Post Midterm Content/Final Exam Material Flashcards
What does a moderator do in a nuclear reactor?
slows down neutrons to increase likelihood of further fission
What does a coolant do in a nuclear reactor?
removes heat energy; maintains temperature. Does this in order to prevent melting
What does a control rod do in a nuclear reactor?
regulate fission by absorbing neutrons. Act like brakes in a car
Describe the steps required for a Pressurize Water Reactor (PWR) to work
(1) reactor heats water in the primary system, (2) this heats water in the secondary system, (3) steam is formed, (4) steam drives the turbine, (5) generates electricity (6) steam is condensed to water and vents from cooling towers
List the human factors that resulted in the Three-Mile incident
(1) Operator over-reliance on Emergency Procedures Manuals - did not cover the incident that occurred.
(2) Site emergency NOT declared
(3) Maintenance check list was thrown away - important because they indicate that the AUXILIARY FEEDWATER PUMPS were closed
(4) Human intervention & poor control room design
What were features of poor room design in the Three-Mile incident
(1) relief valve safety shutoff was located on the BACK of the control panel. Poor accessibility/discoverability in case of an incident
(2) Computer printer was overwhelmed, error message was printed out 3 hours later. Poor feedback
(3) Control panel instruments conflicted. Confusion of what affords what
(4) 100+ alarm lights triggered in 2 minutes. Poor feedback
(5) visual annunciators were disabled
Sheridan reviewed display consoles in nuclear reactors. What were some issues related to the natural principles of design?
(1) Mapping - left side displays were driven by right side of controls. Controls for meters were far away.
Critical displays were located on BACK of a panel.
Operators may accidentally hit controls with their bodies
(2) Signifiers/Affordances - panel meters were unreadable a few feet away.
Ambiguous labels.
(3) Conceptual model
identical side by side displays - each screen provided different values, but were not labelled.
Meshkati explains that power plants should be examined on three levels:
Technological
Human
Organizational
Meshkati explains there should be an overhaul in these areas:
Design Construction Training Operation Regulatory oversight
What is a Light Water Reactor?
include BWR and PWR (Like the Three Mile Island)
Must be shutdown before refuelling
water acts as a coolant and a moderator
What is a negative void of coefficient of reactivity?
LWR’s use this.
Loss of coolant creates steam pockets, or voids.
Reaction stops when the coolant is lost. This is because the loss of coolant results in steam. Because steam is a poor coolant than water, it signals that the power must go off.
Note: high quality enriched uranium is required for this design
What is a RMBK?
Stands for High Power Channel Reactor.
Uses graphite as a moderator instead of water.
Has a positive void coefficient of reactivity.
Unstable at low power
No containment vessel in case of emergency
What is a positive void coefficient of reactivity?
Decreases cooling through steam, just like the NVCR. but the reaction continues due to graphite. This causes more voids. With less water, power increases and the reactor goes out of control
What were contributing factors of the Chernobyl accident?
(1) Reactor Design
(2) Non-routine operation of reactor - doing things that aren’t typical/required in specific situations. Running pumps at inflated levels, and disengaging automatic trip when turbines when offline
(3) Violation of operating regulations - too many control rods removed, power below specified levels
(4) Lack of safety culture
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team
