27aA01
IFMIF/EVEDA, essential step towards a fusion relevant neutron source
Juan Knaster1, Roland Heidinger2, Masayoshi Sugimoto3
IFMIF/EVEDA1, F4E.2, JAEA3
A fusion relevant neutron source for the characterization and qualification of materials capable to withstand thesevere irradiation conditions of the plasma facing components in a fusion power plant is a more than three decades
old worldwide pending step for the successful development of fusion energy. In fusion power plants, the fusion ofdeuterium and tritium will generate neutrons with fluxes in the order of 1018 m-2s-1 and energies of 14.1 MeV; theirsafe design, construction and licensing demands learning the irradiation impact in the structural materials during thelife-time of the fusion reactor. The first wall of the reactor vessel will be most exposed undergoing potentially >15
dpaNRT per year of operation. The understanding of the degradation of the mechanical and physical properties beyond
the defined operational thresholds driven mainly by nuclear safety reasons, but also by investment protection aspects,
will determine the operational program of the fusion power plant; in turn, the understanding of the physicalphenomena will allow the design of suitable radiation hard and low activation materials enhancing the efficiency andeconomical interest of fusion energy. Nuclei are transmuted through nuclear interactions with the incident neutrons tostable or radioactive nuclei via (n,α), (n,p), (n,γ) or other reaction channels. Through elastic and inelastic collisions
neutrons initiate primary recoil knock-on atoms (PKA) with a cascade of Frenkel vacancy-interstitial pairs withthreshold energies as low as 40 eV for Fe and Cr. The damage in the microstructure of the metal contributes to thematerial embrittlement through the internal pressure of accumulated gas molecules resulting from the nuclear
reactions at a rate of about 11 appm He/dpaNRT for fusion neutrons spectrum. The accumulation of helium leads to asignificant mechanical impact even with low concentrations. The materials do not show the same dpaNRT
cross-section under the same neutron irradiation conditions; in addition, the dpaNRT concept neglects relevant factors
such as recombination, migration, and coalescence of radiation defects; representing thus an incomplete atom-based
approximation of the neutron radiation induced damage to materials. For fusion materials irradiation experiments it istherefore essential that the gas to dpaNRT ratios and the PKA spectral distribution be similar to that of a fusion
environment. The number of variables that plays a primary role (neutron flux, spectrum, fluence, material
temperature, mechanical loading conditions, microstructure, thermo-mechanical processing history, latticekinetics…) makes a fusion relevant neutron source become an indispensable step in the different world fusion powerroadmaps. Tuned Li(d,xn) nuclear reactions have been considered for last three decades to be the most efficient way
to simulate the neutronic conditions inside the reactor vessel. Different concepts have been proposed throughout
years; the first initiative took place in the 70s in the United States of America (USA) with the “Fusion Materials
Irradiation Test” project (FMIT), which aimed at obtaining a neutron flux of 1019 m-2s-1 in a 10 cm3 volume by meansof a deuteron accelerator of 100 mA in CW and 35 MeV of beam energy, but the project was cancelled in 1984. A
few years later, JAERI proposed the “Energy Selective Neutron Irradiation Test Facility” program (ESNIT) with 50
mA CW 40 MeV deuteron beam and a 125 cm3 testing volume with a neutron flux of 3 x 1018 m-2s-1. Since 1994, the“International Fusion Materials Irradiation Facility” (IFMIF) is the baseline within the Nuclear Fusion community.
Presently in its “Engineering Validation and Engineering Design Activities” phase (EVEDA) under the frame of theBroader Approach Agreement between Japan and EURATOM signed in February 2007, has the mandate to produce
an integrated engineering design of IFMIF, and to validate continuous and stable operation of each IFMIF
sub-system. IFMIF will generate a neutron flux with a broad peak at 14 MeV by Li(d,xn) nuclear reactions thanks totwo parallel deuteron accelerators colliding in a liquid Li screen with a footprint of 200 mm x 50 mm. The energy ofthe beam (40 MeV) and the current of the parallel accelerators (2 x 125 mA) have been tuned to maximize theneutron flux (1018 m-2s-1) to get suitable irradiation conditions in a volume of 0.5 l that can accommodate around1000 small specimens [1]. The design of IFMIF plant is intimately linked with the validation activities carried out
over the first 6 years of life of the IFMIF/EVEDA phase. The accomplishment of the Engineering Design Activities
arrived on schedule in June 2013 with the delivery of an “IFMIF Intermediate Engineering Design Report”
describing the five major systems: 1) the Accelerator Facility; 2) the Li Target Facility; 3) the Test Facility, 4) thePost-Irradiation and Examination (PIE) Facility, and 5) the Conventional Facility compliant with international
nuclear facility regulations. The validation activities have focused on the main technological challenges of theaccelerator [2], target and test facilities with the construction of the following prototypes: 1) an Accelerator Prototype(LIPAc) mainly designed and constructed in Europe and to be installed in Rokkasho, fully representative of theIFMIF low energy (9 MeV) accelerator (125 mA of D+ beam in CW) to be operational in June 2017 [3]; 2) a Lithium
Test Loop (ELTL) at Oarai [4], integrating all elements of the IFMIF lithium target facility, complemented bycorrosion experiments performed at the LIFUS6 lithium loop at Brasimone; and 3) the High Flux Test Module(Japanese and European designs) and its internals to be irradiated in a fission reactor and tested in the purposedconstructed helium loop HELOKA in KIT. The technological excellence of the validation activities is best
represented by LIPAc in Rokkasho and with ELTL in Oarai. LIPAc will become the leading world Linac in average
beam power with its 1.125 MW; the challenge of running a deuteron beam in CW at 40 MeV will be overcome bysucceeding at 9 MeV since space charge issues are enhanced at lower energies. In turn, ELTL is the world largest
liquid lithium facility; it has been conceived to overcome the most relevant operational aspects required for IFMIF(flow characteristics, free surface stability, purification and diagnoses); the design of the beam target implements thelessons learnt since FMIT times with various different studies worldwide throughout the years presenting a 25 mm
thick flowing lithium screen at 15 m/s flowing speed with a concave shape that increases through centrifugal
acceleration the saturation pressure in the bulk of the liquid lithium dissipating efficiently the 2 x 5 MW deuteronbeam power and providing safe operational margins without nucleation or constructive interferences [5]. The
successful accomplishment of the validation activities will allow a safe construction anticipating cost and schedule ofa neutron source based on Li(d,xn) nuclear reactions timely with fusion roadmaps.
[1] E. Wakai et al., "Development of small specimen test techniques for the IFMIF test cell", Proceedings of IAEAFusion Energy Conference 2012, San Diego[2] J. Knaster et al., “IFMIF: Overview of the validation activities”, 2013 Nuclear Fusion 53 116001[3] Gex D. et al 2012 Engineering progress of the Linear IFMIF Prototype Accelerator (LIPAc) Proc. SOFT 2012
[4] Kondo, H., et al., “Completion of IFMIF/EVEDA lithium test loop construction”, Fus. Eng. Des. 87 (2012) 418[5] J. Knaster et al., “Assessment of the beam-target interaction of IFMIF: A state of the art”, Proc. ISFNT 2013
2 x 125 mA d+ @ 40 MeV
Lithium flowing at 15 m/s

Post Irradiation
Examination FacilityLEBTIon
sourceLithium TargetThickness 25±1 mm
Flow speed 15 m/s

MEBT
RFQ
5 MeV

Ion
sourcenductingcavities

914.5

LEBT

26

5 MeV

MEBT

914.5

26

Be Hot Cell
Lab.

TargetsystemTest
Modules

Buildings
Site General Infrastructures
Plant Services

Test
Modules
Handling
cells

Test
Facility
Ancillarysystems

Liquid MetalLab.
Macrography
Lab.
Microscopy
Lab.

Test Cell

40 MeVLF Maintenancesystems
Impurity control
system

Tritium Hot
Cell Lab.

RH systems

40 MeVuctingSupercondcavities

RFQ
100 keVHEBTSuperco100 keV

AF Ancillary systems

Main Liloop

Quenchtank

Secondaryoil loop

Primary
Heat
Exchanger

EMP

EMPTertiary oilloop

Secondary
Heat
Exchanger

EMFM

Pump

Conventional
Facility

Y TrapTi Trap

Cold trap

Heat removal system

Dump
Tank

Ts corresponding to the centrifugal pressure

Tmax in the liquid lithium

687.5 K
Tertiary
Heat
Exchanger

Pump

Li Dumptank

PIEF Ancillarysystems

Hot CellLaboratory

Access Cell

Maintenancesystems

Test Facility

Accelerator Facility

Cooling waterfrom /toConventional
Facilities

615 K

ΔT = 41 K

574 K

Dump
Tank

LF Ancillary systems

Lithium Target
FacilityFig 1: Schematic of IFMIF plant including its 5 facilities

Fig 2: Tmax envelope in the beam footprint undernominal conditions at different depths vs Ts