Insights Blog
-- Browse All Articles --
Physics Articles
Physics Tutorials
Physics Guides
Physics FAQ
Math Articles
Math Tutorials
Math Guides
Math FAQ
Education Articles
Education Guides
Bio/Chem Articles
Technology Guides
Computer Science Tutorials
Forums
General Engineering
Mechanical Engineering
Electrical Engineering
Aerospace Engineering
Nuclear Engineering
Materials Engineering
Trending
Featured Threads
Log in
Register
What's new
Search
Search
Search titles only
By:
General Engineering
Mechanical Engineering
Electrical Engineering
Aerospace Engineering
Nuclear Engineering
Materials Engineering
Menu
Log in
Register
Navigation
More options
Contact us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
Engineering
Nuclear Engineering
High Pressurizer Level: Consequences & Pressure
Reply to thread
Message
[QUOTE="Hiddencamper, post: 5709493, member: 441646"] They shut off safety injection. Feedwater goes to the steam generators. They had no feedwater at the start of the event because main feedwater tripped due to a maintenance error, and the auxiliary feedwater valves were tagged out for maintenance. This allowed the steam generators to boil dry, causing the primary coolant system pressure to rise, lifting the PORV (which stuck open). Operators did restore auxiliary feedwater (and injected too fast to a dry steam generator causing some tubes to rupture). When aux feed was restored, primary system temperature began dropping, and with the PORV stuck open pressure kept dropping. Safety injection initiated early in the event due to setpoints being too close to the physical system response to a turbine trip, and operators shut down safety injection and blocked its restart in accordance with operating procedures. If safety injection kept running there would have been no accident, however the reactor ended up becoming saturated and the resulting level swell caused the reactor to displace water into the pressurizer giving false high level indications. Today, safety injection cannot be shut down until the reactor is subcooled and pressure is stable or rising (indicating no leaks or stuck open valves), even if level is high or the reactor coolant system may be solid. Additionally the safety injection signals for the reactor back in the 70s had to see a coincident low pressurizer level with low pressurizer pressure (other signals are low steam headed pressure/rate and high containment pressure). It was known before TMI that during a stuck open porv event, the pressurizer would show false high level indications preventing that particular automatic injection signal from running (this happened in Europe first, a few years later at Davis Besse, then at TMI, operators managed to figure it out at the first two plants, and failed at TMI). The NRC knew about this and did not pursue regulatory changes to remove the low level signal from the pressurizer safety injection signal. Today, level is not used for safety injection logic, only pressure. This is acceptable because even in odd / slow scenarios, if water level is dropping, the pressurizer heaters will lock out / shut off and pressure will drop low enough to start safety injection before the core is uncovered. PWR guys please help fact check me. I'm knowledgeable but never licensed on a pwr. [/QUOTE]
Insert quotes…
Post reply
Forums
Engineering
Nuclear Engineering
High Pressurizer Level: Consequences & Pressure
Back
Top