the mutual influence of materials and thermal … of nuclear technology and energy systems the...

Institute of Nuclear Technology

and Energy Systems

The Mutual Influence

of Materials and

Thermal-hydraulics

on Design of SCWR –

Review of Results of

the Project HPLWR

Phase 2

J. Starflinger,

T. Schulenberg

• Design Target Data:

• Operational pressure: 25 MPa

• Core mass flow: 1160 kg/s

• Power output: 1000 MWe

• Constraints:

• Average core exit temp.: 500°C

• Max. cladding surface temp.: 625°C

• Max. linear heat rate: 39 kW/m

10/10/2016

University of Stuttgart – Institute of Nuclear Technology and Energy Systems (IKE)

IAEA - Technical Meeting on Materials and Chemistry for Supercritical Water Cooled Reactors 2

5th Framework Programme of the EU

HPLWR – High Performance Light Water Reactor

AREVA NP, 2005

• „Hot Channel“ by definition is the channel, in which all uncertainties, non-

homogeneities and allowances sum up, leading to the highest enthalpy

rise of the entire core under normal operation conditions!

• Very conservative, provides a very high safety margin

10/10/2016



Definition

„Hot Channel“ Form Factor Analysis of the Core

av

av

h

h

h

hF

max

max

Maximum enthalpy rise in the „Hot Channel“

Average enthalpy rise in the core

10/10/2016



Design Targets of Hot Channel Factors

2.01.6Total

Power control, flow control, pressure control, inlet

temperature control

1.15Allowances

Material properties of coolant and claddings,

physical modelling, hydraulic modelling, heat

transfer coefficient, geometry tolerances

1.2Uncertainties

1.6Axial power factor

1.15Local peaking

factor inside FA

1.25Radial peaking

factor

Fuel enrichment and distribution, water density

distribution, reflector design and properties, fuel

and control rod pattern, burn-up, burnable

poisons, …

Form factors for

power profiles

Key ParametersradialaxialHot Channel Factor

2.01.6Total

Power control, flow control, pressure control, inlet

temperature control

1.15Allowances

Material properties of coolant and claddings,

physical modelling, hydraulic modelling, heat

transfer coefficient, geometry tolerances

1.2Uncertainties

1.6Axial power factor

1.15Local peaking

factor inside FA

1.25Radial peaking

factor

Fuel enrichment and distribution, water density

distribution, reflector design and properties, fuel

and control rod pattern, burn-up, burnable

poisons, …

Form factors for

power profiles

Key ParametersradialaxialHot Channel Factor

Schulenberg, KIT, 2010

10/10/2016



One-Pass Core


• Designed for

500°C core

outlet

temperature

• Coolant

average

conditions

Heinecke, AREVA, 2010

Average

10/10/2016



One-Pass Core


• Hot fuel

assembly

(∙ 1.25)


Average

+ Assembly Power

10/10/2016



One-Pass Core


• Hot rod

(∙ 1.25

∙ 1.15

= 1.44 )


Average

+ Assembly Power

+ Rod Power

10/10/2016



One-Pass Core


• Hot rod +

uncertainty

(∙ 1.25

∙ 1.15

∙ 1.2

= 1.73 )

Average

+ Assembly Power

+ Rod Power

+ Uncertainty

10/10/2016



One-Pass Core



• Hot rod + uncertainty + operation (∙ 1.25 ∙ 1.15 ∙ 1.2 ∙ 1.15 = 1.98 )

• Coolant temperature ≈ 1200°C

• Cladding surface temperature > 1200°C

Average

+ Assembly Power

+ Rod Power

+ Uncertainty

+ Operation

• Simple „Hot-Channel“ analysis revealed the unfeasibility of single-pass

core design. No material available.

• Idea from T. Schulenberg, KIT:

Propose a “Three-pass core” with intermediate mixing in special mixing

chambers.

• One key-issue of a feasible core design is mixing!

• not to overheat the cladding surface temperature

• avoid hot streaks from one assembly to another and hot-spots on the

cladding surface

10/10/2016



Consequences


10/10/2016



Three Pass Core Design Proposal for a HPLWR

1000

1500

2000

2500

3000

3500

4000

Evaporator Superheater 1 Superheater 2

En

tha

lpy

[k

J/k

g]

hot channel

average

Strategy to overcome hot-channel issue: Heat-up in steps with Intermediate mixing of the coolant

Mixing

Mixing

Schulenberg, 2006

4 : 2 : 1

Power ratio of the core zones

10/10/2016



Three Pass Core Design Proposal for a HPLWR

200

250

300

350

400

450

500

550

600

650

Evaporator Superheater 1 Superheater 2T

em

pe

ratu

res

[°C

]

cladding

hot channel

average

Schulenberg, 2006

• A 3-Pass coolant flow in the core allows 500°C average core exit

temperature with 625°C cladding temperature

22/8//2016


IAEA - Technical Meeting on Heat transfer, Thermal-hydraulics, System Design for SCWR 14

Core Arrangement

Evaporator:

52 Clusters

Upward Flow

Superheater 1:

52 Clusters

Downward Flow

Superheater 2:

52 Clusters,

Upward Flow

Köhly, 2010

Downcomer flow

(50%)

Moderator flow

(50%)

Inlet flow:

280°C

25 MPa

1179 kg/s

Core flow

(100%)

Upper dome

Downcomer

Area


IAEA - Technical Meeting on Heat transfer, Thermal-hydraulics, System Design for SCWR

HPLWR Flow Path

3/11/2016 15

Köhly, 2010

• Analyze the core, whether the power peaking factors will be met

• Neutronics:

• Simulate neutronics (BOC, EOC) for core and assembly-wise power

distribution (input from materials and TH needed)

• Thermal-hydraulics:

• Suitable heat transfer correlation with an uncertainty of less than 25%,

especially for fuel rod bundles with wire wraps as spacers.

• Materials & Water Chemistry

• Identify suitable materials for thick wall and thin wall components,

especially for cladding.

10/10/2016



Tasks for the HPLWR Partners

Design Support

• Partners:

VTT, Finland, NRI Czech Republic, CEA, France, EKI, Hungary, JRC-IE,

Petten (supporting)

• Test of 16 materials in autoclaves at different temperatures

• Investigation of general corrosion, stress-corrosion cracking and creep

• Special focus on thin wall materials

10/10/2016



Materials

• 40 fuel pins with 8mm diameter

• cladding thickness 0.5 mm

• wire wraps as grid spacers

• wire diameter 1.34 mm

• assembly box with 3 mm

thickness incl. thermal insulation

• moderator box with 2 mm

thickness incl. thermal insulation

• Insulation material: ZrO2

10/10/2016



Details of the Assembly Design Concept

Moderator

box

Assembly

box

Wire

wrap

spacers

Himmel, Köhly 2008

10/10/2016



Local Temperature Distribution

Fuel Rods with Wire Wrap Spacers

Temperature [°C]

670

590

510

470

390

310

bare rod with wire

Temperatures > 670°C

• Bending (stresses, torque)

• Hot streaks (local corrosion) Lycklama, 2009

10/10/2016



General Corrosion Results

Materials

400°C

500°C

650°C

650°C, HWC

Sample Holder,

VTT

Heikinheimo, 2009

• Alloy 316L tube samples after 1000 h exposure under SCW conditions at

650oC:

10/10/2016



Strong impact of cold work on corrosion

Effect of Surface Treatment

“as received”

surface finish

with #1200

emery paper

surface finish

with #600

emery paper

Machined with blunt

edge hard metal

cutting tool Heikinheimo, 2009

10/10/2016



Influence of high Cr content on oxidation

Materials

after 600h at 650°C

0,1

1

10

100

1000

0 5 10 15 20 25

Cr(%)

Ox

ide

Th

ick

ne

ss

(m

m)

P91

P92

ODS (FZK)

ODS (EU)

PM2000

316NG

1.4970

BGA4

800H

IN 625

Data from VTT, JRC,

UJV Rez

• Oxide thickness on AISI 316NG vs. exposure time after exposure to

supercritical water at 650°C.

10/10/2016



Extrapolation of oxide thickness

Materials

50% cladding

thickness

10% cladding

thickness

Toivonen, Pentillä, 2009

10/10/2016



Initial temperature distribution

Deformation Analysis of the Box

Inlet:

286°C Outlet:

518°C

3 mm stainless

steel plate filled

with ZrO2

Reis, 2008

10/10/2016



Deformation Analysis of the Box

Max. deflection 4 mm

(high strain)

High stress

@ high temperatures

Reis, 2008

10/10/2016



at 500°C

Stress-strain curves

High yield

strength

(good for

designers)

Toivonen, 2010

10/10/2016



at 650°C

Stress-strain curves

Reduced

yield

strength

(concern for

designers)

Toivonen, 2010

Stress-Corrosion cracking

10/10/2016



Alloy Maximum

stress (MPa)

Strain to

failure (%)

TGSCC

(y/n)

IGSCC

(y/n)

Side cracks at the

gauge surface (y/n)

347H

@ 500°C

465 45 No

No Yes, morphology not

identified

347H

@ 650°C

NA NA NA NA NA

316NG

@ 500°C

Interrupted at

330

Interrupted

at 33

NA NA Yes, IG and TG

316NG

@ 650 °C

195 38 Yes Yes No

1.4970

@ 500°C

675 26 No No Yes, morphology not

identified

Toivonen, 2010

Stress-Corrosion cracking (cont‘d)

10/10/2016



Alloy Maximum

stress (MPa)

Strain to

failure (%)

TGSCC

(y/n)

IGSCC

(y/n)

Side cracks at the

gauge surface (y/n)

1.4970

@ 650°C

360 28 Badly

oxidized

Badly

oxidized

Yes, morphology

not identified

BGA4

@ 500°C

425 41 Yes Yes Yes, IG

BGA4

@ 650°C

NA NA NA NA NA

PM2000

@ 500°C

325 Interrupted

at 50

No

No No

PM2000 #8

@ 650°C

100 40 No No No

Toivonen, 2010

• Design rules for high temperature applications

• Creep strength

• Rupture

• Tensile yield strength

@ 1% strain

10/10/2016



From the designers point of view…

Creep

1.4970 (650°C, 250MPa)

SCW: 25 MPa, 100 ppb

O2, deionized water

k<0,1µS/cm (inlet), water

flow rate 2-3 ml/min

Gas: Helium Toivonen, 2010

• SCW environment increases strain rate compared to He environment for

316NG and 347H (short duration tests, usually > 1000 hrs)

• Strong impact on

design expected!

10/10/2016



SCW vs. He-atmosphere

Creep

• SCW environment increases strain rate compared to He environment for

316NG and 347H (short duration tests, usually > 1000 hrs)

• Strong impact on

design expected!

10/10/2016



SCW vs. He-atmosphere

Creep

The reasons for the increased primary

strain rate:

“Give me more money and I will find out why ”

10/10/2016



Thick walled component

Example from Stress Analysis

• Design pressure: 28.75 MPa

• Design temperature: 280 to 500 °C

• Material: 1.4970

• Wall thickness

• Core base plate: 0.300 m

• Bottom plate: 0.050 m

• Separation wall: 0.020 m

• Outer wall: 0.025 m

• Weight: 24.9 t

• 3-D 10-Node Tetrahedral structural + thermal solids:

• 215131 nodes

• 118591 elements

10/10/2016



Thick walled component

Example from Stress Analysis

• Max.: 0.7 mm

10/10/2016



Results: Deformation (cold state)

10/10/2016



Results: Mises stress distribution (cold state)

• Max.: 54 MPa

10/10/2016



Results: Temperature distribution (operational/steady state)

433°C

309°C

• Max.: 12.5 mm

10/10/2016



Results: Deformation (operational/steady state)

• Max.: 603 MPa

10/10/2016



Results: Mises stress distribution (operational/steady state)

• Max.: 603 MPa

10/10/2016



Results: Mises stress distribution (operational/steady state)

Allowed stress peaks: s < 2 x Rp0,2

1.4970: YS (600°C) = 350 N/mm² => 700 N/mm²

Calculated values: 603 N/mm² => below 700 N/mm² => ok!

Materials, thermal hydraulics have a strong mutual interaction on design of

SCWR.

Thick walled components operating at max. 500°C

• No major structural problems with respect to corrosion (fossil plant

technology).

Thin walled components operating at max. 500°C:

• Corrosion problems to be avoided (high Cr steels ?)

at above 600°C:

• High corrosion rate with licensed low Ni alloys (especially fuel cladding)

• High impact on core design! Redesign necessary if no suitable

materials will be found.

10/10/2016



Main findings

Summary

• Closer collaboration between the scientific fields should be established:

• Theory of McElligott and Laurien: Surface roughness plays a role in heat

transfer (disturbing boundary layers)

• Wire wrap helpful to homogenize the surface temperature. However, hot

streaks are visible (also close to the wire) -> Local oxidation?

• Neutronic aspects must be taken into account

• Water chemistry may decide, whether to build a BWR or a PWR-type

SCWR

• In-pile experiments are the next step for SCWR materials selection!

• (for heat transfer: bundle experiments to be performed)

10/10/2016



Some personal thoughts

Conclusions

Thank you!

e-mail

phone +49 (0) 711 685-

fax +49 (0) 711 685-

Universität Stuttgart

Pfaffenwaldring 31 • 70569 Stuttgart • Germany

Prof. Dr.-Ing. Jörg Starflinger

62116

62008

Institute of Nuclear Technology and Energy Systems

[email protected]

Institute of Nuclear Technology

and Energy Systems

the mutual influence of materials and thermal … of nuclear technology and energy systems the...

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