Palo Verde shuts 1 reactor after minor explosion

[bergie321]

http://www.azcentral.com/business/articles/2010/03/08/20100308biz-paloverdeexplosion0308.html

Don't worry though...it was just a "minor" explosion...at a nuclear power plant.

[Bold Lib]

1. "an explosion related to an auxiliary transformer" This is NORMAL kind of

things that go FUBAR in ANY power plant. The fact that is at a nuclear power plant is moot.

[bergie321]

2. "which resulted in the loss of two of the units four reactor coolant pumps"

But cooling the reactors isn't very important....

[Bold Lib]

3. So what? That's why they were safely shut down? These things happen

and there are plans to take care of them. A natural gas plants have the same problems and also have plans to safely take care of these things that are KNOWN to happen and are PLANNED for. It is not that big of a deal.

[Statistical]

5. Reactor is designed so it can run at 100% power on only 2 of the 4 pumps.

Each pump has flow rate of 50% of cooling requirement. So 4 pumps = 200% of necessary flow rate.
The reactor "could" have continued to operate fine for hours, or days, or even months on the 2 remaining cooling pumps.

However as a precaution the loss of redundancy triggers an automatic shutdown. Once scrammed fission stops and reactors heat output drops to 5%-15% meaning even a single pump can cool reactor in emergency situation. For a limited time electrical power is not even needed. Cooling pumps are connected to massive flywheels which allow the pumps to continue to operate using stored kinetic energy in the virtually impossible scenario that all 4 redundant power systems all fail providing yet another level of redundancy.

Of course if all 4 pumps failed there is backup emergency cooling system and if that failed there is still 24-48 hours to cool the reactor (remember once scrammed 95%+ of heat is lost due to no active fission) to restore cooling pumps before heat and pressure get critical. If course if it is impossible to restore any of the 4 primary pumps or two independent backup systems the core could be can be depressurized to reduce heat and pressure. Now if that also failed the molten core will flow out of reactor pressure vessel but still containment but containment building where it will be cooled in cooling tanks below the reactor vessel.


The system worked exactly as it should (yet again). No system is the world is built as redundant as nuclear energy.

These shutdowns are only executed because they if a shutdown didn't occur the likelihood of core breach would go from once in 20 million reactor years to "only" once in a couple hundred thousand reactor years.

[bergie321]

6. "The reactor "could" have continued to operate fine for hours...."

"The reactor "could" have continued to operate fine for hours, or days, or even months on the 2 remaining cooling pumps."

...unless there was another "minor" explosion...

[Statistical]

7. Well more like a near impossible number of simulataneous failures.

However despite that extreme unlikelihood of such an event the reactor shutdown automatically as a precaution to protect the plant, the operators, and the community.

The SCRAM (trip) worked exactly as predicted, the reactor shutdown as expected (nuclear physics is well understood), and cooling systems took care of residual decay heat. Once reactor scrammed fission is impossible. One simply needs to remove residual heat which is easily calculated. The heat isn't magical nuclear heat. It is heat like any other thermal output. If transfer rate of heat out of the reactor is faster than heat generated by residual decay then reactor will get cooler.

You provided another example of how safe, reliable, and redundant nuclear power is.

Compare that result to this explosion:
http://www.reuters.com/article/idUSTRE61619Q20100207

"At least 5 dead in Connecticut gas plant blast".

Lot less redundancy there despite the plant using volatile and unpredictable gaseous hydrocarbons.

No commercial nuclear power operator in the US has ever been killed as a result of plant accident or failure. 50 million operating hours and not a single fatality. Fossil fuels can't make that claim after just this one incident.

[Statistical]

4. A non-nuclear power transforer exploded.

As such as a precaution (despite reactor being able to run on backup power) it shut down automatically and safely with no injury or release of radiation.

Thanks for providing another example on how safe and effective nuclear energy is.