TECPO's triage at Unit 4

My prior post debunking some of the more outrageous myths circulating the internet as to the state of the Fukushima Daiichi Unit 4 spent fuel pools generated some considerable amount of heat, particularly over at its syndicated location at The Energy Collective. Much of this discussion has focused upon the physical state of the Unit 4 reactor building itself (at the top of which the Unit 4 spent fuel pool resides). Yet contrary to popular belief in particular circles, TEPCO has certainly not left the spent fuel pool at Unit 4 to the vagaries of nature, nor have they failed to produce a credible, long-term plan for stabilizing and containing the remaining spent fuel at the reactor units.

Before getting too far into the topic, it's useful to point to a comprehensive companion piece to the prior discussion by Will Davis (of Atomic Power Review) over at the ANS Nuclear Cafe, entitled "Spent Fuel at Fukushima Daiichi Safer than Asserted." (Along with several other nuclear bloggers, I offered a moderate amount of technical consultation for this topic.)

TEPCO's remediation strategy for the Fukushima Daiichi site (original)

Given the concern over the structural state of the reactor building, it is thus useful to look at what TEPCO is actually doing to address the issue. Much of TEPCO's strategy is oriented around immediately stabilizing the site with a focus upon long-term remediation; in a word, triage.

In order to stabilize the earthquake-damaged reactor building, TEPCO has already conducted an evaluation of the structural integrity of the Unit 4 reactor building, deciding to reinforce the foundation of the building with a steel-beamed outer support structure, work which was completed last summer. In this sense then, the immediate concern over the stability of the reactor building (and spent fuel pool) has already been addressed.

However, there remains the issue of the fuel itself in the Unit 4 spent fuel pool. TEPCO has already put measures into place to ensure adequate cooling in the event of a sudden loss of water (i.e., from another large earthquake), including the deployment of concrete pumper trucks (referred to as "giraffes," which were used to originally restore the water levels at the Unit 4 pools). To emphasize - the concern here is not from a loss of water due to evaporation (again, spent fuel pools are kept at atmospheric temperature and pressure under normal conditions; meanwhile, the youngest fuel within the pool is now well over a year old, meaning it is cool enough where sudden evaporation is not a concern). Rather, the planning is again one of being able to respond to issues such as future earthquakes.

Despite the fact that the situation is as stable as can be expected presently at Unit 4, there is a legitimate concern about the impact of future earthquakes. Again, to emphasize - the chief concern over a (rather unlikely) collapse of the spent fuel pool is not the global catastrophe flogged by certain activists lacking in technical credentials (both my prior post and Will Davis' post adequately address why this is so), but rather a mechanical failure of the fuel (which would release local contamination - in particular, radioactive cesium and strontium) and force a local evacuation from the site, thus greatly complicating the cleanup response. (Thus, while far from catastrophic, such a collapse would greatly hinder the ability of TEPCO to clean up the site and add considerable expense to an already vastly expensive project.)

Thus, the medium-term strategy is to relocate the fuel out of the Unit 4 spent fuel pool into the common pool, thus obviating the risk from further damage to the Unit 4 reactor building; current plans call for the fuel from Unit 4 to be fully removed by mid-2013 (and from Unit 3 by the end of 2014). Again, in contrast to the opinions of certain press-seeking political office-holders and activists, this is not a process accomplished with the wave of a wand.

According to TEPCO's mid-to-long term roadmap, this will roughly consist of the following:

• Clear debris from the spent fuel pool which was dropped into the pool due to the hydrogen explosion
• Install a cover over the damaged building to shield heavy equipment from the environment (e.g., wind and rain). Following this, heavy fuel handling equipment (e.g., heavy cranes) will be installed in the reactor buildings in order to begin the process of moving undamaged fuel rods.
• Relocate undamaged, older fuel from the common fuel pool into dry cask storage to make room for newer, hotter fuel from the spent fuel pools at each reactor building. 
• Begin removing spent fuel from the reactor buildings; this will involve placing the fuel from the reactor buildings in temporary transportation canisters and lowering the canisters to ground level, where they can then be relocated to the common fuel pool.

Ultimately, this is not a quick process; nor is it clear how, despite the best intentions of "concerned outsiders" how this could reasonably be expedited beyond the current schedule, as several tasks are contingent upon one another. (i.e., spent fuel pools must be cleared of debris and a temporary cover must be installed before heavy equipment can be installed, and subsequently fuel can be relocated). Yet it is also clear from both current triage efforts as well as long-term recovery plans that the situation is far the looming disaster it is being sold as.

Update: Via TEPCO's English-language Twitter feed comes this presentation specifically addressing their analysis of the structural soundness of the Unit 4 reactor building.

Overheated rods & rhetoric

A little knowledge is sometimes a dangerous thing - particularly when fundamentally incomplete technical knowledge is used to make sweeping engineering recommendations. The latest example of this is the concern over the spent fuel storage pools at Fukushima Daiichi Unit 4, which has been getting attention from several corners. First, there was U.S. Senator Ron Wyden (D-OR), a ranking member of the Senate Energy and Natural Resources committee, who recently toured the stricken Fukushima site and released a very widely reported statement that, "things were worse than reported." In particular, Wyden has singled out the spent fuel pools at Unit 4 for unique concern, calling on both the Japanese and U.S. governments to see to it that the rods are safely relocated elsewhere, citing their storage in unsound structures close to the ocean. Wyden has pushed the NRC and others to relocate these spent fuel rods to dry cask storage elsewhere.

As for Wyden's technical credentials for making this assessment? A J.D. in law and his self-assurance in a Senator's unerring technical omniscience.

I suppose it probably doesn't occur to the Senator that relocating spent fuel rods out of the damaged building is no mean feat, given that the rods which will be relocated need to maintained underwater while they are transferred into concrete casks (in this case, mostly for radiation shielding purposes) using heavy cranes. Meanwhile, TEPCO has already reinforced the damaged building, addressing the concern he has over future tsunamis further damaging the weakened building and leading to a release into the environment. Its current plans call to begin removing spent fuel for relocation within the next two years. To emphasize - this is not a problem that relevant technical experts were ignorant of until one brave Senator stepped in and decided to lead.

Of course, to be fair to Wyden, as Dan Yurman points out Wyden is clearly not the only politician suffering from an acute hubris on technical matters.

Overheated rods & rhetoric

A spent fuel pool (Image: IEEE spectrum)

At least the good Senator can be forgiven for his enthusiasm however, as it's not nearly as obnoxiously hyperbolic as certain other accounts going around the internet. Anti-nuclear activist and self-described nuclear "expert" (to use the term rather loosely) Robert Alvarez has been shopping around the dangers of spent fuel pools for some time, specifically focusing his ire upon the rods contained in the spent fuel pool at Unit 4. This of course is not a new topic for Alvarez, who has gone so far as to argue that such pools are "a ticking time bomb" and that the U.S. needs to move toward dry cask storage of all spent fuel as soon as possible. (More on why this is silly at best and potentially a dangerous misplacement of priorities in a moment.)

Spent fuel rods at Unit 4 (Image: IAEA)

Alvarez's latest work, "Why Fukushima Is a Greater Disaster than Chernobyl and a Warning Sign for the U.S.", hits a new low in terms of outrageous hyperbole. Let's start with the headline premise - Alvarez asserts that the potential danger - a release of radioactivity from the spent fuel rods at Unit 4 - is already worse than something which actually happened - i.e., the Chernobyl disaster. (Perhaps aware of this seeming logical contradiction, Alvarez walks this back to "may be worse" in the first sentence.)

The basis of his reasoning? 1) Spent fuel contains very large amounts of radioactivity, 2) The spent fuel pools have been exposed to air (due to the hydrogen explosion at Unit 4), 3) A collapse of building containing the spent fuel pool would lead to an overheating of the rods contained at Unit 4, 4) Somehow, this would lead to a zirconium fire and release all of the radioactivity present in the rods.

Alvarez' blog post is a perfect example of the trouble one can get into when one extrapolates from a small bit of knowledge to a larger technical issue.

Taking it point-by-point - first we have this:

Several pools are now completely open to the atmosphere because the reactor buildings were demolished by explosions;

First of all, it should be noted that spent fuel pools are generally kept at room temperature and atmospheric pressure to begin with. A spent fuel pool, at its core, is essentially a very deep, very large swimming pool (which is also very radioactive as you reach the bottom). At the top, radiation levels are low enough to safely work without problems - you can even look down inside and see the eerily beautiful blue Cerenkov glow if the lights are dark enough. As for containment? The explosion at Unit 4 was in the secondary containment, which is essentially a thin* metal reinforced concrete shell - again, namely because spent fuel rods are un-pressurized and not at the kinds of temperatures found in the reactor. (In other words, the same kinds of phenomena involved in a core melt aren't relevant here.) The primary containment in any spent fuel pool is the water itself, which isn't hot enough to be going anywhere.

*(Edit: "Thin" being relative to the primary containment, which is 4-8 feet thick; most of my understanding of the secondary containment comes from diagrams such as this one, or this one via TheEngineer which bears much greater detail)

Moving on:

As more information is made available, we now know that the Fukushima Dai-Ichi site is storing 10,833 spent fuel assemblies (SNF) containing roughly 327 million curies of long-lived radioactivity About 132 million curies is cesium-137 or nearly  85 times the amount estimated to have been released at Chernobyl. 

So what does this mean? Without context - absolutely nothing. What Alvarez is trying to imply is that in the circumstance that these materials were released into the environment, the consequences would be far worse than Chernobyl. The problem? Alvarez presents no credible physical mechanism for this to happen.

Then there's this:

Also, it is not safe to keep 1,882 spent fuel assemblies containing ~57 million curies of long-lived radioactivity, including nearly 15 times more cs-137 than released at Chernobyl in the elevated pools at reactors 5, 6, and 7, which did not experience melt-downs and explosions.

Why is it not safe? Well, other than the fact that spent fuel is radioactive, Mr. Alvarez doesn't say. An industrial blast furnace is also not a safe place to be, but that certainly doesn't prevent their use. Instead, we actually take precautions to use them safely - the same way spent fuel pools use deep levels of water to both cool the fuel and shield the high levels of radioactivity.

To wit: certainly no one would want to be next to a spent fuel assembly without the shielding provided by the deep pool of water. (With this shielding, the levels of radiation are low enough where it is quite safe to stand above the pool and look down inside - something I have had the opportunity to do before). But for this radioactivity to be truly disastrous (rather than simply being a dangerous but extremely localized nuisance), something has to cause the radioactive materials in the fuel to change state - i.e., to either melt or be carried away ("lofted") by a fire.

In the beginning of his article, Alvarez eludes to the possibility of a zirconium fire, which he asserts could happen if the rods grew too hot. (Alvarez provides no further explanation or reference to credible technical resources beyond this.) Yet there are several significant problems with this theory. First, this would require the rods growing hot enough to ignite (if this is even possible - zirconium in solid form will not ignite, and its melting point is 1852° C). It second assumes that all of the radioactivity is uniformly lofted into the atmosphere; one of the main reasons for the magnitude of the Chernobyl disaster had to do with the fires in the reactor building which lofted radionuclides high into the atmosphere, where they spread across Europe. (Incidentally, this fire was also not from zirconium - it was a graphite fire from the reactor and control rod design being used.)

(Alvarez also rides his hobby-horse in inveighing against spent fuel reprocessing - a topic beyond the scope of this post but one which we've covered previously.)

A background on spent fuel

Spent fuel heat (click for larger)

Meanwhile, let's back up for a moment such that everyone understands what's going on. As we've covered on this blog before, spent fuel does still produce heat after the fission reaction shuts off. The remaining radioactive materials in the fuel, created both by fission and absorbing neutrons - are decaying. The quickest-decaying materials produce very high levels of radioactivity, and much of this energy is trapped in the fuel itself, heating it. Thus why spent fuel needs to be cooled following the reactor shutdown (which was the resulting source of problems at Units 1, 2, and 3).

Both this radioactivity and decay heat fall off dramatically with time, as the shortest-lived fission products decay away. Within 100 days, the heating rate and the radioactivity in spent fuel have dropped by a factor of 10; within 10 years, this drops to 1/100th of the original values.

Spent fuel radioactivity (click for larger)

Doing my own calculations using ORIGEN-S (a tool for nuclear licensing evaluation which is used to simulate spent fuel inventories), a typical assembly of the type found in the spent fuel pool would produce about 3-4 kW of heat after being stored around 1.5 years (and even less as it grows older) - or about 17-20 watts per pin (which themselves are over a meter long). In other words, while fuel which has just been ejected from a reactor poses a challenge in terms of cooling, it is difficult to conceive of how one gets the type of scenario Mr. Alvarez describes, in which something producing so little heat manages to cause these assemblies to melt or spontaneously catch fire.

A solution in search of a problem

Dry storage casks for spent fuel

Getting back to the main thread now - let's assume for a moment that this scenario, one already demonstrated to be of extremely questionable plausibility, is true - i.e., that there remains a real threat spent fuel pools, in which the cooling water is lost and the rods subsequently overheat and either catch fire or otherwise change state. So Alvarez's solution, to prevent these rods from overheating? Put them into thick concrete casks cooled by circulating air. Apparently, the same rods at risk of spontaneous combustion when exposed to air are fine if put into thick concrete casks. The logical inconsistency beggars belief.

Note that I am most explicitly not criticizing dry storage - in fact, dry storage casks have been demonstrated to be an effective, medium-term solution for isolating spent fuel from the environment. But to simultaneously assert a danger of spent fuel rods melting when exposed to air while simultaneously advocating to put them in thick concrete casks exposes a basic failure of physics reasoning, one which both Mr. Alvarez's employer and the ever-reliable science reporting of the Huffington Post are happy to embrace.

Alvarez and his sponsors at the liberal think tank Institute for Policy Studies are of course using this reasoning to go a step further, arguing that all spent fuel pools at U.S. reactors are at risk and thus need to be moved to dry storage. Let's just watch the errors compound...

First, let's go back to the decay heat issue. Generally speaking, spent fuel isn't suitable for moving into dry storage until it has cooled for a few years in a spent fuel pool - a general rule of thumb for dry storage is 5-10 years cooling time, although less is possible. The heat generated by 10-year old spent fuel assemblies are a hundredth of that generated by recently-ejected assemblies - in other words it would take one hundred assemblies stored for ten years to equal the contribution of one "fresh" ejected assembly.

If the reasoning here is to give greater safety margins for spent fuel pools in the event of a loss of cooling, dry storage is an extremely inefficient mechanism for doing so - namely because of the fact that the assemblies which are eligible to be moved into dry storage casks make at best a marginal contribution to the spent fuel pool heating. In other words, a large expense for very marginal gains in safety.

So here's how it breaks down: "newer" spent fuel rods are too hot to go into dry storage casks, and thus must be kept in the spent fuel pool to cool. Therefore, the integrity of the spent fuel pool must be maintained. Yet if the integrity of the spent fuel pool is maintained, there is no real safety reason (at least in terms of heat or radioactivity) to move older rods, which can be moved into dry storage. (Note: there are other reasons one may choose to do so - spent fuel pools are limited in terms of total capacity, based on a number of safety-related factors, including total heat as well as how closely the assemblies can be placed together in order to prevent assemblies from going "critical" and restarting the fission chain reaction. However, these are far less limiting circumstances.)

What we have is thus a classic case of a solution in search of a problem. Alvarez (and others, for that matter) have found a solution they like - dry storage - and have (by process of scientifically incomplete reasoning) connected this with a problem they see - the vulnerability of spent fuel in wet storage pools - and naturally put the two together. Regardless, that is, of whether that square peg will actually fit in said roundish hole - the solution is, apparently, to just keep pounding.

When well-meaning ignorance actually becomes dangerous

This is where I think Alvarez's (possibly well-meaning) concern actually becomes dangerous. Maintaining the integrity of spent fuel pools for "younger" fuel is vitally important - which is why some of the most recent changes recommended by the NRC as well as industry call for improvements such as better monitoring and instrumentation at spent fuel pools, along with other kinds of contingency plans to ensure water can be delivered to the pool in the case of a loss of coolant. Likewise, ensuring the integrity in the design of spent fuel pools indeed should be a priority.

But herein lies the problem with "experts" like Mr. Alvarez, who has no actually technical background to speak of - starting with the faulty premise that "wet storage" (i.e., spent fuel pools) can be eliminated entirely (they can't), we are then assaulted with faulty recommendations to move fuel out of these spent fuel pools at large expense and very marginal contributions to safety. Yet arguably these are resources that could be better spent on improvements to the safety of spent fuel pools - things like better instrumentation to know what is going on in said pools and improved emergency response capabilities (such as designing easier means of supplying auxiliary water to the pools). The focus on dry storage as a safety measure thus makes for a dangerous distraction which commits attention and resources away from more productive ends, thus potentially compromising safety as a whole.

Alvarez isn't the only one guilty of a single-minded focus on dry storage as a "solution" to spent fuel storage pools - all kinds of individuals (such as Senator Wyden above, and even some people I know of in real life who should know better...) have jumped all over this. The problem comes down to a simple failure to think things through - again, if spent fuel is too hot to be exposed to air, it's too hot to go inside a thick (thermally insulating) concrete cask. If it isn't too hot for dry storage (i.e., older fuel), then it isn't what is driving the safety issue at the spent fuel pool. Thus, in either case, it's a solution in search of a problem - given the fact that hotter fuel cannot be removed from the pool itself, it is more useful to focus upon the problem at hand.

The underlying pathology here - in other words, why seemingly simple-sounding solutions like this are so seductive - is because it gives the illusion of "doing something" about the (perceived) problem. In this case, this is done through a somewhat primitive technical analogy - we  have a thick concrete containment for the reactor as a safety mechanism, therefore spent fuel should similarly always be in a thick concrete containment. It simultaneously ignores where the solution is technically inappropriate ("younger," hotter fuel) and how it fails to address the root problem (i.e., keeping the spent fuel both cooled and well-shielded - which is done by ensuring the integrity of the water levels in the spent fuel pool). Fundamentally, it is an example of how not to do engineering - engaging in a top-down method of choosing a solution first and making it work to fit the problem.

Under ordinary circumstances, this leads to bad outcomes - wasted money and sub-optimal solutions (or even solutions that are simply inappropriate). In the worst-case scenario, this kind of thinking actually makes things worse, namely by committing time and resources away from evaluating actual safety improvements - and thus where well-meaning concern of outsiders who are fixed upon a particular solution without understanding the actual problem can actually do more harm than good.

Support for nuclear: Broad but shallow?

Coming just upon the heels of a recent post about public opinion on energy sources, I couldn't help but also notice this poll by Gallup which NEI points to, indicating a relatively constant support for nuclear following Fukushima. The takeaway? Despite a small uptick in opposition to nuclear following the events at Fukushima (from 38% to 40%), public support for nuclear is still high, sitting at 57% in favor or strongly in favor of nuclear energy. While Republicans (and Republican-leaners) more strongly favored nuclear energy (65% supporting vs. 34% opposed) compared to Democrats (and associated leaners - 50% support / 45% opposed), support across the Gallup poll appears to generally be broad across parties.

The starkest reported differences in opinion were between men and women - 74% of men vs. 42% for women.  Tellingly, a nearly parallel trend occurs for the perceived safety of nuclear (with 72% of men believing nuclear is safe compared to 43% of women).

Given the somewhat less sunny projections from the recent Pew poll, how does one square the difference?

Digging into the Gallup data, one observes that strong support and opposition have both historically ranged around 23% and 21%, respectively; the bulk of support and opposition has been in the more moderated "somewhat support" (33%) and "somewhat oppose" (19%). How has this changed in the events following Fukushima? Overall, not much - overall support remains constant at 57%, although one observes some erosion in self-identified "strong" support. Meanwhile, strong opposition has hardened (growing from 18% to 24% in the last polling period). 

One might square this against the Pew data in the sense that Pew specifically asked about the expansion of nuclear energy (particularly in comparison to other energy sources), while Gallup simply gauged overall public support. If one takes both trends as true, it paints a picture of public opinion over nuclear as stuck in neutral - a public which overall supports nuclear energy but is divided about its expansion in light of other perceived alternatives. 

Meanwhile, going back to the Gallup results, overall public perception of nuclear safety is relatively unchanged (57% responding that U.S. nuclear plants are safe, while 40% respond that they feel U.S. nuclear plants are unsafe). While the continued (accurate!) perception of the safety of the U.S. nuclear industry is encouraging, it speaks to the need for further outreach efforts, as well as perhaps the unique perception of nuclear compared to other sources (i.e., where constant, elevated risk - such as hazards presented by sources such as coal - is tolerated much more readily than low-frequency, highly dramatic events, even if the ultimate public health consequences are minuscule).

Given the above, clearly nuclear is not in danger of a German-style phaseout. Yet the obvious challenge for public support of nuclear - beyond simply tolerating it, but in expanding it - is in making the case to the public that nuclear is both safe and essential - the latter of which comes down to arguments both over economics and the environment.

Cultural bias and nuclear

I was recently perusing the comments on an NPR article on nuclear waste disposal, ("How to find a nuclear waste site? Woo a town."). In perfectly foolish measure, I perused the comments - a bad idea for anyone with an IQ north of room temperature and a level of patience south of Mahatma Gandhi. I found myself taken aback with, to put it bluntly, the level of gross ignorance of nuclear opponents. A couple of examples:

[...]The truth of the matter is that, to prevent dangerous overheating of nuclear waste, the rail cars used to ship the waste would allow air to move freely which also meant radiation could move freely. While it would just be small amounts of radiation, this could add up for families living next to railways and cause a multitude of health problems.[...]

So, we don't UNDERSTAND nuclear and our little waste problem. This condescending, ridiculous bantor from the industry nver ceases to amaze me. The industry's problem is that more people are beginning to understand the dangers of nuclear. The lifespan and inability to rid ourselves of it was reason enough to have never began this horrid mess. Indeed, I DO understand and, therefore,I want this needless perpetuation of nuclear to end! 

 My reaction to the first of the above was almost to say aloud in Morbo fashion (from Futurama, to the uninitiated), "Windmills do not work that way!" In other words, it conveys a serious lack of understanding about just how radiation works.

Image credit: NRC

To explain it briefly - ionizing radiation (i.e., the kind that can cause health problems) doesn't just blow around like dust in the wind - it comes from a source: like the atoms decaying inside nuclear fuel, or the sun for instance. (Yes, the sun - ever wonder why you get a sunburn from staying out in the sun too long? You just got a very mild radiation burn.) For gamma radiation, (i.e., energy emitted from nuclear transitions, ranging from ultraviolet rays to x-rays to gamma rays), this travels in a straight line, just like visible light - because it is light; it doesn't simply scatter to the wind. Further, it attenuates strongly as a function of both distance and shielding; fuel transport casks are designed such that a person standing directly next to the cask would have to stand there for any awfully long time to get anything approaching a dangerous level of radiation exposure, but further, gamma radiation attenuates as the square of the distance. In other words, for every factor of 10 one moves away from a radiation source, the exposure drops by a factor of 100.

A standard rail shipping cask (courtesy Wikipedia)

But getting back to the issue at hand - yes, casks are air-cooled, but so what? For radiation to "move freely" as the commenter describes, this would require radioactive material to move freely. Yet the transportation casks are clearly designed such that heat from the fuel is conducted to the outside of the cask, where it is carried away by convection. In no way does the fuel get exposed to air, the only plausible way in which this event could happen (i.e., particles of the fuel itself allowed to be picked up into the air and carried away). To further put this myth to rest, these same casks have to be tested against all kinds of conceivable accident scenarios - drops, fires, punctures, crushes - anything that the fuel container could possibly experience in an accident condition.

Below is a video released by Sandia National Laboratories demonstrating the types of tests performed on an older design of the transportation casks:

Basically, any cask which is certified to transport used nuclear fuel must go through a battery of punishing tests before it is ever licensed to transport fuel.

Getting back to the main point here - namely, that the information on safety is out there and widely available, how is it that such gross misinformation still manages to persist? The second comment seems to point to a a particular phenomenon - cultural bias which ultimately leads to mistrust of the (accurate) information being given by experts. If you will forgive the (slight) hyperbole:

1. Nuclear energy is an industry run by giant, evil corporations with no regard for human life
2. Information conveyed by nuclear experts and supporters is chiefly in service to the above
3. Therefore, technical experts in nuclear are untrustworthy.

Hence we get have people resorting to "folk science" (in other words, lies) peddled by hucksters with their own agendas - be they political or economic in nature. (One can already begin to see the irony forming here.) Or you get the "proud ignorance" - "I don't need to know anything to know this is dangerous and you're lying to me!"

How do we get around this? I confess that I'm not an expert in this realm (I mean, after all, my first thought reading the above comments was to simply apply palm to face and mutter, "Windmills do not work that way!") But it does seem like there is a strong need to present a human element to this, conveying above all else that we, too share their (valid) concerns over the health and safety of our respective loved ones, and as such we have the utmost interest in obtaining and conveying accurate information.

Of course, a lot of us do this already - sometimes on a daily basis. A large part of the problem seems like an inability to penetrate "hardened" ideological structures where such ideas are formed and reinforced. And certainly, this applies far more broadly than just nuclear technology - think global warming, for example - a near-mirror image of this same phenomenon can be observed (accusations of science being manipulated for economic and political interests, etc.) If anything then, this seems to speak of a larger societal problem in conveying scientific and technical information about risk to the public.

Lessons Learned from Fukushima Daiichi: What the MIT Report Said (and Didn't Say)

The questions that remain from Fukushima Daiichi, as they apply to today's and tomorrow's reactors, could be a very good gauge for the winds of change in the nuclear industry. A lessons learned report from MIT CANES came out recently (hat tip to Steve Darden), and the material is just too important to pass up. It is a great report for anyone wanting to get a grasp on the important questions that stem from the disaster. We have covered the recent IAEA perspective here on The Neutron Economy, which is a great read about the questions regarding what happened. I want to take a moment here to recap and address the enumerated points from the MIT CANES report about "lessons learned".

For some previous attempts at lessons learned, see guests posts from experts at bravenewclimate or Idaho Samazat for just two examples. With that said, here are the points from the MIT CANES report. I'll try to offer a dumbed down version as much as possible for all of these, and of course, plenty of my own spin on things.

Emergency Power following Beyond-Design-Basis External Events
Simplified: How to assure the plant has power to keep the pumps running after a major natural disaster or terrorist attack

This concern is about the Station Blackout (SBO) event. Of course it was the earthquake-tsunami that caused the Daiichi meltdown, but it did it so by causing a SBO, so the relevance to nuclear safety is obvious. Even if we can't prevent tsunamis, we can prevent prolonged SBOs. MIT gives the "place the emergency diesel units on a hill" kind of recommendation, and this is not the first time I've read this. Water-proofing is another possibility, and this was cited in Japanese media as being one reason that the Tokai nuclear power plant did not worsen, but this also applies for the seawater pumps. There are also recommendations to have transportable generators that could be brought. The question on my mind is how much this recommendation does or doesn't overlap with what we already have in place. For the US, there is a good chance, in fact, that the public simply doesn't know about what we have ready to respond to a nuclear emergency with, since many such measures were developed for post-9/11 security, and an anti-terrorism safety feature works best when the public doesn't know the details. The MIT report also mentions passive safety features and asks the question of whether or not new plants should be required to have a mix of passive and active safety features. This question would be most relevant to designs like the EPR, and the performance of a design like the EPR (meaning fewer passive features) during SBO might be indirectly coming under fire here.


Emergency Response to Beyond-Design-Basis External Events
Simplified: Emergency response sums it up pretty well

Not only are things that did happen relevant to the post-Fukushima questions, but what could have happened but didn't is also fair game, this report mentions the possibility of staffing problems due to direct fatalities from an earthquake or tsunami. Additionally, problems in determining the evacuation zone and communicating with the public and with other governments are mentioned. It is suggested that organizations like INPO (an industry group in the US) or an international group could form rapid-response teams for nuclear emergencies. It also notes that there is a tradeoff between evacuation area and stress imposed on the local population, an difficult call that I've written about myself. There is also mention of the need to communicate radiation risk to the public. I would just add, be prepared for outrage. Lately I've been following the Uncanny Terrain documentary effort, which is fantastic on one hand to tell the human story of these tradeoffs between radiation risk and livelihood, but it also shows that people are upset based on social justice issues. This is one of those things you just can't "fix".


Hydrogen Management
Simplified: How to keep Hydrogen from exploding in an accident

The Hydrogen explosions at Fukushima Daiichi are obviously something to address. The MIT report mentions venting via "strong pipes", connecting the pool areas more directly to the plant stack, more hydrogen recombiners and igniters (specifically in the upper building), catalytic recombiners in the ventilation system inside containment (not done as of yet), research into hydrogen flares as a solution for large hydrogen buildup, and use of something other that Zircaloy for cladding. I have previous read about the strong pipes (or hard pipes) topic and in the Idaho Samazat post, using non-Zircaloy cladding materials was mentioned. In my opinion, Changing the cladding material could be very expensive and have a number of unintended consequences, for instance, reduced neutron economy. There is no technical reason the switch could not be made, but it would probably still require significant research and development lead time, if any nation decides to go that route in the first place.


Containment
Note: The focus of this point is on the need to vent the egg-shape primary containment

The report suggests directly that the (primary, or inner) containment should be vented to stack instead of to the secondary containment pools, which led to the hydrogen explosions. That would come with the other solutions mentioned in the hydrogen management point, including new catalytic recombining systems. Use of passive containment cooling is mentioned, but no word on if this has any relevance to existing reactor designs.

Spent Fuel Pools
Note: BWR spent fuel pools are unique and several recommendations are specific to those

It is believed that the spent fuel pools accounted for a lot, if not the majority, of the radioactive releases, so obviously this is one of he most major lessons learned items. The MIT report gives prompt movement of spent fuel to dry storage as an option... with many provisos. There is a safety benefit to doing this, although there are fundamental limitations associated with it, which is a debate the authors of this blog have been through several times. The MIT report notes the following shortcomings of dry storage

• The casks must be secured so they do not tip during an earthquake
• A break in a cask will result in direct and unmitigated release to atmosphere
• The decay heat in spent fuel pools is mostly unaffected by using more dry cask storage because only the old fuel can be moved which don't contribute much to the heat

Very good points. Put together, this means that dry storage may or may not be preferable to other options, which the MIT report identifies as being on-site spent fuel pools (I'm guessing this means not close to the reactor) and centralized interim storage. The interim storage option is being talked about today as a result of the Blue Ribbon Commission on spent fuel management, by the way, although, for reasons that have limited overlap with these post-Fukushima concerns.

Some of the other recommendations are also very worthy of mention. Passive cooling of the spent fuel pools, and the policy of moving fuel out during outage are mentioned as things that need to be looked at for current plants. For the future, it is suggested that spent fuel could have its own containment, regional spent fuel storage facilities are relevant (with a hat-tip to Rokkasho, which is unfinished business), and a national repository could be created.


Plant Siting and Site Layout
Simplified: How do you keep an accident at one reactor from affecting other units?

This report notes the Fukushima Daiichi plant's "compact layout", and of course, cross-unit complications. The tsunami disabled a staggering 13 emergency diesel generators. Also, the Daini and Onagawa plants were at risk, reflecting concerns about regional clustering of nuclear plants. The phrase to remember here is common cause failure, and the report also coins the term unit-to-unit contagion.

A major conundrum that still remains is how to deal with earthquake risk. Saying that we should avoid major fault lines is obvious, but sites in places like Japan and Taiwan are always vulnerable to seismic risk. How do we regulate for this? This is a hard question. The report suggests to develop criteria with which a permissible number of units at a site could be evaluated.


Things not mentioned in the report

As someone who's followed this event and some of the technical aspects of it, I already had my own list of "lessons learned", but almost everything was covered by this report. Of course, there are a few things I had down which were not covered, as well as items other people have mentioned that weren't in there.

• Beyond Design Basis - I had been wondering if the way we look at nuclear safety will be changed due to the sheer magnitude of the event beyond the tsunami magnitude that was planned for. Risk informed analysis and regulation seeks to not place an upper limit on events that can be tolerated (such as a x.x earthquake), and instead seeks to set acceptable accident frequency. I think Fukushima Daiichi strengthens the impetus for this perspective, since if nature is going to exceed the limits you set anyway, then you might as well quantify the risks in a more appropriate manner. Then again, if the problem with Fukushima Daiichi is that the tsunami risk was underestimated, then changing the way we look at risks will not fix that. That is a different type of error.
• A comprehensive approach to flood events - A great read for past presidents that could have helped at Fukushima Daiichi, if it had been applied, is the 1999 flood of a reactor in France. Not to mention, there are plants in the US like Browns Ferry that have both a similar design to Fukushima and a flood risk. Don't forget about Fort Calhoun either, which the media was all over, predicting a catastrophic flood event. Since flooding keeps coming up as a concern, I had been wondering if this could be a sort of Achilles heel that needs more attention. The Japanese plants have certainly drafted plenty of flood mitigation plans in the wake of the Daiichi disaster, could a worldwide revamp of flood safety be in order? Looking at the lessons learned from the 1999 French flood, it would appear that safety measures can be expensive, easily in the $100 million range. Maybe there really isn't a easy fix to this problem, although I admit to have a sense of irony, since the problem that leads to meltdown is the insufficiency of water. Maybe we will ultimately switch to floating nuclear plants and be done with both the concern of flood and long term cooling at the same time.
• Reevaluation of liquid effluent danger - The battle for stability of the stricken Daiichi plants was wrought with problems of radioactive water. Groundwater contamination will be topic for many years to come, and the ocean in the vicinity did prevent fishing for some time. I wonder if any specific solutions in this area will be called for.
• Global regulation and crisis management - This was really addressed by the MIT report in emergency planning, but it could have effects more far reaching than what was mentioned. Accusations that the Japanese government made things worse by failing to promptly accept US assistance were rife. Ultimately, however, the safety of the public in a nation is the responsibility of the national regulator. I wonder to what extent people will continue to be satisfied with this structure. It is personally frustrating to have so many good things to say about the US industry safety record, only to be stonewalled by questions about the safety of the Japanese industry because it's simply not in our regulatory purview. I wondering if something more fundamental to the nature of safety and responsibility could be in the cards.