This is not so strange. Nuclear power plants, by design, will shut down when external power (i.e. grid power) is removed. This is a safety mechanism since the plant loses two redundant cooling power supplies other than it's own power. Normally, reactors can power it's own equipment when running but you don't want to rely on this since, as we all know now, reactors will heat up after shutdown and require power for cooling water. When the reactor shuts down, you would need external power (again grid power) to run cooling pumps. The backup to grid power is diesel generators in which there are usually a whole bank of these in case one or more does not start-up. So, if you lose external power, you lose redundant shutdown power supplies (grid + diesel generators) and thus the reactor shuts down automatically. At this point, diesel generators start up automatically and power the cooling pumps while plant workers attempt to bring back external grid power. This does not happen often, but it does happen when we see blackouts or equipment failures such as this case where a breaker tripped. The report does not mention if the breaker was a main feeder breaker or an internal power supply breaker (these are also three-fold redundant), but in any case the automatic shutdown is a good sign that systems are working as designed.
I think the media has become sensitized to these unplanned reactor shutdowns here in the US. This is similar to the US Air emergency landing into the Hudson river produced by multiple bird strikes. Bird strikes are improbable but normal occurrence and after that incident, the media reported for some time planes that made emergency landings due to bird strikes. They don't report it anymore, however, but bird strikes continue...so do reactor shutdowns. Observing safe recoveries from these events should give us confidence.
Once redundancy is re-established, there is normally a pre-criticality procedure that is followed to the letter to ensure that all systems are ready and then the reactor will be brought back on-line. The safety procedures that the NRC enforces within these plants are quite strenuous.
Submitted by Anonymous (not verified) on Fri, 2011-04-22 13:53.
[edit]Notable activations of BWR safety systems
General Electric defended the design of the reactor, stating that the station blackout caused by the the 2011 T?hoku earthquake and tsunami was a "beyond-design-basis" event which led to Fukushima I nuclear accidents[8]. According the Nuclar Energy Institute, "Coincident long-term loss of both on-site and off-site power for an extended period of time is a beyond-design-basis event for the primary containment on any operating nuclear power plant".[9]
The reactors shut down as designed after the earthquake. However, the tsunami disabled all diesel backup generators which operated the emergency cooling systems and pumps. Pumps were designed to circulate hot fluid from the reactor to be cooled in the wetwell, but they did not have any power. The reactor cores overheated and likely melted. Radioactivity was released into the air as fuel rods were damaged due to overheating by exposure to air as water levels fell below safe levels. As an emergency measure, operators resorted to injecting seawater into the drywell to cool the reactors, but would also ruin them for future operation. Reactors 1-3, and by some reports 4 all suffered violent hydrogen explosions March 2011 which damaged or destroyed their top levels or lower suppression level (unit 2).[10] Fires in spent fuel ponds also released radiation.
As emergency measures, helicopters attempted to drop water from the ocean onto the open rooftops. Later water was sprayed from fire engines onto the roof of reactor 3. A concrete pump was used to pump water into the spent fuel pond in unit 4.
The accident released up to 10,000 terabecquerels of radioactive iodine-131 per hour in the initial days, and up to 630,000 terabequerels total, about one tenth the 5.2 million terabecquerels released at Chernobyl.[11]
[edit]References
So why not phase these reactors out ?mr chiver?
Although I am anti nuclear power I would like to assume new designs are safer than our first generation plants is this a correct assumption? I understand public sentiment is against new plants but we all most realize short of no nuclear power there is a safer plant design than current bwr design .although there is no use or storage areas for spent fuel and decommissioning plants is a huge undertaking of tens of years.we must phase out these bwr reactors...
This is not so strange.
This is not so strange. Nuclear power plants, by design, will shut down when external power (i.e. grid power) is removed. This is a safety mechanism since the plant loses two redundant cooling power supplies other than it's own power. Normally, reactors can power it's own equipment when running but you don't want to rely on this since, as we all know now, reactors will heat up after shutdown and require power for cooling water. When the reactor shuts down, you would need external power (again grid power) to run cooling pumps. The backup to grid power is diesel generators in which there are usually a whole bank of these in case one or more does not start-up. So, if you lose external power, you lose redundant shutdown power supplies (grid + diesel generators) and thus the reactor shuts down automatically. At this point, diesel generators start up automatically and power the cooling pumps while plant workers attempt to bring back external grid power. This does not happen often, but it does happen when we see blackouts or equipment failures such as this case where a breaker tripped. The report does not mention if the breaker was a main feeder breaker or an internal power supply breaker (these are also three-fold redundant), but in any case the automatic shutdown is a good sign that systems are working as designed.
I think the media has become sensitized to these unplanned reactor shutdowns here in the US. This is similar to the US Air emergency landing into the Hudson river produced by multiple bird strikes. Bird strikes are improbable but normal occurrence and after that incident, the media reported for some time planes that made emergency landings due to bird strikes. They don't report it anymore, however, but bird strikes continue...so do reactor shutdowns. Observing safe recoveries from these events should give us confidence.
What you are saying is true.
What you are saying is true. But is it also true for radioactive *spills* instead of just plant shutdowns?
Ontario radioactive spill - March 17, 2011
http://toronto.ctv.ca/servlet/an/local/CTVNews/20110317/pickering-nuclea...
UK - 4 spills in February:
http://blog.alexanderhiggins.com/2011/04/20/leaked-report-uk-covered-4-r...
*cough*stuxnet?*cough*
When will it be able to be
When will it be able to be restarted or put back into service is my ? Do u have to obtain a cold shutdown before resuming operations?
Once redundancy is
Once redundancy is re-established, there is normally a pre-criticality procedure that is followed to the letter to ensure that all systems are ready and then the reactor will be brought back on-line. The safety procedures that the NRC enforces within these plants are quite strenuous.
Safety of bwr
[edit]Notable activations of BWR safety systems
General Electric defended the design of the reactor, stating that the station blackout caused by the the 2011 T?hoku earthquake and tsunami was a "beyond-design-basis" event which led to Fukushima I nuclear accidents[8]. According the Nuclar Energy Institute, "Coincident long-term loss of both on-site and off-site power for an extended period of time is a beyond-design-basis event for the primary containment on any operating nuclear power plant".[9]
The reactors shut down as designed after the earthquake. However, the tsunami disabled all diesel backup generators which operated the emergency cooling systems and pumps. Pumps were designed to circulate hot fluid from the reactor to be cooled in the wetwell, but they did not have any power. The reactor cores overheated and likely melted. Radioactivity was released into the air as fuel rods were damaged due to overheating by exposure to air as water levels fell below safe levels. As an emergency measure, operators resorted to injecting seawater into the drywell to cool the reactors, but would also ruin them for future operation. Reactors 1-3, and by some reports 4 all suffered violent hydrogen explosions March 2011 which damaged or destroyed their top levels or lower suppression level (unit 2).[10] Fires in spent fuel ponds also released radiation.
As emergency measures, helicopters attempted to drop water from the ocean onto the open rooftops. Later water was sprayed from fire engines onto the roof of reactor 3. A concrete pump was used to pump water into the spent fuel pond in unit 4.
The accident released up to 10,000 terabecquerels of radioactive iodine-131 per hour in the initial days, and up to 630,000 terabequerels total, about one tenth the 5.2 million terabecquerels released at Chernobyl.[11]
[edit]References
So why not phase these reactors out ?mr chiver?
Although I am anti nuclear power I would like to assume new designs are safer than our first generation plants is this a correct assumption? I understand public sentiment is against new plants but we all most realize short of no nuclear power there is a safer plant design than current bwr design .although there is no use or storage areas for spent fuel and decommissioning plants is a huge undertaking of tens of years.we must phase out these bwr reactors...
Link please
Link please
http://www.cnn.com/2011/US/04
http://www.cnn.com/2011/US/04/22/georgia.nuclear.plant/index.html