Sweden Nukes shutdown.

[itsmoked]

See:

http://www.aftenposten.no/english/local/article1409304.ece

I was told that there are 4 generators required to shut down the power plant. A transmission problem dropped the plant. Then during the resulting shutdown two of the four generators failed.

I thought reactors were made such that if the power failed things like control rods would drop into the core automatically quenching the reaction.

Questions:
Is the "problem" the stored energy in the system possibly causing damage to the core and closely coupled systems?

Why would half the generators fail in a facility where they must be tested fairly regularly?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

From the article: "I have been to Forsmark myself and there is a large difference between safety thinking there and, for example, in Russian plants," Bøhmer said.

The key word is 'safety thinking'. Thinking does not mean practicing.

I have not done much work on the Swedish nuclear plants. But I remember one time. It was at the Forsmark plant during revision. I had my "action slot" between 00700 and 0900 a certain day. I was there well on time. But something screwed up, so I had to wait. And wait. Finally, at around 1800, I was told that I had turned into a "reportable event" and that my "action slot" didn't exist any more. A report was written and put in one of the loose-leaf binders that existed for that kind of unfinished work.

My memory of this is that it was binder number five or six that was used. The others were already filled with reports. I asked if they were all unfinished and the answer was affirmative. I then asked naïvely if that wouldn't constitute a risk? "No, we have several parallel safety systems. So it doesn't matter if one or two of them is out of order" was the answer I got.

I went home. But I had lost a lot of confidence in the Swedish safety thinking. And even more so in the way theory is practised.

Don't get me wrong. I am all for nuclear power. But the political situation has made it almost impossible to recruit qualified people to handle nuclear power. The government has a very poorly defined power policy. And it is dependent of a couple of minority parties that both use their influence to make things worse. So, not many want to work for nuclear power plants any more. On top of that, there is a law against "thinking nuclear" so it is only natural that the operators (human beings as they are) tend to simplify, ignore, rationalize, forget, eat up margins and so on. It is a sad state of affairs.



Gunnar Englund

http://www.gke.org

 

[ijl]

I do not know the details of the incident, I have only red what the newspapers say. Yes, Itsmoked, what you say is correct, the control rods are dropped or pushed automatically into the reactor (depending on the reactor type). And that did happen.

And yes, the problem is the residual heat produced by the radioactive decay of the (spent) fuel. The heat must be removed by pumping water through the reactor. Electricity is needed for the pumps. If there is a blackout, and the emergency generators do not start, then "Forsmark, you have really a problem".

 

[BJC]

Fosmark is a GE BWR. There are two systems powered by stear HPCI and RCIC that require only battery power for control. The ones I knowuse Terry turbines which will almost run on water ( = low quality wet steam).

 

[waross]

Darlington Nuclear in Canada uses a very large battery bank and inverters to keep the heavy water circulating pumps running until the diesel generators come on-line. Candu reactors are used. In the event that there is a rupture in the cooling system, which may be caused by a failure of the circulating system, the heavy water may be dumped and contained safely.
The core will most likely be unusable because of damage caused by the residual heat, but there should be no release of radio-active material. Dumping the D2O (deuterium oxide(heavy water)) is a last resort to be used only if two or three other levels of protection fail.
Safe but expensive.
respectfully

 

[itsmoked]

So how long does the water have to circulate after the reaction has been quenched? Five minutes? An hour?

[red]"stear HPCI and RCIC"[/red]?????

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BJC]

itsmoked
dsylectic fingers.
That should have been "steam powered HPCI ( High pressure coolant injection ) and RCIC (Reactor core injection coolant). There is a picture of a HPCI pump on this site.

http://www.nucleartourist.com/areas/bwr-in1.htm

Fosmark is the vintage that would have them.
I have seen Terry turbines in refineries and paper mills, if you have spare steam there cheaper than a motor.

 

[itsmoked]

Nice link! Thanks BJC.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Zogzog]

So how long does the water have to circulate after the reaction has been quenched? Five minutes? An hour?

The answer is forever, the reaction is never quenched, the reactor is defined as subcritical after shutdown but heat is still being generated and flow must be maintained (Or be able to restart flow).

 

[TheBlacksmith]

It takes weeks (at least) before the radioactive decay rate, which is not affected by the control rods drops enough and cooling is criticl right after shutdown. Any number of "mistakes" could prevent a n emergency diesl from starting; improper valve lineup, no air in the starting tanks or dead batetries if electric start, improper system lineup so the diesels didn't see the emergecny, etc. As stated above, you need trained, intelligent people.

 

[SphincterBoy]

The plant I worked in had double redundant diesel-generators to power the RHR system (residual heat removal) for the GE BWR 4 reactor, and I think you are right TheBlankSmith: Even these well thought out systems are prone to "the perfect mistake", either human or system, and the all-critical RHR system may endup w/o power.

 

[itsmoked]

Zogzog, TheBlacksmith, SphincterBoy; Thanks for the info. No wonder there is so much emphasis on the circ pumps and powering them. I have worked with COBALT 60 sterilizers and noted the hot smelly product exiting the system but never connected it with the fact that a fuel core doesn't 'turn off' completely. Makes perfect sense.

Even though 'things happen' twould seem to me that separate redundant cooling loops with separately derived isolated power supplies would be danged reliable. Be interesting to read the report on the aforementioned fiasco.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com