lbe-water interaction in lifus v facility under different operating conditions

LBE-Water interaction in LIFUS V facility under different operating

conditions

A. Ciampichetti, D. Bernardi - ENEAT. Cadiou - CEAN. Forgione – Università di PisaD. Pellini - KIT

International DEMETRA WorkshopBerlin, March 4th, 2010

Introduction

The XT-ADS and EFIT reactors’ heat exchangers / steam generator modules are designed to be placed in direct contact with the heavy liquid metal in the main vessel. Since the likelihood of a pipe break is not negligible, the interaction between the secondary coolant and LBE represents an important concern for such a configuration. In fact, the consequences might have a strong impact on safety, design and maintenance of these reactors.

Consequences• The peculiarities of the heavy liquid metals (such as high thermal conductivity,

high density and low surface tension) determine their gift to interact with water energetically, thus producing vapour at high pressure.

• The interaction leads to pressures waves propagation which might damage the surrounding structures, causing an escalation of the accident.

• The seriousness of the consequences is determined by the injection pressure and flow rate, the vapour production rate and the intervention of safeguards.

Description of work

An experimental study focused on LBE/water interaction aimed at assessing physical effects and possible consequences relating to this kind of interaction has been performing in ENEA through LIFUS 5 plant. The main parameters for carrying out the experiments have been selected taking into account the XT-ADS primary heat exchanger design and the indications obtained from the pre-test activity performed with SIMMER code.

The parameters considered have been:- system geometry;- lead temperature;- temperature and pressure of the water The modelling activity with SIMMER code have been performing in CEA and

University of Pisa.

LIFUS 5 Facility

The main LIFUS 5 components are:• the reaction vessel S1, containing at the bottom the water injection device. Its

volume is 100 l• the expansion vessel S5, connected to S1 through four tubes. Its volume is 10 l• the pressurised water vessel S2 • the safety vessel S3• the liquid metal storage vessel S4• Instrumentation: S1 is equipped with water-cooled high precision piezometric

pressure transducers, which allow to achieve very low time constants. A number of K-type thermocouples are also present. A fast DAQ system with a dedicated software acquires the main test parameters in different positions of the system.

LIFUS 5 has been designed to simulate LOCA accidents and to operate in a wide range of conditions (pressure up to 200 bar, initial LM temperature up to 500 °C)

LIFUS 5 Facility

Experimental campaigns

Three experimental campaigns for DEMETRA have been completed and the last one will be completed in March 2010.

Test n.1 Test n.2 Test ELSY Test n.3 Test n.4

LBE temperature 350 °C 350 °C 400 °C 350 °C 350 °C

Water injection pressure

70 bar 6 bar 185 bar 40 bar 40 bar

Water temperature 235 °C 130 °C 300 °C 235 °C 235 °C

Free volume/ LBE volume

5% 20% 20% S1 completely

filled 20%

Water injector device penetration

in the melt 80 mm 80 mm 5 mm 5 mm 5 mm

Reaction system Initial one Modifications on S5 and WI

Possibility to discharge in S3



Time schedule Completed Completed Completed Completed March 2010

Test n.1: experimental results

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ssu

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Pressure evolutions in the

reaction-expansion vessel

First phase: the pressure reaches a maximum of about 65 bar.Second phase: pressure decreases in S1 because of the free flow of gases into S5 is not balanced by an equivalent injection of water.Third phase: there is a further pressure increase in both S1 and S5 due to the further water vaporization. A maximum value of about 80 bar has been reached.Fourth phase: pressure become stable at 70 bar due to the reverse flow-rate.

• Liquid metal temperature: 350 °C

• Water injection pressure: 70 bar

• Water temperature: 235 °C (sub-cooling of 50 °C)

• Test performed with the expansion vessel S5

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Test n.1: modelling

SIMMER model of LIFUS5

March 5, 9 2007 9Forschungszentrum Karlsruhe

SIMMER results (pressure)

Pressure à t=0.2 sInitial state

Reaction vessel

Expansion tube

March 5, 9 2007 10Forschungszentrum Karlsruhe

SIMMER results (Pressure)

Pressure à t=0.5 sPressure à t=0.4 s

Pressure evolutions in the interaction vessel (S1) and expansion vessel (S5)

June 21, 22 2006 6ROSSENDORF

Expansion volume

Interaction tank

J = 1,64

Expansion vessel

Expansion tubes

connected to the different

zones

U tubes bundle

Injector

I = 1, 20Boundary conditions at inlet injector Porous wall

LIFUS modeling with SIMMER

S1

S5


Pressure evolution detected in gas phase followed the same trend as in LBE but the first sharp peak was not present.




• Test performed without the expansion vessel S5

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Temperature evolution detected in three vertical positions.

Test n.2: modelling /1


SIMMER III domains developed by PISA University

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Experimental

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Comparison between SIMMER simulations and

experimental results

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TC18 Bottom- tube n.3

CM2

Pressure evolution

Temperature evolution

University of Pisa

Experimental and SIMMER results of Test n.2 were used to support the assessment of the accidental scenario of “heat exchanger tube rupture” considered as reference accident in the safety analysis of the ICE activity.

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SIMMER domain for Test n.2

Safety activity for ICE /1

ICE simulations with SIMMER have shown that a double rupture of a HX tube produces a fast pressurisation of CIRCE main vessel that strongly overcomes the design value.

Double breakage - Argon Zone

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Injection depht : 900 mm



Double Rupture – Argon RegionDouble breakage - Argon Zone

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Double Rupture – Argon Region

ICE design team has

developed another

solution for the HX

based on the adoption

of water at 1 bar and

double wall tubes

Dead volume

Cylindricalskirt

Dead volume

Cylindricalskirt

Primary coolant Heat Exchanger

(old solution)

Heat Exchanger

(new solution)

Fluid LBE Water Boiling Water

Temperature

in-out 400 – 300 °C 115 – 150 °C 60°C – 100°C

Pressure 1.2 bar (cover

gas) 6 bar

2.5 bar (liquid side)

1 bar (steam side)

Flow rate 55.2 kg/s 5.5 kg/s 0.6-0.8 kg/s

Velocity 0.2 m/s 1.3 m/s 0.5 m/s (liquid)

Material T91 AISI 304

Tubes

- Triangular assembly - “U” shape - Diameter and thickness: 26.7 / 2.9 - Length: 895 mm - Number: 13

- Bayonet double wall (helium gap)

- Diameter 1”, ¾”, ½” - Length: 5000 mm - Number: 91

Safety activity for ICE /2University of

Pisa

In order to simulate the possibility to discharge the vapour/liquid metal mixture outside the steam generator module during a tube rupture accident, the reaction system of Lifus5 facility has been modified. A discharge line directly connecting the reaction vessel S1 with the safety vessel S3 has been designed and constructed.

Modification of LIFUS5

S2

LIFUS5: old and new configuration

Test n.3: experimental results /1

Pressure evolution detected by the different transducers placed in S1




• Possibility to discharge in S3

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Test n.3: experimental results /2

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PT in the flange of S1

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PT close to the water injector

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TC closest to the water injector

TC in the discharge line

Pressure

Temperature

PT close to the water injector PT in the flange of S1

TCs in front of the water injector

Features of the domainSimplified geometry: cylindrical coordinates (r-z) with 30 radial and 39 axial meshes.In LIFUS 5 there is a strong asymmetry in the geometry

Assumptions1. The overall volume of the main elements is

conserved 2. The injector and vent pipe are placed coaxially

with the reaction vessel S13. The flow area of the various pipes is conserved


In the reaction vessel S1, U tubes are represented by 12 “no calculation” regions

The strong asymmetry due to U tube shape and position cannot be adequately accounted for

U tubes are simulated through annular elements which conserve the overall volume

SIMMER III Model (2D): GeometrySIMMER III Model (2D): Geometry

University of Pisa


Comparison between calculated and experimental pressure in S1 vessel

SIMMER III overestimates the maximum value of the pressure in the reaction vessel S1 even though the trend is in agreement especially for the pressurization

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SIMMER III calculations

Comparison between calculated and experimental

temperature in LBE region: top thermocouple

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University of Pisa

SIMMER IV Model (3D): GeometrySIMMER IV Model (3D): Geometry

• 3-D model of LIFUS 5 facility performed with SIMMER IV code

• Simplified geometry: Cartesian coordinates (x-y-z) with 20 meshes along x, 15 along y and 18 along z

• The correct position of the water injector and of the vent tube is preserved

Test n.3: modelling /3 University of Pisa


The 3D version of the code is able to evaluate the first pressure peak associated with the impact between the water jet and the “rigid surface” of the liquid metal.

A better agreement concerning the maximum values reached with respect to SIMMER III results even though some discrepancies still remain.

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SIMMER IV calculations

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ExperimentalSIMMER III calculationsSIMMER IV calculations

University of Pisa


TestTotal mass of injected water

[kg]

SIMMER III 1.66

SIMMER IV 1.13

Experimental data 1.60

Mass Flow Rate: Comparison between SIMMER III and SIMMER IV calculation results

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SIMMER IV calculations

University of Pisa

Possible consequences

The pressure evolution detected during Test n.3 has shown a first sharp peak and a following slower pressurisation of the system. In reactor scale the latter event can be avoided using adequate countermeasures (e.g. rupture disks, stop and check valves on the steam generator tubes). The first sharp peak reached about 15 bar in the pressure transducer closest to the water injector and smaller values in the other pressure sensors. This peak is originated from the impact of the water jet on the liquid metal and it could be a threat for the integrity of the surrounding tubes. Further tests are necessary to investigate this issue.

Conclusions

Experimental results concerning the simulation of water large leaks in LBE have been obtained under different operating conditions. Maximum pressure values higher than the water injection pressure have been detected during Test n.1 and 2.

The experimental results provided helpful data to prove the capability of the SIMMER code to simulate such an accident. SIMMER III was able to reproduce the interaction between a water jet and LBE, even though the 2D feature of the code has represented a limitation in reproducing the LIFUS 5 results. A new activity with SIMMER IV (3D) has been recently launched and is giving promising results.

Test n.2 was used to support the safety analysis of ICE. In this case simulations showed that a double rupture in the LBE–pressurized water shell heat exchanger leads to a fast pressurisation of CIRCE main vessel that strongly overcomes the design value. Considering this warning, the ICE design team has adopted another solution with water at atmospheric pressure.

LIFUS 5 has been modified in order to simulate the possibility of discharging the vapour/liquid metal mixture outside the steam generator module during a tube rupture accident as it might happen in lead cooled reactors. After that, Test n.3 was carried out in the operating conditions fixed for the heat exchanger of XT-ADS.

Test n.3 has shown a first sharp pressure peak and a following slower pressurisation of the system. In reactor scale, the first peak could be dangerous for the surrounding structures while the following pressurisation can be avoided with adequate safeguards.

lbe-water interaction in lifus v facility under different operating conditions

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