ID 527

FIRE RISK ANALYSIS IN ITER TRITIUM BUILDING

Franck Lignini1, Joëlle Uzan-Elbez2, Jean-Philippe Girard2, Maria Teresa Porfiri3, Lina Rodríguez-Rodrigo4, and EISS Team*

1 FRAMATOME-ANP, 10 rue Juliette Récamier, 69456 Lyon Cedex 06, France

2 Direction de l‘Énergie Nucléaire, CEA , 13108 Saint-Paul-lez-Durance, France

3 Association Euratom-ENEA, Via Enrico Fermi, 00044 Frascati (Roma), Italy

4 Asociación Euratom-CIEMAT para Fusión, Avenida Complutense, 22, 28040 Madrid, Spain

Phone: +33 4 72 74 72 78, Fax: +33 4 72 74 73 30 œ Email: franck.lignini@ framatome- anp.com

Abstract

Events as fire have been considered in ITER documentation of low probability and a general approach has been defined in [1] to be developed later for the ITER Specific site.

It was said that —These hazards will be treated according to the industrial safety regulations and practices of the host country“. In the framework of studies for the European ITER site in Cadarache, an assessment of fire hazard has been done in order to ensure compliance with French safety requirements. In this report a summary of existing laws is presented and an example of the deterministic approach to be followed for the Preliminary Safety Report is given on the analysis of Tritium building design.

Keywords: ITER, Safety, Fire event

* See the list of EISS (European ITER Site Studies) Team members in [10].

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1. Introduction œ Objectives

At the end of 2003, Cadarache in France was selected as the host site for the European bid for ITER.

The licensing process in France requires that a Preliminary Safety Report (PSR) should be submitted to the Safety Authority for acceptance before the authorisation for construction is delivered. The PSR should describe the future facility and bring the demonstration that the design will enable the facility to meet the General Safety Objectives (GSO) and to comply with the current regulation. More details of the licensing process in given in [2].

Fire hazard is one of the main concerns for the safety of nuclear (as well as industrial) facilities. The PSR has therefore to include a Fire Hazard Analysis (FHA) in order to demonstrate that:

• preventative measures to limit the risk of a fire have been implemented, • should a fire occur, detection systems would quickly and effectively detect it, • design options combined to fire fighting measures would:

o allow safe evacuation of the staff, o limit the propagation of the fire and prevent the failure of important safety functions, o limit potential radioactive and or toxic release into the neighbouring environment, o allow fire suppression and limit the exposure of the fire team, o enable to maintain the facility in a safe state, during and after the fire.

2. Characterisation of the risk

The Tritium building is part of the ITER main complex. It houses the tritium plant which functions can be summarised as:

• process all tritiated gas streams from sources within the plant to produce the gas streams for the Tokamak fuelling (at specific flow rates and isotopic compositions), • confine tritium with multiple barriers (such as primary components, secondary enclosures and rooms), • detritiate tritium-containing waste streams and contaminated room air, and detritiate tritiated waste water to reject the detritiated remnants to the environment.

Tritium is present under different physico-chemical forms: gaseous tritium, tritiated water, hydride (metal or carbon), with a potential overall tritium quantity up to about 3000 grams. Much process equipment is installed inside glove boxes. Although the transparent materials used for the glove boxes walls will have high flammability temperatures and even higher auto-ignition temperatures, these are combustible materials. Depending on the size of the glove boxes, the corresponding heat load might be not negligible locally [6].

The process also requires use of high temperature device [3].

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Even if the atmosphere inside the glove boxes is filled with inert gas (nitrogen), the combination of combustible material locally in high quantity, with ignition sources and oxygen outside the glove boxes can induce locally a fire hazard.

A fire may lead to the degradation of the confinement function of the radiological barriers.

In a process room, the integrity of the process equipment usually made of stainless steel which forms the primary containment barrier and the integrity of the secondary containment (either ensured by a double metallic envelope or by a glove box) might be jeopardised.

Therefore, the spread of tritium in the atmosphere of the rooms which house these components and furthermore, the risk of tritium release outside the building via the HVAC (Heat Ventilation and Air conditioning) systems or by permeation through the walls must be considered, with subsequent impacts on the health (internal and external exposure to radiation) of the public, of the workers and of the firemen.

In addition, the specific risk bound to the flammability or explosivity of hydrogen isotopes must also be taken into account.

A preliminary design guide based on [4] was issued in order to advise designers, safety assessors, and regulators on the concept of fire protection for the ITER project. Though, it is still necessary to bring the demonstration that the design will meet the requirements fixed by the French regulation should Cadarache be selected as the host site for ITER.

3. Regulation - Methodology

Regulation

On the grounds of French regulations, fire fighting and protective provisions applicable to the design of future facilities and the operation of these facilities are specified in the decree dated 31/12/99 which sets out general technical regulations intended to predict and restrict external risks and harmful arising from the operation of INB (basic nuclear facilities) ([5] œ articles 41 to 44). This general text aims to predict all types of harmful chemical, toxic, radioactive effects. This decree sets out the general design principles with respect to fire and specifies the minimal provisions required.

Methodology

Defence in depth is applied in order to limit fire hazard. Measures related to

• fire prevention, • fire detection, • fire suppression, • compartmentalisation (fire zoning), • other limitation measures (HVAC + atmosphere détritiation management),

are implemented in the design. These measures are reviewed and, if necessary, modifications are proposed in order to improve the safety.

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4. Description of the Tritium building

The tritium building [2] is an eight storey building (~78 m long by 20 m wide by ~45 m high). Two basement levels are dedicated to services (tritiated water holding tanks, chiller units, maintenance. Levels 1, 2 and 3 host the tritium process (Storage and Delivery System (SDS), Tokamak Exhaust Processing (TEP), Analytical system (ANS), Isotope Separation System (ISS), W ater Detritiation System (W DS), Atmosphere (rooms + glove boxes) Detritiation systems (normal + stand-by) for the Tritium and for the Tokamak buildings. The last two levels are dedicated to the HVAC systems (Tokamak + Tritium buildings).

Staircases are provided at the north and south end of the building as well as a lift.

Vertical shafts for electrical cables and HVAC ducts are also implemented at the north and south ends of the building.

5. Application

FHA is an iterative process. Although, fire hazard was not one of the first concerns at the beginning of the ITER project compared to design problems, it was put in the list of priorities when the licensing process was started in the potential host countries. Preliminary analyses were performed in the frame of the EFDA work, starting from 2001 [6], [7], [8], [9].

In [6], the behaviour of the ISS room affected by a fire was studied using a 3D fluid-dynamic code for the simulation. The fire was supposed to be caused by a short circuit in the motor of a helium compressor with consequent burning of its oil content. The conclusion of the study was that a fire was not likely to release the tritium contained in the ISS process, because the temperatures reached in the ISS walls did not impair its containment function.

In [7], the compliance of the ITER design with the recommendations of the French regulation was reviewed and proposals of design modification were expressed in a qualitative way.

In [8], as a basis for the redaction of the FHA in the PSR, a functional analysis was carried out in order to check whether a fire might impair a safety function and whether radiological consequences might be expected. Accidental scenarios were studied. The impact of HVAC and ADS handling during the event were estimated using simple analytical models. More detailed proposals for design modifications or justification studies were expressed.

In [9], a number of rooms in the Tritium building (as well as in the Tokamak building) have been selected for detailed analysis:

• SDS and ANS because it contains the highest inventory of tritium, • Power cubicle rooms, • S-VDS/DRS (Standby Vent Detritiation System / Dryer Regeneration System) where redundant equipment is located in the same room, • Tritium monitoring, necessary for the correct operation of the ventilation systems, • VPS (Vacuum pumping system).

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The analysis is carried on in successive steps. First, a room screening is performed in order to establish hazardous inventories (chemical hazards, radiological source terms, fire loads). Then the simulation work to check the fire evolution and propagation is foreseen in two stages:

• the simplified model FDS (Fire Dynamics Simulation) has been used for the fire evaluation of the fire effects in the rooms selected as possible candidate for the detailed fire analysis, • in the second stage, the CFD code FLUENT will detail the fire event in the most critical zone selected by means of FDS application.

The FDS simulation for the SDS/ANS room (see figure 1) takes into account a fire triggered by a short circuit in a glove box with the subsequent burning of a small cable tray. The results of the simulation (see Figure 2) showed that there should be no propagation of the fire to the other equipment located inside the room, nor along the glove box thanks to the high ignition temperature of the materials. The maximum temperature (~ 350°C) near the roof should not be sufficient to start a new focus. Such a fire should not lead to tritium release into the room.

FDS simulations for the other rooms were also performed. The results did not show any risk of flashover in any of the rooms or any unacceptable consequences.

In the next stage, the FLUENT simulation will be performed in the SDS/ANS room, taking into account another trigger (glove box panel instead of cable tray) in order to check the influence of a higher amount of combustible material burning.

6. Conclusions

Fire Hazard Analysis is an iterative process that was initiated in 2001 with the ITER licensing process in the potential host countries.

Preliminary fire hazard analyses suggested design modifications in the Tritium building such as:

• as far as possible, removal of electrical power cabinets from the tritium process rooms, • modification of glove boxes layout in process rooms and implementation of fire barriers (fire proofed doors, fire dampers on the HVAC ducts) in order to prevent fire propagation to other rooms, • when possible removal of equipment with concentrated fire load and fast burning kinetics material (e.g. compressors), • design of the standby vent detritiation system in such a way that it might be able to operate efficiently should a fire induce tritium release in a room (maintain negative pressure in the room, protect catalyst from poisoning).

So far, the postulated fire scenarios simulated with FDS or FLUENT codes in the preliminary FHA for ITER Tritium showed no risk of tritium release.

Though, preventative fire compartmentalisation measures have been implemented. Fire detection systems will be installed inside glove boxes, electrical cabinets and rooms in order to be able to detect the occurrence of a fire as early as possible.

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The fire detection system and the monitoring of the HVAC and ADS will allow follow the evolution of the fire. Automatic or semi automatic fire suppression systems will be installed. They will be actuated from locations where tritium contamination risk can be excluded.

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References

[1] Technical Basis for the ITER Final Design, EDA Documentation Series I n° 22, IAEA, Vienna 2001 [2] L. Rodríguez-Rodrigo et al. —Progress in licensing ITER in Cadarache“ 23rd SOFT, Venice, Italy [3] Technical Basis for the ITER Final Design, EDA Documentation Series I n° 24, IAEA, Vienna 2002 [4] IAEA Safety Guide n°. 50-SG-D2 rev. 1 —Fire protection in plants“ [5] Arrêté du 31 décembre 1999 fixant la réglementation technique générale destine à prévenir et limiter les nuisances et les risques externes résultant de l'exploitation des installations nucléaires de base, Journal Officiel de la République Française pp. 2359- 2365 (15th Feb. 2000) [6] C. Rizzelo, M.T. Porfiri, P. Rocetti, —Fire Hazard in Tritium building“, ENEA report, august 2002 [7] F. Lignini, —ITER Tritium building œ Impact of the French fire regulation“, FRAMATOME-ANP report, December 2002 [8] F. Lignini, EISS 3 SL31, Rédaction RPrS étape 1, —Analyse incendie bâtiment Tritium“, en support au chapitre I.5.2.7 (Sectorisation Incendie), FRAMATOME-ANP report, October 2003 [9] M.T. Porfiri, —Evaluation of fire risk in ITER nuclear buildings“, EISS Cadarache SL32, EFDA 03-1082, Febrary 2004 [10] C. Lyraud et al. —Readiness of Cadarache for starting ITER construction“, 23rd SOFT, 2004, Venice, Italy

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List of figures

Figure 1: SDS œ ANS room œ FDS scheme

Figure 2: SDS œ ANS room œ FDS results

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Figure 1: SDS œ ANS room œ FDS scheme

Supply and Delivery System Ventilation outlets

Electric trays Ventilation Ducts Gas Chromatographs

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Figure 2: SDS œ ANS room œ FDS results

SDS-ANS room (B2-04) SDS-ANS room (B2-04)

3.0E-01 8.7E+03 4.0E+02 7.7E+03 2.5E-01 3.5E+02 BURN RATE 6(k.7gE/s+)03 HRR (kW ) 3.0E+02 2.0E-01 RAD LOSS (k5W.7)E+03

CONV LOSS (kW ) ) 2.5E+02 g

COND LOSS (kW ) k

4.7E+03 k

s W (

/ 1.5E-01 g s 2.0E+02

k 3.7E+03 s a O2

m 1.5E+02 1.0E-01 2.7E+03 1.0E+02 1.7E+03 5.0E-02 5.0E+01 7.0E+02 0.0E+00 0.0E+00 -3.0E+02 0 600 1200 1800 2400 3000 3600 0 600 1200 1800 2400 3000 3600 time (s) time (s)

SDS-ANS room (B2-04) SDS-ANS room (B2-04)

1.0E+03 1.00E+00 over fire trigger Fuel ventilation outlet 8.00E-01 8.0E+02 O2 )

N2 C ° (

6.00E-01 6.0E+02 e g

H2O r k / u t g a r

k CO2

4.00E-01 e

p 4.0E+02 CO m e H2 t 2.00E-01 2.0E+02 Soot

0.00E+00 0.0E+00 0 0.2 0.4 0.6 0.8 1 0 600 1200 1800 2400 3000 3600 fraction time (s)

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