Institute of Nuclear Technologyand Energy Systems

Experimental and Analytical Investigation of the Performance of Heat Pipes for Residual Heat Removal from Spent Fuel PoolsJ. Starflinger, C. Graß, R. Kulenovic, A. Schaffrath, M. Pöhlmann, T. Fuchs

Annual Meeting on Nuclear Technology, Hamburg, May 10-12, 2016

• Loss of ultimate heat sink,

• Station blackout,

• Loss of infrastructure

• Loss of human ability to deal with the catastrophe beyond personal experience

• The second principle of reactor safety „cooling of nuclear fuel“ must be assured even under severe accident conditions

also for wet storage pools, preferably with passive devices!

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 2

MotivationFukushima Follow-up

Source: Tepco

• Active Cooling• Two strands of the emergency and residual heat removal system (TH)• Active components (pumps, valves, etc.)• Servicing, maintenance, periodic inspection• Time and cost-intensive, particularly in the long-term use!

• Passive Cooling• No active components, control system or operator intervention• Based upon physical principles (buoyancy, etc.)• IAEA Category B of passivity can be reached• Lower failure probability, advantages in operating costs,

particularly in long-term use !

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 3

Active vs. Passive CoolingSpent Fuel Pool Cooling

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 4

Principle of OperationHeat Pipes – Passive Heat Removal Device

heat input

vapour

liquid

evaporation condensation

capillary structure

heat output

evaporator zone adiabatic zone condenser zone

Heat Pipe (with capillary structure)

Thermosiphon(without capillary structure)

• Copper heat pipe (filled with water) and full metal copper rod tug in a glass bowl

• Warm water spilled into the bowl

• Heat transfer through the heat pipe almost instantaneously.

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 5

Demonstration of OperationHeat Pipe

Video: C. Graß, W. Flaig, IKE

Copper Rod Heat Pipe

Glas Bowl

• Selection of working fluid results from the operational temperature range

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 6

Working FluidsHeat Pipes – Passive Heat Removal System

NaLi

Ag

KCs

NH3

C3H8

CH4

H2

Hg

H2OCH4O

C2H6

N2

Freon

Diphenyl, Toluol

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 7

Application for Sensor Cooling (≈1100°C environment temperature)Heat Pipes

Cooling

Heat Pipe

Insulation

Heating

Heat Pipe Test Lab. at IKE

http://www.zim-bmwi.de/erfolgsbeispiele

Sensor-cooling with heat pipes

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 8

Large-Scale Application: Heat ExchangerHeat Pipes

http://www.econotherm.eu/downloads/gas_to_air.pdf

375 Heat PipesHigh redundancy!

measures (estimated): 1500 x 1500 x 3000mm

Cold combustion air

Preheatedcombustion air

Hot exhaust gas

Cooledexhaust gas

Heat pipe heat exchanger

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 9

Master-Thesis by M. Eng. C. GraßPassive Heat Removal System for Generic Spent Fuel Pools

Spent Fuel Pool

Bundles ofHeat Pipes

Air

Air• Passive heat removal from

spent fuel pool to air driven by natural convection

• Heat pipes suspended from the top, no penetrations of pool walls

• Heat pipes will have at least two elbows

• Develop a numerical tool for steady state heat removal calculation from a wet storage pool to the air by means of heat pipes / thermosiphons

• Selection of the appropriate working fluid

• Simulation of operation performance

• Identify open points

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 10

Objectives

• Pool temperatures provided by KTA:

• Coarse geometrical and power data taken from spent fuel storage pool in NPP Gösgen, Switzerland „Masterpiece“

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 11

Boundary Conditions

Operation Conditions

Heat Source / °C

Heat Sink / °C

Driving Force (Temperature difference) / °C

Normal 45 26 19

Abnormal 60 28 32

Accident 80 32 48

• Heat balance between pool and atmosphere

• Chain of iteration loops for the system temperatures along the heat transfer from source to sink

• Equations according to VDI-Wärmeatlas, Section MI, and open literature

• Examination of the performance limits and the modelled performance of the heat pipe

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 12

Steady State Heat BalanceNumerical Iteration Scheme

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 13

Selection of Working Fluid - Figure of MeritHeat Pipes

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 14

Selection of Working Fluid - Figure of MeritThermosiphons

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 15

Example: Results for 40mm pipeSteady State Heat Removal

• Compared to heat pipes, power transferred is higher for thermosiphons because of less friction

≈ 20% difference

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 16

Operation Limits of Heat Pipes / Thermosiphons

• Counter Current Flow Limitation (CCFL) in the order of 4 – 6 kW

• Both heat pipes and thermosiphons have performance margins up to a factor of four.

Example: Results for 40mm pipe

• Feasibility: Heat pipes / thermosiphons are suitable to transfer decay heat from wet storage facilities into the diverse ultimate heat sink (air)

• Dimensions: Length at least 12m (construction reasons)

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 17

Summary of Results

Condenser Zone

Evaporator zone

Adiabatic zone

Inclination

> 1 m

> 6 m

> 5 m

• Support of Gravity: Heat pipes shall be manufactured as thermosiphons without capillary structure. Inclination of adiabatic section >5°.

• Conservatism: With increasing temperature difference, more heat is transported through the heat pipes.

• Heat Transfer Limit: Air side (condensation zone of heat pipe) Measures necessary (e.g. fins, chimney effect).

• Open points:

• Long heat pipes with elbows. High pressure loss? There are no validation data available for long heat pipes.

• In ATHLET (or other system codes) there is no validated modelavailable of heat pipes.

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 18

Summary of Results

• Three year project, start: Dec. 1, 2015

• Funded by BMWi (FKZ 1501515 and RS 1543)

• Scope: • Experiments in laboratory and in realistic environment providing

validation data• Derivation of a correlation for long heat pipes, based upon

experimental laboratory data • Set-up and validation of a mechanistic model of heat pipes in ATHLET• Benchmark of wet storage pool cooling (mechanistic model vs.

correlation)

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 19

Cooperation between GRS and IKE (and AREVA)Project PALAWERO / Heat Pipes

• Planned single heat pipe experiments: • Pipes straight up (base case)• Pipes with two elbows and

different inclination• Different diameters• Different working fluids• With and without capillary

structures

• Validation data base with well defined boundary conditions!

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 20

Laboratory experimentProject PALAWERO / Heat Pipes

4 m

8 m

Water pool (heated)

Water pool (heated)

IKE laboratory hall

Cooling through cryostat

Basement

Ground floor

Roof

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 21

Experiment under realistic environmental boundary conditionsProject PALAWERO / Heat Pipes

IKE and GRS like to thank the Federal Ministry of Economic Affairs and Energy for supporting the projects PALAWERO / Heat Pipes (FKZ 1501515 and RS 1543)

12/5/2016University of Stuttgart – Institute of Nuclear Technology and Energy Systems 22

Acknowledgements

Thank you!

e-mailphone +49 (0) 711 685-fax +49 (0) 711 685-

University of Stuttgart

Pfaffenwaldring 31 • 70569 Stuttgart • Germany

Prof. Dr.-Ing. Jörg Starflinger

6211662008

Institute of Nuclear Technology and Energy Systems (IKE)

joerg.starflinger@ike.uni-stuttgart.de

Institute of Nuclear Technologyand Energy Systems