Hi, I just finished my studies and am now in my first job. I have to design the drivers for the emergency stop of a nuclear reactor that will be in the centre of the country. The moderator rods are shot in by big electromagnets, I think I will drive these with MOSFETS, but do I really need diodes as protection? So far I can do it with an 8 pin PIC and some dual gate MOSFETS to fine tune the power, but maybe I should use some trimpots?
Sorry for this question, I thought I'd better ask as you have all more experience then me and it will give me a safer feeling when we start up next week.
For _real_ emergency cooling, like a meltdown, feed the water from the tower into the _bottom_ of the vessel. When you just sprinkle it, the water flashes into steam before it ever even hits the core. When you shove the water into the bottom, then when it flashes to steam (or maybe even dissociates, depending how hot it is), it actually carries heat away from the core.
As far as your control rods thing, I'd seriously look for something commercial - remember, it has to operate with the power off!
On a sunny day (17 Dec 2006 02:18:40 GMT) it happened jasen wrote in :
Well, I go way back, and I remember reading how it started like this:
A labor strike prevented the construction of the pile at a laboratory in the Argonne forest preserve, so Fermi and his associates Martin Whittaker and Walter Zinn set about building the pile (the world's first "nuclear reactor," although that term was not used until 1952) in a racquets court under the abandoned west stands of the university?s Stagg Field. The pile consisted of uranium pellets as a neutron?producing "core" separated from one another by graphite blocks to slow the neutrons. Fermi himself described the apparatus as "a crude pile of black bricks and wooden timbers." The controls consisted of cadmium-coated rods that absorbed neutrons. Withdrawing the rods would increase neutron activity in the pile to lead to a self-sustaining chain reaction. Re-inserting the rods would dampen the reaction.
I love it. First an extremely graphic description of the chaos and danger during the fire:
"A canister of lithium and magnesium, also in the reactor to create tritium for a British H bomb, was probably the first can to burst and ignite in the soaring temperatures. This coupled with igniting uranium and graphite sent temperatures soaring to 1,300 degrees centigrade."
"As the fire raged radioactivity was carried aloft. Blue flames shot out of the back face of the reactor and the filters on the top of the chimneys could only hold back a small proportion of the radioactivity. An estimated 20,000 curies of radioactive iodine escaped along with other isotopes such as plutonium, caesium and the highly toxic polonium."
"Then they tried to pump in carbon dioxide gas to try and smother the flames, but the heat was such that oxygen was produced from the gas and thus fed the flames higher. The scientists then had to gamble on flooding the reactor with cooling water. The risk they were aware of was that explosive hydrogen and or acetylene gas could be created and then flash over into an explosion. As this critical decision was being taken the temperatures were climbing by 20 degrees a minute."
The the aftermath:
"Yet even today as the fateful chimneys are slowly taken down by shielded robots the centre of the fire crippled reactor of Pile One still contains molten uranium and still gives off a gentle heat. There is still unreleased Wigner energy in the graphite and water hoses are still left connected to the charge face as a final safety precaution."
Then a well-placed ad:
"Thousands of warm beds in the English Lake District"
"Where to stay in the Lakes | What to do and see in the Lakes"
There may be no connection between these, but my first instinct would be to go somewhere else.
I didn't realise it Mike but the second search result is even more graphic.
Read the bit where a chap named Tom Tuohy actually climbed the 80ft to the top of the burning reactor in order to look down into the discharge trough.
:) Apparently nearly 50 years later there are about 1700 farms in that area that are still under some sort of restriction.
With the UK's military secrecy very little of this was public at the time. One of the search results even remarks that the govt's Meteorological Office wind direction charts for those days are still missing and a check with other available charts shows that the govt gave out a misleading wind direction.
Don't know how you can work with all this talk of pushing in rods.
You might want to look in Wikipedia or elsewhere regarding "fail safe" designs.
The general trend is to use electromagnets to hold the safety rods UP. Then if something happens, like you don't pay your electric bill, the rods will FALL INTO the reactor, if it hasnt blown up already. Also use solenoids to hold closed a valve, which will open when the power fails and admit some pressurized boron liquid into the coolant.
Also since the SL-1 blowup, it's traditional to post signs "WorkPeople: Don't work if you're tired, don't pull the center control rod out by hand more to see if it moves freely. If it doesnt move when you pull with a 40lb scale, dont' pull any harder" .
Also since Chernobyl: "Don't pull out all the control rods, even if the boss says so. If the reactor isnt responding to the normal control-rod schedule, something's wrong. It may be in a Xenon-poisoning well and needs to sit until the Xenon breaks down. See the computer printouts. Follow the rules."
Actually the carbon rods slow down the neutrons making them more absorbable by the reactant uranium content. This also converts the kinetic energy into thermal energy. This is called "thermalizing" the neutrons. Moderator rods are boron, gadnolinium, cadmium or other neutron absorbers.
Gegen dummheit kampfen die Gotter Selbst, vergebens.