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MULTI-MW TARGET DEVELOPMENT FOR EURISOL & EUROTRANS. Y. Kadi & A. Herrera-Martinez (AB/ATB) European Organization for Nuclear Research, CERN CH-1211 Geneva 23, SWITZERLAND [email protected] Multi-MW Target Challenges. High-Power issues Thermal management Target melting

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MULTI-MW TARGET DEVELOPMENT FOREURISOL & EUROTRANS

Y. Kadi & A. Herrera-Martinez

(AB/ATB)

European Organization for Nuclear Research, CERN

CH-1211 Geneva 23, SWITZERLAND

[email protected]


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Multi-MW Target Challenges

  • High-Power issues

    • Thermal management

      • Target melting

      • Target vaporization

    • Radiation

      • Radiation protection

      • Radioactivity inventory

      • Remote handling

    • Thermal shock

      • Beam-induced pressure waves

    • Material properties


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Thermal Management: Liquid Target with window

The SNS Mercury Target

Harold G. Kirk et al. (BNL)


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Thermal Management: Liquid Target with window

  • MEGAPIE Project at PSI

  • 0.59 GeV proton beam

  • 1 MW beam power

  • Goals:

  • Demonstrate feasablility

  • One year service life

  • Irradiation in 2005

F. Groeschel et al. (PSI)

Proton Beam


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Thermal Management: Liquid Target with window

F. Groeschel et al. (PSI)


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Thermal Management: Liquid Target with free surface

DG16.5 Hg Experiments nominal volume flow 10 l/s

BEAM

Close to desired configuration

  • intermediate lowering of level

  • some pitting

  • axial asymmetry

High-speed flow (2.5 m/s)permits effective heat removal


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Thermal Management: Target Pitting Issue

Before

ESS team has been pursuing the Bubble injection solution. SNS team has focused on Kolsterizing (nitriding) of the surface solution.

SNS team feels that the Kolsterized surface mitigates the pitting to a level to make it marginally acceptable. Further R&D is being pursued.

After 100 pulses at 2.5 MW equivalent intensity

Harold G. Kirk et al. (BNL)



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Thermal Management: radiation cooled rotating toroidal target

  • Distribute the energy deposition over a larger volume

    • Similar a rotating anode of a X-ray tube

rotating toroid

toroid magnetically levitated and driven by linear motors

R.Bennett, B.King et al.

solenoid magnet

toroid at 2300 K radiates heat to water-cooled surroundings

proton beam


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Thermal Management: JET

J.Lettry et al. (CERN)

TT2A


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Target Module with jumpers

Outer Reflector Plug

Target Inflatable seal

Core Vessel water cooled shielding

Core Vessel Multi-channel neutron guide flange

Moderators

Radiation Management

The SNS Target Station



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Radiation Management

The JPARC Kaon Target

~18m

Concrete

shield block

~10m

Service space:

2m(W)1m(H)

Water

pump

Iron shield

2m

T1 container

Concrete

shield

Beam


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EURISOL – Multi-MW Target

Objectives

The objective is to perform the technical preparative work and demonstration of principle for a high power target station for production of beams of fission fragments using the mercury proton to neutron converter-target and cooling technology similar to those under development by the spallation neutron sources, accelerator driven systems and the neutrino factories.

This high power target that will make use of innovative concepts of advanced design can only be done in a common effort of several European Laboratories within the three communities and their proposed design studies.

In this study emphasis is put on the most EURISOL specific part a compact window or windowless liquid-metal converter-target itself while the high power design of a number of other more conventional aspects are taken from the studies in the other EURISOL tasks or even in other networks like ADVICES, IP-EUROTRANS.


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EURISOL Target Stations

  • 3x100 kW direct irradiation

  • Fissile target surrounding a spallation n-source

    • >100 kW Solid converters (PSI-SINQ 740 kW on Pb, 570 MeV 1.3 mA / RAL-ISIS 160 kW on Ta, 800 MeV 0.2 mA / LANL-LANSCE 800 kW on SS cladded W, 800 MeV 1.0 mA )

    • 4 MW Liquid Hg (windowless or jet)


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EURISOL Hg-converter and 238UC2 target

60 kV

60 kV

> 2000º

Grounded

< 200º


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EURISOL – Multi-MW Target

Participants

Contributor

P4 – CERN

P18 – PSI Switzerland

P19 – IPUL Latvia

C5 – ORNL USA






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Preliminary Studies

  • Projectile Particle: Proton

  • Beam Shape: Gaussian,  ~1.7 mm

  • Energy Range: 1–2–3 GeV

  • Target Material: Hg / PbBi

  • Target Length: 40–60–80–100 cm

  • Target Radius: 10–20–30–40 cm

  • Spatial and energy particle distribution


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1 GeV Primary Proton Flux

1 GeV Proton range ~46 cm

  • The beam opens up to ~20 degrees, with some primary back-scattering

  • Primaries contained in ~50 cm length and ~30 cm radius


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Energy Deposition for 1 GeV protons

  • Maximum energy deposition in the first ~14 cm in the beam axis beyond the interaction point, ~30 kW/cm3/MW of beam dT/dt ~14 K/s (Hg boiling point at 357 ºC)

  • Energy deposition drops one order of magnitude at the proton range (~46 cm)

  • Large radial gradients (dE/dr ~200) in the interaction region


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Neutron Flux Distribution for 1 GeV Protons

Radial

Front Cap

End Cap

  • Neutron flux centered radially around ~10 cm from the impact point

  • Isotropic flux after ~15 cm from the center, decreasing with r2

  • Escaping neutron flux peaking at ~300 keV (evaporation neutrons), with a 100 MeV component in the forward direction (direct knock-out neutrons)


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Neutron Energy Spectrum vs Fission Cross-Section in Uranium

  • Very low fission cross-section in 238U below 2 MeV (~10-4 barns). Optimum neutron energy: 35 MeV

  • Alternatively, use of natural uranium: fission cross-section in 235U (0.7% wt.) for 300 keV neutrons: ~2 barns

  • Further gain if neutron flux is moderated


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Alternative Target Configurations

Standard Configuration

Alternative Configurations

Reflector?

UCx Target

Reflector / UCx Target

Protons

Protons

Hg Target

Hg Target

Deuterons

UCx Target

Reflector / UCx Target

UCx Target

Reflector?

Low-Z Filter (?)


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Alternative Target Configurations

Alternative Configurations

Reflector / UCx Target

Protons

Hg Target

Deuterons

Reflector / UCx Target

UCx Target

Low-Z Filter (?)

  • Increasing HE neutron flux through the End-Cap with decreasing Hg target length

  • Increasing charged-particle and photon escapes with decreasing Hg target length

  • Possible use of a low-Z filter to “tune” the average neutron energy to 35 MeV (maximise fission probability in 238U)


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Neutron Balance Density for 1 GeV Protons

Neutral balance boundary

Neutron absorbing region

Neutron producing region

  • Neutron absorbing region ~6 cm behind the interaction region, following the primary particle distribution

  • Neutron producing region extending to the end of the target

  • Small contributions from regions beyond the proton range

  • Neutron producing region not extending beyond r =10–13 cm


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2 GeV Primary Proton Flux

2 GeV Proton range ~110 cm

  • Forward peaked primary distribution at ~10 degrees

  • No back-scattering and rare radial escapes

  • Few end-cap escapes:

  • 210-3 escapes/primary with an average energy of 1 GeV for 80 cm

  • 2 10-5 escapes/primary with an average energy of 0.7 GeV for 100 cm


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Energy Deposition for 2 GeV protons

  • Largest energy deposition in the first ~18 cm beyond the interaction point, ~16 kW/cm3/MW of beam dT/dt ~8 K/s (40% lower compared to the use of 1 GeV primary protons)

  • Identically, smaller radial gradient in the interaction region (dE/dr ~100)


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Neutron Flux Distribution for 2 GeV Protons

Neutron Yield (2 GeV proton) : 57 – 77 n/p

  • Neutron flux centered radially around ~15 cm from the impact point, presenting a forward-peaked component

  • Escaping neutron flux peaking at ~300 keV, with a 100 MeV component in the forward and radial directions and few 1 GeV neutrons escaping through the end-cap

  • Harder neutron energy spectrum and higher flux and in the target compared to the 1 GeV case


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Neutron Balance Density for 2 GeV Protons

  • Increase in the relevance of the axial region in the neutron production

  • Neutron producing region still not extending beyond r =10 – 13 cm

  • The neutron capturing region gains relevance (–610-4 bal/cm3/prim) compared to 1 GeV (–610-5 bal/cm3/prim)

  • Significant reduction in neutron captures (one order of magnitude) by reducing the radius to 20 cm

Neutral balance boundary

Neutron absorbing region

Neutron producing region


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3 GeV Primary Proton Flux

3 GeV Proton range ~175 cm

  • The beam opens up to ~8 degrees, no back-scattering and few radial escapes (even for 20 cm radius)

  • Some primaries escapes through the end-cap (~ 5 10-5 escapes/primary)

  • Average energy of the escaping protons ~750 MeV


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Energy Deposition for 3 GeV protons

  • Largest energy deposition in the first ~22 cm beyond the interaction point, ~12 kW/cm3/MW of beam dT/dt ~6 K/s (60% lower compared to the use of 1 GeV primary protons)

  • Smaller radial gradient in the interaction region (dE/dr ~50) compared to the 1 GeV case


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Neutron Flux Distribution for 3 GeV Protons

Neutron Yield (3 GeV proton) : 82 – 113 n/p

  • Neutron flux centered radially around ~20 cm from the impact point, with a larger forward-peaked component

  • Escaping neutron flux peaking at ~300 keV, with a 100 MeV component in the forward and radial directions and some 1.5 GeV neutrons escaping through the end-cap

  • Slightly higher neutron flux in the target compared to the 2 GeV case


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PbBi Alternative – 1 GeV Primary Particles

1 GeV proton range in Hg: ~46 cm

Hg

1 GeV proton range in PbBi: ~60 cm

PbBi


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PbBi Alternative – Energy Deposition

Maximum energy deposition ~30 kW/cm3/MW of beam

Hg

Maximum energy deposition ~21 kW/cm3/MW of beam

PbBi



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PbBi Alternative – Neutron Balance

Hg

Neutron absorbing region

Neutral balance boundary

Neutron producing region

PbBi

Neutron producing region



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Summary of the Results

  • Optimised for neutron production:

    • Radius: 10 – 15 cm target radius from neutron balance point of view is enough

    • Length: Extend to the proton range to maximise neutron production and avoid charged particles in the UCx

  • Energy Spectrum of the neutrons:

    • Dominated by the intermediate neutron energy range ( 20 keV - 2 MeV)

    • Harden neutron spectrum by reducing the target size (but reduce yield and increase HE charged particle contamination)

    • Use of natural uranium to take advantage of the high fission cross-section of 235U in the resonance region  Improvement thorough neutron energy moderation

    • Alternatively, axial converter-UCx target configuration for depleted uranium target

  • Very localised energy deposition, 20 cm from the impact point along the beam axis ~30 kW/cm3/MW of beam power, reduced with the increasing proton energy

  • Possibility of using PbBi eutectic to improve neutron economy and reduce maximum energy deposition


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Future Work

  • Optimise the energy deposition once the size is fixed

    • Study the effect of the shape of the beam (parabolic, annular, variations in the sigma of the Gaussian distribution)

  • Activation of the target (calculate the spallation product distribution)

  • Model the fission target (including moderator/reflector) and optimise the fission yields

  • Analyse alternative target disposition to improve the fission yields

  • Study the use of deuterons as projectile particle


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