Re: RBMK reactor low power instability. Chernobyl


"Martin Hogbin" <goatREMOVETHIS123@xxxxxxxxxx> wrote in message
news:kI6dndJc29pnVm3ZRVnyqQ@xxxxxxxxx
|
| "Sorcerer" <Headmaster@xxxxxxxxxxxxxxxxxx> wrote in message
news:0I3Ig.63846$fV1.63824@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
| >
| > "Chris" <chrisvine9@xxxxxxx> wrote in message
| > news:1156627361.972820.284270@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| > | Hi, New to this group so hope not to go over previous ground.
| > |
| > | I am interested in the power surge which destroyed the rbmk reactor at
| > | Chernobyl. Have read up a lot on the web and understand (I hope) the
| > | following:
| > |
| > | There was a strong positive void coefficient in the reactor design
| > |
| > | At the time of the test the control rods were pulled out too far and
| > | their design increased the reactivity as they were lowered because the
| > | neutron aborbing water was displaced.
| > |
| > | That the reason that the control rods had to be pulled out so far was
| > | because of Xenon poisoning following the previous higher power levels
| > |
| > | That most of the safety systems were disabled.
| > |
| > | That there are something like 6 concurrent equations describing the
| > | reactivity.
| > |
| > | However on almost every description of the accident the reactor is
| > | described as unstable at low power outputs. What I have not seen
| > | explained is why the instability is worse at low outputs than at high
| > | outputs.
| > |
| > | Is there an explanation which can make sense to a good physics
(school)
| > | student and a mechanical engineer?!
| > |
| > | Thanks in advance
| > | Chris.
| >
| > Yes.
| > As an analogy, think of a puncture in a bus tyre. One tiny hole
| > can cause the tyre to deflate, the bus becomes unstable, the
| > driver loses control and the occupants are killed. The reason
| > for the puncture was the tyre was under inflated and that
| > caused the tyre wall to flex more than usual.
| >
| > Nuclear reactors are designed to produce energy in quantity.
| > Running such a system below it's minimum rated output results
| > in the core not having sufficient cooling, hot spots develop.
| > While the reactor as a whole is at a common temperature all is fine,
| > but when it is too cool a hotspot causes local distortion from
| > thermal expansion because (perhaps) one control rod was not all
| > the way in. Once one spot has melted it's all over, out of control.
| > Androcles
|
| Sorcerer/Androcles is a well known crackpot in this group.
| Ignore him.
|
| Martin Hogbin

Pigbin is a well known one-sentence troll in this newsgroup
who does not know how to measure the speed of a train.
Listen to him and decide for yourself.

Androcles




.

Relevant Pages

  • Re: RBMK reactor low power instability. Chernobyl
    ... | I am interested in the power surge which destroyed the rbmk reactor at ... | That the reason that the control rods had to be pulled out so far was ... think of a puncture in a bus tyre. ...
    (sci.physics)
  • Re: RBMK reactor low power instability. Chernobyl
    ... | I am interested in the power surge which destroyed the rbmk reactor at ... | That the reason that the control rods had to be pulled out so far was ... think of a puncture in a bus tyre. ...
    (sci.physics)
  • Re: OT- Portable Nuclear Power Plants
    ... A decision was made to test the ability of the reactor's turbine generator to generate sufficient electricity to power the reactor's safety systems, in the event of a loss of external electric power. ... Chernobyl's reactors had a pair of backup diesel generators, but because there was a 40-second delay before they could attain full speed, the reactor was going to be used to spin up the reactor's turbine generator. ... In order to increase the reactivity of the underpowered reactor, automatic control rods were pulled out of the reactor beyond what is allowed under safety regulations. ...
    (rec.crafts.metalworking)
  • Re: RBMK reactor low power instability. Chernobyl
    ... | I am interested in the power surge which destroyed the rbmk ... | There was a strong positive void coefficient in the reactor design ... | That the reason that the control rods had to be pulled out so far ... think of a puncture in a bus tyre. ...
    (sci.physics)
  • Re: "The Chernobyl disaster very probably a sabotage" ["no, just same procedure as last year"]
    ... to generate power after the reactor was shutdown. ... See any good reactor physics text to understand why Xe ... power level, the flow of coolant through the core was adjusted downward ... insertion of the control rods would actually *increase* power initially ...
    (sci.energy)
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