Reliability and long term behaviour of novel accident ...

Reliability and long term behaviour of novel accident level measurement devices in simulated fuel pool environment

S. Berger1, R. Kilian1, S. Estevez Hernandez1, G. Hasse2

1AREVA GmbH, Germany 2EPCM Global Engineering (Pty) Ltd, South-Africa Ottawa, August 12th 2015

Reliability and long term behaviour of novel ALM –Devices - 17th EnvDeg - S. Berger - 12/08/2015 - AREVA GmbH Proprietary - RESTRICTED AREVA – © AREVA - AL: N - ECCN: N - p..2

All rights are reserved, see liability notice.

Background (1/2) Accident Proof Level Measurement (ALM) devices shall be capable to measure water levels during normal operation as well as during and after a covered accident. ALM-Systems for pressurized water reactors such as the AREVA EPRTM (European Pressurized Reactor) require high robustness and reliability For the EPRTM reactor such systems are used in the:

Fuel Pool

In containment Refuelling Water Storage Tank (IRWST)

Containment Flooding Valve

Heat Removal and Safeguard Pump Sumps

Venturi Vessel

ALM-Requirements:



Novel Accident Proof Level Measurement (ALM) device based on the magnetic switching technology (Reed-switches).

The specific design features:

Floater Guide Tube Unit (FGTU) Magnetic Floater Unit (MFU) these systems were assumed to be sensitive to boric acid crystallization caused locking (blockage) in the annular clearance* between the MFU and the FGTU

Background (2/2)

Top-view (section)

MFU Systematic test program using original components to target the influence of boric acid crystallization

*: ID(FGTU) = 53,9 mm; OD(MFU) = 45 mm, annular clearance ~ 4,45 mm (8,9 – 0 mm)



Experimental (1/3) Components & Materials

Magnetic Floater Unit/Floater Guide Tube (MFU/FGTU) assemblies used Original MFUs made from titanium

Two different types (materials) of FGTUs* are used:

Original FGTUs (stainless steel) German Material 1.4550 (similar to type 347)

Acrylic glass (PMMA) FGTUs for in-situ investigations of H3BO3 crystallization

Surface conditions tested:

MFUs: current design (as received)

mechanically polished

FGTUs: current design (as received)

electropolished (only outside surface)

*: The overall length of the FGTUs is adjusted to 400 mm to fit the climate chamber



Experimental (2/3) Test Setup (3500 ppm B)

Parameters

Parameter Set value Comment Recording interval

Test duration 3 months Start:17.07.2012 End: 15.10.2012

Not applicable

Ambient humidity

~ 52 % RH (40 % RH*

) Climate chamber Continuous

Ambient temperature

24.5 °C Climate chamber Continuous

Water temperature

30 °C Thermocouple Continuous

Initial Water level

250 mm

In the course of the test the level was controlled

decreased at 1 mm/2 days

Daily

Boron-concentration

Basin 1 3500 ppm Accelerated conditions Weekly

Basin 2 1750 ppm Realistic conditions

Surface quality MFU/FGT

U

MFU: current design, mechanically polished

FGTUs: current design, electro-polished (only

outside)

Not applicable

*: 40 % RH was initially chosen according to specifications. However, this value could not be achieved (see 3.1).



Experimental (3/3) Test Setup

Basin 1

Basin 2



Results

Humidity and Temperature (Climate Chamber)C Evaporation Rate

Highly stable and reproducible environmental conditions

Evaporation rate Basin 1 < Basin 2 (influence of dissolved species)



Results

Boron Concentration Humidity and Temperature

(SS FGTU)

TWater = 30 °C

Highly stable and reproducible environmental conditions

Humidity inside SS FGTUs < Humidity in the Climate Chamber



Results: MFUs MFU in PMMA FGTU (in situ)

MFU in SS FGTU (post test)

No significant H3BO3-Crystal growth on any of the MFUs observed

MFU in PMMA FGTU (post test)



Date FGTU current design (3500 ppm B) FGTU electropolished* (1750 ppm B)

17.07.2012 (Start)

20.08.2012

24.09.2012

15.10.2012 (End)

FGTU inner surface

MFU

Results: in situ (in SS FGTU)

H3BO3-Crystal growth on the Inner surface of the SS FGTUs observed First visible crystals are obtained after ~ 1 month of exposure



Results: FGTUs

(outer surface)

Significant H3BO3-Crystal growth on the outer surface of the current design SS FGTUs observed Surface condition plays a key role



Results: Profilometric

scans (post test)

Pos. Basin 1 (3500 ppm B) FGTU current design

Basin 2 (1750 ppm B) FGTU electropolished*

Inner surfac

e

0 °

tmax = 0.171 mm tmax = 0.050 mm

90 °

tmax = 0.160 mm tmax = 0.023 mm

180 °

tmax = 0.290 mm tmax = 0.020 mm

270 °

tmax = 0.265 mm tmax = 0.042 mm

H3BO3-Crystal growth inside the SS FGTU Influence of H3BO3 concentration tmax values used for growth rate estimation



Results: H3BO3 growth

tmax after 3 months /mm

growth /mm/month

extrapolated growth in /mm 12 months 24 months

FGTU current design (3500 ppm) 0,290 0,097 1.164 2,320

FGTU_current design* (1750 ppm) 0,050 0,017 0,204 0,408

*: electropolished only on the outer surface.

Linear extrapolation (high conservatism) reveals a sufficiently big clearance after 24 months No blockage of the MFU is expected



Summary ► H3BO3 crystallization takes place at surfaces where the solvent (water) can easily

and completely evaporate. ► The boron concentration and the surface condition (roughness, scratches) generally play a major

role for the crystallization behaviour of H3BO3 ► The humidity and temperature measured in the SS FGTUs indicates the existence of a micro climate

that inherently impedes H3BO3 crystallization. ► After the full testing period of 90 days no crystal growth could be obtained on any of the exposed

MFUs. ► On the inside of the SS FGTUs crystal growth was obtained and quantified by means of

profilometric scans. Assuming a linear growth law (conservative approach) growth rates for H3BO3 are estimated:

Using this growth rate a remaining annular clearance of 4.05 mm is calculated after 24 months

The functionality of the ALM-devices will not be jeopardized during 24 months*. (definition of specific maintanance intervals)

H3BO3 Deposit 3500 ppm B 1750 ppm B

Max. thickness [mm] 0.29 0.05

Estimated growth rate [mm/month] 0.097 0.017

*:under the investigated conditions (IRWST set-point conditions)



Editor and Copyright [Date]: AREVA GmbH – Paul-Gossen-Straße 100 – 91052 Erlangen, Germany. It is prohibited to reproduce the present publication in its entirety or partially in whatever form without prior written consent. Legal action may be taken against any infringer and/or any person breaching the aforementioned prohibitions. Subject to change without notice, errors excepted. Illustrations may differ from the original. The statements and information in this brochure are for advertising purposes only and do not constitute an offer of contract. They shall neither be construed as a guarantee of quality or durability, nor as warranties of merchantability or fitness for a particular purpose. These statements, even if they are future-orientated, are based on information that was available to us at the date of publication. Only the terms of individual contracts shall be authoritative for type, scope and characteristics of our products and services.

End of presentation Reliability and long term behaviour of novel accident level measurement devices in simulated fuel pool environment

S. Berger1, R. Kilian1, S. Estevez Hernandez1, G. Hasse2

1AREVA GmbH, Germany 2EPCM Global Engineering (Pty) Ltd, South-Africa Ottawa, August 12th 2015

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