Electrochemical
Enhancement of Nuclear
Decontamination
Solutions
(ELENDES)
Dr Steven Brewer
10th April 2014
[email protected]
+44 (0)151 347 2967
Presentation Overview
• Collaborating Partners
• Introduction to ELENDES
• Process Detail
• Results
• Next stages
• Questions
‘This project is co-funded by the Technology Strategy Board,
the Department of Energy and Climate Change and the Nuclear
Decommissioning Authority’
C-Tech Innovation Ltd
•
Origins in ‘ECRC Capenhurst’, a research centre
for the electricity industry. Independent since
2001.
• Turnover > £5M.
• 65 people with around 40 degree qualified
engineers and scientists.
• Organised in 3 groups: Industrial Products,
Research & Consultancy.
• Core technical strengths are:
1. Electrochemical and chemical engineering
2. Industrial RF and Microwave Processing
3. Resource Efficiency and recycling technologies
Crown copyright 2000
0
50
100 km
Manufacturing Development
Business growth is fuelled by successful application of
new scientific discovery
We develop and commercialise processes and build
equipment for the food, chemical and advanced material
industries
Specialisms include
• Thermal processing
– microwave, radio frequency, ohmic,
plasma
•
Electro-chemistry
– waste treatment, metals processing, fuel
cells, flow batteries
Engineering Design Service
• Commercially available design, analysis,
manufacturing and life cycle assessment
capability
4
Example Electrochemical rig builds
National Nuclear Laboratory
• 6 locations:
– Sellafield, Workington, Harwell,
Stonehouse, Risley and
Springfields (Preston)
• £80M turnover (2010/11)
• Key customers:
– Sellafield Ltd, EdF Energy, NDA,
MoD, Magnox Electric Ltd,
Westinghouse, AWE
ELENDES Overview – What
• Decontamination system that enables the
use of HCl, nitric and complexants (and
combinations thereof).
• Permits local treatment (trolley based
units), decoupling decontamination from
central infrastructure.
• Or as an addition to centralised
decontamination facility.
ELENDES Overview – Why
• During the decommissioning of nuclear plant
large amounts of pipework and vessels require
processing (e.g. 300,000 metres of steel pipework
within Thorp).
• Previous work has demonstrated the
effectiveness of aggressive acids (e.g. HCl).
• The same applies for complexants, such as EDTA.
• However downstream processing issues have
limited their use.
• More rapid and lower volume decontamination
approaches can lead to significant savings in
terms of time and burden on infrastructure.
Overview – How
• Low volume deployment of reagent
• Electrochemical removal of chloride and destruction of
organics (complexants, surfactants etc.)
• Recycle reagent.
• Treatment of spent solution (e.g. precipitation/IX) if
required.
ELENDES Overview – How
Characterise
• e.g. HiRad/ LIBS/ Raman (to give rad
non rad characteristics).
Decontaminate
• e.g. cycles of nitric/ HCl/ complexant
followed by nitric wash.
Re-characterise
Repeat /refine
Recycle acid
Accept/reject
Treat effluent
(locally or
bowser)
Discharge
• ELENDES electrochemical removal/
destruction and reagent recycle.
Process Detail – Benefits
• Use of reagents to increase treatment
rate/efficiency (minutes/hours).
• Relative volume (10’s litres cf. 1000’s).
• Reagent recycle.
• Tuneable/controllable.
• Potential savings – increased man access,
localised treatment, programme
acceleration, BPM.
Process Detail - Electrochemistry
• Chemical reactions by electron transfer at
the electrodes.
• Charge balance required.
• ANODE – addition of electrons =
OXIDATION.
• CATHODE – loss of electrons = REDUCTION.
• Applied potential defines reactions that
happen – standard reference potential,
overpotentials, mass transport and kinetics.
Process Detail - Electrochemistry
Anode reactions
Potential
Reaction
vs SHE
0.163 UO22+ + e− ⇄ UO2+
+
+
−
4+
0.273 UO2 + 4 H + e ⇄ U + 2 H2O
O2(g ) + 2 H2O + 4 e − ⇄ 4 OH−(aq )
0.4
0.7
O2(g ) + 2 H+ + 2 e − ⇄ H2O2(aq )
0.77
0.8
Fe3+ + e − ⇄ Fe2+
NO3−(aq ) + 2 H+ + e − ⇄ NO2(g ) + H2O
1.18
ClO3− + 2 H+ + e − ⇄ ClO2(g ) + H2O
1.19
ClO2(g ) + H+ + e − ⇄ HClO2(aq )
1.2
ClO4− + 2 H+ + 2 e − ⇄ ClO3− + H2O
1.23
O2(g ) + 4 H+ + 4 e − ⇄ 2 H2O
1.33
Cr2O7− − + 14 H+ + 6 e − ⇄ 2 Cr3+ + 7 H2O
1.36
Cl2(g ) + 2 e − ⇄ 2 Cl−
1.49
2ClO3− + 12 H+ + 10 e − ⇄ Cl2(g ) + 6 H2O
1.63
2 HClO(aq ) + 2 H+ + 2 e − ⇄ Cl2(g ) + 2 H2O
1.67
2.87
3.05
HClO2(aq ) + 2 H+ + 2 e − ⇄ HClO(aq ) + H2O
F2(g) + 2 e− ⇄ 2 F−
F2(g ) + 2 H+ + 2 e − ⇄ 2 HF(aq
Cathode reactions
Potential
vs SHE
-2.92
-2.899
-2.03
-1.66
-1.185
-0.877
-0.74
-0.52
-0.44
-0.42
-0.25
0
Reaction
Cs+ + e - Cs(s )
Sr2+ + 2 e− ⇄ Sr(s)
Pu3+ + 3e− → Pu(s)
U3+ + 3 e− ⇄ U(s)
Mn2+ + 2 e− ⇄ Mn(s)
2 H2O + 2 e− ⇄ H2(g) + 2 OH−
Cr3+ + 3 e− ⇄ Cr(s)
U4+ + e − ⇄ U3+
Fe2+ + 2 e− ⇄ Fe(s)
Cr3+ + e − ⇄ Cr2+
Ni2+ + 2 e− ⇄ Ni(s)
2 H+ + 2 e − ⇄ H2(g )
Detail – The cell
Off gas (Chlorine & Oxygen)
Off gas (Hydrogen)
Fresh nitric acid
Effluent In
ANOLYTE CIRCUIT
CATHOLYTE CIRCUIT
Purge gas in
Purge gas in
Further Treatment
Re-use in decontamination solution
Illustrative rig
Catholyte tank
Anolyte tank
Control panel
and power
supply
Cell
Recirculation pumps
Electrochemical System
For a system sized to treat 1 cubic meter per day:
• Electrochemical cell 30 (w) x 50 (h) x 60 (t) cm.
• Power consumption 15 kW around giving an
operating electrical cost of around £ 35 / m3.
• Estimated capital cost £50,000 – 100,000
depending upon configuration.
• Readily both up and down scalable from this size.
Proces Detail - The system
Decontamination
Stream
Aerial Discharge
Receipt Vessel
Off-Gas
Treatment
Coarse Solids
Removal
Chemical
Dosing
Cell
Solids
Precipitation/
Activity removal
Solids
Discharge
Liquid Effluent
Discharge
Development programme – current phase
• Review contamination characteristics.
• Model decontamination.
• Produce inactive simulants.
• Evaluate operability, rate of removal of
chloride and complexant (EDTA/SDG3/N10).
• Active trials at Lab scale, NNL central lab at SL
• Design for pilot module capable to treat 10s
of L of spent decontamination solution.
Results
Chloride removal
• Analysis is simple
• Chloride concentration in solution measured
• Target less than 10 ppm in final solution.
Complexant destruction
• Analysis is complex
• TOC in solution measured
• Target is for final solution to have no
remaining complexing capability.
• Relying on TOC means process is required to
mineralise all organics.
• New analytical method being developed to
measure complexant concentration.
Results – chloride removal
100
Membrane no metals
Separator no metals
Membrane with metals
Separator with metals
With metals and complexent
Chloride [g/l]
80
60
40
20
0
0
2
4
6
Time (h)
8
10
12
Results – complexant destruction
400
3500
3000
300
2500
250
2000
S DG 3 T OC
N10 T O C
200
S DG 3 C l
C onc
N10 C l C onc
-
1500
150
1000
100
500
50
0
0
0
1
2
3
4
T ime (hours )
5
6
C l C oncentration (ppm)
T otal O rganic C arbon (ppm)
350
7
Conclusions from experimental Program
• Current efficiency for chloride evolution is high
down to around 0.2 M but gradually reduces as
the concentration in solution reduces further.
• However, the chloride conc in nitric acid can be
effectively removed down to less than 1ppm.
• Organic complexants can be readily oxidised
down from 1g/L EDTA to 13mg/L TOC.
• Combined chloride and complexant/organic
effluents can be treated with negligible reduction
in either process efficiency.
• Metals are not electrodeposited within the
system.
Summary
• A means of enabling local deployment of HCl and
complexant for decontamination operations has
been developed using electrochemical cells which
destroy/remove residuals.
• More aggressive decontamination reagents
permits low volumes of reagent to be used in a
tuneable manner. This means small mobile plant
can be used to process resultant effluent.
• A possible extension would be to treat
(precipitation step) to remove activity locally if
required.
Next stages
Current TRL status estimate
Acid decontamination: nuclear 3
Electrochemical complexant destruction: non-nuclear 9, nuclear 6
Electrochemical chlorine evolution: non nuclear 9, nuclear 9
Off-gas treatment: non-nuclear 9, nuclear 3
‘System’: 3 with rapid progression to 6 expected
Identify deployment
opportunities/scenarios
Progress/refine underpinning
R&D and design
Active demonstration
Deployment
Electrochemical
Enhancement of Nuclear
Decontamination
Solutions
(ELENDES)
Dr Steven Brewer
10th April 2014
[email protected]
+44 (0)151 347 2967