Generation IV Reactors - Institute of Physics · Generation IV Reactors ... of nuclear-generated process heat ... – can only be served by the High Temperature gas-cooled Reactor,

Institute of Physics, University of Birmingham, 2 November 2016

Generation IV Reactors

Richard StainsbyNational Nuclear LaboratoryRecent Ex-Chair of the GFR System Steering Committe eEuratom member of the SFR System Steering Committee

Slide 2Institute of Physics, University of Birmingham, 2 N ovember 2016

What are Generation IV reactors ?


Objectives of Generation IV Reactors• SUSTAINABILITY

• To make better use of natural uranium• Continued avoidance of greenhouse gas emissions

from electricity generation• To displace fossil fuels from traditional process heat

markets• To minimise the volume and long-term radiotoxicity of

spent fuel wastes • ECONOMICAL• SAFE – to be as safe as, or safer than current Gen III+

reactors• PROLIFERATION RESISTANT


Motivation for Generation IV• SUSTAINABILITY

• Nuclear Power with today’s Gen II (and soonGen III/III+) reactor technology avoids significant greenhouse gas emissions from electricity generation

• Other than some application to desalination of seawater and district heating, no use has been made of nuclear-generated process heat

• All current Gen II/III reactors run on uranium (natural and enriched in U235)

• Uranium is a very finite resource (~100 years “conventional” U remaining)

• Plutonium extracted from spent fuel can be used as a fuel, but Gen II/III reactors make inefficient use of Pu.


• Natural uranium occurs with "fissile" and "fertile" isotopes:– A fissile isotope can undergo fission easily in the world’s power

(thermal) reactors to release energy.– A fertile isotope does not fission readily in a the rmal reactor, but some

of it is converted into a fissile isotope in reac tor.

• Only 0.72% of natural uranium is fissile (uranium-2 35):– 0.72% uranium-235– 0.0055% uranium-234– 99.2745% uranium-238

• Global reserves of natural uranium:– Known reserves, 7x10 6 tonnes– Speculative reserves, 10.4x10 6 tonnes

• Annual global consumption:– 2010, 64x103 tonnes/year for a 375 GWe global fleet

– 2035, 98x103 → 136x103 tonnes/year for a 540 → 746 GWe fleet

Some facts about natural uranium

5

(Source: 2011 OECD/NEA-IAEA "Red Book")


PWR fuel element (Mitsubishi Nuclear Fuel Co. Ltd)


Spent Fuel

Fresh Fuel20 kg of fissile material

9.3 kg of fissile material

Spent fuel is not so spent !


Open versus closed fuel cycles

Open fuel cycle

Closed fuel cycle


Minor Actinides (Transuranic elements)

• A small fraction of heavy elements are produced in the reactor through neutron captures in plutonium:

• Americium (Am)• Curium (Cm)

• Neptunium (Np)• Whilst a small fraction of waste these nuclides are very

significant radiologically:• Very radiotoxic + very long half lives

• At present minor actinides are disposed of along with spent fuel (no reprocessing) or along with the fission products (after reprocessing).


Uranium ore (mine)

Time (years)

Rel

ativ

e ra

dio

toxi

city

Spent fueldirect disposal

Pu +MA +FP

Plutonium recycling

MA +FP

P&T of MAFP

Benefit of removing Pu and minor actinides from HLW


Nuclear process heat – co -generation

•Lower temperature applications: e.g., seawater desalination, district

heating

– uses for waste heat so can be served by all reactors types

•Higher temperature applications: e.g., chemicals production, oil refining,

hydrogen production or advanced steelmaking.

– can only be served by the High Temperature gas-cooled Reactor, or HTR.


“New” technology is needed to make better use of natural uranium – better by two orders of magnitude

Reactor operating temperatures need to be increased dramatically compared with Gen II/III light water reactors to become a versatile source of process heat.


Basic elements of a reactor system

Fuel to undergo fission to generate neutrons and heat

Coolant to remove heat and to convert into

useful work

System to enable and

control fission reaction

System to confine radionuclides


Coated particle fuels

But we have a zoo of options !

Uranium fuel Metal fuelMetal fuel

Oxide fuelOxide fuelNitride fuelNitride fuel

Carbide fuel Plutonium-uranium fuelPlutonium-uranium fuel

Uranium-thorium fuel

Molten salt fuel

Metal clad fuelMetal clad fuelCeramic clad fuel

Graphite moderatorLight water moderator Heavy water moderator

Molten salt coolantAlkali liquid metal coolant

Heavy liquid metal coolant

Gas coolants

Light water coolant

No moderatorNo moderator

Plutonium-thorium fuel


Revision of Fission


… And the energy comes from …

• Source: hyperphysics.phy-astr.gsu.edu


Critical Fission Chain Reaction

n U235 U235 U235

n (absorbed without fission)

n (leakage)

n

n (leakage)

n

n

n

n

This reaction is termed a “critical” reaction because the number of fissions remains constant in each generation (multiplication factor k=1)

The neutrons liberated in a fission event can cause further fissions, provided they are not absorbed within or lost from the system


Avoiding resonance capture in U238

Thermal neutrons

Fast neutrons

Epithermal neutrons

Thermal reactors, e.g.,AGR, PWR

Fast reactors, e.g., SFR, LFR, GFR


Capture without fission in U238

n U235 U235 U235

n (leakage)

n n

n (leakage)

n

n

n U238

Np239 Pu239 U239

n (leakage) U238

Pu239

U235

β-

β-

23 min 2.3 days

2.3 days

2 β- 0.063 sec

Fissile Isotopes

Fertile Isotopes

Neutrons captured by U238 are not lost completely as they make Pu239, but they are lost from the immediate population that is needed to sustain fission.


Plutonium breeding reaction

U23892 + n1

0 → U23992

Starts with neutron capture in uranium-238

Uranium-239 has a half-life of 23 minutes and decays to neptunium-239 by beta decay

U23992 → Np239

93 + β- + ν

Np23993

→ Pu23994 + β- + ν

Neptunium-239 has a half life of 2.3 days and decays to plutonium 239 by a further beta decay


What are the ingredients of a self-sustaining closed fuel cycle ?

Three important commodities:– A stock of fissile material– A stock of fertile material– Excess neutrons

•Stock of fissile material– Dictates the size of the reactor fleet

•Stock of fertile material– Dictates how long the fleet can operate

•Excess neutrons– More than two neutrons from each fission event must

survive, i.e., avoid leakage and absorption in everything other than U238


Neutron yields per neutron captured in fissile nucl ides

• U233 yields the most neutrons in a thermal spectrum• Pu239 yields the most in a fast spectrum


How far can we go with breeding ?Scenario 1: LWR fleet• All reactors that contain uranium 238 will breed pl utonium:

• The measure of how good a reactor is at breeding is the “conversion ratio” (or exactly the same thing – the breeding rati o), CC = number of fissile items created / number of fis sile atoms consumedFor thermal reactors C < 1. For fast reactors C ≥ 1 (but can be < 1 if we

wish)

Start with N fissile atoms, after one irradiation w e get C×N fissile atoms.

Theoretically, after many recycles the total number of fissile atoms is:

NT = N + CN + C2N + C3N + C4N + ….

For C < 1, NT → N / (1 - C) , so for a LWR C ~ 0.5, so N T → 2 N

Conclusion – large-scale MOX recycle in LWRs results in very limited conservation of uranium - in practice degradation o f Pu vector means that only on recycle is feasible in a thermal react or.


How far can we go with breeding ?Scenario 2: Fast Reactor fleet

Using fast reactors we increase the amount of fissi le material available by a factor of up to 100

Because:

NT = N + CN + C2N + C3N + C4N + ….→∞ for C ≥ 1

In reality we are limited by the amount of uranium 238 that have …

But we still have enough fuel to last for about 4000 years !

…. and as much, or more, again in thorium reserves.

Pu vector does not degrade in fast reactors so we ca n recycle indefinitely (or as long as we have U-238 as a feedstock)


World energy reserves without fast reactors


World energy reserves with fast reactors



Making sense of the options in Gen IV





Molten salt fuel





Gas coolants

Light water coolant





VHTR SCWR MSR

Oxide fuelOxide fuel Uranium-thorium fuel

Molten salt fuelMetal clad fuelMetal clad fuel

Graphite moderatorLight water moderator

Heavy water moderator Molten salt coolantGas coolants Light water coolant

Plutonium-thorium fuelPlutonium-uranium fuelPlutonium-uranium fuel

Oxide fuelOxide fuel

Uranium fuel

Graphite moderator

Uranium fuel

CorePrismatic graphite rodsWith TRISO particles

Hot duct

Concentriccold duct

Shut-downrecirculator and IHX

Gas turbine

The Gen IV Thermal Reactors







Molten salt fuel





Gas coolants

Light water coolant



Making sense of the options in Gen IV


SFR GFR LFR

Nitride fuelNitride fuel

Carbide fuelPlutonium-uranium fuelPlutonium-uranium fuel


Molten salt fuel

Metal clad fuelMetal clad fuel

Ceramic clad fuel

Molten salt coolant




Gas coolants

Plutonium-uranium fuelPlutonium-uranium fuel



Metal fuelMetal fuel

Nitride fuelNitride fuel

Metal clad fuelMetal clad fuel

Alkali liquid metal coolant

Plutonium-uranium fuelPlutonium-uranium fuel




MSFR

The Gen IV Fast Reactors


Generation IV – Proposed systems• 3 Fast Reactors

–Sodium Cooled Fast Reactor (SFR)–Lead Cooled Fast Reactor (LFR)–Gas Cooled Fast Reactor (GFR)

• 3 other systems ( thermal, epithermal )–Molten Salt Reactor (MSR)

(Epithermal) –Supercritical Water Reactor (SCWR)

(Thermal or possibly fast)–Very High Temperature Reactor

(VHTR) (Thermal)

• Fast spectrum versions of the MSR and the SCWR have been proposed since the publication of the roadmap


Sodium -cooled fast reactor (SFR)


Superphenix – Creys -Malville , France

Images courtesy of NERSA


Superphenix core map

Image courtesy of NERSA


Current SFR demonstrator concepts

ASTRID – Pool type - France JSFR – Loop type - J apan

Secondary pump

Steam generator

Reactor Vessel

Combined pumpand IHX


UK fast reactors• Dounreay Fast Reactor (DFR) – metal fuel, highly enri ched U235/U238

fuel, sodium-potassium eutectic liquid metal coolan t, 72MWth (1959-1977).

• Prototype fast reactor (PFR), also at Dounreay – mixe d oxide fuel, Pu/U238, sodium liquid metal coolant, 600MWth (1974 -1994).

� Both now shut down and partially decommissioned.

� Developed the Commercial Demonstration Fast Reactor (CDFR) – 1970’s and 80’s

� UK was an equal major partner in the development of the European Fast Reactor, EFR, (with France and Germany) 1988-1998


Gas-cooled fast reactor (GFR)


Generation IV GFR - Summary

• Helium coolant • Fast neutron spectrum• High outlet temperature• Back-up for SFR+ Transparent coolant+ High temperature/efficiency+ Strong Doppler effect+ Weak void effect+ Chemically and neutronically inert coolant+ Zero activation cooant- Decay heat removal (LOCA)

- High power density- Low thermal inertia

- High coolant pumping power

• Thermal power 2400 MWth

• Coolant in/out 400°C/850°C

• System pressure 70 bar


GFR fuel – initial composite concept

• A reference GFR core considered by CEA.

• Cylindrical core filled with hexagonal subassemblies, containing a triangular pitch rod array.

• Fuel : (U,Pu)C

• Cladding : SiC/SiCf with an internal metallic liner for leak tightness to prevent fission gas release to coolant)


Gas Cooled Fast Reactors: Fuel Element


The lead-cooled fast reactor (LFR)

41


Gen IV LFR reference concepts

CLOSURE HEAD

CO 2 INLET NOZZLE

(1 OF 4)

CO2 OUTLET NOZZLE

(1 OF 8)

Pb-TO-CO2 HEAT EXCHANGER (1 OF 4)

ACTIVE CORE AND FISSION GAS PLENUM

RADIAL REFLECTOR

FLOW DISTRIBUTOR HEAD

FLOW SHROUDGUARD VESSEL

REACTOR VESSEL

CONTROL ROD DRIVES

CONTROL

ROD GUIDE TUBES AND DRIVELINES

THERMAL BAFFLE

Small transportable system(SSTAR) (10 - 100 MWe)

Evolutionary changesmay include

Forced coolingOxide fuelSteam cycle

ELSY (600 MWe)

ELFRHexagonal Wrapped FasFAs extended to cover gas from lower support

Generation IV Nuclear Energy System for the Lead-cooled Fast Reactor

Preparing Today for Tomorrow’s Energy Needs

Revised on 18 October, 2010

Slide courtesy of Alex Alemberti, Ansaldo42

Slide 43Institute of Physics, University of Birmingham, 2 N ovember 2016 43

Molten Salt (thermal) Reactor (MSR)

• ORIGINAL GenIV concept uses an epithermal neutron spectrum.

• The fuel is a liquid and the fuel is also the primary coolant.

Slide 44Institute of Physics, University of Birmingham, 2 N ovember 2016 44

MSFR – Closed On -Site Fuel Cycle(Equilibrium Conditions)

U238 or Th232

Fission products + U + Pu + minor actinides (Am, Np, Cm)

On-site reprocessing

plant

Fission products

U + Pu + minor actinides

Molten Salt Reactor


The MSFR can maintain a sustainable breeding reaction with thorium

Image courtesy of H Boussier (CEA)45


Molten Salt Fast Reactor (MSFR)

46


Conclusions• The case made for the development of Fast Reactors made in the

1940’s and 1950’s is still relevant today.• There is a tendency to base decisions about the lon g term

development of fast reactors and closed fuel cycles on the spot price of uranium at the time the decision is taken.– Spot prices of commodities just reflect demand at t hat time and do

not necessarily reflect the scarcity of the resourc e.• Majority of systems being considered in Generation IV are fast

reactors (or have fast spectrum variants)• Without fast reactors, nuclear fission will have a lifespan of only

about 100-200 years. • With fast reactors we can generate thousands of yea rs of electricity

(and other energy forms) using a small refinement o f 1970’s technology.

• Even if the fuel supply arguments are discounted, f ast reactorss offer an effective means to manage the build up of spent fuel from Gen II/III plants and to manage Pu stockpiles

Documents

Generation IV Reactors - Institute of Physics · Generation IV Reactors ... of nuclear-generated process heat ... – can only be served by the High Temperature gas-cooled Reactor,