Transmutation of nuclear waste in Accelerator Driven Systems
Janne Wallenius
Reactor Physics, KTH
Radiotoxic inventory in spent LWR fuel
Specific radiotoxic inventory of spent LWR fuel in the repository is dominated by transuranic elements (TRU).
The fission product (FP) contribution to the
radiotoxic inventory vanishes with the decay of
90Sr and 137Cs.
Equilibrium radiotoxic inventory of uranium in nature ~ 19 mSv/g.
300 000 years of storage required for spent fuel to return to “natural inventory”.
0.001 0.01 0.1 1 10
100 Radiotoxic inventory [Sv/g]
102 103 104 105 106 101
TRU FP
Uranium in nature
t[y]
Radiotoxicity of transuranium nuclides
Long term radiotoxic inventory of spent fuel is dominated by
241Am ~ 1 000 years
240Pu ~10 000 years
239Pu ~100 000 years
Radiotoxic inventory due to presence of 237Np is less than that of uranium in nature.
102 103 104 105 106 0.01
0.1 1 10 100
101
Radiotoxic inventory [Sv/g]
243Am
242Pu
239Pu
238Pu
240Pu
237Np
241Am TRU
t [y]
Unat
Double strata fuel cycle
By transmuting the higher actinides in accelerator driven systems, the fraction of power produced in reactors using innovative fuel is
reduced to a minimum
Proton Accelerator: 10–15 MW Spallation target: liquid lead Core power: 400 MWth
Sub-criticality: k <0.97 Coolant: lead
Fuel: (Pu
0.4,Am
0.5,Cm
0.1)O
2-x- Mo
Accelerator Driven System
Proton accelerator
Two types of high intensity proton accelerators exist:
Cyclotrons – power up to 10 MW
Linear accelerators (LINAC) – power up to 100 MW (100 mA x 1 GeV).
Main issue for ADS: reduction of beam trip frequency.
Today: several beam trips per hour longer than three seconds.
Goal: few beam trips per year.
PSI1 MW cyclotron
LANSCE 1 MW LINAC
Linear Accelerators
Current limit: ~ 100 mA for reliable operation
LEDA (7 MeV Low Energy Demonstration Accelerator) was operated in Los Alamos at 100 mA for eight hours
Superconducting cavities today provide > 25 MeV/m gradient Length of Oak Ridge Spallation Neutron Source LINAC: 300 m.
Reliability can be achieved by operation below design values
Input power for 1 GeV LINAC: P
grid= 27 MW + 1.9 x P
beamSpallation target
Main task: provide regulated neutron source Technological challenges:
Heat deposition (50–75% of beam power) Radiation damage to beam window
Liquid metal corrosion & embrittlement
Life time of beam window for 0.7 MW LBE target
operated for four months at PSI (MEGAPIE) estimated to be about 0.5 years, limited by embrittlement.
Windowless target solution preferred for prototype ADS
ADS source neutron spectrum
20 40 60 80 100 120 140 0.95
0.96 0.97 0.98 0.99 1
E [MeV]
Fraction of neutrons with energy below E exiting the target wall
0.01 0.1 1 10 100 1000 0.01
0.1 1
En [MeV]
! (E
n) dE
nSpectrum of source neutrons exiting
an LBE target with radius 20 cm
Neutron source yield
Neutron yield increases with radius due to (n,2n) reactions Yield per proton energy ~ constant for E > 1000 MeV
500 1000 1500 2000
10 20 30 40 50 60
Neutron yield [n/p]
Proton energy [MeV]
Yield [n/p/GeV]
5 10 15 20 25 30
5 10 15 20 25 30
Neutron yield [n/p]
Target radius [cm]
|z| < 50 cm
Neutron transport in target
Spallation neutrons are multiplied, scattered and moderated in the target
-100 -50 0 50 100
Axial distribution of neutrons exiting the spallation target
z [cm]
r = 10 cm r= 20 cm r= 30 cm
Beam impact: z = 18 cm, E
p= 1 GeV
Radius Median energy
10 cm 1.42 MeV
20 cm 0.91 MeV
30 cm 0.68 MeV
Median source neutron energy lower
than median fission neutron energy!
Exercise
Calculate the conversion efficiency for electrical to proton beam power of a 1 GeV LINAC with 10 respectively 20 MW beam power.
P
grid= 27 MW + 1.9 x P
beamCalculate the fraction of electricity produced by the ADS that
is needed to operate the accelerator, assuming a thermal
power of 400 MW and a conversion efficiency of 40%.
Core design
Core map
Fuel column height: 0.9 – 1.2 m Clad outer diameter: 6 – 8 mm P/D = 1.50 – 1.75
Linear rating: 20–30 kW/m Core power: 400 – 800 MWth Pu-fraction = 30–50%
k-eigenvalue @ BOL: 0.97 Radial power peaking: 1.30
Core design
Core map
Radial power peaking & matrix fraction
Matrix Zone 1 Zone 2 Zone 3
92
Mo 0,8 0,62 0,5
EFIT cermet fuel matrix fractions
for D = 8.5 mm & P/D = 1.50
Radial power peaking & matrix fraction
10 20 30 40 50 60 70 0.5
1.0 1.5 2.0
Power density [relative]
Pin number counted from target
Zone 1 Zone 2 Zone 3
Matrix Zone 1 Zone 2 Zone 3
92
Mo 0,8 0,62 0,5
EFIT cermet fuel matrix fractions
for D = 8.5 mm & P/D = 1.50
Radial power peaking & matrix fraction
10 20 30 40 50 60 70 0.5
1.0 1.5 2.0
Power density [relative]
Pin number counted from target
Zone 1 Zone 2 Zone 3
Radial power peaking factor: 1.30
Matrix Zone 1 Zone 2 Zone 3
92
Mo 0,8 0,62 0,5
EFIT cermet fuel matrix fractions
for D = 8.5 mm & P/D = 1.50
Matrix versus void worth
ADS core must never become super-critical.
Fuel matrix influences void worth Less amount of oxygen reduces void worth.
Cermet fuels have advantage Cr matrix gives lowest void worth!
1.2 1.4 1.6 1.8 2.0 2.2 2.4 1000
2000 3000 4000 5000
6000
LBE void worth [pcm]
P/D
ZrO2 MgO W
Mo Cr
Di = 5.0 mm
