In-cell solvent fire for presentation · solvent fire at a reprocessing plant Mr. Yoshikazu...
Transcript of In-cell solvent fire for presentation · solvent fire at a reprocessing plant Mr. Yoshikazu...
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Probabilistic examination of an in-cell solvent fire at a reprocessing plant
Mr. Yoshikazu Tamauchi, Mr. Satoshi Segawa, Mr. Katsuyoshi Omori, Mr. Kunihiko Ogiya, Mr. Yoshiaki Hayashi, Mr. Kazumi Takebe and Dr. Shingo Matsuoka
Safety Technology Office, Japan Nuclear Fuel Limited
October 16-18, 2007
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Introduction
An in-cell solvent fire is a typical accident for assessment in any reprocessing plant
The purpose of this report is to reexaminethe fire from a probabilistic viewpoint quantifying
its occurrence frequency and consequence
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Contents
Safety measures and accident scenario of an in-cell solvent fire
Quantification of frequency
Quantification of consequence
Conclusion
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The cause of an in-cell solvent fire
Three conditions are necessary to occur simultaneously.
Organic solventleakage
Ignitionsource
In-cellfire
may occur Heat source
Piping rupture, etc…
Electrostatic spark, etc…
Decay heat, etc…
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The outline of safety measures
Leakage detector
SJP
Connected to ground
Temperature indicator
HW
Heat exchangerHW
SR
Fire damper
CO2
extinguisher system
CO2 Injectionnozzle
Firedetector
Main stack
Cell exhaust blower
Stripping pulsed column
Plutonium purification Column cell
From other cells
HW:Hot WaterSR: Stripping RegentSJP: Steam Jet Pump
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Discussion on accident scenario
Piping rupture, etc…Frequency of occurrence was set 1x10-3/yr
Electrostatic spark, etc…
Organic solventleakage
Ignitionsource
In-cellfire
may occur Heat source
1. Abnormal condition of process which heat up the org. solvent
2. Back flow from the steam jet pump during recovery
3. Decay heat
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Heat source (Hot water)
The possibility to heat solvent above its flashpoint is less than 1x10-3.
The flashpoint of 30% TBP/ n-dodecane is approx. 354 K
Temperature of hot-water is 353 K.
It is necessary to heat solvent over 354 K by the following simultaneous abnormalities.
Supplied hot water has to be over heated.Temperature controller fails.
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Heat source (Decay heat)
It has been confirmed by using FLUENT ( thermal hydraulic analysis program) that the temperature rise due to decay heat was only a few degrees
303.0 305.0 K303.5 304.0 304.5
Approx, 304K
Approx, 305 K
Overhead view of drip tray
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Hot water
Hot water
Org. solvent
Hot waterSteam
Striping regent
Heat source (Steam back flow from SJP)
Pipe choking and steam back flow. A probability was 1X10-2.
Approx, 463K
Organic solvent leakage
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Back flow from the steam jet pump during recovery
Organic solvent leakageInitiating Event
Safety function Eliminate a ignition source
An in-cell solvent fire breaking
Start of recovery using SJP
Choke of SJP (back-flow of steam)
Doesn’t reachits flashpoint
An in-cell firedoesn’t occur
Success
The outline of the accident scenario
It occurred
Failure
It didn’t occur
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Org.solvent is ignited at 100% probability after a year by electrostatic spark, etc.
The ignition probability is 100%
The duration of heated up solvent above its flashpoint is several hours
One year
Assumption of the ignition probability
The ignition probability of one hour is 1 / 8,760 = 1.2x10-4
The Ignition probability of several hours is 1x10-3
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○ Initiating event (leakage) : 1x10-3/yr○ Failure of heat source removal : 1x10-2
○ Failure of ignition source removal : 1x10-3
◎ Frequency of fire occurrence : 1x10-8/yr
The result of accident occurrence frequency
The frequency of occurrence of in-cell solvent fire
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Temperature rise analysis in the cell
Analysis model
To quantify the consequence, the behavior of fire was analyzed as a function of time by using FIRST program
The geometric data : based on the Rokkasho Reprocessing Plant
Large-scale fire Small-scale fire
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The result of temperature rise analysis
Temperature of the cell atmosphere(Large-scale fire)
300
350
400
450
500
550
600
650
700
0 50 100 150 200 250
Time (sec)
Tem
pera
ture
(K)
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The result of temperature rise analysis
The position of the boundary of hot and cool layer zones in the cell
0
5
10
15
20
0 50 100 150 200 250
Time (sec)
The p
osi
tion o
f hot
layer (
m)
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Amount of burnt solvent
Large-scale fire small-scale firebecause of lack of oxygen in the cell
Less than 500 liters
Therefore we considercombustion continues 3 hours by ventilation
The amount of organic solvent burnt will be limited by operator actions such as stoppage of ventilation, etc.
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The estimation of consequence
Amount of consumed solvent : 500 liters in 3 hours
There is no degrading of the filter function in case of the fire of 500 liters
The five-factor formula method is used for quantification
Its consequence is calculated as 0.1 mSv
(Considering the main stack release)
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Conclusion
The accident occurrence frequency
Less than 1x10-8/yr
The consequence of accidentApprox. 0.1mSv
There is a room for reconsideration about the importance of in-cell solvent fire
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Conclusion (continued)
• We hope that the reexamination is made not only for the fire described in this presentation but also for other postulated accidents, based on the recent knowledge accumulated in the world, and the results are reflected to a near future reprocessing plant after international discussion and agreement.