FEDERATION UNIVERSITY, AUSTRALIA
IIBIT CAMPUS, ADELAIDE
MREGC5007 RISK ENGINEERING
ASSIGNMENT #2
Submitted by:
Khaja Mohiddin Shaik
30436045
Assignment A:
1..
The top event is "Loss of AFW Supply System," which is the undesired outcome we're trying to analyze.
E1 - "No Water Supply from Three Storage Tanks"
E2 - "Failure of Pumps"
E3 - "Failure caused by malfunction of Electric Power Supply". Further there are 2 events "Failure of
Electric Pump 1" and "Failure of Electric Pump 2"
E4 - "Failure of Turbine Pump"
2.. This Event Tree diagram is based on the availability of Auxiliary Feed Water (AFW) supply and its
various components with loss of main feed water (MFW) as the initiating event.
Explanation:
The initiating event is the "Loss of Main Feed Water" (MFW)
The pivotal event is the "Availability of AFW (Water from storage tanks)"
If the "Availability of AFW" event occurs:
If "Electric pumps" are available; the AFW system works
If "Electric pumps" are not available; two possibilities arise:
If the "Turbine pump" works
If the "Turbine pump" doesn't work
If the "Availability of AFW" event doesn't; the MFW and AFW systems both fail (MFW & AFW
fails).
3..The likelihood of the loss of the main feed water and AFW supply system will be due to 2 paths only –
a) Path A – Loss of MFW-> No availability of water in storage tanks. i.e. 0.2*0.00001 = 0.000002
b) Path B – Loss of MFW -> Availability of water in storage tanks -> Electric pumps not working ->
Turbine pump does not work i.e. 0.2*0.99999*0.002*0.01 = 0.0000039
Total = 0.0000059 or 5.9*10^-6
Assignment B:
1.. The undesired outcome is a runaway reaction due to cooling water failure while the protective trip
system is inoperative. The fault tree will illustrate the different paths that can lead to this outcome based
on the provided failure rates.
Let's break down the fault tree into different branches and gates:
a. Cooling water failure
b. Protective system inoperative
2.. To calculate the likelihood of the runaway reaction,
Let's calculate the probabilities for each path leading to the runaway reaction:
A. Detection system fails Probability = Low coolant flow trip * High Temperature Trip Failure Probability
= 0.01 * 0.01 = 0.0001
B. Shutdown system fails Probability = Dump valve fails shut = 0.001
C. Protective system inoperative Probability = Detection system fails + Shutdown system fails =
0.0001+0.001 = 0.0011
D. Cooling Water failure Probability = Line blockage + Pump Failure + Exhausted water supply = 0.2 +
0.01 + 0.1 = 0.31
Total Probability = Cooling water failure * Protective system inoperative = 0.31*0.0011 = 0.000341
3.. Since the total probability of the runaway reaction is calculated as the product of Cooling Water Failure
and Protective System Inoperative, it becomes evident that the sensitivity is influenced more significantly
by the Cooling Water Failure probability due to its relatively higher value compared to Protective
System Inoperative.
Assignment C:
1.. The specific undesired outcome, in this case, the motor "Overheats." Each event or condition is
represented as a node in the diagram, and their relationships are depicted using logic gates. Here's a
textual representation of the fault tree diagram for the "Motor Overheats" scenario you described:
In this representation:
• "Motor Overheats" is the top-level event.
• "Primary Motor Failure - Overheated" OR "Excessive Current Thru Motor"
• Under "Excessive Current Thru Motor,"
• "Fuse fails to Open" is caused by "Primary Fuse Failure - Closed."
• "Excessive Current in Circuit" is caused by either "Primary Wiring Failure - Shorted" OR "Primary Power
Failure - Surge."
2.. Likelihood of Motor Overheats –
Now, let's calculate the probability of "Excessive Current in Circuit":
This event occurs when either "Primary Wiring Failure - Shorted" OR "Primary Power Failure - Surge"
happens.
Since these events are independent, we can sum their probabilities: Probability of "Excessive Current in
Circuit" = Probability ("Primary Wiring Failure - Shorted") + Probability("Primary Power Failure - Surge")
Probability = 0.01 (from "Primary Wiring Failure - Shorted") + 0.1 (from "Primary Power Failure - Surge") =
0.11 per year
Probability of "Fuse fails to Open" = Probability ("Primary Fuse Failure - Closed") = 0.01 per year
Since these events are independent, we can multiply their probabilities: Probability of "Excessive Current
Thru Motor" = Probability ("Fuse fails to Open") * Probability("Excessive Current in Circuit") Probability =
0.01 (from "Fuse fails to Open") * 0.11 (from "Excessive Current in Circuit") = 0.0011 per year
Since these events are mutually exclusive, we can sum their probabilities: Probability of "Motor
Overheats" = Probability ("Primary Motor Failure - Overheated") + Probability ("Excessive Current Thru
Motor") Probability = 1 (from "Primary Motor Failure - Overheated") + 0.0011 (from "Excessive Current
Thru Motor") = 1.0011 per year
Assignment 2(d):
1.. Event Tree diagram –
Explanation:
The top event is "Fire Starts," which is the initiating event
The first level of the tree has two branches: "Flame/Temperature Detection works" and "Detection
system doesn't Start”
If the "Flame/Temperature Detection" occurs, the next level has two branches: "Fire Alarm System
works" and "Fire Alarm Doesn't Activate”
If the "Fire Alarm System" activates, the final level has two branches: "Fire Sprinkler System works"
and "Sprinkler System Doesn't Activate."
2.. To calculate the probability of death or injury (extensive damage),
A. Fire Starts -> Flame/Temperature Detection works -> Fire Alarm System works -> Sprinkler System
Doesn't Activate
B. Fire Starts -> Flame/Temperature Detection works -> Fire Alarm Doesn't Activate
C. Fire Starts -> Flame/Temperature Detection does not works
For path A:
Probability = Probability of Fire Starts × Probability of Flame/Temperature Detection × Probability of Fire
Alarm System × Probability of Sprinkler System Doesn't Activate
Probability = (1/100) × (95/100) × 0.8 × (15/100) = 0.00114
For path B:
Probability = Probability of Fire Starts × Probability of Flame/Temperature Detection × Probability of Fire
Alarm Doesn't Activate
Probability = (1/100) × (95/100) × (1 - 0.8) = 0.0019
For path C:
Probability = Probability of Fire Starts × Probability of Detector Doesn't Start
Probability = (1/100) × (1 - 95/100) = 0.0005
Now, sum up the probabilities of these paths to get the total probability of death or injury (extensive
damage): Total Probability = Path A + Path B + Path C = 0.00114 + 0.0019 + 0.0005 = 0.00354
3.. To calculate the probability of limited damage,
Fire Starts -> Flame/Temperature Detection works -> Fire Alarm System works -> Sprinkler System
Activate. Probability = Probability of Fire Starts × Probability of Flame/Temperature Detection ×
Probability of Fire Alarm System × Probability of Sprinkler System Activates
Probability = (1/100) × (95/100) × 0.8 × 0.85 = 0.00646 or 0.646%.
Assignment 2(e):
