My mom and sister live near Crystal River Florida's nuclear power plant. I want to know how the reactor and spent fuel is kept cool after the plant is shut down. What source of power is used to perform that function? CR3 has two generators and a 30 day supply of fuel to keep them going. Why shouldn't I be concerned that all the nuclear power plants are Chernobles in the making when the national grid goes down and their 30 supply of fuel for their generators runs out. What about the compliance of generators also?

-- Anonymous, August 01, 1998

Answers

According to Gary NOrth, if nuclear power plants are not Y2K compliant by a certain time, they woill be shut down my the Nuclear Regulatory Agency.

-- Anonymous, August 01, 1998

Along time ago, I use to be a design engineer on nuclear power projects. The emergency generators at a nuclear plant are designed to provide full emergency power for all nuclear systems, which includes spent fuel pool emergency cooling system.

The Nuclear Regulatory Committee is pretty strict about anything that has radioactive material within it. The spent fuel pool is therefore strictly regulated by the NRC. I remember doing containment, HVAC, and water clean-up analysis on the spent fuel pool building on one plant.

As to diesel generator compliance, that is problamatic. The types of large generators at nuclear projects, if not y2k compliant, will be well before the year 2000, based on my understanding of how nuclear plants are regulated and operate. I would not loose a minutes sleep over y2k concerns causing a radiation release at a nuclear plant in the U.S.

Bob Schneider

-- Anonymous, August 02, 1998

I think Robert Schneider can confirm this; I was kind of surprised he didn't mention it. The cluster of fuel rods in the reactor (aka the "core") have graphite rods interspersed between them. When the rods are lowered into the core, the graphite absorbs the neutrons and prevents fission. The fission, or chain reaction, is what generates most of the heat.

If I remember right, the spent fuel pool is basically an artificial pond... if so, the water itself should do a pretty good job of keeping the fuel cooled down.

Finally, with 30 days of backup power, that should be plenty of time to dismantle the core if necessary.

A Chernobyl-style disaster is highly unlikely, since commercial reactors have lots of shielding (unlike Chernobyl, where the Soviets weren't concerned with getting re-elected). Three-Mile Island was actually a partial meltdown; some radioactive material was released but the shielding did its job.

-- Anonymous, August 04, 1998

OK, the two previous answers have been somewhat correct, but not exactly. I actually am a nuclear engineer so here is a somewhat technical answer.

A nuclear power plant has several safety systems to ensure a safe shutdown. If there is a loss of offsite power (the grid goes down), then diesel generators come on to provide power to the coolant pumps (primary and secondary loops). At the same time that the diesels are coming on-line, the reactor scrams (emergency shutdown).

What that means is control rods (usually made of galodinium or europium which will absorb neutrons & stop the reaction--control rods are NOT made of graphite.) will drop into place forcing the nuclear fission process to stop. This is a DESIGN BASIS accident. Nuclear power plants are designed with this type of accident (and a lot of others) in mind. If you can think of the most outrageous, improbable scenario, then the NRC probably has a regulation that says that scenario must be planned for.

The 30-day fuel supply is more than adequate to assure core cooling. What you have to worry about is decay heat in the fuel after the fission reactor has stopped. You will still have appreciable heat in the core for 5-6 days after the fission process has stopped. However, after about 6 days, the core will be cool enough where there isn't any real danger of fuel melt.

Finally, why not worry about Chernobyl? Well, US reactors are designed with containment domes to prevent any radioactive releases to the environment. Chernobyl has no such containment dome and vented directly to the atmosphere. The designs of US plants and Chernobyl are totally different as well, but the overriding difference is philosophy. The US emphasizes safety whereas the Soviets emphasized efficiency of design. Efficient versus safety is always a tradeoff. The US traded efficiency for safety.

-- Anonymous, August 08, 1998