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 possible in various configuration of the barriers in the NBI cell M. T. Porfiri Garching 10th October 2006 Meeting on Occupational Radiation Exposure – ALARA in ITER: further refinement

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Outline Accident scenarios Accident scenarios Inventories Inventories Technical solutions Technical solutions Data necessary for the analysis Data necessary for the analysis Tools Tools Schedule Schedule

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 NB COMPONENTS - MAINTENANCE SCHEME MODIFICATION (Tesini 12/05) NB CELL HOT CELL LIFT 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 LIFT NB CELL HOT CELL LIFT Corridor Design to be developed

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Accident scenarios The starting point for this task is the definition of the accident scenarios in order to have a clear picture of all possible paths for dust, tritium, water and helium releases of all possible paths for dust, tritium, water and helium releases of all the possible impair of the containment as a consequence of coolant or energy releases. of all the possible impair of the containment as a consequence of coolant or energy releases. After the achievement of the design documentation it will be possible to describe the accidents and select between them those affecting the NBI containment in normal operation, maintenance and baking conditions. What we are proposing is not a real FMEA but a simplified picture of basic failures and verification of the effectiveness and correct intervention of the existing barriers. It is important to define the operating parameters of the NBI system.

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006Inventories Design Description Document (DDD 5.3) Neutral Beam Heating & Current Drive (NB H&CD) System - N 53 DDD R 0.1, July 2001, ITER T Dust Energies

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Technical solutions It is not the scope of the task to find the technical solutions but the scope is to investigate the possible problems presented, from the safety point of view of the different configurations like, for example: - additional barriers like double walls in the NBI cell - bypass duct to isolate the break in the piping - reinforcement of the weak points in the interconnection of the ducts (bellows) (bellows) - double wall pipes for the ducts directly connected with the VV By means of a parametric approach the different configurations for the position of the radiological barriers will be anlayzed. for the position of the radiological barriers will be anlayzed.

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Data necessary for the analysis Geometrical data of the zones and components in the NBI system Geometrical data of the zones and components in the NBI system Features of the materials (density, conductivity, thermal capacity, Features of the materials (density, conductivity, thermal capacity, melting point, etc.) melting point, etc.) Lay out of the different components in the NBI cell Lay out of the different components in the NBI cell Inventories (dust, tritium, activation corrosion products, water, Inventories (dust, tritium, activation corrosion products, water, helium, energies) helium, energies) Features of ventilation and detritiation system and logic of their Features of ventilation and detritiation system and logic of their intervention (timing, set points) intervention (timing, set points) Instrumentation and control logic Instrumentation and control logic decay heat decay heat

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Tool: 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 1. TH boundary conditions for CH reactions; 2. quantity of each chemical compound in gaseous phase; 3. concentration of airborne reactants; 4. TH boundary conditions for AV transport phenomena; 5. heat sources associated to transported species & aerosol concentrations capable to modify gas physical 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

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Thermal-hydraulic models Two-region model adopted inside each control volume: liquid sump & atmosphere (steam + mixture of incondensable gases). Thermal equilibrium assumed in each region Two-region model adopted inside each control volume: liquid sump & atmosphere (steam + mixture of incondensable gases). Thermal equilibrium assumed in each region Solution of mass, energy & momentum balance equations Solution of mass, energy & momentum balance equations Non-equilibrium effects due to superheated steam injection into the sump or subcooled water spray in the atmosphere separately accounted for Non-equilibrium effects due to superheated steam injection into the sump or subcooled water spray in the atmosphere separately accounted for Steam condensation modelled by splitting bulk and wall condensation (influencing, respectively, aerosol growth and aerosol diffusiophoretic deposition) Steam condensation modelled by splitting bulk and wall condensation (influencing, respectively, aerosol growth and aerosol diffusiophoretic deposition)

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Thermal-hydraulic models (cont’d) Actual pool levels to account for aerosol scrubbing & wetted heat structure surface Actual pool levels to account for aerosol scrubbing & wetted heat structure surface Allowance for counter-current flow conditions at junctions (two- dimensional flows) Allowance for counter-current flow conditions at junctions (two- dimensional flows) Heat transfer accounting for wall thermal conductivity changes due to aerosol deposition, decay heat sources or chemical reactions heat Heat transfer accounting for wall thermal conductivity changes due to aerosol deposition, decay heat sources or chemical reactions heat Account for local thermal-hydraulic parameters with strong influence on aerosol deposition & resuspension mechanisms (i.e. hydraulic diameter, local fluid velocity & Reynolds number, etc.) Account for local thermal-hydraulic parameters with strong influence on aerosol deposition & resuspension mechanisms (i.e. hydraulic diameter, local fluid velocity & Reynolds number, etc.)

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Aerosol and vapor models Aerosols assumed as well-mixed inside volumes Aerosols assumed as well-mixed inside volumes Corrective action provided for volumes having only a radial mixing, like long pipes having a concentration gradient Corrective action provided for volumes having only a radial mixing, like long pipes having a concentration gradient Sub-nodalization of volumes as regards gas-aerosol-wall interactions Sub-nodalization of volumes as regards gas-aerosol-wall interactions Correction to account gas recirculation influence on aerosol transport (recirculation velocity) Correction to account gas recirculation influence on aerosol transport (recirculation velocity)

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Phenomena considered by Aerosol and Vapor Transport section for each control volume and structure 2/4

Kick off meeting EFDA Task TW6-TSS-SEA2.1 Garching 10th/10/2006 Schedule 1. Achievement of the main documents of the updated design and radiation field data and radiation field data November 2006 November Outline and discussion of the accident (or accidents) to be analized analized December 2006 December Accident analysis February 2006 February Draft report March 2006 March Final report April 2006