Safety Analysis of the European Test Blanket Systems in ITER using MELCOR

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Safety Analysis of the European Test Blanket Systems in ITER using MELCOR

Andrew Grief and Simon Owen

EMUG 2016

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Overview

1. Introduction to fusion and the ITER machine

2. Tritium self-sustainment and Test Blanket Modules (TBMs)

3. The Helium Cooled Pebble Bed (HCPB) and Helium Cooled Lithium Lead (HCLL) TBMs

4. Hazards and safety analysis modelling of TBMs using MELCOR 5. Methodology / approach

6. Case studies

This presentation describes work conducted for Fusion 4 Energy under contract F4E-OMF-331-04-01-01. Amec Foster Wheeler wish to thank F4E for allowing us to present this work

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ITER (Latin for ‘The Way’, previously ‘International

Thermonuclear Experimental Reactor’) under construction at Cadarache in southern France

► An experiment, not a power plant – no electricity generation

► Produce heat using magnetically confined deuterium-tritium fusion International project led by the ITER Organisation (IO)

► European Union, India, Japan, China, Russia, South Korea, USA

► European contribution is through

‘Fusion for Energy’ (F4E)

3 Introduction to ITER

Images: http://www.iter.org/

*Off by ~ ⁸

*

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The ITER Experiment

Aims

► Produce 10 times more energy than input (500 MW fusion power)

► Achieve a burning plasma – sustained reaction for a long duration (100s of seconds)

► Test integrated technologies and demonstrate safety How?

► Use the largest ever tokamak (840 m ³ ) to magnetically confine a high temperature plasma (ionised gas)

Facts and figures

► 23,000 t machine weight

► Temperature of the plasma: 150 million °C

► Temperature of the magnets: -269°C

► Cost ~ 13 billion $

► Large Hadron Collider ~ 10 billion $

► International Space Station ~ 150 billion $

4 Image: http://www.iter.org/

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Vacuum vessel Magnets

► 48 magnets Cryostat

► The vacuum vessel sits inside the cryostat

Blanket

► 440 water cooled modules, each 1 m x 1.5 m and ~4 tonnes

► Shields vacuum vessel from high energy neutrons and removes heat

Divertor

► This removes impurities (exhaust) from the plasma

► Very high heat loads

► At bottom of vacuum vessel

5 The ITER Machine

Interactive graphics available:

http://www.iter.org/mach Plasma in here

2 9 .3 m

28.6 m

Image: http://www.iter.org/

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Tritium Breeding

Tritium self-sustainment is a requirement of any commercial fusion plant

► Tritium resources currently estimated at ~20 kg

► The envisaged fusion power demonstration plant (DEMO) will require 300 g per day to produce 800 MW electrical power

► Approximate cost of tritium: $100,000 per gram…

6 Estimates: S. Willms, ITER Test Blanket Module Meeting, UCLA, Feb 2004

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Tritium Breeding

ITER will use the high energy neutrons produced in the fusion reaction to test tritium breeding concepts

Six designs of Test Blanket Module (TBM) will be tested at ITER

► The TBMs all contain lithium; Beryllium and lead are used as neutron multipliers Europe will provide two designs:

► Helium-Cooled Pebble Bed (HCPB) TBM

► Helium-Cooled Lithium Lead (HCLL) TBM

Image: http://www.hiper-laser.org/

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The Test Blanket Modules

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Test Blanket Module (TBM)

Test Blanket Module

This is a

technology test programme

The aim is to test technology that will be used heavily in the next fusion reactor after ITER (which will be

called DEMO)

In future reactors these components will be arranged in the ‘blanket’ around the plasma chamber A full blanket of

tritium breeding modules will be needed to create enough tritium to run a power reactor

The curved wall of the plasma chamber is lined with many hundreds of individual ‘modules’

At ITER most modules are just for shielding and cooling – these are

called ‘blanket shield modules’. There are 6 tritium-producing test blanket modules

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Location of HCLL and HCPB TBM

10 Water-cooled blanket shield module

Test Blanket Modules

Port Plug

Supporting

systems

Slice of the

tokamak

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Helium-Cooled Pebble Bed TBM

11 1.7 m

Heating and neutrons from plasma

HCPB TBM

Shielding and pipework

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Helium-Cooled Pebble Bed TBM

► There are 16 pebble-filled breeder units. The breeder units are held behind the plasma-facing ‘first wall’

and separated from each other by stiffening plates

► Li ₄ SiO ₄ pebbles are enclosed by EUROFER-97 cooling plates

Plasma-facing first wall (red)

12 Images: F. Cismondi et al. , ‘Design Description Document of the HCPB TBM generic box (Part.1 TBM Box)’, F4E report;

F. Cismondi et al. , ‘Design Description Document of the reference option for the HCPB-In TBM Breeder Units’,F4E report

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Helium-Cooled Pebble Bed TBM

► Due to the high heat loads most of the structural components contain helium coolant channels

► All component in red box have coolant channels within them

► The curved plates separating the beryllium pebbles and the lithium pebbles also contain helium coolant channels

► These multiple sets of coolant

channels are the main heat removal system for the whole TBM

► Spaces between plates at the back of the TBM box form 4 manifolds for the helium coolant

13 Images: F. Cismondi et al. , ‘Design Description Document of the HCPB TBM generic box (Part.1 TBM Box)’, F4E_D report;

F. Cismondi et al. , ‘Design Description Document of the reference option for the HCPB-In TBM Breeder Units’,F4E report

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Helium-Cooled Pebble Bed TBM

► Images show helium cooling channels in:

► Side caps

► First wall (~15 mm Ø)

► Horizontal stiffening grids

► Breeder unit cooling plates

14 Images: F. Cismondi et al. , ‘Design Description Document of the HCPB TBM generic box (Part.1 TBM Box)’, F4E report

F. Cismondi et al. , ‘Design Description Document of the reference option for the HCPB-In TBM Breeder Units’,F4E report

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Helium-Cooled Pebble Bed TBM

How is the tritium extracted?

► A second, separate, slow low pressure (~1 bar) helium flow is passed through the beryllium and lithium pebble beds in each of the 16 breeder units

► Tritium diffuses out from the pebbles, into this

‘purge gas’ flow

► Carried off to the Tritium Extraction System (TES)

► Yellow arrows show purge gas flow

► The plates and caps (not shown) around the beryllium and lithium pebbles constrain the purge flow

15 Images: F. Cismondi et al. , ‘Design Description Document of the HCPB TBM generic box (Part.1 TBM Box)’, F4E report;

F. Cismondi et al. , ‘Design Description Document of the reference option for the HCPB-In TBM Breeder Units’,F4E report

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Helium-Cooled Lithium Lead TBM

► Basic box structure very similar to the HCPB TBM

► Liquid lithium lead (PbLi) used to breed tritium and transport it from the TBM

► High tritium breeding capability, relatively high thermal conductivity, immunity to irradiation damage

► Lithium lead flow strongly affected by magneto hydrodynamics

(MHD)

16 Image: G. Aiello, A. Li Puma, G. Rampal, H. Simon, ‘Design Description Document of

the Reference Option for the HCLL TBM Generic Box, Version 1.0, F4E report

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Auxiliary systems

► Helium Coolant System (HCS) – primary TBM heat removal system

► Coolant Purification System (CPS)

► Lithium lead ancillary system (for HCLL)

► Tritium extraction system (for HCPB)

► Port plug – water-cooled structure that houses the TBMs

► Instrumentation and control systems

17 Image: G. Aiello, A. Li Puma, G. Rampal, H. Simon, ‘Design Description Document of

the Reference Option for the HCLL TBM Generic Box, Version 1.0, F4E report

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TBM Hazards

As complex nuclear systems, we must demonstrate the TBMs will operate safely in operational and accident scenarios.

Examples of key hazards include:

► For both HCPB and HCLL systems

► Leaks or pressure relief systems releasing helium / tritium / activated corrosion products / dust into ITER buildings

► HCLL

► Hazardous PbLi leak into Vacuum Vessel (VV) / ITER buildings

► Hydrogen production through PbLi chemical reaction (with steam/water)

► HCPB

► Hydrogen production through beryllium chemical reactions (with air or steam)

Plasma ‘disruptions’ can deposit large amounts of energy on the TBM:

► Plasma control is difficult!

► May damage the TBM and the water-cooled blanket shield modules

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Accident Analysis Methodology

19 Accident analysis for fusion systems is not as highly developed as for most fission reactors

► Common elements (choked flow, decay heat, convective heat transfer, …) but also many ‘novel’

phenomena

► Validation is much less developed than for LWRs

► Necessary to develop a coherent methodology that addresses these challenges and maintains consistency with ITER licensing approach

Outline of the methodology

► Selection of accident scenarios based on failure modes and effects analysis (FMEA) studies

► Development Accident Analysis Specifications (AAS)

► Use of Phenomena Identification and Ranking Table (PIRT) to identify required physical models to aid selection of the analysis code

► Objectives / Acceptance criteria

► System assumptions

► Development of TBS models using the selected analysis codes

► Qualification of the models via comparison with finite, element calculations, code-to-code comparisons, and sensitivity studies

► Application of the qualified models to the selected accident scenarios

► Ongoing sensitivity studies to address uncertainties, demonstrate conservatism

► Iterative updates as knowledge improves

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Requirements for TBM Accident Analysis

Key requirements for the analysis code:

► ‘Typical’ flow / convection heat transfer models for gases, heat structure models for solids

► ‘Typical’ control system models

► Multi-dimensional heat conduction modelling

► Flow of molten PbLi

► PbLi as working fluid

► Pressure drops induced by magnetic field (MHD)

► Chemical reaction modelling (Beryllium – steam / air reaction)

► Robust numerics

► Modelling flexibility

► Consistency with ITER accident analysis desirable

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Use of MELCOR

The fusion-adapted MELCOR codes, produced by Brad Merrill at Idaho National Laboratory based on the MELCOR 1.8.x code base meet the key requirements

► Work described today uses fusion-adapted 1.8.2 and 1.8.5 MELCOR code versions

► Multi-fluids 1.8.5 code for HCLL TBS (ability to simulate liquid PbLi)

► ITER 1.8.2 code version for HCPB TBS (sufficient control functions for modelling complex thermal conduction network in pebble bed)

► We look forward to using the new (double precision) fusion adapted 1.8.6 code in upcoming work… (and maybe a fusion-capable MELCOR 2.x code in due course!)

► Main MELCOR packages used so far: CVH, FL, HS, TF and CF modules

► MELCOR models qualified against finite element analysis and RELAP5-3D model

In this talk we present MELCOR work – however, Amec Foster Wheeler have also developed RELAP5-3D models of these systems and

performed code-to-code comparisons

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Modelling the Helium Coolant System (HCS)

► Start simple – modelling the cooling system:

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TBM

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MELCOR modelling of the HCPB Test Blanket System

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Modelling the HCPB TBM

24 16 Breeder Units (BUs)

Helium

manifolds

Plasma-facing

First Wall (FW)

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Helium-Cooled Pebble Bed Model Design

► ‘Single BU’ and ‘Multi BU’

nodalisation allows us to

separately analyse the behaviour of a damaged Breeder Unit (BU) from the fifteen intact BUs

► Interaction between damaged BU and the ITER VV differs from the intact BUs

► The damaged BU may receive enhanced cooling in the case of a coolant leak

► Developed a nodalisation of the TBM First Wall (FW) which

accounts for the different behaviour of the (thermally) connected BUs

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Modelling the HCPB Breeder Units

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Modelling the HCPB Breeder Units

Modelling conduction in the pebble bed

► Heat transfer between two pebble bed zones:

► Conductivity of a pebble bed zone:

► A single MELCOR ‘ADD’ control function computes heat source for each heat structure (four terms for each conduction path):

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Modelling the HCPB TBM

Temperature (°C)

912.72 972.47 374.95 434.7 494.45 554.21 613.96 673.71 733.46 793.22 852.97

Breeder unit temperature distribution predicted using MELCOR

28 As in CFD, highest

temperatures in

lithium pebbles

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0 s

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

0 0 0

0

0 0 0

0 0

321 320

0

0 0

0 0 0

0 0

321 320 361 360

0 0

0 0 0

0 0

191 192

0

0 0 0

0

0 0 0

0 0

0

0 361 360

0 0

0 0 0

0 0

350

0 0

0

0 0

0

180 Bottom HSG

0

0 0 0

0

345

0 0 0

351 350

0 0

0 0 0

0

193 192

HS 5394

196 195

0 0 0

0 0 342

0 0

331 330

0 0

344 343

0

194 195

192

HS 5395 195

181 Top HSG

0 0 00 0 0

HS 6395

0 0 0

351

191 192

0 0

0

0 0 0

0

196 195

HS 5396

180 Bottom HSG

0 0 0

0

0 0

331 330

90050 90060

194 195

192

195

193 192

HS 6394

0 0

181 Top HSG

HS 6396 0 0 342345 344 343

Steam Ingress into HCPB TBM

A plasma ‘disruption’

ruptures an ITER water-

cooled blanket module and the first wall of the TBM

► Plasma chamber fills with steam

► Steam can enter the TBM and react with beryllium pebbles, producing H ₂

► 15 intact breeder units

► 1 damaged breeder unit

► Connecting manifolds

► Steam concentration in pebble regions shown by dark blue shading

29 100% helium

100% steam

Steam from plasma chamber

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

1.60951E-05 0.000774362 0.019764776

0.209933237 0.535060018 0.836810415

0.617802884

0.980765003

0.211983118 0.539015397 0.838384537

0.144988698 0.435140601

321 320

0.293458986

0.711908206

8.45721E-16 9.44467E-19

0.082605781 0.28967298 0.614650116

0.00959091 0.166431674

321 320 361 360

2.85619E-08 1.93446E-06

0.000268867 0.00971146 0.167292235

4.5125E-05 0.002045087

191 192

0.049604505

4.73572E-13 7.09339E-16 3.74036E-19

6.43967E-17

3.018E-20 0 0

3.25251E-20 0 0

3.03954E-20 0 0

0.00670607 0.038298932

0.083966608

9.65791E-19 361 360

6.89462E-14 6.37023E-17

2.96756E-20 0 0

3.19557E-20 0

9.88154E-08 2.53129E-10

4.68335E-13 5.97894E-16

350

7.38183E-08 1.32952E-10

1.63464E-13

9.91927E-08 2.54163E-10

4.77802E-13

180 Bottom HSG

0.980407478

4.46459E-05 0.00201843 0.049296446

0.000267581

345

1.62608E-05 0.00078492 0.019896818

351 350

1.92832E-10 3.48221E-08

4.45965E-06 0.000476572

0.050449982 0.264039372

0.006630343 0.037840864

0.143702841 0.431612162 0.709721248

0.000565122

193 192

HS 5394

196 195

0.962105416 0.993818546 0.999923938 0.547375829 0.838852449 342

4.50228E-06 0.000476627

331 330

2.8445E-08 1.92024E-06

344 343

5.17645E-06

194 195

192

HS 5395 195

181 Top HSG

4.75413E-11 2.83784E-05 04.67283E-13 5.9646E-16 5.69787E-19

HS 6395

2.96105E-20 0 0

351

191 192

0 5.79257E-19

0

4.71842E-13 7.14715E-16 3.81728E-19

6.93275E-14

196 195

HS 5396

180 Bottom HSG

0 0 0

1.99439E-16

1.77494E-19 0

1.55563E-13 3.56727E-17

1.64981E-13 1.98263E-16

331 330

90050 90060

194 195

192

195

193 192

HS 6394

4.75389E-13 8.52753E-16

181 Top HSG

HS 6396 0 0 342345 344 343

1 s 2 s

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

0.1195708 0.484962695 0.837061862

0.982319409 0.995197313 0.999138322

0.996123322

0.999997613

0.982848126 0.995427389 0.999180551

0.984443078 0.996107103

321 320

0.985977102

0.998543604

1.18541E-08 8.62712E-11

0.960004558 0.98536556 0.995937039

0.573647608 0.871178792

321 320 361 360

0.002067753 0.020000018

0.188341743 0.577178826 0.872441991

0.108307351 0.448515887

191 192

0.812944294

9.85544E-07 9.9528E-09 3.43223E-11

1.11048E-09

3.46284E-12 4.06539E-15 8.33554E-16

3.67546E-12 4.26055E-15 1.32496E-18

3.4873E-12 4.08011E-15 9.45837E-18

0.887785493 0.945408749

0.961139656

8.8216E-11 361 360

1.82008E-07 1.09987E-09

3.41022E-12 3.95933E-15 9.51656E-18

3.61597E-12 4.12359E-15

0.003802862 7.44039E-05

9.74694E-07 8.41238E-09

350

0.002854027 3.92442E-05

3.42729E-07

0.003806989 7.45734E-05

9.94447E-07

180 Bottom HSG

0.999997411

0.107175032 0.444896211 0.811308485

0.187293561

345

0.120817003 0.488733894 0.838641715

351 350

0.000180448 0.003660352

0.047957417 0.362412486

0.97509257 0.996797997

0.886036003 0.944256598

0.984007349 0.995917654 0.998470032

0.404177095

193 192

HS 5394

196 195

0.999997176 0.999998917 0.999999865 0.999062297 0.999965966 342

0.048392378 0.362635944

331 330

0.002053861 0.0198228

344 343

0.05500761

194 195

192

HS 5395 195

181 Top HSG

1.85479E-05 0.11639538 2.10271E-13

9.72716E-07 8.38107E-09 5.22177E-11

HS 6395

3.40235E-12 3.938E-15 8.38526E-16

351

191 192

1.33778E-18 5.30923E-11

2.1911E-13

9.81919E-07 1.00391E-08 3.50283E-11

1.8287E-07

196 195

HS 5396

180 Bottom HSG

3.92259E-13 1.78384E-13 6.34511E-16 2.83491E-09

1.67225E-11 2.2622E-13

3.26199E-07 5.13304E-10

3.45868E-07 2.81737E-09

331 330

90050 90060

194 195

192

195

193 192

HS 6394

9.89548E-07 1.19625E-08

181 Top HSG

HS 6396 4.39767E-16 4.43703E-15 342345 344 343

3 s

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

0.691593065 0.909542779 0.981125967

0.999963903 0.999986924 0.999992126

0.999988385

0.999999637

0.999966378 0.99998756 0.999992368

0.999975631 0.999989726

321 320

0.999968304

0.999992576

8.03087E-06 1.69921E-07

0.999876082 0.999965495 0.999987732

0.907580244 0.979562061

321 320 361 360

0.120305729 0.355193734

0.710561653 0.909308723 0.980003565

0.615959236 0.86915137

191 192

0.967228748

0.00022534 6.76332E-06 6.83428E-08

9.24231E-07

7.4063E-09 1.86316E-11 1.49073E-11

7.85828E-09 1.9504E-11 6.74222E-14

7.45828E-09 1.86828E-11 4.73677E-13

0.999343196 0.999804467

0.999885133

1.73645E-07 361 360

5.7629E-05 9.13381E-07

7.25858E-09 1.76417E-11 4.78645E-13

7.69387E-09 1.83844E-11

0.082321349 0.0055109

0.000222951 5.73248E-06

350

0.063157185 0.002935971

7.89286E-05

0.082394604 0.005521586

0.000227369

180 Bottom HSG

0.999999635

0.613030036 0.866863917 0.966578789

0.708970488

345

0.69423304 0.911355743 0.981589857

351 350

0.016596917 0.107658985

0.381125002 0.755345164

0.99995693 0.99999776

0.999311904 0.99979205

0.999973973 0.999989327 0.999992362

0.793022357

193 192

HS 5394

196 195

0.999998142 0.999999206 0.9999999 0.999997983 0.999998076 342

0.383275274 0.755524507

331 330

0.119482861 0.353081782

344 343

0.416188926

194 195

192

HS 5395 195

181 Top HSG

0.002186955 0.511477214 1.19775E-09

0.000222488 5.71305E-06 1.0353E-07

HS 6395

7.24227E-09 1.75779E-11 1.50603E-11

351

191 192

6.85338E-14 1.05226E-07

1.24507E-09

0.000224551 6.81871E-06 6.97227E-08

5.79364E-05

196 195

HS 5396

180 Bottom HSG

2.23849E-09 1.03335E-09 1.03538E-11 1.93608E-06

3.40452E-08 1.34264E-09

7.51841E-05 3.60447E-07

7.96225E-05 1.92426E-06

331 330

90050 90060

194 195

192

195

193 192

HS 6394

0.000226297 8.1002E-06

181 Top HSG

HS 6396 7.63493E-12 7.47339E-11 342345 344 343

16 s

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

0.999997901 0.999997886 0.999997827

0.999988328 0.999989571 0.999991518

0.999990642

0.999999578

0.999988827 0.999989807 0.999991736

0.999988809 0.999990002

321 320

0.999989282

0.999991796

0.308831199 0.096322226

0.999987951 0.999988958 0.999990363

0.999997874 0.999997805

321 320 361 360

0.99997703 0.999995793

0.999997883 0.999997873 0.999997805

0.999997708 0.999997894

191 192

0.99999783

0.570202641 0.281463462 0.048321235

0.115290556

0.01464483 0.000585978 0.001224225

0.01542702 0.000574799 0.000103766

0.014735383 0.000560624 0.00038609

0.999987476 0.999988023

0.999988411

0.097292638 361 360

0.379613526 0.114390001

0.014422509 0.000535461 0.000389147

0.015167642 0.000548503

0.936931736 0.811759013

0.567476325 0.255780768

350

0.907435826 0.702615433

0.360950865

0.93706957 0.81227393

0.572358324

180 Bottom HSG

0.999999575

0.999997702 0.999997895 0.999997831

0.999997884

345

0.999997902 0.999997885 0.999997826

351 350

0.982163914 0.994662478

0.998372899 0.999596719

0.999993641 0.999997749

0.99998665 0.999987344

0.999988294 0.999989836 0.999991655

0.999800214

193 192

HS 5394

196 195

0.999997747 0.999999107 0.999999881 0.999997736 0.999997719 342

0.998398083 0.999596363

331 330

0.999976749 0.999995746

344 343

0.998942126

194 195

192

HS 5395 195

181 Top HSG

0.673761755 0.986183576 0.01006827

0.567866097 0.256101706 0.067234242

HS 6395

0.014391587 0.000561542 0.001234579

351

191 192

0.000105019 0.06762674

0.010285045

0.568949539 0.281956903 0.048794335

0.380534494

196 195

HS 5396

180 Bottom HSG

0.015043895 0.008692855 0.001056103 0.127250967

0.025882196 0.009410388

0.352458676 0.037933289

0.362651418 0.126780101

331 330

90050 90060

194 195

192

195

193 192

HS 6394

0.571013344 0.309543825

181 Top HSG

HS 6396 0.001194753 0.005030279 342345 344 343

46 s

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

0.999995865 0.999995615 0.999993986

0.999894722 0.999857345 0.999807682

0.999855646

0.999985797

0.999902748 0.999859479 0.999812318

0.999879081 0.999829613

321 320

0.999890586

0.999807304

0.74812268 0.503283675

0.999912926 0.999887933 0.999851818

0.999995239 0.999991056

321 320 361 360

0.999996028 0.999995928

0.999995825 0.99999523 0.999991024

0.99999587 0.99999558

191 192

0.999993458

0.878589989 0.723316256 0.341713686

0.454244986

0.138812635 0.013004436 0.034526039

0.14456245 0.011616795 0.006772612

0.139553785 0.011805606 0.017081682

0.999938158 0.999925068

0.99991827

0.500430878 361 360

0.727995858 0.451659158

0.136660517 0.011266805 0.017274582

0.142071141 0.011028934

0.990215506 0.959172498

0.875640433 0.692993198

350

0.980687925 0.912548002

0.736374551

0.990353747 0.959826805

0.87976947

180 Bottom HSG

0.999985774

0.999995871 0.999995584 0.999993477

0.999995826

345

0.999995864 0.999995611 0.999993972

351 350

0.999514873 0.999786416

0.999783216 0.999733768

0.999867328 0.999985384

0.999930057 0.999916466

0.999867826 0.999827764 0.999804979

0.999750156

193 192

HS 5394

196 195

0.999918028 0.999964767 0.999993488 0.99997666 0.999954619 342

0.999768637 0.999732852

331 330

0.999996029 0.999995929

344 343

0.99982958

194 195

192

HS 5395 195

181 Top HSG

0.875514907 0.998726104 0.14923651

0.877636603 0.69785394 0.418540077

HS 6395

0.13647405 0.012515532 0.034936772

351

191 192

0.006884523 0.412296863

0.145508825

0.876523793 0.720210768 0.33767989

0.729012044

196 195

HS 5396

180 Bottom HSG

0.184789873 0.129821382 0.031801368 0.502330439

0.221616313 0.133011538

0.730371775 0.244374209

0.739536516 0.503227421

331 330

90050 90060

194 195

192

195

193 192

HS 6394

0.877900584 0.746115121

181 Top HSG

HS 6396 0.041370013 0.106364269 342345 344 343

(30)

HS 6388 HS 6386 HS 6384 HS 6382 HS 6380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 6309 HS 6307 HS 6305 HS 6303 HS 6301

MF3 HS 6390

185 Side Cap

HS 6391 MF3

HS 6392 186 Side VSG

MF3

HS 5388 HS 5386 HS 5384 HS 5382 380

369 367 365 363

368 366 364 362

359 357 355 353

358 356 354 352

339 337 335 333

338 336 334 332

329 327 325 323

328 326 324 322

HS 5309 HS 5307 HS 5305 HS 5303 HS 5301

180 Bottom HSG

2.36E-06 2.48E-06 7.80E-06

1.86E-06

4.95E-06 5.78E-06 1.71E-05

2.41E-06

HS 5394

5.56E-06 7.24E-06 3.11E-06 3.71E-06

321

196 195

330

193 192

320

345 344 343

9.01E-06 2.82E-05

2.44E-06 8.35E-06

4.88E-06

HS 5395

7.83E-06 1.02E-05

1.98E-06 7.59E-06

5.62E-06 195

194 195

350

192 3.58E-06 7.27E-06

342

331 351 361

191 192

360 181 Top HSG

1.80E-06

4.58E-06 5.56E-06 1.61E-05

2.23E-06 2.42E-06 7.41E-06

HS 5396

5.25E-06 6.78E-06

2.25E-06 2.99E-06 3.55E-06

180 Bottom HSG

321

193 192

320

HS 6394

6.67E-05 6.89E-05

1.82E-05 1.22E-05 1.46E-05

3.97E-05 2.87E-05 4.31E-05

2.00E-05 1.50E-05 1.20E-05 3.69E-06

331

196 195

330

HS 6395

1.01E-04 1.06E-04

1.12E-05 1.01E-05

3.19E-06

6.69E-05 2.05E-05

1.66E-05 1.84E-05

351

194 195

350

192 6.52E-06 1.13E-05 5.26E-06

195345 344 343 342

361

191 192

360

5.31E-06 4.17E-06 9.68E-06 1.63E-06

90050 #N/A90060 #N/A 181 Top HSG

HS 6396

3.45E-05 2.76E-05

4.75E-06 5.16E-06 3.75E-06

8.74E-06 1.07E-05 1.13E-05

Hydrogen production

► Red colouring indicates mass of hydrogen produced over the duration of a simulation

► Hydrogen production is dependent on pebble temperature and steam partial pressure

30 0 mg H ₂

100 mg H ₂

Hydrogen production correlation

MELCOR model prediction

Lithium

pebbles

(no H ₂ )

(31)

HCPB in-box LOCA

In-box LOCA

► High pressure coolant helium leaks into (pebble-filled) low pressure purge gas region of TBM.

31

(32)

HCPB in-box LOCA

32 Leak integrated mass flow Pressurisation of TBM

(33)

HCPB in-box LOCA

33 TBM EUROFER-97 temperatures TBM pebble temperatures

(34)

Impact of Round-off Error

Average TBM temperatures

► We noticed

discontinuities in the average TBM first wall temperatures.

► The discontinuities

occur at the same time as changes to the user- defined maximum

timestep.

34

(35)

Impact of Round-off Error

Investigating the issue

► The discontinuities occur at the same time as large changes in the helium coolant temperature.

► This coolant is stationary and at

~1 MPa.

► Flat-lining behaviour in MELCOR 1.8.2

simulations is usually a sign of round-off error, due to the code being single precision.

35

(36)

Impact of Round-off Error

Mitigating the issue

► Reduce natural convection heat transfer (for

rectangular heat structures, internal flow)

► In the new simulation (in red), the FW heat structures reach higher temperatures and the coolant temperatures do not change after 1020 s.

► Behaviour in the zero transient and first 20 s is unaffected.

36

(37)

37 OLD average temperatures NEW average temperatures

(38)

MELCOR modelling of the HCLL Test Blanket System

38

(39)

Nodalisation of the TBM

► Must balance accuracy / detail against complexity / computer time.

► FW nodalisation (Courant limit)

► Represent 16 BUs with 8 modelled BUs. Nodalisation allows simulation of PbLi drain-down during an accident.

Modelling PbLi

► Incompressibility of PbLi results in very small timesteps (~10 ^-9 s) required for numerical convergence in MELCOR 1.8.5 in PbLi filled volumes!

► We include very small volumes of gas in each CVH (<0.1% by volume) to resolve these issues for normal operation cases

► We refer to these as ‘buffer gas’ volumes

► ‘Trap’ this gas through careful specification of junction elevations

HCLL TBM Model

39

(40)

CV548 CV568

CV547

CV546

CV545

CV544

CV543

CV542

CV541 CV521

C V 5 2 3

C V 5 6 2 C V 5 2 5

C V 5 6 4 C V 5 2 7

C V 5 6 6

FL522 FL524 FL526

FL563 FL565 FL567

FL521 FL523 FL525 FL527

FL562 FL564 FL566 FL568

FL541 FL543 FL545 FL547

CV503 CV502 CV501

FL520 FL502 FL501

From PbLi Ancillary Loop

FL500

CV595 CV597 CV598

FL569 FL596 FL598

To PbLi Ancillary Loop

FL599

HCLL In-Box LOCA

40 HCLL Design 16 PbLi-filled MELCOR model breeder units

(8 shown)

PbLi distribution / collection

manifolds

PbLi inlet /

outlet pipes

(41)

HCLL TBM Model

41 ► Fusion-adapted codes include

‘FUN1’ control function

► Very valuable for modelling

combined conduction and

thermal radiation

(42)

HCLL TBM Model

42 Modelling MHD

► Use control functions to reproduce MHD pressure drops observed in:

L. Bühler et al., ‘Magnetohydrodynamic Flow in a Mock-Up of a HCLL Blanket. Part II Experiments’, Forschungszentrum Karlsruhe, Report FZKA 7424, September 2008.

► Pressure drop proportional to velocity

► ‘Quick-CF’ pump input used to produce the appropriate pressure drop in MELCOR PbLi flow paths.

► Under-relaxation scheme

implemented for numerical stability.

► But this method crashes in a transient situation with voided control volumes.

► INL have implemented implicit MHD model in new version of fusion-adapted MELCOR 1.8.5.

► Also in 1.8.6

(43)

HCLL Qualification

43 TBM temperatures during an ITER power pulse

► Compared to RELAP5 simulation and design finite element analysis Maximum TBM FW

temperatures during / after plasma pulse

PbLi temperatures during / after plasma

pulse

(44)

CV548 CV568

CV547

CV546

CV545

CV544

CV543

CV542

CV541 CV521

C V 5 2 3

C V 5 6 2 C V 5 2 5

C V 5 6 4 C V 5 2 7

C V 5 6 6

FL522 FL524 FL526

FL563 FL565 FL567

FL521 FL523 FL525 FL527

FL562 FL564 FL566 FL568

FL541 FL543 FL545 FL547

CV503 CV502 CV501

FL520 FL502 FL501

From PbLi Ancillary Loop

FL500

CV595 CV597 CV598

FL569 FL596 FL598

To PbLi Ancillary Loop

FL599

HCLL In-Box LOCA

44 HCLL Design 16 PbLi-filled MELCOR model breeder units

(8 shown)

PbLi distribution / collection

manifolds

PbLi inlet / outlet pipes

Simulate leak of helium coolant into PbLi

compartment

(45)

► Prior to accident - full power steady state conditions

► Solid blue shows that TBM is full of lithium lead (PbLi)

► Accident starts at 1000 s

► Results shown for analysis with MHD effects off

(46)

► Leak occurs, almost immediate pressurisation of TBM

► TBM initially full of PbLi – very low compressibility

(47)

► Within 0.5 s, significant voiding in TBM (helium displaces PbLi)

► Pressure relief (bursting discs) attached to the TBM pipework open

► Severe pressure oscillations occur in both the TBM and PbLi circuit

(48)

Severe pressure oscillations when the LOCA occurs

► Breeder unit pressures exceed 30 MPa despite the helium coolant pressure being only 8 MPa.

Pressure Oscillations

► The sizing of gas buffer volumes (which are used to give numerical stability) plays a role.

► Some ‘PbLi hammer’ may be

expected, but how is this affected by MHD, elasticity of structures?

► Open issue.

(49)

► After 2 s, leaked helium can vent through TBM outlet pipework without needing to displace further PbLi

► This allows the helium leak mass flow to increase rapidly

(50)

► 4 s after the start of the accident the TBM pressure reduces

► Helium supply through leak drops (helium coolant system is isolated)

► Leaked helium vented first to PbLi storage tank then relief tank

(51)

► 11 s, leak flow rate approaches zero, end of initial phase of accident

(52)

► 50 s, long term drain-down of PbLi into storage tank is occurring

► Temperatures of TBM structures reducing (not shown)

(53)

(54)

(55)

(56)

Summary

► ITER will be the world’s largest fusion reactor, and the first to produce more energy than is required to sustain its operation. It will provide the test data required for designing a prototype commercial reactor.

Safety Analysis of the European Test Blanket Systems in ITER using MELCOR