This is one of their newest one and it’s clear that a couple of the PR guru’s mentioned earlier are now in full out spin mode. And who could blame them? Even thought the full consequences of the accident are not yet in, already we have seen numerous nuclear energy projects suspended, scrapped or put under further review. The view from the industry, a typical example of such cheery rosy tintedness can be found here , is that the reactors took the full force of a magnitude 9 earthquake they had not been designed to withstand (the limit they were actually designed to hold up to was much lower) yet still contained everything with “minor releases” of radiation, little serious damage to the reactors and only a low dosage of radiation to the workers at the plant.
First of all, if Fukushima is a “triumph” for the nuclear industry, I hope I’m not around when they have a genuine disaster! It contrasts vividly with the desperate images of water cannons and helicopter drops of water being used to cool down the reactors, 3 of whose containment buildings have now been reduced to smouldering piles of rubble. The way this lot go on you’d swear they’re planning to take they’re holidays this year at the beach at the foot of the plant (in fact if they’re so confident the radiation levels are low why not make themselves useful and form a bucket brigade and refill the evaporating cooling ponds!).
The reality is of course very different. The epicentre of the earthquake was a good 100 km’s away from the plant, the shaking experienced at the plant would have been fairly mild. The plant shut down, as indeed procedures required, but it was at this point that the backup power systems failed. Several other critical systems on Reactor 2 also failed, the Tsunami then rolled in and overtopped the seawall (which was specifically suppose to stop it) and further exacerbated the situation on site by flooding the diesel tanks and generator buildings. In short, a lot of stuff didn’t do the job it had been design to do. Its also emerged that the IAEA warned the Japanese that some of its older plants were not up to the task of resisting a large earthquake back in 2008.
One of the first rules of engineering is always have multiple backup systems. One of the other rules is, never rely on you’re backup systems (if you have to something has gone horribly wrong). As I mentioned in a pervious post, such a string of failures happening to one reactor would be just vaguely excusable, but all three active units! The fact that within the first 2 days they’d already resorted to venting hydrogen from the cores (knowing full well this risked an explosion) as well as flooding the reactors with boric acid and seawater (all but guaranteed to write the reactor off via corrosion) shows you how close to the edge things came. Had the earthquake been closer to the site its likely the consequences of the accident could have been much more serious, i.e control rods jammed, structural collapse of parts of the buildings and its possible one of the reactors could have gone into full scale meltdown, with a substantial release of radiation. If it had been reactor 3 (which was fuelled with MOX) this could have been not only as bad as Chernobyl but much worse.
The Radiation emissions from the plant have been occasionally quite high, the situation with the Reactor 4 cooling ponds only kicked off because radiation levels were so high (from reactor 3) that the staff couldn’t approach it. The dose of radiation taken by the staff is likely to be reasonably high, not high enough to kill any from radiation sickness, but probably high enough to give a number of them some long term health problems. Casing point, they had to raise the radiation limits that the workers could be legally exposed too, i.e. some workers at the plant may well have picked up a dose of radiation in a week or two, equal to what they’d normally expect to be exposed to during an entire career of working in a nuclear plant.
Beyond the plant levels have occasionally risen to high levels (50-20 times normal background levels, there’s one record of 10 times normal just outside Tokyo), but the weather has largely co-operated blowing much of the radiation emissions out to sea (as well as the radiation discharged into the sea from cooling water and leaks). Of course one downside of this is that the Japanese get most of they’re food from the sea, so we could well see some long term health issues and food scares in the future.
All in all, it’s a little too early to say what the radiation effects are likely to be. But to jump to the conclusion that they are “negligible”, something that the nuclear cheerleaders have been repeatedly saying since the accident started (ignoring all evidence to the contrary since then) is probably not accurate.
More widely, this accident has underlined a number of critical flaws of many existing nuclear power stations, notably:
1) There are two main barriers to radiation within a modern reactor, the pressure vessel itself and a concrete and steel containment structure surrounding it (often called the containment dome or biological shield). At the TMI accident, while radioactive gases managed to escape from the pressure vessel, they were (for the most part) prevented from escaping further by the presence of the containment dome. The Chernobyl reactor lacked a containment dome, and the Russians were strongly criticized for this fact, while at the same time people in the west were reassured that the presence of such structures on most Western reactors (thought not all, notably the British Magnox reactors also lack a containment dome) would prevent a similar accident. The Russians, while acknowledging that with the benefit of hindsight they should have included a containment dome over the reactor, its presence at Chernobyl would have been largely moot. The shear ferocity of the explosion from the core would have blasted a hole straight through it. The breaching (or total destruction) of the containment structures around 4 of the reactors at Fukushima (one of which wasn’t even running!) by hydrogen/steam explosions seems to confirm this assertion. It was only the fact that the pressure vessels held out against these explosions that a wider catastrophe was avoided it.
This fact compromises a critical safety assumption currently applied to many operational reactors worldwide. It is possible to strengthen such domes, but obviously that would be expensive. Sufficiently costly in fact that given the age of many reactors worldwide (average age 24 years) it would probably make economic sense to simply shut many of them down and rebuild them, than make the necessary modifications.
2) The whole situation in Fukushima only kicked off because of a loss of on-site power. This serves to highlight the vulnerability of large light-water reactors to loss of on-site power, something that’s been a problem for quite sometime. Even if all the control rods go in successfully (which in the case of a BWR is a risk as unlike other reactors they cannot be relied upon to simply fall into place under they’re own weight by releasing they’re electro-magnetic clamps), light water reactors still need water circulating for several days afterwards to siphon off residual decay generated heat. It should be noted that irony of ironies on the night of the Chernobyl disaster the reactor technicians were running a “safety test” to test various strategies for coping with a loss of on-site electrical power.
Whether this failure of on-site power at Fukushima was due to earthquake/Tsunami damage, or that the systems just didn’t work (noting that this won’t be the first such incident), is still unclear. It should be noted that more modern designs of reactors, such as the EPR or ABWR rely on passive natural convection to circulate water, making them less vulnerable to such a failure, thought not entirely immune (they still need electricity to operate valves, etc. as well as pumps to drive the outer cooling loop, else the heat has nowhere to go). Of course modern designs like these are much more expensive to build that the older designs.
Either way Fukushima highlights the need for a rethink of how these backup power systems operate, unless we fancy decommissioning a large chunk of our existing reactor fleet. One possibly solution is to build smaller reactors in future, which are less vulnerable to the risk of overheating, or better still gas cooled reactors. However, both of these options come with the disadvantage of lower economies of scale and higher costs.
3) The whole situation at Fukushima was made worse by the presences of MOX fuel in Reactor number 3. In the wake of this accident, it would be prudent to reassess the wisdom of MOX fuel. Its presence in the event of an accident greatly raises the stakes and complicates matters, there are many other risks associated with its production, as well as the huge costs of reprocessing in general. One of the most sensible decisions of the Ford Adm. In the US was to abandon all reprocessing of commercial reactor fuel on grounds that included the fact that it simply isn’t economic. Most countries in the world now also utilise a “once through” policy for nuclear fuel. At the very least you’d have to argue MOX should now only be used in our very best and safest of new reactors, although personally I’d favour phasing it out completely now. A phase out of MOX would blow a huge hole in the long term potential of nuclear energy as it would great limit the number of reactors we could keep running on any given year, and ultimately the fact that we would exhaust all the world’s fissile material within a few generations (or less!).
4) The situation at reactor 4 was also rather worrying as it highlighted an Achilles heel of many nuclear plant designs – In short, is it sensible to store large amounts of nuclear waste in close proximity to an active reactor? Particularly in light of what was said earlier about the now suspect integrity of the outer containment dome. While the material in the ponds is in a “passive” state there are a lot of things that could easily tip things over and create a more serious emergency (such as them boiling dry, a leak in the base of the ponds or a fire within the containment dome spreading to the ponds). It’s not unusual for such cooling ponds to contain large quantities of nuclear material, often as much if not more than the reactor itself. Indeed its been suggested that the reactor 4 cooling pond had been racked with far more waste that it was supposed to hold, likely a result of the fact that the Japanese lack a proper deep waste repository to dispose of their nuclear waste. They lack such facilities due to their commitment to reprocessing, despite a limited capacity to reprocess fuel, leading to large stacks of spend fuel piling up in reactor cooling ponds or in interim storage pens. Of course modifying or rebuilding nuclear facilities to overcome this problem is certainly possible (by building a separate series of containment domes nearby for the spent fuel rods…or better still taking the stuff offsite as soon as that’s possible), but this would be expensive and time consuming to implement.
5) Finally, as several critical components failed, possibly due to the effects of the earthquake, a major review of earthquake/Tsunami resistance at all nuclear power stations might be a good idea. The Tsunami issue in particular, as many power stations in non-earthquake prone regions have probably never considered the effects of a Tsunami, even thought many of the world’s nuclear fleet are built on coastlines, and that Tsunami can be triggered thousands of miles away and yet still cross entire oceans. Obviously building new power stations in earthquake prone regions, while not out of the question, it should now require a rethink. Furthermore areas of the world with lots of earthquakes tend to have good geothermal resources, the Japanese for example have excellent such resources, which it might prove to be more sensible to exploit rather than nuclear power.
Fukushima doesn’t by itself disprove the case for nuclear power. But it would require any sane and rational person to recognise the need for a major rethink of our nuclear energy strategies. A proposed “stress test” of all nuclear plants sounds like a good idea, although that entirely depends on who runs these tests! Of course to the nuclear cheerleaders such an action is wholly unjustified, they just “know” that nuclear energy is perfect and Fukushima is all much ado about nothing and overblown, and in fact its all the media’s fault for reporting it!