Thermalhydraulic and Conjugate Heat Transfert Analysis of ... · 2 Ensight UGM Paris, France -...

Thermalhydraulic and Conjugate Heat Transfert Analysis of a 1300 MW PWR Core Internal Baffle Structure

Isabelle RUPP

EDF R&D

2 Ensight UGM Paris, France - September 27, 2010

Outline

1. Introduction2. Geometry description3. Numerical tools and

computation methodology4. Configurations simulated

and results5. High Parallel Computations

with SYRTHES


Introduction : the reactor vessel internals

About 1800 bolts required for connection between vertical sheets, horizontal formers and core barrelPWR vessel and location of the baffle

- It allows the transition between the polygonal core and the cylindrical core barrel- It protects the vessel (radiation and temperature)

It is important for the lifetime of the power unitsA better knowledge allows maintenance optimization

The internal structure is a baffle-former-barrel bolted assembly


The problem studied

The internal baffle structure is affected by a strong internal energy deposit induced by gamma radiation (proximity of the core)

After controls, a certain number of bolts were found cracked. Thisphenomenon is attributed to Irradiation Assisted Stress Corrosion Cracking (IASCC)

Temperature is one of the main factors playing a part in the IASCC phenomenon

the goal of this numerical studiy is to gain a better and precise knowledge of the temperature distribution inside the whole structure and particularly around and inside the bolts.


Methodology

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TRIPOLI calculation

Interpolation of the heat deposit on the SYRTHES mesh

Conjugate heat tranfert calculationSYRTHES / Code_Saturne

Code_Aster

Temperature in the structures

Stresses and strain in the whole structure

Bolts grid for mechanical computation


1300MWe geometry description

CPY

4 m1.7 m

• 10 formers• Baffle• Core barrel• 1840 bolts

One underlines the large geometrical scale difference between the whole structure and the bolts

After going down through the down-comer, the cold fluid goes up through the core but a small by-pass flow is in charge of cooling the internals structure and the bolts

sector of 45 degrees

Former Baffle

6 cm


1300 MWe Geometry description – solid part

SYRTHES is a general purpose thermal code using afinite element approach on tetrahedra in 3D. Here the difficulty has been to take into account both a large global geometry and very fine details.

Solid mesh counts 47 million tetraedra

Bolt

Former with bolts


1300 MWe Geometry description – Fluid part

fluid domain is very complex to mesh because of the cylindrical holes around each bolt

Finite volume approach is used to solve Navier-Stokesaveraged equations. The fluid is assumedincompressible, Newtonien with mass only temperature dependent.Turbulence model used is a classical k-eps model.

Fluid mesh counts 7 million cells


Energy deposit induced by gamma radiation

The 3D heat source in the solid is calculated thanks to the neutroniccode TRIPOLI IV using a monte-carlo approach on a standard fuel pattern case. As expected the maximum deposit is located around corner near the core in a limited area.Then the deposit field is interpolated on the SYRTHES mesh


Calculation methodology

Solid32 parts

Fluid256 parts

A coupling between the parallel CFD code Code_Saturneand the parallel thermal code SYRTHES is usedNumber of processors for each domain is chosen to keep a good CPU load balance

Calculation expense : 70 hoursPartitionning is done thanks to METIS


Results – Fluid flow

Dynamic jets are coming from simple holeswhere small jets are induced by cooling passages around the bolts


Results – Fluid temperature

The fluid temperature increases when the flow goes upward. But the temperature increase stays moderate.


Results – Solid temperature

Global temperature

Temperature inside former 6

High temperatures are locatedaround the corner close to

the assemblies


Former 9

Thickness of former 9 induces high temperatures due to the lack of cooling inside the structure

Results – Solid temperature

F. 6


High parallel computation with SYRTHESThermal temperature for 6 formers and full 360 degreesHigh parallel computation with SYRTHESThermal temperature for 6 formers and full 360 degrees

Geometry :• Internal baffle• 6 formers (where temperature is much higher)• full 360 degrees• 1128 bolts

View with the core barrel removed

View with the vertical sheets removed

Upside view


Thermal temperature for 6 formers and full 360 degreesThermal temperature for 6 formers and full 360 degrees

Mesh : 1.1 billion of linear tetrahedra partitionned in 2048 parts

Due to the size, the mesh has been generated by blocks (here by Simail).

Then, “home-made tools” based on octree approaches have been used to join the different blocks and eliminate the common nodes.

METIS 5 has been used to partition each block

Global mesh with the 2048 parts represented


Calculation has been performed on BlueGene L• 2048 processors used• 100 Mo memory used by processor• Steady state reached in 1h30 CPU time

Temperature field

Thermal temperature for 6 formers and full 360 degreesThermal temperature for 6 formers and full 360 degrees


Postprocessing with Ensight

Softwares Simail : mesh generatorMetis : mesh partitionningSYRTHES : thermal calculationCode_Saturne : CFD codeEnsight : postprocessing

Mesh file = 72 GbResult file = 3 Gb

EnsightGold file format is required

Minimal configuration required for this case4 processorsBetween 64 Gb and 128 Gb RAM depending on the visualization (cut plane, shadows, iso-values,…)

No particular problem encountered !

Thermalhydraulic and Conjugate Heat Transfert Analysis of ... · 2 Ensight UGM Paris, France -...

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