ENGINEERING-16
Fire Suppression Performance Evaluation of
Sodium Leak Collection Tray
n EXECUTIVE SUMMARY
Sodium Leak Collection Trays (LCT) are deployed as a passive sodium fire protection device under the secondary sodium
pipelines in the Steam Generator Buildings of Fast Breeder Reactors (FBR). The design of Leak Collection Trays (LCT) is
based on immediate channeling of burning liquid sodium on to the funnel shaped Slopping Cover Tray (SCT) to the
Sodium Hold-up Vessel (SHV) below it, in which sodium fire extinguishes due to oxygen starvation. Performance of LCT is
measured by the proportion of un-burnt sodium left over and it is a strong function of sodium leak rate, amount of sodium
leaked and initial sodium temperature. Processes involved in the operation of the LCT are thermal hydraulics of the flow of
hot sodium over the cold surface of the SCT, gravity draining into the SHV and combustion kinetics of sodium, with almost
all the processes occurring simultaneously. Several performance evaluation tests have been carried out on a prototype
LCT and valuable data have been obtained, which can serve as an excellent benchmark. Simplified and more detailed
CFD simulation for predicting the behavior of the device have also been carried out
n OUTLINE
Liquid sodium is used as a coolant in
Fast Breeder Reactor (FBR) systems. In
the rare case of failure of a sodium
bearing component, sodium can leak
out and react with oxygen in the air and
catches fire, when oxygen concentration
in the air is more than 5% and the
sodium temperature is more than
0
200 C. Design provisions to defend
against such sodium leaks and the
resultant fires play an important role in
the safe operation of a fast reactor. In
order to collect the leaked sodium and
mitigate the consequences of sodium
fire in the Steam Generator Buildings
(SGB) of FBR, Leak Collection Trays
(LCT) is provided.
Experimental studies on the evaluation
of a PFBR leak collection tray have been
carried out in the Safety Engineering
Division. Twenty eight thermocouples
were mounted at different locations of
the tray for continuous monitoring of the
temperatures.
The maximum tray
surface temperature is in the range of
0
900 to 950 C in all the tests.
Temperatures at different depths in the
sodium collected in the hold–up vessel
monotonically decreased with time, with
0
the maximum at 350 C. The chemical
analysis of the samples indicated
burning of sodium was only in the range
of 4 to 25%, depending on the test
conditions, as against about 70 % that
normally occurs in a large open pool
exposed to air, which is considered as
satisfactory.
Processes involved in the operation of
the LCT are thermal hydraulics of the
flow of hot sodium over the cold surface
of the SCT, gravity draining into the SHV
and combustion kinetics of sodium,
with almost all the processes occurring
simultaneously. This gives a challenging
opportunity for modeling and predicting
the behavior of the device. Hence, the
data available from the test results, as
given in the Table 1, can form a good
benchmark.
Table 1
Data available from the test results
Test Numbers
Test Variables
MS-2
MS-3
MS-4
Mass of Sodium (kg)
40
38
35
Sodium Temperature ( °C)
530
538
550
Dumping Period (s)
120
180
210
3
1
1
Relative Humidity %
73
76
65
Ambient Temperature ( °C)
31
28
28
Mass of Sodium burnt (kg)
10
1.5
3.5
Un-burnt Sodium left over SCT (kg)
4
0.5
0.5
Un-burnt Sodium collected in SHV (kg)
26
36
31
Overall un -burnt sodium (% loaded)
75
96
90
No. of Drain Pipes open in
SCT
Fig. 1 : Performance testing of sodium leak collection tray
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ENGINEERING-16
n ADDITIONAL INFORMATION ON THE SODIUM LEAK COLLECTION TRAYS
The leak collection tray mainly consists of two sloping plates (angle 200) forming a funnel like structure supported on the
sodium hold-up vessel. These sloping plates with V-shape orientation rapidly guide the leaked sodium to a central drainpipe, which ends at 20 mm above the bottom surface of the hold-up vessel. The drained sodium is accumulated in the
hold-up vessel with limited exposure to air. A vent pipe of smaller diameter is provided on the slopping plates to facilitate
the easy draining of the leaked sodium.
The size of the bottom hold-up vessel of the tray chosen is 1200 mm x 500 mm x 500 mm and that of the top funnel like
structure is 1200 mm x 1000 mm. The capacity of the hold-up vessel is 300 liters. Drain-pipe of 50 NB size and a vent
pipe of size 25 NB are used. Three experimental runs were carried out by pouring sodium at 530 - 550 0C into the tray in
open-air conditions. Fig. 1 shows the sodium just being let into the tray in one of the tests and a sketch of the LCT is
available in Fig.2.
n GENERAL EXPLANATION RELATED TO THE DESCRIPTION
CFD analysis of sodium fire in LCT is being carried out at IIT Madras, by using general purpose CFD code FLUENT. Fig. 3
shows the temperatures on SCT and in SHV while sodium combustion. Sodium burning rates observed in this analysis are
in good agreement with the experimental results. Further optimization of LCT is being carried out.
Temperatures on LCT Top
Part
Temperatures in LCT Bottom Part
Fig. 2 : Details of Prototype of LCT
Fig. 3 : Simulation of Sodium Combustion in LCT
n ACHIEVEMENT
The data collected in the evaluation tests of the Leak Collection Trays can be considered as a good international
benchmark for validating the mathematical models being developed to describe the transient thermal hydraulic and
combustion phenomena involved. The design of LCT for secondary sodium systems of PFBR will be optimized using the
numerical model developed and validated with the test results.
n PUBLICATIONS ARISING OUT OF THIS STUDY AND RELATED WORK
1. F.C. Parida, P.M. Rao, S.S. Ramesh, B. Malarvizhi, V. Gopalakrishnan, E.V.H.M. Rao, N. Kasinathan and S.E.Kannan,
th
14 International Conference on Nuclear Engineering (ICONE - 14) July, 17 - 20, 2006, Florida, USA.
2. S.V. Diwakar, T. Sundararajan, S.K. Das, P. Mangarajuna Rao and N. Kasinathan, ICONE15-10403, Proceedings
th
15 International Conference on Nuclear Engineering, April 22-26, 2007, Nagoya, Japan.
Further inquiries:
Shri P. Mangarjuna Rao and Shri. N. Kasinathan, Safety Engineering Division
Safety Group, IGCAR, e-mail: [email protected]
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