regard to materials irradiation, we note that therst wall sees primarily the same 14 MeV neutron flux that exists

n a fusion reactor, while the actinide blanket sees a spectrum thats more characteristic of a fast reactor. Thus, the hybrid could ben important technology bridge between Gen-IV reactors and pureusion reactors. Development of a hybrid will require knowledge ofoth fission and fusion reactor technologies and materials.

As described by Petti at the 2006 APS Division of Plasmahysics conference (http://meetings.aps.org/Meeting/DPP06/vent/52084) there are many technology issues that are commono advanced fission and fusion reactors, including power con-ersion technologies, materials corrosion, welding and joiningechnologies, materials response under neutron irradiation, highemperature materials and coolants compatibility, first-principles

aterials modeling, materials design rules, and tritium/hydrogenehavior in materials. For example, the Gen-IV prismatic very highemperature reactor [16], the In-Zinerator, and the Aries-AT [17]usion reactor designs all use a Brayton cycle for power conversion.n addition, the effect of He impurities on high temperaturetructural materials, the joining of both ferritic steels and highemperature Ni superalloys, and the response of advanced ferriticteels and SiC composites to neutron damage all detailed areas ofommon interest. Furthermore, because of the impact of high tem-erature on thermal efficiency of both fission and fusion systems,here is a strong push to develop materials that can accommodateigh temperature operation (700–1000 ◦C), which will requirextensions of ASME design rules for nuclear environments.

. Predictive modeling of advanced materials

A central scientific issue that is common to Gen-IV, hybrid,nd fusion reactors is to understand, model, develop, andemonstrate advanced materials that withstand high-temperature,igh-irradiation environments. We suggest that this could pro-ide the basis for a synergistic research program that bridges theransition from a fission to a fusion energy economy. The com-

onality of advanced material properties for fusion and spallationeutron sources [18], and for these systems and Gen-IV fission reac-ors has already been recognized [19]. The common mission ofusion hybrids and spallation neutron sources to destroy nuclearaste makes the commonality of their materials issues clear. The

tructural materials in all of these systems are subject to degrada-ion of their physical and mechanical properties through long-termeutron irradiation and associated chemical interactions, isotopichanges, and secondary particle production and interactions. Com-onent lifetimes can be limited by radiation-induced swelling,hase instability, hardening, flow localization, and embrittlement.

For Gen-IV fission reactors, the importance of material issues haseen recognized through the creation of the AFCI. According to the

en-IV Ten-Year Roadmap, the AFCI will develop fuel systems foreneration IV reactors and create enabling fuel cycle technologies

i.e., fuel, cladding, separations, fuel fabrication, waste forms, andisposal technology) to significantly reduce the disposal of long-

ived, highly radiotoxic transuranic isotopes while reclaiming the

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pent fuel’s valuable energy. AFCI technologies will support bothurrent and future nuclear energy systems, including GenerationV systems, and emphasize proliferation resistant, safe, and eco-omic operations. The DOE Office of Science held a workshop in006 on “Basic Research Needs for Advanced Nuclear Energy Sys-ems” where one of the key technology challenges was found to beignificant improvements in the predictive modeling of the designnd performance of advanced energy systems, including fuel cycleodeling.While a typical reactor spectrum has few neutrons above

MeV, in fusion systems the DT fusion neutron spectrum peakst 14.1 MeV. Therefore, special attention must be paid to the highnergy portion of the neutron spectrum where the two damageechanisms that are of greatest concern are the creation of dis-

laced atoms (quantified as displacements per atom – dpa) and theeneration of gas, particularly helium. The displacement damage isrimarily produced by high energy primary knock-on atoms (PKA)reated via elastic scattering of the DT fusion neutrons. Hydro-en and helium are produced by transmutation reactions, whichave high production rates for high energy neutrons. The increasingvailability of high speed computers with large amounts of mem-ry has led to an increase in the use of modeling and simulationo study these fundamental damage mechanisms in fusion mate-ials. For example, the creation of damage by PKA energy effectsre being studied using displacement cascade simulations basedn molecular dynamics (MD) methods (cf. Stoller [20]). Recently,eletskaia [21] has used Density Functional Theory (DFT) to studylectronic structures related to the relaxation, formation, and bind-ng energies of small helium clusters in iron.

In our hybrid In-Zinerator design study we identified materialerformance issues at elevated temperatures and high neutronuences to be one of the most significant technical challenges.urthermore, IFE systems operate in a pulsed mode, which cre-tes cyclic stresses. For example, in the In-Zinerator, the energyeposition from the fusion pulse and subsequent fission energyultiplication occurs almost instantaneously. Removing the heat,

nd engineering the chamber for large temperature changes remains challenges to be tackled in future work. The constant 14 MeVeutron bombardment on the In-Zinerator first wall damages thetructure of the chamber over time; this in turn limits the life ofhese components. The life-limiting criterion for Hastelloy-N is aey factor in determining the service lifetime of the first wall andube walls. There are no firm guidelines for Hastelloy as for theerritic steel components of fusion systems where the life-limitingriterion has traditionally estimated to be dpas ranging between00 and 200. In our analysis, a dpa limit of 200 for the Hastelloytructure was assumed, which means that, in the present design,ortions of the chamber wall would need to be replaced at 15-year

ntervals (where the expected facility lifetime is 40–45 years). Thisuggests that we need to iterate our design to decrease radial fluxeaking and overall neutron irradiation of the first wall by either

imiting the power level or examining high temperature operationhat extends the lifetime of components. Improvements in mate-ials for the first wall and actinide pipes could also play a role inaking this fusion hybrid more practical. In addition, there arenumber of safety and control concerns with using a fluid fuel

even in a sub-critical configuration) that will need to be more fullyxplored. Another material issue that must be explored is relatedo the thermal properties and materials compatibility of the liquiduel.

This research has prompted us to begin exploring the creationf an expanded a nuclear materials science program at Sandiaational Laboratories to study the synergistic issues of Gen-IV

eactors, fusion hybrids, and pure fusion reactors that is based onur emerging computational capabilities. Such a program could be

tarty

and Design 83 (2008) 948–953

atterned after the approach exemplified in Sandia’s Qualificationlternatives to the Sandia Pulsed Reactor (QASPR) project, whichses a combination of DFT simulations, validation methodology,nd scaled experimentation to create models for neutron damagen electronic materials. In this Gen-IV/fusion materials program

e propose that actinides, coolants, and structural materials betudied for performance, corrosion, and response to irradiation.

e believe that it is timely to investigate applying our model-ng and simulation capabilities to an advanced nuclear materialsrogram based on our significant progress in related material sci-nce areas. With advances in computing power, DFT calculationsave expanded from the calculation of static properties to dynami-al and temperature-dependent simulations. For example, we haveecently validated our DFT simulations of the electrical conductivityf aluminum in warm dense matter [22] and the EOS and conduc-ivity of high energy density water [23]. Furthermore, as the powerf high performance computers, such as Sandia’s Red Storm [24],ontinues to increase, it appears feasible that quantum calculationsan be performed on numbers of atoms that are relevant to theesoscale.

. Role of materials testing

While it is apparent that high performance modeling and sim-lation will have an increasing impact on the understanding andevelopment of nuclear materials, it is equally apparent that appli-ation of modern verification and validation (V&V) methodologieso the experimental validation of these simulations will be essentialo the formulation of an effective advanced materials R&D program.s noted by Mansur [19], critically important data on highly irradi-ted materials have been obtained from high flux fission reactorsuch as the HFIR, ATR, HFR, JMTR, JOYO, BOR 60, and the LANSCEnd SINQ spallation sources. There will be a continued need for datarom these facilities, as well as new experimental platforms. Forxample, the fusion materials community has an ongoing researchrogram in advanced materials for fusion reactors [25,26]. As partf this research, the magnetic fusion energy community has devel-ped a “broader approach” to facilitate the step between ITER andDEMO reactor. This program includes an IFMIF-EVDA (Interna-

ional Fusion Materials Irradiation Facility Engineering Validationnd Engineering Design Activity) [27] to develop a platform onhich to perform the experimental testing of fusion materials for

he Demo. We propose to leverage Sandia participation in the ITERrst wall project [28] to develop a more complete view of how toollaborate with the U.S. and international communities in theseheoretical and validation efforts. Such a materials science effort isonsistent with current DOE Office of Fusion Energy Science prior-ties, and could act as the stimulus for a future fusion technologyrogram.

. Conclusions

Gen-IV reactors will play an important role in providing electric-ty without producing greenhouse gases. Fusion hybrids can play aynergistic role in transitioning from a fission to a fusion energyconomy. Hybrids can transmute reactor waste, extracting latentnergy, and extending the capacity of repositories. Energy multipli-ation within the hybrid blanket reduces the fusion energy requiredor a practical system, and can lead to an earlier introduction of the

echnology into the energy market. We have described the results ofthree-year study of a pulsed power-driven Z-pinch hybrid system

equiring only 20 MW of fusion yield that can drive a sub-criticalransuranic blanket that transmutes 1280 kg of actinide wastes perear and produces 3000 MW through the fissioning of the actinides.

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his transmuter utilizes the Z-pinch ICF recyclable transmissionine concept and includes a hybrid blanket, which contains the onlyctinides in a liquid eutectic. A liquid lead coolant loop operatingt 950 K removes the heat from the blanket.

Over a 50-year period, we calculate that this transmuter couldssion 64 metric tons of actinides, which decreases the waste heaty a factor of 10 after a cooling period of 10 years, and by a factor00 after 50 years. This could significantly extend the life of theucca Mountain Waste Repository. As compared to fast reactors,ybrids do not require fertile materials in the blanket, so they canurn waste without generating additional actinides. If the pluto-ium from the waste stream is recycled to light water reactors, one

n-Zinerator could burn-up the waste of ten light water reactors.ur economic studies indicate that reprocessing and transmuta-

ion are likely to add at least 2.0 million/kWh to the cost of nuclearower in the US.

There are many technical risks and challenges that will requirentensive R&D before such an In-Zinerator could be formally pro-osed including demonstration of a significant fusion output,epetitive pulsed power operation, processing the liquid actinidetream, and the removal of heat from the blanket. Gen-IV, hybrid,nd pure fusion reactors have many common technology issues thatan be synergistically explored, especially in a common advancedigh-temperature, high-irradiation materials research program.uch a program should take advantage of advances in computa-ional materials capabilities and validation methodologies to defineacility requirements to accomplish scaled testing. This materialsrogram could form the basis of a science-based research pro-ram that stimulates fusion technology research within the U.S.ommunity.

cknowledgements

Sandia is a multiprogram laboratory operated by Sandia Cor-oration, a Lockheed Martin Company, for the United Statesepartment of Energy’s National Nuclear Security Administra-

ion under Contract DE-AC04-94AL85000. The authors wouldike to acknowledge the support of Laboratory Directed Researchnd Development Project 81753 and Z-IFE Project 102362. Theorresponding author also acknowledges Wil Gauster, Richardygren, and John Kelly for technical discussions and editorial

eview.

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