Nuclear power

[spaces]

Move along folks, nothing to see here, nukes are safe.

That's a spectacularly inappropriate comment, given the facts. You should work for the government.

[SteveH]

Move along folks, nothing to see here, nukes are safe.

That's a spectacularly inappropriate comment, given the facts. You should work for the government.

 In the 80's it was OK...

[Ivan]

Hydrogen-production occurs when the zinc(?) fuel rod casings are exposed to water at high temperatures (1100C+). Meltdown occurs at 2000C. So it makes sense that we're at least half-way to meltdown temperatures already.

[biff]

hi good folks,
        having read through the posts i can see how upset some members are by the nuclear accident in japan,the first thing you have to realise is,there is no other country on the planet that cares about its enviroment more than japan does.the second is,their engineers are second to none,and if i saw an explosion blowing off the cladding round one of their reactors i would hope that this would be part of their strategy or plan to relieve unwanted pressure or to encourage cooling, thirdly,japan does not do bullshixxers or people who tell big porkies,simply because if they get found out they get their head on a block,,,they might have annoyed the western world by hunting the whale but they are the people to watch when accidents like this happen.they are well organised and if anyone can put it right it is the japanese people and their engineers.
       we will learn from this,it is a test of the outmost importance, they will pay the price for our advancement in experience in this type of nightmare disaster. i am absolutly sure they will have everything under control before long.
                                                                                       biff

[dhaslam]

If 1000C plus water  produces hydrogen and oxygen why doesn't it  then get hotter by burning the hydrogen or does the process  have a net cooling effect? 

[Philip R]

When a fission power reactor trips from full load, assuming the fuel is partially through its burnup, heat is produced not from a the chain reaction but from the decay of fission waste products at about 4 % of the nominal power that the reactor was operating at. Within 2 hours it decays to about 1% of its former heat output. The output decays further to fractions of % over the next few days and weeks.

That is why the post trip cooling is required post trip. Newer designs of LWR like the APR1000 and EPR use more natural circulation (convection) to provide this cooling as it relies less on electrical / diesel operated pumps.

With respect to the steam/ hydrogen explosion seen in Japan, If the plant was a Boiling Water reactor, the steam passing through the turbines is water that passes through the reactor core, therefore capable of releasing delayed neutrons, however none exist as the reactor was long tripped, but it would be contaminated with fission product especially if the fuel clad had breached. By the way, Ivan, Zinc is not allowed anywhere near a reactor core, It melts and form eutectic low melting point alloys with reactor components and will become neutron activated to become a high gamma source. The material in question is Zircalloy, principally zirconium, ( Lower neutron cross section than stainless steel used in UK AGRs.)

My concern about the gas/ steam explosion, would likely have incapacitated Operational and Engineering staff at the plant!, i.e. those on damage assessment and remediation. Philip R

[spaces]

Biff, I agree with most of what you say about the Japanese, but from what I've read their nuclear industry hasn't been very 'forthcoming' in the past. 

[Philip R]

The disassociation of water into hydrogen and oxygen is highly endothermic, most of the oxygen is locked up as metal oxide in this case which oxidises  the internals of the reactor. The attempt to direct sea water cool these units will prevent any restart of the unit without the pressure vessel and steam pipework being replaced.

All I would say is roll on generation 4 nuclear technology, pool type reactors; high -ve temperature coefficients of reactivity, no positive void cooefficients, strong convective cooling characteristics, lower core inventory. All good attributes.

The accident at the Monju plant whereupon a steam pipe in the turbine hall eroded from within by wet steam was not dissimilar to a what happened at a coal plant not far from East Midlands airport a few years back, albeit boiler feed pipework in the boiler house. Similar degraded pipework was found across the coal fleet, repaired before any more accidents occurred. Luckily, the Nuclear fleet in the UK had a better inspection regime in operation, so this problem did not manifest itself.

PhilipR

[pogster]

"Workers at the Tokaimura uranium processing facility added too many buckets of uranium directly into a precipitation tank, causing it to go critical, killing two, and exposing one more to radiation levels above permissible limits"

"Steam explosion at Mihama Nuclear Power Plant kills 5 workers and injures dozens more"

Yep Biff, Those Japanese really know what they are doing...

[billi]

Sad story ,  .... question that remains is.... can we control ?

http://en.wikipedia.org/wiki/Japan#Science_and_technology

Gozzilla, frankenstein , or others  we create  and  try to be clever , but we are  helpless creatures   to cope/deal with them  , when they get loose ...

So nothing that can be dangerous has a place in our future world


Billi

[Ivan]

Whereas we perhaps cannot expect the Japanese to have considered a tsunami (but then again, they're located in an Earthquake zone, so perhaps they should have planned this), there should be more reliable back-up power available to maintain emergency-critical cooling systems (Chenobyl's fate was partly due to lack of / failure of emergency power systems required for cooling - and in fact triggered by testing this).

Sorry, I can't accept the roof being blown off the building as planned emergency protocol. If there was a proper mechanism for venting, it would involve pressure relief valves, and they certainly wouldn't be venting hot steam/hydrogen from the reactor core inside the building! So how can planned pressure-relief cause the roof of the building to explode? It seems more likely that steam pipes inside the building have ruptured due to the high pressure.

Although the containment vessel is thought to be intact at present, we have a situation where material from directly within the reactor core is being vented / ignited / blown-up. Although it may be only a relatively small amount, it still constitutes a serious radiation leak (which is why there are over 100 people being treated for radiation exposure and a few for radiation poisoning (which means they have a strong chance of dying within the next few weeks).

[billt]

The Japanese did consider a tsunami. The first Fukushima reactor was designed to survive an earthquake of 7.3 on the Richter scale; it survived an earthquake of 8.9 and shutdown correctly. The plant did have a protective wall, but wasn't designed for a 10M wave, which was considered (and is) an extremely uncommon event. The plant was designed for area; it shutdown properly and the backup generators started properly after loss of grid power, it was the extraordinarily large tsunami overtopping he protective walls that shutdown the generators.

In other words the plant was designed for the conditions, but the event was so enormous that it was not reasonably foreseeable.

Japan has 53 nuclear reactors, all the rest seem to have survived without significant damage. Even if the cores melt down at Fukushima, the number of deaths that result will be in tens; it would seem that over 10,000 people have died from physical results of the earthquake which makes the nuclear accident trivial in the context of the event.

The Japanese efforts to design buildings to survive earthquakes have been shown to have worked very well. Considering the magnitude of the earthquake they suffered very few casualties from the earthquake itself.

[martin]

"but the event was so enormous that it was not reasonably foreseeable" rather sums up the problems with such things as nukes in this modern world - although this wasn't one, climate events are shattering records yearly, and thanks to the effects of climate change are likely to continue to be more severe and often than ever before, making necessary safety margins almost impossible to predict, and certainly necessitating colossal precautions, adding, as I've said (ad nauseam) to the fact that nuclear is FAR too expensive to do safely/properly

[guydewdney]

Ivan - triple back-ups isnt good enough?

system 1 - primary - control supplied by mains
system 2 - backup - diesel genny supplies mains to controls
system 3 - secondary backup - UPS supplies power for 8 hours
system 4 - steam powered turbines supply uncontrolled cooling flow.

[wyleu]

Given our presence on this forum, one assumes a fairly high faith in technology. It's probably not the actual proess itself that worries me as much as the economics that will inevitably apply. We are still in the nacent stages of our use of fusion and whatever people may say if the lights go out here then we will clammer for a reactor over there if it gets them back on. Quite what the implications are for those that live where ever over there happens to be is a further debate.
It's interesting to see the time constants of the basic rhythm of all this. Phillip R demonstrates considerable understanding of the processes involved and if we are to assume that there will be a nuclear component for some considerable time then I am encouraged that there is real engineering knowledge building up around how to deal with the events that the politicians say are impossible. ( I suspect few genuine technologists would make such statements ). The concerns are that we left the control to private companies, who will de-skill the process as much as they can. Easy profit whilst things run well, but a decreased level of expertise when problems occur. Be it the japanese pumping sea water in or the fellows at Windscale( calder Hall/Sellafield/Snuggly Bunny land or whatever they call it next) doing the same with their 1957 graphite fire, we can control these devices, but it has to be done by people with understanding, not by semi skilled bouncers more obsessed with perceived security rather than ability. In the present world climate the resulting deaths disappear into statistics when compared to famine, natural disasters, roads, passive smoking or military sales missions in various parts of the world.

 The early days of most technologies are littered with death, not so much as a result of technologies failings but companies greed and indifference till brought up short. An MP was killed on the first day of operation of the Liverpool Manchester railway ( rather a positive move, I've always felt) and yet railways are now probably the safest form of transport. But those lessons were learnt at the cost of many Armagh.
The complex ties between the military and the atomic energy industries are not as complex in Japan as they are here in the UK. I suspect this incident and the reaction to it will increase the likelihood of the next piece of gesture politics from either India & Pakistan, the Korean brothers or our industrious house building friends in Israel, given we now tend to fight our successful wars in the media rather than on the ground. However the ultimate results from an energy perspective for any future use will be brighter, until the technology is eventually replaced by something better.
It is up to us not to define better in purely financial terms. Ultimately we must do less, but to expect people to live without electricity is a recipe for community meltdown and if nukes help prevent that, if only in the short term, they have my grudging support.