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
ATOMIC POWER REVIEW