how long will spent nuclear fuel rods remain hot if not placed in water?
June 22nd, 2010 | by Michael |
tjcsonofallnations asked:
It seems incredibly dangerous that the only way these rods don’t explode is if they are kept in pulls of cooled water/boric acid. What would happen if the power went out and the backup generators failed? Would the rods explode, spewing radiation out into the populous? So how long do these rods generate heat like that, upwards of 10,000 degrees? Thanks for the info.
JAMAR
It seems incredibly dangerous that the only way these rods don’t explode is if they are kept in pulls of cooled water/boric acid. What would happen if the power went out and the backup generators failed? Would the rods explode, spewing radiation out into the populous? So how long do these rods generate heat like that, upwards of 10,000 degrees? Thanks for the info.
JAMAR
3 Responses to “how long will spent nuclear fuel rods remain hot if not placed in water?”
By muneepenee on Jun 25, 2010 | Reply
em stae hot in or outta water. Dekae av radioaktiv isotopes not affekted bi wot is around em. purpus av water is tu absorb the heet & the nuetrons & radiashun so yu kan go neer the pool & not get fried. Water is a good absorber av nuetrons.
By technidigm on Jun 25, 2010 | Reply
Where are you getting all this? You seem to be alarmed by silly possibilities that are made up by typical “anti-nukes” such as a lot of teachers and professors who only know enough about nuclear energy to be dangerous themselves. The spent nuclear fuel rods remain hot for a length of time that depends on the definition of “hot”.
After a reactor shuts down, the reactor core (fuel) continues to produce “decay heat” from the radioactive decay of the fission products. The amount of heat thus produced is relatively small and continues to decay down exponentially, but never really reaching zero. It does get low enough so quickly that the heat can be removed simply by being immersed in water and, later, the heat is so low that it can be removed without the immersion of the spent fuel rods in water.
So, the spent fuel in a spent fuel pool is merely there for storage and to allow the gradual decay of the heat producing radiation from the unstable fission products. Even without submerging the spent fuel in water, the fuel would not explode. It would simply heat up and melt. If enough of the spent fuel in a spent fuel pool heated up and melted, it is conceivable that it would drop down to the bottom of the pool such that the remaining uranium-235 could congregate and get to a configuration such that it would be a critical critical mass again. Thus, the boric acid is handy since it absorbs neutrons and ensures that spent fuel does not go critical even in a situations where some of the fuel might melt due to lack of cooling. All that would likely take several days and would actually be discovered long before anything bad would happen since it is a simple matter to keep track of the temperature of the water in the spent fuel pool. Then the water could boil for weeks before anything got much above 212 degrees F, the boiling point of water.
The populous is not at risk since the fuel pins/rods are easily managed whether before, during, or after they are in the reactor.
So the electric power going out and generators failing is of little consequence since power is only needed to recirculate the water in the pool to equalize temperatures and avoid boiling the water until the decay heat is so small that the boiling point can not be reached. We are talking, at the most, a few weeks. You could also keep adding water to the spent fuel pool manually.
As for temperature, it is of course possible that spent fuel could heat up to any temperature as long as no cooling at all was going on.
By Nukemann on Jun 25, 2010 | Reply
It would be incredibly dangerous, if it were true. If power went out, (both the local power grid and the main generator at the power plant) and the back-up emergency diesel generators (two independent generators) and the portable generator most plants have. The spent fuel pool could be manually cooled through the addition of water from the service water, city water, fire extinguisher water or pumper trucks from the local fire department. If all of that were unavailable, we would only have a few weeks before we would have to find a way to cool the water or the fuel assemblies might melt.