ML18213A077
| ML18213A077 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/2018 |
| From: | Tammie Rivera NRC/RES/DRA/FRB, Electric Power Research Institute |
| To: | |
| Shared Package | |
| ML18213A072 | List: |
| References | |
| Download: ML18213A077 (16) | |
Text
Module III - Fire Analysis Fire Fundamentals Compartment Fires Joint EPRI/NRC-RES Fire PRA Workshop August 6-10, 2018 A Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES)
Outline Compartment fire dynamics - qualitative description Pressure profiles and vent flows The hot gas layer Heat transfer Combustion products 2
Qualitative Description Extraction System (e.g., smoke purge system)
Ceiling Jet Plume Smoke Layer Injection System (e.g., HVAC)
Figure 2.1: Overview of enclosure fire processes 3
Phases in a Compartment Fire Ignition: Process that initiates an exothermic combustion reaction
- Piloted or auto (spontaneous) ignition
- Accompanying process can be flaming or smoldering combustion Growth
- Can occur at different rates depending on type of fuel, interactions with surroundings, and access to oxygen Hot gas layer buildup and room heat-up Flashover: Rapid transition to a state of total surface involvement of combustible materials within an enclosure
- Temperatures between 500°C (930°F) to 600°C (1,110°F), or
- Heat fluxes between 15 kW/m2 to 20 kW/m2 4
Phases in a Compartment Fire Fully developed fire: The energy released in the enclosure is at its greatest level and is very often limited by the available oxygen
- Gas temperatures between 700°C (1,300°F) and 1200°C (2,200°F)
Decay: Fuel becomes consumed, fire intensity decreases
- Hazard indicators (temperature and heat fluxes) start to decrease Other terminology may include
- Pre-flashover fire Focus on life safety and sensitive targets In NPP, cables damage at 218°C (424°F) for thermoplastic cables and 330°C (626°F) for thermoset cables Main focus of NPP analysis
- Post-flashover fire:
Focus in structural stability and safety of firefighters Not generally an issue for NPP applications 5
Compartment Fires 6
Compartment Fires 7
Sense of Scale 8
Pressure Profiles & Vent Flows H
Ho Z
+
amb Pressure H
Z
+
Ho amb Pressure H
Z +
Ho amb Pressure 9
Pressure Profiles & Vent Flows H
Z +
Ho Zu amb Pi (h ) = Pi (0 ) o gZu u g (h Zu ) Inside Profile Po (h ) = Po (0 ) o gh Outside Profile Pi o (h ) = Pi (0 ) + o g (h Zu ) + u g (Zu h ) P Profile 10
Pressure Profiles & Vent Flows Under Normal Over Pressurized Pressurized In Out Out In Out In pi-o(0) pi-o(0) pi-o(0) 11
Hot Gas Layer or Smoke Layer Accumulation of hot gases in the upper part of the room Mass: entrainment (~90%) and combustion products (~10%)
Volume: entrainment, combustion products, and expansion due to energy added Temperature rise: expansion generates a larger volume than corresponding mass resulting in lower gas densities.
Conservation of mass and energy 12
Hot Gas or Smoke Layer Room size:
Simulation Results
- 22 x 7 x 3.7 m Upper Layer Height Fire: ~1 MW 4.5 4
Door: 2 x 2 m 3.5 3 MAGIC 2.5
[m]
2 CFAST 1.5 Data 1
0.5 0
0 200 400 600 800 1000 1200 Time [Sec]
13
Hot Gas or Smoke Layer Conservation of Mass
- Rate of change of mass in the control volume Accumulation
- Mass flow through the control surface Plume flow Supply and exhaust systems Flow through doors and windows 14
Heat Transfer To walls
- Convection and radiation
- Conduction losses To targets
- Convection and radiation Heat losses from the compartment include:
- Conduction through walls
- Convection (gas flow) and radiation escaping through openings and vents 15
Heat Transfer Conduction Convection Radiation 16