Jonathan_S wrote:cthia wrote:Also, the ejection sequence does not have anything to do with how much time-to-holy-hell is left on the reactor. The reactor is going to blow when it damn well pleases and the ejection may not even clear the ship, let alone the radius of the sidewalls in some cases.
Actually it does. Ejection is only used as a last ditch attempt to save the ship; when there isn't time to cut the fuel feed to the reactor and the automatic shutdown failsafes haven't worked.
If the reactor wasn't just about to explode there would be time to cut the fuel and starve the fusion reaction - safeing the reactor without the damage and risk of blowing the side off the ship and then applying massive acceleration to an already unstable grav bottle.
You are discussing two different sequences...
1. Shutdown sequence.
2. Ejection sequence.
There may be some overlap. Such as the aforementioned cutoff of fuel before ejection which
may serve to both minimize explosion and or increase time to critical. But it is still part of the shutdown sequence, as you perform the exact same steps in the exact same order as if you were shutting down. As in a nuclear power plant, the
SCRAM button is an emergency shutdown switch which is also a part of the normal shutdown.
The term is usually cited as being an acronym for
safety control rod axe man, which was supposedly coined by Enrico Fermi when the world's first nuclear reactor was built under the spectator seating at the University of Chicago's Stagg Field, but NRC Historian Tom Wellock suggests that the acronym was invented after the fact, and that it was first used as a reference to the slang, to 'scram' (to run). It could also stand for "Safety Control Rods Activation Mechanism" or "Control Rods Actuator Mechanism", both of which are probably backronyms. "Scram" is English slang for leaving quickly and urgently, which has been cited as the original basis for the use of scram in the technical context.
I am a Civil Engineer and did some work at a particular plant. Having been onsite, I was fortunate enough to be invited to sit in on
a simulated trip similar to this one.Then another in another state like this one.A completely unrelated loss of offsite power simulation.Even nicer.That was years ago. Since then, I became addicted to nuclear power plant operation. Which led me to the very nice simulation for the Windows environment developed by
AE4RV.com. It is the only reason I bought a Windows computer.
Which brings me to my point. Once she is ejected, there is no control of time to critical. Which means that she may blow before she clears the ship or sidewalls. Or before she reaches minimum safe distance.
SHUTDOWNIn a nuclear reactor, shutdown refers to the state of the reactor when it is subcritical by at least a margin defined in the reactor's technical specifications. Further requirements for being shut down may include having the reactor control key be secured and having no fuel movements or control systems maintenance in progress.
The shutdown margin is defined in terms of reactivity, frequently in units of delta-k/k (where k is taken to mean k-effective, the effective multiplication factor) or occasionally in dollars (the dollar is a unit equal to the change in reactivity needed to go from critical to prompt critical). Shutdown margin can refer either to the margin by which the reactor is subcritical when all control rods are inserted or to the margin by which the reactor would be shut down in the event of a scram. Hence, care must be taken to define shutdown margin in the most conservative way in the reactor's technical specifications; a typical research reactor will specify the margin when in the cold condition, without xenon. Under this specification, the shutdown margin can be simply calculated as the sum of the control rod worths minus the core excess.
Minimum shutdown margin can be calculated in the same way as shutdown margin, except that the negative reactivity of the most reactive control rod and non-scramable rods is ignored. This definition allows the reactor to be designed so that it remains safely shut down even if that most reactive control rod becomes stuck out of the core.
A reactor is in cold shutdown when, in addition, its coolant system is at atmospheric pressure and at a temperature below 100 °C (210 °F). This temperature is low enough that the water cooling the fuel in a light water reactor does not boil even when the reactor coolant system is de-pressurized.