Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 ENEA Engineering approach of the potential accident scenario leading to the worst release.

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006

ENEA

Engineering approach of the Engineering approach of the potential accident scenario potential accident scenario leading to the worst release leading to the worst release

possible in various configuration possible in various configuration of the barriers in the NBI cellof the barriers in the NBI cell

M. T. PorfiriM. T. Porfiri

Garching 10th October 2006

Meeting on Occupational Radiation Exposure – ALARA in ITER:

further refinement


OutlineOutline

Accident scenarios Accident scenarios

InventoriesInventories

Technical solutionsTechnical solutions

Data necessary for the analysisData necessary for the analysis

ToolsTools

ScheduleSchedule


NB COMPONENTS - MAINTENANCE SCHEME MODIFICATION (Tesini 12/05)

NB CELL

HOT CELL

LIF

T

2005

The NB cell is a RED ZONE

No cask use in NB cell (proposal)

1 NB source cask, small, traveling in corridor only (proposal)

1998 – 2003

The NB cell is a GREEN ZONE

1 NB source cask, big

Direct HC access from NB cell

2003

The NB cell is a GREEN ZONE

1 NB source cask, big

1 NB shuttle cask, small

HC indirect access through lift

Components’ double handling

NB CELL

HOT CELL

LIF

T

NB CELL

HOT CELL

LIF

T

Cor

ridor

199

8 -

2003

200

320

05

Design to be developed


Accident scenariosAccident scenarios

The starting point for this task is the definition of the The starting point for this task is the definition of the accidentaccident scenariosscenarios in order to have a clear picture in order to have a clear picture

of all possible paths for of all possible paths for dustdust, , tritiumtritium, , waterwater and helium and helium releasesreleases

of all the possible impair of the of all the possible impair of the containmentcontainment as a consequence of as a consequence of coolant coolant or or energyenergy releases. releases.

After the achievement of the design documentation it will be After the achievement of the design documentation it will be possible to describe the accidents and select between them those possible to describe the accidents and select between them those affecting the NBI containment in normal operation, maintenance and affecting the NBI containment in normal operation, maintenance and baking conditions. baking conditions.

What we are proposing is not a real FMEA but a What we are proposing is not a real FMEA but a simplified picture of simplified picture of basic failuresbasic failures and verification of the effectiveness and correct and verification of the effectiveness and correct intervention of the intervention of the existing barriersexisting barriers..

It is important to define the It is important to define the operating parametersoperating parameters of the NBI system. of the NBI system.


InventoriesInventories

Design Description Document (DDD 5.3) Neutral Beam Heating & Current Drive (NB H&CD) System - N 53 DDD 29 01-07-03 R 0.1, July 2001, ITER

T Dust

Energies


Technical solutionsTechnical solutions

It is not the scope of the task to find the technical solutions but the It is not the scope of the task to find the technical solutions but the scope is to investigate the possible scope is to investigate the possible problemsproblems presented, from the presented, from the safety point of view of the safety point of view of the different configurationsdifferent configurations like, for example: like, for example:

- additional barriers like additional barriers like double wallsdouble walls in the NBI cell in the NBI cell

- bypass bypass duct to isolate the break in the piping duct to isolate the break in the piping

- reinforcement reinforcement of the weak points in the interconnection of the ductsof the weak points in the interconnection of the ducts (bellows)(bellows)

- double wall pipesdouble wall pipes for the ducts directly connected with the VV for the ducts directly connected with the VV

By means of a By means of a parametric approachparametric approach the different configurations the different configurations

for the position of the radiological barriers will be anlayzed.for the position of the radiological barriers will be anlayzed.


Data necessary for the analysisData necessary for the analysis

Geometrical dataGeometrical data of the zones and components in the NBI system of the zones and components in the NBI system Features of the Features of the materialsmaterials (density, conductivity, thermal capacity, (density, conductivity, thermal capacity, melting point, etc.)melting point, etc.)

Lay out of the different components in the NBI cellLay out of the different components in the NBI cell

InventoriesInventories (dust, tritium, activation corrosion products, water, (dust, tritium, activation corrosion products, water, helium, energies)helium, energies)

Features of Features of ventilationventilation and and detritiationdetritiation system and logic of their system and logic of their intervention (timing, set points)intervention (timing, set points)

InstrumentationInstrumentation and and controlcontrol logic logic decay heatdecay heat


Tool: ECART CodeTool: ECART Code Computer tool developed by a pool of Italian research

institutions (CESI, Pisa University, Milan Polytechnic), with the support of EU and French EdF (& ENEA FUS for fusion models)

Simulation of chemical reactions and transport of radioactive gases and aerosols under two-phase flow transients using a built-in thermal-hydraulic model

THERMAL

HYDRAULICS

AEROSOL

TRANSPORT

CHEMICAL

EQUILIBRIA

1

2

3

4

5

1.1.TH boundary conditions for CH TH boundary conditions for CH reactions;reactions;

2.2.quantity of each chemical compound in quantity of each chemical compound in gaseous phase;gaseous phase;

3.3.concentration of airborne reactants;concentration of airborne reactants;4.4.TH boundary conditions for AV TH boundary conditions for AV

transport phenomena;transport phenomena;5.5.heat sources associated to transported heat sources associated to transported

species & aerosol concentrations species & aerosol concentrations capable to modify gas physical capable to modify gas physical properties.properties. Information about the most representative compounds for LWR SA

Further compounds involved in fusion problems included Simulation of TH transients, CH reactions capable of producing H2 and

dust transport Includes materials of typical tokamak designs & steel and Cu corrosion

products Models for reactions between air or steam and Be, W and graphite walls

and dusts


Thermal-hydraulic modelsThermal-hydraulic models

Two-region model adopted inside each control Two-region model adopted inside each control volume: liquid sump & atmosphere (steam + volume: liquid sump & atmosphere (steam + mixture of incondensable gases). Thermal mixture of incondensable gases). Thermal equilibrium assumed in each regionequilibrium assumed in each region

Solution of mass, energy & momentum balance Solution of mass, energy & momentum balance equationsequations

Non-equilibrium effects due to superheated steam Non-equilibrium effects due to superheated steam injection into the sump or subcooled water spray in injection into the sump or subcooled water spray in the atmosphere separately accounted forthe atmosphere separately accounted for

Steam condensation modelled by splitting bulk and Steam condensation modelled by splitting bulk and wall condensationwall condensation (influencing, respectively, (influencing, respectively, aerosol growth and aerosol diffusiophoretic aerosol growth and aerosol diffusiophoretic deposition)deposition)


Thermal-hydraulic models (cont’d)Thermal-hydraulic models (cont’d)

Actual pool levels to account for Actual pool levels to account for aerosol scrubbingaerosol scrubbing & & wetted heat structure surface wetted heat structure surface

Allowance for counter-current flow conditions at Allowance for counter-current flow conditions at junctions (two-dimensional flows)junctions (two-dimensional flows)

Heat transfer accounting for wall thermal conductivity Heat transfer accounting for wall thermal conductivity changes due to aerosol deposition, decay heat sources changes due to aerosol deposition, decay heat sources or chemical reactions heat or chemical reactions heat

Account for local thermal-hydraulic parametersAccount for local thermal-hydraulic parameters with with strong influence on aerosol deposition & resuspension strong influence on aerosol deposition & resuspension mechanisms (i.e. hydraulic diameter, local fluid velocity mechanisms (i.e. hydraulic diameter, local fluid velocity & Reynolds number, etc.)& Reynolds number, etc.)


Aerosol and vapor modelsAerosol and vapor models

Aerosols assumed as Aerosols assumed as well-mixedwell-mixed inside volumes inside volumes

Corrective action provided for volumes having only Corrective action provided for volumes having only a radial mixing, like long pipes having a a radial mixing, like long pipes having a concentration gradientconcentration gradient

Sub-nodalization of volumes as regards Sub-nodalization of volumes as regards gas-gas-aerosol-wall interactions aerosol-wall interactions

Correction to account gas recirculation influence on Correction to account gas recirculation influence on aerosol transport (aerosol transport (recirculation velocityrecirculation velocity))


Phenomena considered by Aerosol and Vapor Transport section for each control volume and

structure

2/4


ScheduleSchedule1.1. Achievement of the main documents of the updated design Achievement of the main documents of the updated design

and radiation field dataand radiation field data

November 2006November 2006

2.2. Outline and discussion of the accident (or accidents) to be Outline and discussion of the accident (or accidents) to be analizedanalized

December 2006December 2006

3. 3. Accident analysisAccident analysis

February 2006February 2006

4.4. Draft report Draft report

March 2006March 2006

5. 5. Final reportFinal report April 2006April 2006

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 ENEA Engineering approach of the potential accident scenario leading to the worst release.

Documents

nb cell proposal

nb source cask

meeting efda task tw6tss

nb shuttle cask

nbi cell bypass duct

possible paths

porfiri garching

possible problems