ADSR Systems - the Reactor
Tony Roulstone
13 April 2010
Contents
•
Challenge of the ADSR proposal
3
•
System considerations
5
•
Reactor Concept Studies
6
– Carlo Rubbia - Aker Solutions
7
– Weinberg - Molten Salt
9
– LFR - Ceballos
10
– MYRRHA
11
– ELSY/LEADER
13
•
Some Key Design Issues
15
•
ADSR Reactor Strategy
21
•
Reactor Work Programme Requirements
22
2
Challenge of the ADSR proposal
•
‘Towards an Alternative Nuclear Future’ is a substantial and impressive piece of work on
both the ADSR system and on the accelerator elements - which are both key to bringing the
ADSR concept to reality;
•
ADSR could provide the opportunity for UK to lead in a new and large industry – utilising
Thorium for electrical power;
•
The aim is show that an ADSR system at commercial scale, and on the timescale of 2025, is
an ‘entirely feasible and achievable’ objective - if adequate R&D is undertaken now;
•
The level of definition of the accelerator plan and hence its technology development is at a
fuller level than the reactor;
•
ThorEA should develop a matching conceptual R&D strategy and work plan for the reactor:
–
Collaboration and/or reference designs;
–
System considerations;
–
Key design issues.
Reactor System Considerations – 1 of 2
•
ADSR is a means of breeding fissile fuel (Uranium233) from Thorium and burning the fuel
that is created;
•
This can occur either with:
– An open fuel cycle in which a driver of fissile fuel, either enriched Uranium or
Plutonium provides the subcritical assembly for the Thorium fuel which is bred and
burned in situ. Limits to Thorium utilisation are set by: the performance of the
materials under high burn-up and the management of the fissile inventory/criticality
through the life of the fuel.
Hence, open cycles may be able to utilise only a small part (~10%) of the potential of
the Thorium fuel;
– Closed fuel cycle in which an initial fissile fuel is progressively replaced by
reprocessed Uranium 233 bred from Thorium. Because the fuel is reprocessed, the
materials and criticality issues above can be managed more effectively and the
potential energy yield from a closed cycle would be much enhanced.
•
ADSR enables these fuel cycles concepts - using a sub-critical, rather than a critical,
nuclear reactor.
4
Reactor System Considerations – 2 of 2
•
ADSR concept poses several important questions of reactor design, including:
– What type of reactor would be best suited to ADSR:
• thermal or fast neutron?
• solid fuelled or liquid fuelled (ie MSR)?
• liquid metal, water or gas cooled?
– Is the relatively low ‘worth’ of the external neutrons (Keff~0.015) sufficient to
provide safe control and to management the variation of reactivity during the fuel
burn-up?
– How would positive or negative changes of neutron from accelerator affect the
power in the reactor – on what timescales?
– Would the localised generation of neutrons around the Spallation target affect the
power distribution across the reactor – fast or thermal neutrons?
•
Why would an ADSR be preferable to a critical reactors for breeding fissile
material from Thorium for nuclear power:
–
–
–
Safety?
Cost ?
Availability?
5
Reactor Concepts
•
Much interesting work has been done on the reactor design issues around a specific
systems concepts:
– by Carlo Rubbia & Aker Solutions - Lead cooled Fast Reactor with reprocessing,
but separation of only fission products and no partition of heavy metals – Thorium,
Uranium and Actinides.
– by Alvin Weinberg on the use of Molten Salt Reactors within an ADSR system.
– MYRRHA Belgium LFR based on a proton Linac.
– European program for Lead-cooled fast reactor is completing – ELSY
– by Ceballos Castillo – a PhD study of enhanced-natural circulation LFR – core
kinetics & safety
6
Keff =
0.9986
Gain =
700
Initial fuel:
Pu/Th
Refuel: recycle U233 & Th
10 yr fuel cycle burn-up
150 GWd/tne
7
8
9
LFR modelling - Ceballos
•
•
•
•
•
•
Lead-Bismuth fast reactor 600Mth with natural
circulation enhanced by bubble flow riser;
Fuel in pins with steel (T91) clad in shrouded
sub-assemblies;
Zoned core both axial & radial;
Flat core: 4m dia 1m height, with 10m high riser;
Keff = 0.95 β = 0.35%;
Conventional steam cooling/power cycle.
•
Considered reactor kinetics & thermal
hydraulics:
– Modelling core power & fuel pin
temperatures;
– Examined core protection and some
standard safety cases LOHS, beam trip etc.
– Protection demonstrated for cases in which
shut-down systems operated;
– Clad creep at high temps & clad fatigue
due to frequent beam loss.
10
MYRRHA - 1 of 2
•
MYRRHA is an Accelerator Driven System (ADS) under
development at Mol in Belgium, with extensive international
collaboration, as a multipurpose irradiation facility for research;
•
It aims to serve as a basis for the European XT-ADS(*) and to
provide protons and neutrons for various R&D applications.;
•
MYRRHA consists of a proton accelerator delivering a 600 MeV 2.5 mA (or 350 MeV - 5 mA proton beam) to a liquid Pb-Bi
Spallation target that in turn couples to a Pb-Bi cooled, subcritical
fast nuclear core – in part based on a Russian military technology.
•
System parameters are as follows:
•
–
Proton beam power of 1.5 MW (600 MeV * 2.5 mA)
–
Windowless liquid Pb-Bi ‘free surface’ Spallation target
–
Sub-critical core (60 MWt nominal) made of MOX fuel with a
plutonium content limited to 35 wt%, cooled by pumped
Pb-Bi and LBE-water heat exchangers.
The choice of MYRRHA components is driven by the need to use
established core technology and provide a large margin of subcriticality (Keff = 0.95, Core temp – 337o C) to facilitate safety
clearance;
11
MYRRHA - 2 of 2
•
There is a substantial R&D program in support of MYRRHA design and construction & aligned
with operation timescales of 2022-23;
–
Pre-cursor test reactor - GUINEVERE deuteron accelerator directed into an Uranium
rod/lead core in 12*12 assemblies;
–
Target modelling & testing:
• Hydrodynamics to create free surface;
• Interaction of beam and surface;
• Location & control of surface;
• Gas flow above the surface;
• Target circuit clean-up.
–
Visualisation under Lead-bismuth
–
Robotics for fuel management and in reactor inspection or manipulation;
•
MYRRHA is a ambitious and well developed proof of principle project rather than a design vehicle
for a commercial ADSR reactor system.
•
Once MYRRHA has demonstrated the concept, it can be expected that further safety and
performance work/testing will be required to design a commercial ADSR.
12
ELSY/LEADER - Concept
Parameters
ELSY
Power [MWe]
600
Conversion Ratio
~1
Thermal efficiency [%]
42
Primary coolant
Lead
Primary coolant
circulation (power)
Forced
Primary coolant
circulation (decay heat )
Natural
Core inlet temp [°C]
400
Core outlet tem [°C]
480
Fuel
MOX, (Nitrides)
Fuel cladding material
T91 (aluminized)
Peak cladding temp [°C]
Fuel pin diameter [mm]
Primary pumps
Power Cycle
Primary/secondary heat
transfer system
550
10.5
8, mechanical,
integrated in the SG
Water-superheated
steam at 18 MPa, 450°C
Eight Pb-to-H2O SGs
13
LFR is candidate for ADSR but Gen IV program issues
R&D needs in fuels materials & corrosion control - 2 step process: 2025 reactor with low
primary coolant temperature & low power density; & by 2035 more advanced designs.
LFR - General issue
Corrosion in Lead
Seismic design
SGs are installed inside the reactor
vessel
with risk of water ingress in lead in
case of SGTR accident
Specific issue
Proposed strategy
Tendency for material corrosion with
increasing temperature
Mean core outlet temperature for the large
plant is limited to 480°C
Dissolved oxygen provides barrier against
corrosion
Reactor vessel
Temperature limited by design to 400°C
Fuel cladding
Use of aluminized surface treatment of steels
Reactor internals
Dissolved oxygen control
SG tubes
Use of aluminized steels to avoid lead
pollution and heat transfer degradation
Pump impeller degradation
Use of innovative materials
Challenge related to the large mass of lead
Use of 2D seismic isolators + short vessel
design
Rupture of the SG collectors in lead
Eliminated by design
Steam entrainment in the core in case of SGTR Excluded by design
Pressure waves inside the primary system in
case of SGTR
Harmless by specific design features
DHR
Diversification, reliability and passive
operation required
Diversification and reliability by means of use
of both atmospheric air and stored water
Refuelling in lead
High temperature makes refuelling difficult
Access to fuel assemblies is in cold cover gas
14
Key Design Issues
1.
Thorium as a fuel:
– Thermal neutrons are feasible for breeding but easier
to establish conditions for breeding with fast neutrons;
– Requires a fissile driver core –
either enriched Uranium or Plutonium – 15-20%
– Some studies of the feasibility of direct breeding
from the accelerator neutrons, using only Thorium fuel
concepts need to be developed;
– Without reprocessing - ADS Reactors can only exploit limited part of Thorium potential – require
very long-life/high burn-up fuel (150GWd/tne ~10 years) to exploit Thorium - emphasis on:
• In-core breeding/burning – demonstration that very long core life time can be achieved, by
• Use and management of burnable poisons, and
• Burning & breeding fuel mix to ensure critical/sub-critical margins are maintained
– With reprocessing - core power shapes will be affected by fuel management in both fissile & fertile
regions – re-load fuel is much more active than discharged fuel;
– Aqueous reprocessing is more difficult than for Uranium, requiring HF or other means to dissolve
oxide fuels, otherwise pyro-metallurgical processes - & potential problems with re-fabrication of fuel
due radio-active Uranium232 daughters.
– Reprocessing & re-fabrication development would requires their own development programs.
15
Key Design Issues
2. Spallation Source
–
Spectral effects of neutrons on criticality – prompt neutron #/yield is a function of
neutron/proton energy.
Neutron per fission as a
function of neutron energy
–
–
–
Localised source of neutrons – potentially affecting core power shape & power peaking;
Neutron coupling differences between thermal and fast systems – diffusion lengths;
Source materials which withstand the high level of energetic neutrons - life related to
consumption/transmutation of the target material – ~50mg/s => tne pa?;
16
Key Design Issues
3. Source/Target Sub-System
Topic
MEGAPIE – Zr, Pb, PbBi
Issues
Window materials & lifetime in hostile
conditions
Window-less, or with window - material choice & design?
MEGAPIE - window
MYRRHA - window-less
Spallation Source Target materials
Solid – materials choice & configuration /cooling
Liquid – material choice, containment & clean-up of spallation
products – Polonium210 production (LD50 ~1 μg)
contamination of primary coolant, control/removal of other
spallation products: X, Kr, Hg, Cs, I, Br etc. .
Target cooling & lifeing of targets;
Material transmutation, thermal & damage assessment of
designs
MEGAPIE - 1/10 of commercial power levels
Beam tube penetrates shielding &
containment
Conceptual design of shield with penetrating beam tube
Potential for flooding of tube affecting
criticality?
Criticality effect of flooding beam tube
17
Key Design Issues
Shape of core burn-up
reactivity profile
depends on reactor
type – fast/thermal.
4. Reactivity Control
Keff =1
2-3%
Core Lifetime
Effect of core burn-up/breeding
8-9% ΔK/K
Source-free K
Start of Life
•
End of Life
Through-life:
– Either accelerator must be capable of providing neutrons for ΔK/K at EOL ~ 9% and is
modulated during operation, or
– Complex fuel management/shuffling/breeding together with burnable poisons to manage
reactivity with the aim ΔK/K at SOL ~ ΔK/K at EOL, or
– Control rods provide macro control of reactivity & accelerator has fixed neutrons capacity.
Reactivity safety may appear to be little different from a conservatively-designed conventional/
critical reactor;
18
Key Design Issues
4. Reactivity Control(cont’d)
•
Short term :
– Changes in accelerator beam current affect core power in prompt neutron timescales ~10-6 s
Delayed fissions neutrons - Nd
λ =101 s (β)
Prompt fissions neutrons - Np
λ = 10-6 s (1- β)
Power at time = Zero
–
Delay
< 1%
Accel
FP
1-6%
Fission Power = (Np + Nd) * Ef * Keff
ν
1 - Keff
Amplification ~ 60
Prompt Power = Np * Ef * (Keff - β)
ν
1 - (Keff - β)
Amplification ~ 50
Fission products decay heat - depends on power
history – change is slow function of time ~ t -1.2
Thermo-structural core reactivity effects – fuel expansion & bowing, core structure expansion
& dilation etc - compensated for either by neutron source strength modulation, or by
mechanical trimmer control rods.
19
Key Design Issues
5. Thermal/Hydraulic Design
–
–
–
Power density – need for radial zoning of enrichment to flatten core power distribution;
Power peaking - optimising of coolant pumping power v pin spacing & bundle shrouding etc.
Choice of core coolant affected by a range of factors:
• Thermal systems – H2O, D2O, CO2 or He:
– Diffusion length effects;
– Neutron economy;
– Safety & decay heat removal.
• Fast systems:
Coolant
Activation
Chemical
n leakage
effects
Heat Removal
Loss of Coolant
Gas: He/CO2
None
Low
Steam +ve void
coefficient
High Pressure
Decay heat after leak?
Lead/LeadBismuth
Po208/209/210
from Bismuth
Corrosion
products
Low
Inherently good - boiling point
>1670oC though exposed coolant
will release activity above core
Structural design of vessel with
large mass of coolant.
Sodium
Na24
Sodium water
reactions
Phase change
+ve void
coefficient
Low likelihood of vessel breeching
– Sodium burns in air activation
products.
20
ADSR Reactor Strategy
•
Current reactor systems concepts, are informative, but:
– Have substantial technological risks and hence similarly long development
timescale as other Generation IV reactors;
– Will require many £bn of development/demonstration programs before they become
ready for commercialisation.
•
To support the claim that a commercial ADSR is an ‘entirely feasible and achievable’
objective - ThorEA either has, or should have, a work program that;
– Addresses the key technical design issues, and
– Produces a concept or reference design which makes the Reactor proposal clear.
•
Scale of challenge is large - therefore need to make choices about systems &
collaboration:
1. Join in the EU work of MYRRHA/LEADER in support of fast reactor development;
2. Develop a distinctive fast reactor ADSR proposal;
3. Investigate feasibility of thermal ADSR – light, heavy water, gas cooled.
•
Map out a collaborative work program, that provides impetus to the concept in the UK .
21
Reactor Development Work Program
•
Technology/Components:
1. Thorium as a fuel – including the Fuel Cycle technology;
2. Spallation Source;
3. Source Sub-system;
4. Reactivity Control;
5. Thermal-hydraulic Design;
6. Materials R&D needs/means – Spallation Source & Reactor.
•
System Concept:
– System studies that identify the preferred design configuration;
– General arrangement layout of reference design;
– Fuel Cycle flow sheet;
– Preliminary assessment of design against NII SAPs & outline PSA;
•
Development Program:
– Outline schedule for technology, component/systems demonstrator and the approach to
commercialisation;
– Identification of technological and development major risks;
– RoM Development, Capital & Operating costs.
22
End
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