close

Вход

Log in using OpenID

embedDownload
Recycle of 241Am obtained from
long term stored plutonium for use
in Radioisotope Power Systems
Presented by : Tim Tinsley
Contents
• Background to the project
• Why
241Am?
• 241Am flowsheet results
• Next phase of the project
• Conclusions
What is a RPS?
• Uses thermoelectrics or other
methods to convert heat to
electrical power
Image courtesy of NASA and US DoE
Isotope candidates
•Initial criteria for isotope
selection
Power density acceptable
Shielding not restrictive
Availability
Lifetime (> 20 year mission)
•Then considered
chemical form; feasibility of
production; costs…
241Am
favoured because of
accessibility and cost
Am241 Production
Courtesy of ESA
Isolating Am241
• Am241 can be isolated by chemical separations
Dissolve PuO2
Separate Pu
from Am/Ag
Separate Am
from Ag
Precipitate Pu
oxalate
Precipitate Am
oxalate
Calcine to
PuO2
Calcine to
AmO2
Recover Ag
Image courtesy of NNL
Dissolution of PuO2 with Silver II
PuO2
2Ag2+
PuO22+
2Ag+
2eAnode
Ag+ → Ag2+ + e-
Cathode
2H+ + NO3- + e- → NO2 + H2O
Image courtesy of NNL
Silver II dissolution
Up to 200gPu/l
dissolved in 1 hr
demonstrated
Old and new PuO2
dissolved
Run at 35±5°C to
avoid splitting of
water
2Ag2+ + PuO2(s) → PuO22+ + 2Ag+
Pu/Am separation objectives
• Obtain a Ag free Pu product
• Obtain a Pu free Am/Ag product
• Monitor where U and Np is routed to
• Underpin the Decontamination Factors (DFs) used
in conceptual flowsheet
Full scale
ESA 1
Feed
flowsheet
g/l
flowsheet
g/l
Np
0.27
0.23
U
0.39
0.33
Pu
94.5
88.7
Am
3.5
0.92
Ag
10.79
10.79
Solvent extraction – batch tests
2-phase batch system:
solvent
Mix &
Separate
Pu
Am + Ag
aqueous
Extraction
Pu
Am + Ag
Mix &
Separate
Backwash
Next separation process
Distribution coefficient measured
DAm = [Am]org/[Am]aq
Pu
Pu/Am
Separation - flowsheet
S1
30%TBP/OK
12
9
8
Extract
5
4
Extract
AP1
[Ag]: 5.4g/l
[Am]: 0.51g/l
[HNO3]: 2.21 M
1
Scrub
Feed (F8)
A3
[Pu]: 99.1g/l
[Am]: 1.1g/l
[Ag]: 10.8g/l
[HNO3]: 3.5M
[HNO3]: 2M
SP1
SR1
[Pu]: 30g/l
[Am]: Trace
[HNO3]: 0.32M
[Pu]: Trace
[HNO3]: 0.07M
13
16
Backwash
17
20
Backwash
21
24
Backwash
25
28
[Pu]: 33g/l
[HNO3]: ~0.64M
Solvent
Aqueous
UV/vis celll
•Am product stage 12
Backwash
A4
AP2
Centrifugal
contactors
[HNO3]: 0.2M
HAN: 0.5M
H4N2.HNO3 0.05M
•Pu product stage 13
•Solvent waste stage 28
Image courtesy of NNL
Ag and Am rejection from Pu
• Am recovery > 99.7%
1
[Am] g/l
• Less than 0.001g/l Am
follows Pu stream
Americum extract/scrub
0.1
0.01
0.001
0.0001
Am aq UV_vis
0.00001
Am aq gamma
Am org gamma
0.000001
Am org estimated
0.0000001
• Model needs work at low
[Am]
0
2
4
6
8
10
Stage no.
12
Silver aq profile extract/scrub
6
• Ag follows the Am stream
[Ag] (g/l)
• U follows Pu and Np is
split evenly between Pu
and Am streams
Org flow
5
4
Aq flow
3
2
1
0
0
2
4
6
8
10
12
Stage no.
Solvent selection
• Extract at ~2M HNO3
1000.00
• Rejects silver
100.00
• Backwash at 0.1M HNO3
10.00
DAm
• Radiation resistant
1.00
• Good metal loading
0.10
• Need to minimise Am in
aqueous waste
C8H17
N
N
O
Good
backwashing
0.01
0
1
2
3
[HNO3]ini (M)
C8H17
O
C8H17
Good
extraction
C8H17
O
N,N,N’N’, TetraOctyl DiGlycolic Acid (TODGA)
O
C6H13
N
C7H15
C6H13
N,N’, Dihexyloctanamide (DHOA)
4
5
Am/Ag separation –extract/scrub
• Am is extracted into solvent
1.00E+00
• ~ 1 x 10-6 g/l Am in aqueous
[Am-241]org
1.00E-02
[Am-241] (g/l)
• Ag is rejected to the aqueous
stream
[Am-241]aq
Solvent
1.00E-01
1.00E-03
1.00E-04
1.00E-05
1.00E-06
Aqueous
1.00E-07
• ~97% residual Pu was
extracted
1.00E-08
0
2
4
6
8
10
12
Stage No
14
• 90% of the Np remained in
AR1
[Ag] (g/l)
10.000
1.000
0.100
0
2
4
6
8
10
12
Stage No
14
Am/Ag separation – backwash
• Am is backwashed with >
99.99% recovery
•< 1 x
solvent
1.00E-01
g/l Am left in the
• Residual Pu in Am product
stream = 0.0023 g/l
• Residual Np in Am product
stream = 0.0049 g/l
[Am-241]aq
1.00E-02
[Am-241] (g/l)
10-6
1.00E+00
[Am-241]org
1.00E-03
1.00E-04
1.00E-05
1.00E-06
1.00E-07
12
16
20
Stage No 24
Americium oxalate precipitation
2Am(NO3)3 + 3H2C2O4 +10H2O
Am2(C2O4)3.10H2O + 6HNO3
Ideal precipitation conditions depends
on what outcome is required
•Minimise Am losses to supernate?
•Minimise excess oxalic acid?
•Control particle morphology?
G.A. Burney, J.A. Porter,
Inorg. Nucl. Chem. Letts., 3, 79, (1967).
Americium oxalate precipitation
• Temperature
has a minor
effect on % Am
recovery
• Increase temp
causes larger
crystal growth
Nd oxalate 60°C
Nd oxalate 25°C
Image courtesy of NNL
Isolating
241Am
• Plant concept design – simplifications made
Image courtesy of NNL
What is next?
• Increase the amount of 241Am recovered (0.5 to
4.2g) and optimise the separation process
• Assess the best chemical form (AmO2-x)
• Press and sinter to produce a LWRHU sized pellet
(~2.6g 241Am)
• Explore other pressing options such as Spark
Plasma Sintering (surrogates)
Conclusions
• There is an ample supply of 241Am in the
plutonium stocks at Sellafield to fuel multiple RPSs
(>2000kg and growing)
• An 241Am recovery plant design has been
technically underpinned demonstrating high 241Am
recovery (>99.9%) with high purity (> 99%)
• A 5-10kg 241Am per year plant could be sited in
NNLs existing facilities for a substantially lower
cost than a European 238Pu production facility
Acknowledgements
The authors would like to acknowledge the
European Space Agency for funding the
isotope separation study
1/--pages
Пожаловаться на содержимое документа