Ian Scott

The Simple Molten Salt

Reactor

Ian R. Scott M.A., Ph.D

John Durham

Moltex Energy LLP

Practical, safe and cheap

WHERE IS ELECTRICITY

GOING TO COME FROM?

US EIA forecast 2012 1000’S TERAWATT HOURS

COSTS OF ENERGY

US EIA (2013) LEVELISED COSTS 2018

(COST OF CARBON EMISSIONS STRIPPED OUT)

0

1000

2000

3000

4000

5000

6000

1971 1978 1988 2004 2008 2011

Cost

$ per KW

NUCLEAR PLANT CAPITAL

COSTS (USA constant 2008 $)

H

I

N

K

L

E

Y

C

US EIA (2013) Updated capital cost estimates for

utility scale electricity generating plants

2012 Dual unit pulverised coal (no CCS)

MAJOR NUCLEAR COST FACTORS

Control of excess reactivity

Failsafe multiply redundant systems

Large volatile fission product inventory

Failsafe emergency fuel cooling

Multilevel expensive containment systems

High pressures in reactor core

Specialised forgings, expensive construction

On site construction

GEN III+/IV NUCLEAR OPTIONS NO EXCESS

REACTIVITY

FEW

VOLATILE

FISSION

PRODUCTS

LOW

PRESSURE

OPERATION

MOSTLY

FACTORY

MADE

SMALL

MODULAR PWR GAS COOLED

FAST REACTOR LEAD COOLED

FAST REACTOR MOLTEN SALT

FAST REACTOR SODIUM COOLED

FAST REACTOR SUPERCRITICAL

WATER COOLED

REACTOR

VERY HIGH TEMP

FAST REACTOR ()

HISTORY OF MOLTEN SALT

REACTORS

Aircraft reactor experiment

1954

Molten salt reactor

Experiment 1964

Gen IV reactor

2070?

ALL PUMP MOLTEN FUEL SALT THROUGH CRITICAL

REACTION CHAMBER TO A HEAT EXCHANGER

PROBLEMS WITH PUMPING

THE FUEL SALT

Pumps and heat exchangers – novel materials needed to resist corrosion

Low M. Pt. requires very expensive 99.995% pure 7Li

Fission products in fuel salt corrode and clog Need for helium sparging and foam separators

Need for continuous/batchwise chemical reprocessing

Need for continous monitoring and adjustment of salt chemistry

Rapid failsafe emergency fuel draining system

Systems to prevent/manage fuel salt freezing

CAPITAL COST UNLIKELY TO BE LESS THAN A PWR

HISTORY OF MOLTEN SALT

REACTORS

1954 1964 2070 1950

Low thermal conductivity of molten salts would

result in boiling in tubes over 2mm diameter

CONVECTION IN MOLTEN

SALT FUEL TUBES CFD using Ansys mesher and Fluent simulator by

Wilde Analysis Ltd

Temp dependent fuel salt properties 30% UCl3 /NaCl

Vertical neutron flux based on EVOL reactor

Molten salt coolant outside tube ~ 200°C temp. rise

Salt boiling pt.

SIMPLE MOLTEN SALT

REACTOR Fuel tubes

Coolant salt Fissile fuel salt

Steam

Water

Boiler tubes Neutron reflector

Turbines

CURRENT DESIGN OUTLINE MOLYBDENUM FUEL TUBES

Used in crucibles to 2000°C

Thermodynamically resistant to molten salts

Lower neutron damage than nickel or carbon

Practical to manufacture, no new materials

NICKEL SUPERALLOY BOILER TUBES

Low corrosion in molten salt up to 750°C

Already used in coal fired boilers

Excellent manufacturability

COOLANT SALT

10% NaF/48% KF/42% ZrF4

Melting Pt 385°C, Boiling Pt ~ 1150°C

Viscosity 0.47 cP

Hafnium content in Zirconium shields neutrons

Low cost (<£5 million)

FUEL SALT

~80% UCl3/20% reactor grade PuCl3

Melting point ~750°C, Boiling Pt ~1700°C ~2% (UCl4/AlCl3/ZrCl4 (Vapour M. Pt. <600°C)

High delayed neutron fraction – 238U fission

Viscosity 2-3 cP

REACTOR CONTROL

CONTROL BY FUEL HEATING NOT NEUTRON ABSORBERS

No excess reactivity, high negative temp coefficient of reactivity

Loss of cooling (accident or design) heats fuel to sub-criticality

Start up by external heating of coolant then controlled cooling

Shut down by allowing decay heat to heat salt to sub-critical condition

REQUIRED SECONDARY CRITICALITY CONTROL

Dump europium fluoride into coolant – fast neutron poison

MANAGING FISSION PRODUCTS

UCl3 traps iodine so only volatiles are noble gasses

Perforate fuel tubes at level of reactor gas phase

Noble metals plate out on inside of tubes

Other metals and lanthanides form miscible chlorides

Se/Te form complex chlorides or chalconides

Net chlorine release from fission neutralised by UCl3→UCl4

FILTER

CRITICALITY REQUIREMENT

Molybdenum, chlorine, zirconium, hafnium all capture neutrons

2.5m diameter core with 2293 fuel tubes @45mm diameter

Initial Monte Carlo simulation* indicates ~12% 239Pu needed

5 tonne transuranics from spent fuel (3 tonne 239Pu)

*Tim Abram and James Buckley – Univ Manchester

REFUELLING

Fissile consumption @1500MWth~15% per annum, no initial excess reactivity

In situ 239Pu breeding ~0.75 so net loss of fissile material ~ 4% p.a.

Fuel tube array design to flatten power density across core

Dummy fuel tubes towards centre of array (~20% of total) replaceable

with filled fuel tubes

Start with higher fissile conc in peripheral tubes and migrate to centre

Allow loss of power to increase reactivity

Small temp fall → large reactivity increase (Doppler + fuel contraction)

CFD shows 100°C avg temp drop only lowers power output by ~15%

CLOSING THE FUEL CYCLE

Low fuel purity acceptable

No manufacturing tolerances (unlike oxide fuel)

Fast reactor so tolerant of fission waste poisons

Chloride based, lanthanides/Pu freely soluble

Simple, low cost electrolytic pyro-processing?

SIMPLE MSR ADVANTAGES

Engineering simplicity,

replaceable components,

factory manufacture

Passive safety due to

pool structure - fuel tube

damage or coolant loss

Low cost, simple

reprocessing of PWR

waste and SMSR fuel

Intrinsic criticality safety

no excess reactivity and

high thermal expansion

Intrinsic disaster safety

due to minimal volatile

radioactivity

Self shielding - only fuel

tubes experience highest

neutron flux

Chemical reprocessing

only of spent fuel tubes

No fuel salt chemistry

adjustment as UCl3

maintains low redox

0

1000

2000

3000

4000

5000

6000

1971 1978 1988 2004 2008 2011

Cost

$ per KW

NUCLEAR PLANT CAPITAL

COSTS (USA constant 2008 $)

US EIA (2013) Updated capital cost estimates for

utility scale electricity generating plants

2012 Dual unit pulverised coal