MANAGEMENT OF FIRE RISK INSIDE INB

(Installations Nucleaires de Base)

22 April 2013

A. Polato*

* The research project has been supported by a Marie Curie Early Initial Training Network Fellowship of the European Community’s Seventh Programme under contract number (PITN-GA-2010-264330-CATHI)

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Contents

• Basic Definitions and Concepts• Reference Laws• Fire and ventilation• Conclusions• Tests results

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BASIC DEFINITIONS AND CONCEPTS

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INB definition is given by the “Décret 2007-830 art-3” : legifrance

• Are considered as INB:– Nuclear Reactors,– Nuclear combustible treatment plants (enriching, fabrication, waste)– Installations handling radioactives or fissiles (art.2) (ISOLDE, N-TOF);– Particle accelerators (art.3) (Primary area of CERN)

2° Les accélérateurs d'ions, si les deux conditions suivantes sont simultanément remplies :a) L'énergie pouvant être communiquée aux ions est supérieure à :

300 MeV pour les ions de nombre de masse inférieur ou égal à 4 ;75 MeV par nucléon pour les ions de nombre de masse supérieur à 4 ;

b) La puissance correspondante du faisceau d'ions est supérieure à 0,5 kW.

• Design, construction, running and dismantling of INBs are managed with the supervision of the Autorite de surete nucleaire (ASN)

INB: Installation Nucleaire de Base

Law not applicable to CERN but good practice on nuclear installation may be requested byTripartite

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Combustion is the result a fast and exothermic reaction of oxidation.Necessary for a combustion is the presence of 3 ingredients described by the fire triangle:

FIRE

• Fuel: metals, solids, liquids, gases (higher and lower heating value;

• Comburent: Oxygen• Energy: f(combustible, physical state, T, p)

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Energy is released by a fire to the environment via:• Convection: 80% of the energy• Conduction: 10% of the energy• Radiation: 10% of the energy• Projection: of glowing objects

RESULT OF A COMBUSTION

Fuel + Comburent → products of combustion + Energy Complete combustion of methane:

CH4 + 2O2 → CO2 + 2H2O + Energy

If combustion is incomplete (low oxygen) other products like CO maybe present (CO is a Fuel)

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Examples:• 1 kg wood: 17 MJ• Offices and houses: 500 ÷ 900 MJ/m²• Furniture factories: 1300 MJ/m²• Printing works: 2800 MJ/m²• Electronic racks: 800 MJ/m³ with a 100 % full rack (CEA)

CHARACTERIZATION OF FUELS INSIDE A ROOM

Heat Load: amount of heat released by the complete combustion of the combustible materials inside the room [MJ]Heat load density: MJ/m²

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FIRE IN AN OPEN ENVIRONMENT

• Fire is continuously fed in comburent (air through open windows);• High and clear flames (evidence of a fire);• Heat is released from the openings• The driving force of the fire is the amount of fuel that will carry on

burning unless it will undergo to complete oxidation;• The only way to prevent a fire or reduce its consequences is

– The reduction of the combustible material;– Reduce the amount of fuels that is in the form of chops,dusts, liquids and

gases;– In case of liquid reduce the amount of free surface exposed to comburant.

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FIRE IN AN CLOSED ENVIRONMENT

TYPICAL CASE IN INB• No continuous flow of comburent (the environment is closed);• The driving force is the amount of oxygen that is present in the room;• Fuels undergo to incomplete combustion, with no flames;• Heat is not released hence high temperature and high pressure inside the room

(isolated walls);• Incomplete combustion generates a high amount of unburnt gases at high

temperature (two ingredients of the fire triangle)• As soon as comburent goes into the volume: backdraft or smoke explosion

backdraft backdraft2 • The only way to prevent a fire or reduce its consequences

– The reduction of the air renewal rate (until its complete stopping in case of fire)

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REFERENCE LAWS (applied in France)

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ARRETE DU 31/12/99 MODIFIE 31/01/2006

• Defines the technical regulation to prevent, limit the consequences of accidents resulting in the running of INB;

• From July 2013 the arrêté will be updated with a new modification;

• It is applied to new installations and to existing installations;• It covers different domains (noise, pollution, wastes etc.) but

articles from 28 to 47 are dedicated to the fire and nuclear risks;

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MAIN CONCEPTS EXPLAINEDSafety measures with respect to the fire risk are taken in order to:• Limit the propagation of a fire;• Protect the nuclear safety functions (sureté);• Limit the propagation of smokes and Toxic, Radioactive, Inflammable, Corrosive, Explosive (TRICE) materials;• Allow to put and keep the INB in a safe state;• Allow and facilitate the evacuation of workers;• Allow and facilitate the access of rescue teams;Very general concepts regarding the:• Automatic detection system;• Fire sectors, confinement sectors, fire zones (to be avoided);• Fire resistant doors;• Fire resistance of structures;• Confinement (static/dynamic);• Fire fighting techniques• Handling of extinguishing products

The arrete is not a real technical guide.A “guide inter-exploitant sur le thème incendie de l’arrete du 31/12/99 modifie” has been developed and is in use in AREVA. It take into account also the “Code du travail”.

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Guide inter-exp.: ART. 42. VI - VENTILATION

1. Avoid the fire propagation via the ventilation;2. Limit the risk of explosive atmospheres;3. Avoid the spread of TRICE via the ventilation;4. Keep-on the pressure cascade;

That bring to:• Ensure Dynamic confinement also during a fire event;• Select fire resistant ducts (not always, but as a result of the fire analysis);• Preservation of the last level of filtration;• Preservation of the pressure cascade;• Limitation of the air supply during a fire.

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Guide inter-exp.: ART. 42. VI – SMOKE EXTRACTION1. Avoid the fire propagation via the smoke extraction2. Avoid the spread of TRICE via the smoke extraction;3. Allow rescue teams to intervene;4. Maintain the smoke extraction system operative;

Smoke extraction system is described in the Code Du Travail and should be compulsory for all the installations. But a smoke extraction system:• Enhance the spread of TRICE;• Doesn’t ensure the dynamic confinement during fire;• Doesn't pass through the last level filter• Doesn’t limit the supply of air to the fire;• Doesn’t keep the pressure cascade active;

As a conclusion no INB respect the Code du Travail concerning the smoke extraction, because of the priority given to the confinement of TRICE in case of fire

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FIRE AND VENTILATION

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FUNCTIONS OF A NUCLEAR VENTILATION SYSTEM

According to the ISO 17873:2004: Criteria for the design and operation of ventilation systems for nuclear installations other than nuclear reactors1. Confinement;2. Purification;3. Monitoring of the installation;4. Cleaning of the atmosphere;5. Conditioning;6. Comfort;

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CONFINEMENT

Protect workers, public and environment from the risk of spread of contamination.Confinement is made of two parts: 1. Static barrier: physical obstacle to the spread of contamination (walls).

The leaktightness is ensured during normal operation, but not during accidental or incidental situations;

2. Dynamic barrier: created by the sense of the air flow (ΔP) towards zones at a higher levels of contamination;

The combination of the two barriers is defined as:Confinement System

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DYNAMIC CONFINEMENT

1. Dynamic confinement shall compensate the non perfect leak tightness of the static barrier (way misinterpreted at CERN in the past decades );

2. Preferential flows of air towards most contaminated zones;3. ISO 17873 proposes for different zones at different levels of

contamination (normal and accidental) pressure values to be used.

4. The pressure hierarchy of the different rooms of an installation shall be decided on the base of the outcomes of risk analysis;

5. Main effects to be considered for the definition of the pressure cascade:– Building leak tightness;– Local thermal effects;– Wind effect on the external walls;

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DYNAMIC CONFINEMENT – LEAK TIGHTNESS

Some values:• Leak rate through a non classified door of 2 x 1.7 m² with a 3 mm

gap on the frame and 3 mm on lower part @ ΔP=40 Pa: 1100 m³/h

• In preliminary design phases a first approach value of the leak rate of a room shall vary from 0.4 h-1 to 0.2 h-1(the last for optimized building constructions)

• Real life examples in ISOLDE:– Average leak rate of the Class A laboratory: 0.65h-1;– Average leak rate of the ISOLDE Tunnel: 2 h-1;

DYNAMIC CONFINEMENT – THERMIC EFFECTS

equipment

Contaminated zone

Clean Zone

Clean Zone

h= 10m

Ttop=50°C

T=15°C

T=15°C

Chimney Effect:The air density difference between the hot air at the top (Ttop) and the cold air at the floor level, causes a pressure difference:

~ 15 Pa

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DYNAMIC CONFINEMENT – WIND

BUILDINGWIND

WIND

WIND

WIND

WIND

WIND

Height Positive pressure(wind speed 25 ÷ 130 km/h)

Negative Pressure(wind speed 25 ÷ 130 km/h)

10 m +23 Pa ÷ +650 Pa -15 Pa ÷ -410 Pa

20 m +31 Pa ÷ +860 Pa -20 Pa ÷ -540 Pa

30 m +36 Pa ÷ +1000 Pa -23 Pa ÷ -630 Pa

Height

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PURIFICATION

• Collect all the aerosols, and activated gas into well defined equipment (filters)• Different kind of filters according to the action to be performed (from

industrial to HEPA filters, charcoal filters and bubbling filters).• Filters shall be placed as close as possible of the contamination source. • Two levels of filtration shall be foreseen:

ΔP

ΔP

ΔP

ΔP

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MONITORING

• Function that ensures that the detection systems give a good picture of what is really happening in a room;

• Ventilation plays an important role, because an “omogeneous” ventilation of a room avoids dead zones where the sampling could be not reresentative.

• In this sense important is the difference between supplying and extraction :

• Supply: after 63D air speed is reduced by 90%

• Extraction: after 1D air speed is reduced by 90%;

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SF - SC• Fire Sector (SF): volume enclosed by physical barriers with a fire resistance selected

in accordance of the possible fire and with the intervention times considered for the rescue team;

• Confinement Sector (SC): volume enclosed by static and dynamic barriers whose characteristics shall, in case of fire limit the dispersion of TRICE out of the volume;

• Fire-Confinement Sector: existing in the past, not today

SC

SF

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FIRE SECTOR - PROTECTION MEASURES

Walls and passages, doors

fire resistant

Supply Fire Damper

Extraction Fire Damper

DAI

Fire Automatic Detection

Link between DAI

and FD

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CONFINEMENT SECTOR - PROTECTION MEASURES

DAI

SC Necessary if > 1mSv in case of fire

Confinement around the SF

Separation of the extraction of SC and

SF

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FIRE DAMPERS• External casing to be leaktight;• Able to be operated also during fire;• No intumescent gaskets;• No fuse for the closing of the damper;• Leaktight at 1500 Pa• Remote and manual controllable• Fire resistant cables

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FIRE DAMPERS

• Fire dampers shall be operated at 200°C or 400°C;• Ductworks shall resist to these temperatures;• The trigger temperature for the closing of the extraction fire damper

shall be 200°C (to avoid gas re-inflammation inside the ducts);• The extraction ducts shall be fire resistant;

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VENTILATION DURING A FIREThe role played by the ventilation system during a fire of an INB is:• Limit the release of TRICE materials in environment;• Limit the dissemination of TRICE materials in the building;• Protect the last levels of filtration;• Facilitate the evacuation of the installation• Facilitate the rescue teams intervention

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VENTILATION DURING A FIRE – initial state

DAI

T T S

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VENTILATION DURING A FIRE – fire detection

DAI

T T S

Fire detection:• Allow workers to go out of the SF• Close the supply fire damper

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VENTILATION DURING A FIRE – fire detection

DAI

T S

First level of filtration clogged:• Bypass the first level of filtration

DAI

T

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VENTILATION DURING A FIRE – fire detection

DAI

T S

If temperature after extraction fire damper >200°C• Close the extraction fire damper

DAI

T

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VENTILATION DURING A FIRE – fire detection

DAI

T S

If:• Last level of filtration clogged;• Smoke detected after the last level of filtration;• High temperature before the last level of filtration;Then:• Close the extraction• Shut all the fire dampers off

T T S

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CONCLUSIONS

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CONCLUSIONS - 1

FIRST LEVEL OF FILTRATION INSIDE THE SF, AND NO WAY TO BYPASS IT.

filter can be bypassed.

SINGLE LAST STAGE OF FILTRATION

Redundant solutions may be studied

SIMULTANEOUS CLOSE OF THE FIRE DAMPERS.

A change in the controls can change the behavior of the dampers

NO SC, POSSIBLE RELEASE OF

CONTAMINATION

Modifications to the existing systems can be made in order to move in the direction of a nuclear ventilation system

T

Additional T sensor can be added

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CONCLUSION - 2

• Modifications to existing installations can move in the sense of the nuclear good practice.

• Nevertheless if today there were an inspection from an Authority for Nuclear Safety (ASN like) CERN should carefully motivate the reasons that brought to non-conformities.

• Normally CERN doesn’t undergo to the full procedure of the INB, so there are no inspections from the ASN or similar Swiss authorities.

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TEST RESULTS

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SRIN 6 AND SRIN 7

T T

P

SRIN 6

T T

P

SRIN 7

-100 Pa

-100 Pa

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SRIN 6

SRIN 7

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SRIN 6 AND SRIN 7

P

LIC2 CA

P

FLIP10.1

-100 Pa

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LIC2 CA

FLIP10.1