ÚJV Řež, a. s.
Project ALLEGRO
He-Cooled Fast Reactor
Demonstrator
Ladislav Bělovský
[email protected]
Tel. 724 446 735
Seminar, ÚJV Řež, March 28, 2014
What is a fast reactor ?
A fast reactor makes use of fission induced by fast neutrons
(E > 0.1 MeV)
Characterised by having:
Compact core
(no moderator)
High power density
(~100-400 MW/m3 versus ~5 MW/m 3 for thermal reactors)
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Why have fast reactors ?
Only 0.72% of natural U is fissile. For nuclear power to be sustainable
it is essential we make better use of the natural resource.
0.72%
U235
0.0055% U234
99.2745% U238
Enrichment industry produces large quantities of depleted U
(e.g. 500 000 t in France)*
Breeding of Pu from U238 in fast reactors allows
considerably more of the natural U to be used.
Both breeding and the utilization of Pu are
more efficient in fast fission systems.
Long lived minor actinides that occur in nuclear waste
(Am, Np and Cu) can be burned.
Reduces radio-toxicity of wastes
Significantly reduces waste storage times (~300 years)
C. Béhar: FR13 Conference, Paris
2
Plutonium Breeding Reaction
Starts with neutron capture in U238
238
92
U + n 
1
0
239
92
U
U239 has a half-life of 23 minutes and decays to Np239
by beta decay
239
92
U  239
Np
+


+
93
Np239 has a half life of 2.3 days and decays to Pu239
by a further beta decay
239
93
Np 
239
94
Pu + - + 
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Why have Gas-Cooled Fast Reactors ?
Sodium-cooled FRs are the shortest route to FR deployment,
but the sodium coolant has some undesirable features :
Chemical incompatibility with air and water
Historically, has a strongly positive void coefficient of reactivity
Avoiding sodium boiling places a restriction on achievable core outlet T
Advantages of GFRs
Chemically inert & optically transparent coolant (He)
Void coefficient is small (but still positive)
Single phase coolant eliminates boiling
Higher outlet temperature ~800  C allows non-electric applications
High efficiency (not higher than ~50%)
Hard spectrum (good breeding)
4
… but
Necessity of high-temperature resistant (refractory) fuel
High gas pumping power
Relatively high pressure in primary circuit
Rapid heat-up of the core following loss-of-forced cooling due to:
Lack of thermal inertia (gaseous coolants & the core structure)
High power density (100 MW/m3)
Difficult removal of decay heat in accident conditions (LOCA)
Relatively high temperature non-uniformities along fuel rods
High coolant velocity in the core (vibrations)
He leakage from the system
5
GCFR concepts: A historical perspective
USA: General Atomics – The GCFR programme
Started in the 1960’s
Capitalised upon High Temperature (thermal) Reactor (HTR) experience
(Peach Bottom and Fort St Vrain)
Funded by US DOE
Collaboration with European partners
Main features:
300 MWe helium cooled reactor, water/steam in secondary circuit.
Multi-cavity pre-stressed concrete pressure vessel.
Vented fuel pin fuel element design to reduce fuel clad stresses.
6
USA: General Atomics 300 MWe GCFR concept
7
Europe: The Gas Breeder Reactor Association
1970-1981: A, B, D, F, CH, Japan, SE, UK and USA
He
He
CO2
Pre-stressed concrete vessel
He
GBR 4
1200
90
124
260
560
11.8
MOX/SS
8
SiC coated part. fuel
MOX/SS
Europe: GBR-4 (1200 MWe, He-cooled, vented MOX/SS)
Developed to overcome the complexities
of the particle bed fuel elements.
Vented SS clad fuel pins held in
spacer grids.
The clad surface was ribbed to maximise
the core outlet temperature whilst
respecting clad temperature limit.
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Europe: German KWU-1200
10
Europe: UK: ETGBR/EGCR (1970s-1990s)
Based on the UK AGR
(thermal) architecture
Metallic clad fuel
Carbon dioxide coolant
Pre-stressed concrete
pressure vessel
11
Japan: Prismatic Block Fuel (1960s – present day)
Japan investigated block fuel
containing ZrC coated particles
and packed bed (GBR-2) type)
fuel elements.
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Present days: Gas Fast Reactors in GIF
2000: Generation-IV Int. Forum: A renewal of interest in fast reactors
for sustainability,
waste minimisation,
and non-electricity applications.
2002: A Technology Roadmap for Gen-IV Systems (update Jan 2014)
Six systems are proposed:
SFR
LFR
GFR
MSR
SCWR
VHTR
Sodium Fast Reactor
Lead Fast Reactor (Pb or Pb-Bi eutectic)
Gas Fast Reactor (He)
Molten Salt Reactor fuelled with molten salts
Super-Critical Water-cooled Reactor
Very High Temperature Reactor (He)
2009: EU initiative SET-Plan/SNETP/ESNII
Support of SFR, LFR, GFR demonstrators & MYRRHA
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Current Gen-IV GFR Performance Requirements
Self-generation of Pu in the core (not breeding).
Optional fertile blankets to reduce the proliferation risk.
Limited mass of Pu in the core.
Ability to transmute long-lived nuclear waste (spent fuel recycling)
(without lowering the overall performance of the system).
Favourable economics owing to a high thermal efficiency.
Fundamental safety requirements:
Control of reactivity/heat generation by limiting the reactivity swing over the
operating cycle; the coolant void reactivity effect is minor.
Capacity of the system to cool the core in all postulated situations, provision of
different systems (redundancy and diversification).
A “refractory” fuel element capable of withstanding very high temperatures
(robustness of the first barrier and confinement of radioactive materials).
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The Gen-IV GFR system (as per the Roadmap)
Now
2400 MWth
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GFR Power conversion system options
G
F
R
Steam Turbine
Turbine
•
IC

~
Compressors

GC
PC
PC – pre-cooler
IC – Intercooler
FP – Feed water pump
GC – Gas circulators
Recuperator
Direct Recuperated
Helium GT
IC
G
F
R
G
F
R
Indirect Pure Steam Cycle


G
F
R
Turbine
•
~
GC
FP
GC
Compressors
PC
Steam Turbine
Gas Turbine
FP
Recuperator
Indirect Recuperated
Helium GT
Images courtesy of
Chris Neeson, Rolls-Royce plc
Euratom: GFR Research & Development (1)
FP5 GCFR (2000-2002) – EC contribution 0.25 M€
Review of experience in gas reactors
Formulation of future R&D
The Gen IV GFR exploratory phase defined the following options:
Reactor unit size:
600 MWt, 2400 MWt
Power cycle options: Direct, Indirect
Core power density: 50 MWt/m3 up to 100 MWt/m3
Fuel forms:
Plate, particle or pins
Seven basic cases were constructed from combinations of these
attributes.
FP6 GCFR-STREP (2005-2009) – EC 2 M€
600 MWt case (plate fuel & direct He Brayton cycle) abandoned after first year.
Continued were mainly GFR2400 (direct, indirect) & its demonstrator (ETDR, ALLEGRO).
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Euratom: GFR Research & Development (2)
FP7 ADRIANA (2010-2011) – CSA, EC 0.99 M€
Mapping of the existing & required experimental infrastructure
for SFR, LFR & GFR research.
FP7 GoFastR (2010-2013) – CP-FP, EC 3 M€
Design & Safety of GFR2400 and its demonstrator ALLEGRO.
FP7 ALLIANCE (2012-2015) – CSA, EC 0.86 M€
Support of the ALLEGRO Preparatory phase.
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CEA: GFR Plant layout studies
640,00
600 MWt Direct cycle
7 000
9 080,0 0
673 8,27
15 5,00
68 9
2500,00
656,2 5
1 200,00
26 50
19
1200
7 50,00
1950,00
990 ,0 0
4700
68 9
14 4,36
2400 MWt Indirect cycle
GFR Reference combined cycle (GFR2400)
1.
2.
3.
4.
5.
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Direct cycle, Tin = 480°C: η ~ 47.5 %
Indirect cycle, Tin = 480°C: η ~ [45.5 – 45.6] %
Direct cycle, Tin = 400°C: η ~ 44.8 %
Indirect combined cycle, Tin = 400°C: η ~ [44.4 - 44.7]%
Indirect cycle, Tin = 400°C: η ~ [42.4 – 42.8]%
CEA GFR2400 (Indirect cycle): I. circuit
1 RPV
2 MHX
3 DHR
4 He tanks
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CEA GFR2400: Specific technical challenges
High-temperature resistant fuel (tolerant to overheating)
(U,Pu)C in SiCf-SiC tubes
Safety systems – Reliable shutdown and decay heat removal (DHR)
With use of natural circulation
Fuel handling machine
Under He flow to cool the fuel
He/gas main heat exchanger
Large dimensions
Materials & components & helium-related technology
Heat shielding, He-sealing, …
Helium purification
…
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GFR Specific challenges: Fuel
Robust high-temp. refractory fuels and core structural materials
Must be capable of withstanding the in-core thermal, mechanical and radiation
environment whilst retaining radionuclides.
Safety (and economic) considerations demand a low core pressure drop, which
favours high coolant volume fractions.
Minimising the plutonium inventory leads to a demand for high fissile material
volume fractions.
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GFR Specific challenges: Decay heat removal (DHR)
HTR “conduction cool-down” will not
work in a GFR
High power density, low thermal inertia,
poor conduction path and small surface
area of the core conspire to prevent
conduction cooling.
A convective flow is required through
the core at all times;
At pressure: A natural convection flow
might be OK (to be confirmed)
After depressurization: A forced flow
Gas density is too low to achieve nat. conv.
DHR blower pumping power very large at
low P
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Need of a (first ever GFR) demonstrator ALLEGRO
To establish confidence in the innovative GFR technology with the
objectives:
A) To demonstrate the viability in pilot scale and
to qualify specific GFR technologies such as:
core behavior and control, fuel and the fuel elements
specific safety systems, in particular, the decay heat removal function,
Gas reactor technologies (He purification, …)
together with demonstrating that these feature can be integrated successfully
into a representative system.
B) To contribute by Fast flux irradiation to the development of future fuels
(innovative or heavily loaded in Minor Actinides)
C) To provide test capacity of high-temp components or heat processes
D) To dispose of a first validated Safety reference Framework
Power conversion system in ALLEGRO was not planned in 2009.
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GFR demonstrator ALLEGRO
Three distinct phases of operation  three different core configurations:
Starting core
MOX/SS with 25% Pu (metallic hexagonal sub-assemblies).
Core outlet temperature limited to ~550  C.
A GFR-style all-ceramic demonstration core.
Intermediate core in which 1 to 6 MOX fuel assemblies are replaced by the
tested ceramic fuel elements
Test assembly (U,Pu)C/SiCf-SiC with 29-35% Pu fuel pins bundle within an
internally insulated metallic hex-tube.
Test assembly outlet temperature ~850  C (reduced flow rate at inlet)
Average core outlet temperature limited to ~550  C.
Final core composed of the ceramic fuel assemblies only.
Average core outlet temperature increased to ~850  C.
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ALLEGRO CEA: Global facility
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ETDR CEA 2001-2008 (50 MWt)
DHR IHX
Experimental
Technology
Demonstration
Reactor
DHR loop
RPV
Main IHX (50 MW)
Main blower
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ALLEGRO CEA 2009 (75 MWt)
DHR blower
DHR HX
DHR loop
RPV
Main IHX 2 x 40 MW)
HT IHX
Main blower
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(10 MW)
Optional IHX
10 MW
ALLEGRO CEA 2009: I. circuit in Guard Vessel (GV)
- Helium back-up pressure in case of LOCA:
~2-3 bar
- Higher back-up pressure in case of N2 injection: 10 bar or more
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ALLEGRO CEA 2009: First core layout
Experiment
MOX
Control
Shutdown
Reflector
Shield
Number of assemblies:
81 MOX
10 control & shutdown
174 reflector (not shown)
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Experimental ceramic fuel assembly
(insulated wrapper tube)
ALLEGRO CEA 2009: MOX/SS Fuel Sub-Assembly
Based on PHENIX fuel assembly (hex SS wrapper tube)
169 PHENIX-type MOX/SS pins, OD 6.55 mm
Fissile length ~0.86 m
110 mm
To be fabricated
1793 mm
PHENIX pin
Fissile column
Fertile column
Gas volume
ALLEGRO pin
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~ 1300 mm
ALLEGRO CEA R&D and Experimental support
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Thesis & Diploma works - Design & Safety (UJV)
Diploma works (for a generic GFR demonstrator)
MOX core degradation study by MELCOR code (underway).
Goal: To get ideas about the progress and timing of a severe accident in ALLEGRO.
Mitigation measures for severe accident (underway).
Goal: To get ideas about a potential core catcher design for ALLEGRO.
Heat removal (& Ventilation) from the guard vessel (underway).
Goal: To get ideas, how to maintain the required temperature in the ALLEGRO GV
(keeping in mind the space limitations).
Performance of the DHR system (not yet assigned).
Goal: To get ideas about conditioning of the DHR loops in ALLEGRO.
Thesis
Removal of activity from primary helium (underway).
Goal: Methods & approximate sizing of the He purification system for ALLEGRO
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Next steps - Conclusions
GFR has a good potential between fast reactors
High T, good breeding, ... : Technology must be first tested before to judge.
CZ has an opportunity to obtain competence in development of GFRs
Is closed fuel cycle attractive in long-term for CZ ? Is it feasible ?
Is financing of ALLEGRO feasible through EU ?
CEA ceased the GFR financing and focuses on the SFR demonstrator ASTRID
New financing through V4G4 is under negotiation (EU)
Establishment of a legal frame within V4G4
IPR, background, foreground, responsibilities, duties, ... must be formulated.
The role of France/CEA must be clarified.
Who will develop & supply the MOX & ceramic fuel ?
V4 countries have not competences to develop & test Pu fuel.
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