APR: your source for nuclear news and analysis since April 16, 2010

Monday, April 11, 2011

APRA Special: Observations on Fukushima Daiichi.

People are beginning to look for answers, especially as the Japanese seem prepared to upgrade the INES status at Fukushima Daiichi to a Level 7. It's a bit early for really specific answers, and we do not panic around here either. What we do offer is this general discussion of a couple of very early results, we might say, covering some very general issues noted both here on this site and elsewhere. As the operations continue at Fukushima Daiichi and specific events known to have occurred come out we'll have much better data on which to pin specific actions or specific design problems or personnel problems or such things as are found in investigations later on.. and probably we'll be doing that for years. But for now, we have this report.

-A special presentation with some early observations and discussion regarding the reactor accident at Fukushima Daiichi. Copyright 2011 APRA.-

Observations on Fukushima Daiichi

Many outlets have begun making predictions about the future of nuclear energy based on what little is known, and what less they themselves know, about the accident at Fukushima Daiichi. It's too early to even know for certain how events at the site will play out, but it may not be too early for us to make a few specific observations and recommend some alterations both for Japanese plants and for plants in general everywhere in the future.

BACKUP POWER: So far as is known now, performance of the plants and associated equipment after the Great East Japan earthquake on March 11, 2011 was nominal. The triggering event for the accident sequence initiation was the tsunami that overwhelmed the plants' physical structures, causing inundation or wetting of many components not previously assumed vulnerable, and made many areas inaccessible during the inundation and thus made further operations impossible during that time. The resulting accident sequence is essentially total SBO, with no battery power either after a period so that the sequence was extended or long-term SBO. As predicted in just about any RPA or other analysis, core damage resulted in all three reactor plants which were operable at the time of the earthquake.

Much has been made about the failure of the on site EDG units, which as we now know did run for about an hour between the time of the quake and the arrival of the tsunami. The fact that this natural disaster was of unprecedented scope and size somewhat eases any accusations of fault on the part of the operators. However, at an entirely different plant, much later, it was revealed after a near SBO event that two of the site's three EDG units were disassembled simultaneously for periodic inspections. The addition of this fact, coupled with the tsunami-related failure of all EDG units at Fukushima Daiichi now thrusts Japan's attitude about EDG units, SBO events and their relation to reactor and public safety squarely into the limelight. While staunch pro-nuclear advocates rightly point out the massive natural disaster that took out Fukushima Daiichi's diesels as off the top end of the scale as regards regulatory provisions for events to be protected against, the notion that a reactor plant could have two of three diesels simultaneously disassembled as a matter of normal, natural conduct of business is appalling.

Solutions to this set of problems include more diesels at each site, and placement, construction and water and shock proofing to guard against a duplication of the inundation-related loss of all onsite EDG capacity that occurred at Fukushima Daiichi. Specifically, it may be that diesels should be placed on the top of nearby hills, or placed several stories up and fully enclosed, and must be shock isolated. Further, as in primary equipment there should be the assumption that the first diesel to start fails, so that there must always be at least two available and set for auto start for every reactor plant.

Standardized external power connections are now a must. This situation is hampered a bit in Japan as some areas are 50 Hz and some are 60 Hz, but this is not a problem in terms of the provision of standard external connections and portable generating equipment.

REACTOR PLANT SITE DESIGN In the early days of commercial nuclear power plants, very rarely was consideration given to the idea that a particular site chosen for a nuclear plant might in the future accommodate further plants. Perhaps the first one that was designed this way was Indian Point; the initial plant built there, a Babcock & Wilcox PWR with separate two-unit oil-fired superheater, was not only enclosed in a partially below-grade vapor containment sphere but was also further enclosed by a reinforced concrete structure outside of the sphere to reduce personnel exposure on-site if other plants were built, both from an operating standpoint and from a future potential accident standpoint. (As we know, two further plants were in fact later built there.)

A number of factors led to the step to include multiple reactors at one site from the initiation of a plan to build a nuclear generating site. First, siting issues became complicated so that any one given utility company was not likely to find a multitude of possible sites; multi-reactor power stations helped solve that problem if they could be built far enough from population centers since multiple source terms for accidents had to be considered. Second, reactor plant technology progressed far enough that confidence in design and operability took this question out of the minds of investors and utility customers. Third, production of power at fewer sites made the design, construction and operation of the distribution system for electric power ('the grid') theoretically easier.

We then began to see, before the end of the 1960's, a number of multi-reactor sites being planned. In the United States, the maximum number of nuclear reactor plants operating on any one site is three. In many cases, the plants are very close to each other and in some designs (Browns Ferry) the reactor buildings are literally built in a large block, with no external space between, even though they are physically isolated from each other internally, sharing only the space above the refueling floor as common volume.

Getting to the 'lesson learned' from Fukushima, it appears now that these design and orientation considerations for nuclear plants generally all over the world are a mistake. Not only did the hydrogen explosions at the reactor buildings in Fukushima damage and contaminate the other adjacent reactor buildings, they also limited access to the other buildings as well. This means that there is a high likelihood, with this type of arrangement, that a serious accident at one plant could hinder operations at another or worse. It might be best in the future to physically separate the reactor buildings by a large distance, perhaps 1000 feet or more. Plants on one site using a single inlet area could theoretically be arrayed like spokes on a wheel, with their turbine building ends near the water front, but splayed apart radially so that wide separation of the actual reactor buildings is accomplished. This would help prevent damage at one from affecting the others directly or indirectly as described.

ACCIDENT MANAGEMENT AND MITIGATION Keeping in mind the number of multi-reactor sites that exist worldwide, and particularly in Japan, it might now be time for utility companies, governing agencies and governments to make better whole-site accident plans. Both NISA and TEPCO have apologized publicly for their handling of the accident, and it appears from what information has been gleaned so far that there were no adequate preparations for accident operations and management at four reactor plants simultaneously. Manpower to sufficiently respond to shift work in these difficult situations might have to be borrowed from other plants, and even other utilities. People with direct operating experience who are employed by governing agencies might need to be called in to assist the utility companies in accident management.

Certainly, the reactor vendor for any involved plant must be available immediately and on site immediately in force to assist in analysis and operation in an accident situation. Nuclear reactor plants are not automobiles; it is and has been incumbent upon the reactor vendor (or in some cases contracted operator, as was Combustion Engineering at the SL-1) to be onsite immediately in support as was the case with Babcock & Wilcox's instantaneous response to the Three Mile Island accident. General Electric seems now to be providing full support to TEPCO; their announcement of full support to the utility was very late indeed and was proceeded mainly by press releases combating media reporting.

Situations such as the one at Fukushima Daiichi are hard indeed to deal with on any level. However, if part of the procedure involved what in the old days would have been a phone list / phone tree that once sparked and activated would automatically result in plenty of manpower, brainpower and equipment on site then operations might well have been much easier and damage even prevented or at least better controlled. Of course the gigantic natural disaster that was the triggering event for this accident would have greatly hindered the arrival of such assistance but this may not always be the case and given the lessons learned it might well be best to seriously over-react to future events.

Certainly, the massive disaster which caused the Fukushima Daiichi accident transcended all previous accident plans. However, while it is still too early to find full lessons learned and place any responsibility, the suggestions mentioned here might well help such a situation or any other accident scenario at other plants, and future multi-reactor plants.

6:20 PM Eastern Monday 4/11


  1. The absence of coherent incident management in this disaster is hurting the entire industry.
    To admit so belatedly that this is a level 7 event, after initially classifying it as a level 4, undermines whatever credibility the Japanese regulatory authorities may have had left.
    It is a fundamental of disaster management that it is better to tell the worst case truth, because then any subsequent disclosure will be neutral at best.
    This has not been the case here.
    So how does the industry rebuild public trust?

  2. Seriously? Now we decide that it might not be a good idea to build nukes cheek to cheek? (And on an earthquake fault, to boot). If this is the level of foresight in the nuclear biz, color me not impressed.

    Interesting, too, that they skipped right over Accident Level 6. Are they preparing us for the next complication: recriticality, steam explosion as the melted core hits the groundwater?

    The fundamental problem is that there will always be at least one thing "unforeseen". Yet the arrogance of the industry continues...

  3. @netudiant: I don't have the answer as to how the nuclear industry in Japan will rebuild its trust; the level of trust here should remain unchanged, because there are so many differences between how we do business and how they do business.

    @david: Thanks for your insight. It's very easy to be a Monday morning quarterback, isn't it? Did you write any proposals in the past regarding plant arrangement on-site? Things that seem inherently obvious now certainly weren't back when some of these plants were designed.

  4. Perhaps the japaneese are rating it as 7 due to the panic it caused, I really cant see any other reason considering kashtym was listed as 6.

  5. according to nhk, the level 7 figure is based on combining the 4 level 5 events as one event.

    apparently, by iaea standards leaking radioactive water is considered just as significant release as airborne leakage.

    so, nothing has gotten worse, but by technicality it is a level 7 even though it has had less impact than the only level 6 event, and likely less health impact than the windscale fire.

  6. Agree, jl, except that the health impact from the Windscale fire was probably less, since no-one was injured in explosions.

  7. @Will: You are making my point for me.

    @jl: The minimizers and apologists always turn out to work for the industry, in the industry, for the regulators or for some other reason have a faith based commitment to it.

  8. omments:
    netudiant said...
    So how does the industry rebuild public trust?

    The answer is always aggressive public education and unabashed safety/injury record comparisons with all related and unrelated industries and accidents -- the chemical industry in India comes to mind. To be blunt, the majority of the fear here springs from ignorance and unbridled non-professional -- and often agenda driven speculation. It will be through the media's tinted lenses that will most mold public perception of this event so it behooves the nuclear industry to climb into the ring instead of turning the other cheek to rampant misinformation and fear-milling intended to bury anything nuclear, from power stations to spacecraft. Long ago the nuclear industry should've had a "Carl Sagan" spokesman and educator with whom the public could relate with by grass-roots perspectives and comprehension of a highly technical subject. You put on the carpet the media's portrayal of this event, often seeming to blatantly pass off the quake's destruction as Fukushima's effect. You also challenge the specious "Green-PC" mentality that forsakes reason and science for illusionary ideas. On a window sill at my niece's middle school is a solar-cell powered bicycle toy that has an on/off switch taped-labeled as "save energy switch". Think that over. You're not supposed to question of the logic of that, yet it's the mindset that permeates the green movement that anything "natural' are sensible safe and ready concepts, from solar-powered airliners to algae fuel. Fear, gullibility and ignorance are tools used by those implacably and philosophically opposed to nuclear power, and it's up to the industry to actively stand up for itself. Nuclear research itself as well as power is on the line here as fear throws the baby out with the bathwater as it had extinguished highly successful nuclear space propulsion research forty years ago and retarded opening up the solar system in ways we could only wish for now all over again.

    James Greenidge

  9. Will, thanks for the detailed thoughts about future nuclear plant designs. I fully agree with the notion that the first diesel should be regarded as possible to fail.

    Would it be better that nuclear plants were built on large tethered pontoons that way overcoming the impacts of earthquake and tsunami? It seems that any landbased ones will always be vulnerable to unexpected earthquake. Plus tsunami are realtively easily ridden out at sea they only become dangerous as they approach land.

    I have no nuclear experience only large coal fired units plus some long ago marine engineering so please excuse my naivety.

  10. @david: The only points you've successfully made are that you don't understand anything, really, about nuclear energy, and that you're one of those elitists that is always in the "I told you so" crowd AFTER something happens. They're never in the process, or even around, prior to that. But they spring up like weeds afterward.

  11. @old man: There have been a number of proposals to mount nuclear plants either on artificial islands decently off shore that transmission lines can be run, and that they're not subject to violent weather out in the open water. There have also been a number of proposals for submerged power plants. However, from the standpoint of the utility companies the incredible increase in plant cost per kilowatt hour (and you know that's the bottom line, really) is so appalling with no federal input that the ptoposals were all dropped. The focus became one of vastly improved containment, redundant safety features, and operator training here so that such proposals really later on could not get any legs when compared with the most improved, newest nuclear plants. When the flood gate of orders for new nuclear plants shut off in 1978, that probably killed any future for offshore plants because many of those being built at that time and ordered at that time were never finished. The nation is covered with scattered nuclear plant sites that were never completed.

    Seismic considerations are very noteworthy in US plants, which also have design basis quake accidents taken into account for design and do have safe shutdown earthquake limits. There were a number of sites selected for nuclear plants which were never built because of seismic considerations.

    Thanks for your comments, "Old man!" Nice to see another person commenting who has some experience on the water!

  12. There seem to me to be at least three possibilities for securing emergency generators against tsunami:
    1. Locate them high up, as speculated above
    2. Build them to survive full saltwater immersion for 30 minutes (say)
    3. Locate them on (constrained) buoyant platforms.
    And as stated, in all cases, protect them and their fuel supplies against the initial shock loading, although probably aspects of this will be already factored into earthquake design.

  13. @joffan: Good points. I've also been toying around (and that means sketching) with enclosed but ground mounted designs with essentially what amount to high snorkel type intakes and exhausts, sort of like you see on vehicles used on safari, or military vehicles that can cross streams. Or submarines. You'd have to enclose the generator (alternator, technically) and provide forced cooling for it, and of course watertightness of the electrical conduits will be the major problem. But any number of ways, this problem CAN be solved.

  14. http://www.youtube.com/watch?v=G6Q7VfWdgEg
    I created this dosimetry method for the people of Japan.

  15. Do you also have any thoughts on

    1) the spent fuel pools, their location and lack of containment

    2) the age of some of the reactors involved - should this particular old design be taken as a reason for retiring plants?

  16. @dan: I think that the spent fuel pools should be external to the reactor buildings; that is the case in many other plants. It's a poor design, even though it is very convenient from the standpoint of work done above the reactor and at the fuel pool itself.
    As far as the older designs, I don't think right now we can say that. At this point we have to remember that we're seeing a highly exaggerated instance of the predicted SBO sequence with extreme equipment derangement from the tsunami exacerbating the SBO event and tying up the hands of the operators. Given that we can't yet say that there's now a precedent to retire, say, all Mk I containment plants, or all BWR/3 and BWR/4 cores. Now, that isn't to say that once all the facts are out we might not see some other things that could push us in that direction... but right now it's looking like there is nothing to indicate that this is necessary.

  17. Please excuse an uneducated person's simple question about nuclear power plants and the possibility of uncontrollability in a time of emergency ... if an enemy exploded an electromagnetic pulse type "bomb" high above, lets say the North-East U.S., would it mean all the various electrical backup and/or control systems for all the nearby nuclear power plants would be rendered uncontrolled and uncontrollable and if so what would prevent melt-downs for all of them? I do apologize for being very ignorant.

  18. @jim: Short answer: No. I've never read of any such study that indicates that this would happen, and the EMP would not have any effect on DC systems to my knowledge.

  19. Found an article that says in the event of an EMP (and apparently any event that prevents outside power to the plant for an extended period):
    "The bottom-line is that if the spent fuel cooling pumps cannot be operated or the system cannot be cross-tied with the reactor shutdown cooling system, then the fuel assemblies in the spent fuel pool will melt, catch fire, and radioactive fission products will be released into the atmosphere and much of the countryside downwind of the nuclear power plant will be contaminated for many years. Thus, an EMP attack has the potential to cause a Chernobyl type accident at every nuclear power plant in the country!"