Proposal for Fukushima-I post-accident scenario analysis
I’m a retired nuclear scientist with experience in basic nuclear physics research as well as two decades experience as a reactor physicist at the Fast Test Flux Facility, a 400 MW (thermal) sodium-cooled reactor in eastern Washington state operated by Westinghouse Hanford Company for the U.S. Department of Energy. The primary mission was to support fuel and material testing for the then U.S. Breeder Reactor Program, cancelled by President Carter in the late 1970’s about the same time as startup testing began at the FFTF. I was the lead technical person on a variety of reactor startup tests, including some safety testing that seems eerily similar to what happened at the totally different Fukushima-I reactors in the aftermath of Japan’s recent earthquake and tsunami. I also led a special investigation of advanced fuel cycle and advanced reactor options for Westinghouse Hanford, with some international collaboration (including Japan) in the early 1990’s.
Since I took an early retirement from Westinghouse Hanford in 1995 and have lost contact with almost everyone there after moving to Bellingham, WA, I no longer have access to any technical resources to answer what may turn out to be a silly question about a possible scenario that I thought was not even credible a week ago. So I’m writing this brief note for general reading here, in an open attempt to stimulate formation of a technical team to evaluate whether some follow-up analysis (and maybe even long-term monitoring) is worthwhile. Since I’ve been out of the business for a long time and want to continue with my food gardening activities (after learning about peak oil six years ago), I really want no further part of any nuclear work after writing this note - although I would remain extremely curious about any outcomes.
At the time of the earthquake, three out of the six Boiling Water Reactors (BWRs) at the Fukushima-I Daiichi plant were operating, presumably at full power. My understanding of the general progress of events is as follows. All operating reactors shut down (by rapid control rod insertion) immediately, and offsite electrical power failed rapidly. Backup diesel generators activated and provided temporary electricity to operate Emergency Core Cooling Systems (ECCS). An hour later, the tsunami overwhelmed plant defenses, shut down the generators, and perhaps inundated various plant wiring installations. This meant there was no longer any ability to cool the fuel in-reactor, or to cool high-burnup fuel stored in spent fuel pools associated with each of the six reactors, as well as a common plant spent fuel storage pool.
Without forced cooling, water in all fuel locations began to evaporate and/or boil, with the result (as I write) that there has probably been substantial fuel melting in some of the reactors, perhaps one or more primary containment breaches, apparently some zircaloy fuel pin cladding fires in at least one spent fuel storage location, apparently still no offsite power, and rising radiation levels seem to be preventing operators from getting close enough to continue sporadically covering the reactor cores or spent fuel with seawater (a jury-rigged procedure I immediately interpreted as a last-ditch emergency measure that almost surely means writing off the entire plant). Each day, the situation appears to be much worse than the day before, and plant workers appear to be working in higher and higher radiation fields as time goes on - in persistently primitive circumstances.
I didn’t really start thinking about possible off-site consequences until two people close to me asked whether they should buy iodine pills. After a few giggles, I did find an east coast pill vendor who said he has sold buckets of pills to worried left-coasters, as well as a separate blog-post estimating air transport risks to west coast residents (more giggles). (What a world we live in!) Then I did a personal brainstorm of other potential delivery pathways for radiation from the plant to the U.S. west coast, and thought of one possibly worrisome long-term scenario (no more giggles). The Fukushima-I plant is RIGHT on the Japanese east coast, and I wondered about ocean currents and where they might deliver any radiation entering the ocean, AND what uptake and concentration mechanisms might be operable in sea-life in the various ocean ecosystems.
I found just enough information about ocean currents to worry me. First, the following link shows currents just off the eastern Japanese coast. The main current appears to be the northward flowing Kuroshio current.
The next link sketches the merging of the Kuroshio Current with the southward flowing Oyashio current, and the combined current (the North Pacific current) then heads due east toward Puget Sound, then splits into a component heading north to Alaska and a component flowing south to California and the Baja peninsula before returning west toward Asia (where it began).
I was unable to locate any detailed current maps in the vicinity of the split or closer to the U.S. west coast. Seafood is an important part of diets in the Pacific Northwest region, and much of it is salmon (and some halibut and rockfish) from Alaskan water.
The simplistic (and poorly informed) sketch of a complete scenario would be something as follows:
The source term would be all the fuel in all six reactors and in all spent fuel pools at the Fukushima-I plant, in some degraded state like an amalgam of molten fuel and zircaloy cladding. At least one of the reactors uses mixed oxide fuel with some recycled light water reactor plutonium. Most of the fuel would be high-burnup BWR fuel. One should pay special attention to where the cesium, strontium, and plutonium end up in the melt-down sequence and beyond. The source-term configuration is anyone’s best guess, concentrated at the present plant location and far too radioactive for anyone to approach for decades into the future; it is open to the atmosphere and ocean. The total source term might be one or two orders of magnitude greater than that at TMI or Chernobyl.
Somehow (rain water leachate, ocean wave action, ....) radioactive species enter the ocean (literally only tens of meters distant), and the ocean currents deliver some of it to fishing grounds off the U.S. west coast. Along the way, contaminants are available for uptake by organisms throughout the Pacific ocean as well, including just off the Japanese coast where the potential for uptake might be the highest. Migration of some species could be important.
The contaminants move through the ocean’s various food-chains, ultimately to species humans eat, potentially accumulating near the top of the food chains.
Here on the U.S. coast we have become attuned to food-chain concentration of mercury in aquatic and other life, although I have no knowledge of the environmental pathways. Are we facing the possibility of a similar problem with some radioactive and heavy element species one, two, or three decades hence? Will my children need to purchase gamma ray monitoring equipment to survey seafood they purchase?
This would seem to be an interesting and fun problem to pose to a group of advanced undergraduate and/or graduate students from disparate fields. Specialists at Battelle’s Pacific Northwest National Laboratory (http://en.wikipedia.org/wiki/Pacific_Northwest_National_Laboratory) would likely be available for consultation on several aspects of the problem.
It’s a nice spring-like day here, and I’m going to plant some seeds and try to forget about the hideous mess confronting courageous Japanese workers at the Fukushima-I plant.
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