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The GDT-based fusion neutron source as a driver of sub-critical nuclear fuel systems

Presented by A.A.IvanovBudker Institute Novosibirsk, FZD Rossendorf, Joint

Institute for Nuclear Research, Dubna, VNIITF, Snejinsk

Budker INPNovosibirsk

Joint Institute for NuclearResearchDubna

Layout of the talk

Physics of GDT–based neutron sourceApplication as a driver for sub-critical fission reactorApplication as a MA burner Possible re-optimization GDT-NS for application as a driverConclusions



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Gas Dynamic Trap



Basic principles of GDT operationThe Gas-Dynamic Trap is a version of a standard simple mirror whose characteristic features are – a very high mirror ratio, R , in the range of a few tens;– a relatively large length, L ,exceeding an effective mean free path, λiilnR /R, with respect to scattering into the loss cone.The warm target plasma is almost Maxwellian– behaves like an ideal gas in a container with a pinhole leakMHD-stable even though system is fully axially symmetric– non-negligible amount of plasma in the regions beyond the mirror throats, where magnetic field has favorable curvature– MHD ballooning/interchange modes limit stability at β 40-60%The electron neat flux to the end walls is suppressed by strong reduction of magnetic field in expanders

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Requirements to VNS for fusion materials testing

Fusion neutron spectrumAbout 2MW/m2 neutron flux or higher for accelerated testsSmall enough gradient of neutron flux densityContinuous operationAvailability more than 70%Reasonable tritium consumption



Schematic view of the GDT-NS for the material tests



Basic set of parameters for two and three component version of GDT-NS

Parameter Two component version Three component versionTritium beam energy (keV) 240 94

Deuterium beam energy (keV) - 80

Tritium beam power (MW) 20 6.5

Deuterium beam power (MW) - 8.5

Electron temperature (keV) 0.6 1.1

Plasma density (m-3) 2 x1020 2 x1020

Plasma radius at the center (m) 0.06 0.08

Mirror ratio 20 15

Central field (T) 1.25 1.8

Injection angle (deg.) 20 40

Max. neutron flux (MW/m2) 3.9 1.8 – 2.0

Power consumption (MW) 50 60



Neutron spectrum in GDT-NS



GDT-NS: reference set of parametersPOWER CONSUMPTION - 47 MW

MAGNETIC FIELD IN MIRRORS, Bm = 13 T; MIRROR RATIO R =10

INJECTION ANGLE, θ = 300

INJECTION ENERGY - 65 keV

PLASMA DIAMETER AT MIDPLANE, 2a = 16 cm

RATIO OF ELECTRON TEMPERATURE TO THEINJECTION ENERGY Te / EINJ = 10 -2

MIRROR-TO-MIRROR, 11.4 mNEUTRON SOURCE INTENSITY – 7 1017 s-1



Neutron flux density vs injection energy



Neutron flux density vs electron temperature

Injection energy 65keVPower consumption 60MW



Cutaway view of the GDT-NS



Elevation view of GDT-NS



Neutron yield profile in GDT-NS



Neutron field characteristics



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GDT device – general view



Physics issues addressed in the experiments

Factors controlling electron temperatureMicrostability of fast ions Steady state operation Ballooning instability thresholdEffect of ambipolar fields on confinementEffect of plasma rotation/vortex barrier formationNon-paraxial effects due to high β



GDT device - important resultsMHD – stable confinement of plasma with β exceeding 0.4 is achieved in axially symmetric magnetic fieldStability of high-β plasma is demonstrated with external anchor cells (expander and cusp)Plasma stabilization by vortex barrier is demonstratedPlasma energy balance is determined by energy transfer from fast ions and losses through end mirrorsElectron heat conduction to the end walls is suppressed by strong reduction of magnetic field in expanderRelaxation rates of anisotropic fast ions are classical – no micro-instabilitiesSkew injection of neutral beams at midplane provides formation of fast ion density peaks near turning pointsPlasma is sustained during several characteristic times with extended neutral beams

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Measured axial profile of DD-reaction intensity



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NB energy 65keV

Neutron flux vs plasma temperature

65keV injection energy



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Electron temperature vs time



βmax ≈ 40%

nf ≈ 5x1019 m-3

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Plasma β in steady stay with D0

beams



Formation of vortex barrier



End loss reduction by fast ion density peaking near the ends

Peak density in local mirror cell vs trapped NBpower

Reduction of end loss current density with beam injection into local mirror cell



TeMean

ionenergy

Confinementtime

Injectedpower

Electron density

Experiment with max Te 230eV 8.0keV Transient

regime 3.5MW 1.5x1019m-3

Standard experimental scenario

160eV 10keV 0.001s 3.5-4.0MW 5.0x1019m-3

Fusion triple product (nτEi=2.0x1017keVm-3s)

Maximum stored energy 1.2 KJ

Maximum β <beta>≈50% at B=0.5TMaximum density >1020m-3

Values in bold are maximum attained ones.

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Plasma parameters in GDT



Existing GDT-NS version as a driver for sub-critical reactor



Results of simulations

Neutron production in driver 2.4 1017 s-1

Overall multiplication factor ≤ 0.95Thermal power generated ~0.5GWNeutron shield for SS coils Pb+water

60cmFilter material Pb 10cm



„Energy amplifier“ proposed by C. Rubbia (1995):

• Accelerator↓particle beam↓

• Target↓neutrons↓

• Sub-critical system(arrangement of nuclear fuel)↓Strong neutron field inside thewhole volume of the fuel systemby means of fissions !

Release ofnuclear energy

Transmutation of nuclear waste !

(protons)

(heavy metal)(spallation)

Principles of an ADS:

Important features:

1. Sub-criticality: keff ≤ 0.98 !

2. No control rods !Power control by proton beam !



Reflector

Core

● Driven sub-critical system, ADS, FDS ?z

r

Effective multiplication factor: keff

Sub-critical system: keff < 1 = 0Reactor: keff = 1 =const. > 0Driven system: keff < 1 ~ S

n

Accelerator

Introduction – Nuclear systems

pEp ≈ 1 GeVIp= 10 … 200 mA

Spallationn´s/p=10-30

Driven systems:keff determines the self-multiplicity of the system:

keff < 1: 0.95 ... 0.97

Meff=keff/(1-keff): 20 ... 30feff=Meff/ν : 6 ... 10



● Energy spectra of ADS and GDT neutron source:



total

n,2n

n,3nn,γ

10 MeV



Consideration of GDT-NS for fission fuel systems

Re-arrangement of neutron production zone (elongation (keff<0.97) to L ≈ 5 m on each side gives: Sn=2.5·1018 n/s, Pfus=7.1 MW, Pfis ≈ 1400 MW, Pinp ≈ 200 MW)Re-optimization of operational parametersIncrease of electron temperature (Te higher than 1.5keV would provide higher efficiency than ADS)Reduction of axial losses by ambipolar potential peaks (demonstrated)On-site tritium breeding

K. Noack,et al, Annals of Nuclear Energy,35(7), pp.1216-1222, (2008)

P.Bagryansky, et al, Fusion eng. and design,70, pp. 13-33, (2004)

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