FOCUS ON THE STUDIES IN SUPPORT OF FIRE SAFETY ANALYSIS: IRSN FIRE MODELLING APPROACH FOR NUCLEAR FUEL FACILITIES

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FOCUS ON THE STUDIES IN SUPPORT OF FIRE SAFETY ANALYSIS: IRSN FIRE MODELLING APPROACH FOR NUCLEAR FUEL FACILITIES

Raphael Meyrand, Julien Espargilliere

To cite this version:

Raphael Meyrand, Julien Espargilliere. FOCUS ON THE STUDIES IN SUPPORT OF FIRE SAFETY ANALYSIS: IRSN FIRE MODELLING APPROACH FOR NUCLEAR FUEL FACILI- TIES. International Workshop on Developments in Safety Assessment Approaches and Safety Man- agement Practices of Fuel Cycle Facilities, OECD/NEA/CSNI/WGFCS, Oct 2019, PARIS, France.

�hal-02635659�

International Workshop on Developments in Safety

Assessment Approaches and

Safety Management Practices of Fuel Cycle Facilities

Paris – october 7^th / 9^th, 2019

Focus on the studies in

support of fire safety analysis:

IRSN fire modeling approach for nuclear fuel facilities

Raphaël MEYRAND - IRSN Julien ESPARGILLIERE - IRSN

 Use of numerical simulations for fire effects evaluation on safety equipment

• Definition of malfunction/degradation criteria for safety equipment

• Definition of fire scenarios including possible propagations

• Evaluation of the fire development according to the success or failure of the actions on room ventilation control and human intervention

 For the case-study, the SYLVIA code was used to perform computations

 SYLVIA (IRSN zone code) is a simulation tool adapted for a fire modeling in an industrial facility equipped with a ventilation network

• Fire and plume flow are modeled with a correlative approach from the literature

• Ventilation network is modeled as an electric circuit:

pressure cascade ↔ electric potential & flow-rate ↔ intensity

IRSN approach: use experimental results to define safety criteria (malfunction, degradation…) and SYLVIA fire inputs (HRR, combustion products…)

IRSN safety assessment method

Case study description (1/2)

 Fire Room (225 m³)

 Connecting Zones (CZ)

• Equipment (67 m³, double door)

• Staff (20 m³, door)

 Corridors (283 m³)

• Fire cell: fire resistance duration 90 min

• Containment cell

• Electrical cabinets row - ensure power of equipment important for safety

→ Cabinet: volume = 1.6 m³, mass of components = 170 kg (~1700 MJ)

• Glove boxes (GB): contain radioactive materials

 Fire and containment compartmentation

 GB design

• Volume: 0.97 m³

• Pressure: -200 Pa

• 4 metal panels: floor, roof, 2 facing walls

• 2 “working” panels with 4 glove holes

→ LEXAN (10 mm) + leaded PMMA (50 mm)

Case study description (2/2)

 Nuclear ventilation system

• Ventilation rate: GB (15 h^-1), room (5 h^-1), CZ (8 h^-1) and corridors (1.5 h^-1)

• Room and GB ventilation closed after fire detection (~ 2 min 30 s)

 Containment cell - Pressure cascade

• Fire room and CZ: 30 Pa

• CZ and corridors: 20 Pa

-12 daPa -9 daPa

-7 daPa

-9 daPa

-7 daPa

Experimental program: PICSEL

 PICSEL program objectives:

• Characterize the behavior of an electrical cabinet fire in free atmosphere

 Experimental setup:

• SATURNE hood, IRSN Cadarache (Fr)

 Relevant data:

• Fire heat release

• Heat flux

• Amount of soot produced

« Propagation de l’Incendie de Combustibles Solides dans un

Environnement Laboratoire et usine »

Ref.1: M. Coutin, Phenomenological description of actual electrical cabinet fires in a free atmosphere – INTERFLAM 2007

Experimental program: Glove box fire

 GB fire program objectives:

• First subprogram: characterization of glove box fire

• Second subprogram: characterization of release factors for GB fire with Pu

surrogate

 Experimental setup:

• SATURNE hood, IRSN Cadarache (Fr)

 Relevant data:

• Fire heat release

• Heat flux

• Amount of soot produced

• Release factors (Pu surrogate)

Ref.2: Coutin M., Glove box fire behaviour in free atmosphere, Smirt Post conference Seminar), 2017

Experimental program: STARMANIA

STARMANIA experimental setup

 STARMANIA experiments main objectives:

• Determination of the differential pressure value for equipment failure (rupture)

• Determination of the aeraulic resistance evolution of the equipment

 Experimental setup:

• STARMANIA, IRSN Saclay (Fr)

 Relevant data:

• Equipment aeraulic resistance evolution

• Equipment rupture threshold

Ref.3: L. Bouilloux, Characterization of the Behavior of Containment Equipment under Mechanical and Thermal Stresses in STARMANIA Facility – EUROSAFE 2003

 Calculations performed with SYLVIA 1.6.3 (IRSN zone model code)

 Fire modeling

• Fire modeled as a pool fire  effect of O₂ depletion on fire duration (pyrolysis)

• Simple reaction model: fuel + Y_O2 O₂ → Y_CO2 CO₂ + Y_CO CO + Y_H2O H₂O + Y_soot C

• HRR and species mass production rates from IRSN experiments (cabinet and GB)

 Containment effect (O₂ depletion) - models for limiting the burning rate

• Lower Oxidant Limit [LOL] (fire extinguishment below a defined O₂ threshold)

• Peatross & Beyler [P&B] (linear decay of pyrolysis rate with O₂ concentration)

 Ventilation modeling

• Simple ventilation network modeling: pressure gap boundary condition

→ Ventilation resistances calculated with steady-state conditions

• Leakage resistances (dampers, doors) from IRSN experiments (STARMANIA)

• 2 ventilation control modes: closed or maintained (fire detection failure)

Generic model assumptions

 Scenario: fire starting in the open-door electrical cabinet facing GB, spreading to adjacent closed-door cabinets after 15 minutes (assumption)

 Issues

• Loss of containment of GBs?

Gloves: 2 kW/m² (incident flux) or 85°C (material) Ventilation pipe: 4 kW/m² or 125°C

• Fire spreading to GBs?

PMMA: 15 kW/m² or 250°C Flashover: gas > 500°C

• Fire cell failure?

Fire duration > 90 minutes Gas temperature > ISO-834

• Containment cell failure?

P[cell] > P[connecting zone] > P[corridor]

Double-door break if ΔP_door > 18 hPa

Scenario – Description

A conservative approach assumes that a material ignites or breaks as soon as the critical flux is reached

Scenario – Results (1/6)

 Does cabinet fire cause a loss of containment of GBs?

[G] gloves: surface temperature = 85°C or incident heat flux = 2 kW/m²

[V] GB ventilation pipes (PVC): surface temperature = 125°C or incident heat flux = 4 kW/m²

Maintained ventilation

Closed ventilation

LOL - 8 % Yes - [G] [V] Yes - [G] [V]

LOL - 10 % Yes - [G] [V] Yes - [G] [V]

LOL - 12 % Yes - [G] [V] Yes - [G] [V]

P&B - 11.5 % Yes - [G] [V] Yes - [G] [V]

 Safety conclusion: in case of an open-door cabinet fire, glove box containment is always lost  fire protections requested

Scenario – Results (2/6)

 Does fire spread from cabinet to glove boxes ?

[P] leaded PMMA: surface temperature = 250°C or incident heat flux = 15 kW/m² [F] flashover conditions: ambient gas temperature > 500 °C

Maintained ventilation

Closed ventilation

LOL - 8 % No No

LOL - 10 % No No

LOL - 12 % No No

P&B - 11.5 % No No

 SYLVIA results predict no fire spreading to GBs:

• Flashover conditions not reached in the fire room

• Limit of SYLVIA (point source model)

Scenario – Results (3/6)

 Critical analysis of SYLVIA radiative flame model

• SYLVIA uses a point source model + target modeled as an elementary surface

→ Point source model is valid for a far-off target & under-estimates configuration factor

 Computation of a solid flame model radiative flux

→ Inputs: SYLVIA computed data (HRR + flame height)

→ Flame considered as a plane source

Maintained ventilation

Closed ventilation

LOL - 8 % Yes - [P] Yes - [P]

LOL - 10 % Yes - [P] Yes - [P]

LOL - 12 % Yes - [P] Yes - [P]

P&B - 11.5 % No No

 In most case, solid flame model predicts that fire could spread to GB

 additional analysis of the O₂ limitation law validity is required

Scenario – Results (4/6)

 Critical analysis of O₂ limitation law

• LOL: Solid flame predicts fire could spread to GB

→ results are consistent with IRSN experimental observations in PICSEL program

• P&B: Solid flame predicts no fire spreading

→ SYLVIA HRR with a P&B law is underestimated for all of open-door cabinet fire tests performed in a confined atmosphere

→ P&B could be unsatisfactory for a complex solid fire source

 Safety conclusion: in case of an open-door cabinet fire, fire could spread to glove boxes  perform SYLVIA calculation considering GB ignition

PICSEL xp isoflux map for open-door cabinet fire (Ref.1)

Ref.4: M. Coutin et al., Characterisation of open-door electrical cabinet fires in compartments, Nuclear Engineering and Design (286) pages 104–115, 2015

Comparison of xp/computed HRR for open-door cabinet fire in a room (Ref.4)

Scenario – Results (5/6)

 Does the fire duration cause a failure of fire cell?

[D] fire duration > 90 minutes (5400 s)

[G] gas temperature > ISO-834 fire curve (ISO fire growth)

T_ISO-834 = 20 + 345.log( 8.t + 1 ) [ T_ISO-834 in °C, t in minutes ]

Maintained ventilation

Closed ventilation

LOL - 8 % No No

LOL - 10 % No No

LOL - 12 % No No

P&B - 11.5 % No No

 Safety conclusion: in case of an open-door cabinet fire followed by a GB fire, fire cell is properly designed (thermal effects)

Scenario – Results (6/6)

 Does the fire cause a failure of containment cell?

[R] reversal of pressure cascade system: P[cell] > P[connecting zone] > P[corridor]

[D] double-door breaking: P[cell] – P[connecting zone] > 18 hPa

Maintained ventilation

Closed ventilation

LOL - 8 % Yes - [R] Yes - [R]

LOL - 10 % Yes - [R] Yes - [R]

LOL - 12 % Yes - [R] Yes - [R]

P&B - 11.5 % No No

 Safety conclusion: in case of an open-door cabinet fire followed by a GB fire, containment cell is not properly designed. Improvement leads:

• Action on ventilation control mode: increase pressure cascade, ventilation rate of CZ

• Implementation of an automatic fire-extinguishing system…

Conclusions

 Key issues for a relevant use of simulations in a safety analysis:

• A perfect knowledge of the plant input data (rooms, ventilation network, leakage rates…)

• A improved knowledge of the fire input data (HRR, combustion products…)

• A strong knowledge of damage criteria for safety equipment (gas temperature and concentration of soot leading to the malfunction/failure of components…)

 Case-study conclusions

• Impact on close targets have to be carefully assessed and may have to be rerun (limit of point source model)

Further Research and Development studies are needed

to assess the use of simulations in a safety analysis !

Thank you for your attention

More details:

[email protected]