Transcript GSI0603.ppt

A Radiatively Cooled ADS
Beam Window
Caroline Mallary, Physics MQP
2007
What is ADS?

Accelerator Driven System
– A means of transmuting
nuclear waste, or
– A new type of fission
reactor, or
– Both
 Runs on a sub-critical pile:
reaction cannot run away
 Can be designed to burn
existing nuclear waste
Fig 1. Concept of a Power & Transmutation system for long-lived radioactive nuclides by JAERI.
From Y. Kurata, T. Takizuka, T. Osugi, H. Takano, JNM 301, 1, (2002)
What is ADS?

How?
– Some of the “afterheat” of
spent nuclear fuel can be
captured in a power
generator, instead of a
mountain
 Goal is 95% of MA &
LLFPs transmuted
 250 kg/300 days
– But, reaction needs a catalyst
Fig 2. Radioactive power from decay of fission products and actinides. This decay-power
results from the waste of 1 mo. of operation of a 1000-MW power plant. Solid curve is the
sum of contributions of individual isotopes. From B.L. Cohen, Rev. Mod. Phys 49, 1 (1977)
The Concept


Proton accelerator creates neutrons by spallating high-Z target
nuclei (smashing them to bits)
Spallation neutrons used to maintain fission reaction where not
normally possible
– Subcritical piles
– In waste actinides
– Chain reaction can’t exist w/o accelerator: To stop, just unplug it
Some Facilities

Current generation of experiments
focus on spallation
– J-PARC’s TEF is planning work with
U, Pu, and minor actinides

Experimental Facilities
– Oak Ridge Nat’l Laboratories,
Tennessee (SNS, April 2006
[sns.gov])
– J-PARC, Japan (TEF, October 2006
[j-parc.jp])
– SINQ, Switzerland (MEGAPIE,
August 2006 [megapie.web.psi.ch])
A Problem

Proton accelerator is BIG
–
–
–
–

~1 GeV protons needed for spallation
Proton fluences >1014 /s /cm2 needed to make power generation practical
That kind of radiation can damage any material, besides which…
This beam melts most things you put in front of it
Accelerator needs to be kept at high vacuum (<10-9 atm)
– How do you make the window that the beam
comes out of?
One of the window designs considered for SNS. Note domed
central portion. From Proceedings of the Particle Accelerator
Conference, ORNL team (2003)
One Solution

Liquid-metal cooling
– Mercury or Lead-Bismuth Eutectic
targets, in direct contact with window




Liquid metal removes heat fast
Can be used to cool core as well
Flows: no accumulated radiation damage
Most popular design
– Direct contact with target damages
window
 Corrosive
 Pulsed beams cause shock-waves and
pitting … dT/dt ~ 107 K/s!*
*John R. Haines.
Target Systems for the Spallation Neutron Source, PowerPoint (2003)
Fig 3. Pitting in an annealed
316LN window (SNS). From J.
Hunn, B. Riemer, C. Tsai, JNM
318, pg. 102, (2003)
Other Solutions

Windowless design
– Liquid metal can evaporate into accelerator vacuum

Multiple beams
– Reduces power needed per beam

Gas-cooled window
– Much more difficult to cool than with liquid metal
– Core should have separate, passive liquid cooling system

Radiative cooling
– Window must be thin & stable at high temperatures
Radiative Cooling
It’s an Optimization Problem
Thicker window  greater heat
deposition by beam
Thinner window  higher stress for
same ambient pressure
Window melts if it receives more
heat than it can radiate away
High temperatures & long-term
stresses weaken metals
To radiate, must have:
Window Equilibrium Temperature > Ambient Temperature
Material Investigation

Alloy bases examined:
Aluminum
Titanium
Vanadium

Chromium
Iron
Nickel
Zirconium
Niobium
Molybdenum
Tantalum
Tungsten
Rhenium
Want
– Maximal proton flux
– Window strong enough
 Assume must hold back 1 atm
– Heating by Beam = Power Emitted
 Temperature remains constant
– Good radiation tolerance
 Experiments needed
 Some calculations possible
For each material there is an ideal thickness & operating temperature
Material Investigation

Material Properties Considered
– Tensile Strength = f (T, t)
– Electronic Stopping Power  Density
 ( MeV cm2/g )  (g/cm3) = MeV/cm of thickness
– Oxidation Resistance
– Emissivity reviewed but not used
 Assume is feasible to blacken to 90% of Blackbody

Procedure
– Literature Review
– Lots of Spreadsheets
– Irradiation experiment (to be completed)
Material Investigation
Sample Spreadsheet* : For V-40Ti-5Al-0.5C

Density = 5.3 g/cc; Stopping Power = 1.62 MeV cm2 /g;
Ambient Pressure = 1 atm; Ambient Temp = 300 K; Window Radius = 10 cm
Temperature
(K)
UTS (MPa):
100-hr rupture
Total Emitted
Power (W)
Center Thickness Flux/cm2 at
4 safety (mm)
Center
673
920
632
0.015
773
772
1119
0.018
1.0  1015
1.5  1015
873
283
1836
0.048
8.9  1014



Window is 1.5 as thick at edge, hemispherical
Beam is continuous, not pulsed
Beam profile is adjusted so that heating is even across window
Total Proton Flux = (Flux/cm2 at Center)  (314 cm2)  0.519
*Data Source: Rostoker. The Metallurgy ofVanadium, 1958
Best Materials

Low Temperature
– Can be run in air
______________________________
Inconel-718 or Udimet 901
(Nickel-based)

Refractory
– Higher flux possible
– May anneal rad. damage
– Harder to blacken?
______________________________
Vanadium - 40Ti - 5Al - 0.5 C
Molybdenum TZM
31HT or 316 Steel
Thoriated Tungsten
Inconel-718 was the best but little
data was available: 1 short-time
elevated temperature strength and no
lifetime data. Used factor of 4 safety
in window thickness to compensate
Molybdenum-TZM (Mo-0.5Ti0.08Zr, Stress-Relieved) has v. good
lifetime but should not be run in air
at high temperatures.
Best Materials
Material
Max total flux
(p / s), [mA]
Thickness
(mm)
Op.Temp
(C)
Safety factor; max
lifetime data found
1. Moly-TZM
1.3 1018 [200]
0.036
1316
4; 100-hr rupture, but
v. stable (NASA)
2. W-ThO2
1.5 1018 [240]
0.010
1093
2; 1,000-hr rupture
3. Inconel-718 4.6 1017 [73]
0.012
650
4; none given
4. Udimet 901
4.5 1017 [70]
0.013
649
2; 1,000-hr rupture
5. V-40Ti-5Al0.5C
2.4 1017 [39]
0.018
500
4; 100-hr rupture
6. 31HT Steel
1.8 1017 [28]
0.025
595
1; 100,000-hr rupture
7. 316 Steel
1.7 1017 [27]
0.020
538
1; 10,000-hr 1% creep
Is it Enough?
Assume:

–
–
–
–
30 spallation neutrons / proton
97% critically w/o spallation neutrons
1017 1-GeV protons/second (16 mA, 16 MW beam)
Beam is 15% power efficient
Calculation:

i.
ii.
iii.
iv.
v.
3% free neutrons are from spallation
(30 n/p) (1017 p/s) / (0.03) = 1020 free neutrons/s
If 80% of free neutrons cause a 200 MeV fission, then have 1.6 1022 MeV/s.
If generation system is 30% efficient have 4.8 1021 MeV/s = 770 MW
770MW - 16 MW/0.15 = 660 MW plant
Conclusion:

–
Any of the best window material can be run below max flux and still sustain a
commercial-size power plant
Radiative ADS Issues

Solid target better here
– Would require core redesign
– Can neutron brightness be maintained?
– May still want reactor cooling system to be liquid metal

Window may be meters away from target & core
– Greatly reduces damage from neutrons & gammas, but…
– How do exotic materials respond to proton irradiation damage?
 Spallation
 Transmutation Gases (H & He embrittlement)
 Crystal Damage
 1 dpa = 0.4S(N)flux
t
TDE  z
Some Formulas

Heating
Temperature
Emissivity Level (90% Bb)
Some Formulas

Load on the window
– Only the part of the window facing outwards
matters…Approximate as a disc
Disc approximation works for radiative area, too
Some Formulas

Z = Safety factor x R x Ambient Pressure
2 x Strength x 1.5

Max Flux =
Emitted
.
Density x Stopping Power x Thickness x 1.602 x 10-13
SNS Image