(This is only a layperson's opinion, so YMMV. No special expertise involved here, just trying to get numbers to match up.)
From the beginning, we have struggled to get decent information about the quantities and locations of nuclear fuel assemblies that were present in various storage locations around the Fukushima Daiichi nuclear power plant.
The issue is now attracting more interest from reporters and government officials.
As you will see below the fold, I still have a major question about how TEPCO both viewed and presented the authorized "capacity" of its storage facilties for fuel assemblies.
According to one presentation, the plant was approaching its maxiumum capacity for storing fuel assemblies. Under another it had room for literally thousands more of those spent fuel assemblies.
At some point, failure to provide accurate, detailed, current and definitive information about this issue will start people to wondering whether there is some reason that those details are being withheld or obscured.
Until we get those numbers, we'll just have to keep muddling through on our own.
HHT to all those contributing to the Japan Nuclear Incident Liveblogs and those manning the mainsails for the Japan Nuclear Disaster Motherships and plumbing the depths of this issue in the ROVs. Many of those dk stalwarts provided information and understanding that contributed to this diary but none should be blamed for any errors or lack of said understanding that may follow below the fold. So proceed at your own risk because as the old maps used to say:
Here, there be dragons.
Reuters was focussing on this aspect of the disaster on Monday:
...
When the massive tsunami smacked into Fukushima Daiichi, the nuclear power plant was stacked high with more uranium than it was originally designed to hold and had repeatedly missed mandatory safety checks over the past decade.
The Fukushima plant that has spun into partial meltdown and spewed out plumes of radiation had become a growing depot for spent fuel in a way the American engineers who designed the reactors 50 years earlier had never envisioned, according to company documents and outside experts.
At the time of the March 11 earthquake, the reactor buildings at Fukushima held the equivalent of almost six years of the highly radioactive uranium fuel rods produced by the plant, according to a presentation by Tokyo Electric Power Co to a conference organized by the International Atomic Energy Agency.
Along with questions about whether Tokyo Electric officials waited too long to pump sea water into the plants and abandon hope of saving them, the utility and regulators are certain to face scrutiny on the fateful decision to store most of the plant's spent fuel rods inside the reactor buildings rather than invest in other potentially safer storage options.
That debate has direct implications for nuclear policy in the United States about whether changes enacted after the September 11, 2001 attacks go far enough to protect potentially vulnerable fuel stored at the nearly two dozen U.S. power plants that have the same design as the Fukushima Daiichi plant, experts say.
In Japan, the crisis has also focused attention on Tokyo Electric's spotty record on safety issues that continued until days before the quake, its cost-cutting drive under current chief executive Masataka Shimizu, and a relationship with Japanese government regulators that critics say remains shot through with conflicts of interest.
...
The numbers on exactly how much fuel (and of what type) was stored in the troublesome 'Spent Fuel Pools" (storage facilities located adjacent to each of the 6 reactors) and how much was stored in the seperate "Shared Pool" (located in a seperate building) and in the Dry Cask Storage facility (also a seperate facility on the plant grounds), has been difficult to pin down. So far, it appears that neither the Shared Pool, nor the Dry Cask facility has presented any danger.
The numbers on storage capacity and quanties of fuel stored come in different forms (most often Fuel Assemblies but sometimes in "Tons"). The various sources for this information also describe different things (sometimes only "Spent Fuel" but occassionaly also included is the fuel also sometimes present in the "Spent Fuel Pools" that is not yet "Spent", but rather temporarily removed from the adjacent reactor for maintenance or for other reasons such as during a refueling process (which if only partially spent would still be irradiated) and fuel that has not yet been used in the reactor making it neither "spent" nor "irradiated" - therefore correctly referred to as "Un-irradiated"). So in essense you have un-used (Un-irradiated) and used (Irradiated) fuel. The latter could be either partially used or completely used (Spent), but both would be correctly classified as "Irradiated". Whether all sources I have used to compile the data presented here have applied the same categorization is not confirmed, but until we know otherwise it seems logical to operate on that assumption. [The preceding bf text was UPDATED to more correctly describe the different 'categories' of fuel assemblies. HT to whitis and rja for their help in getting a better handle on that aspect.]
The totals for either capacity or amounts actually stored rarely match.
Back on March 17th, the NYT article on storage pegged the number of Spent Fuel Assemblies at 11,125.
The electric utility said that a total of 11,125 spent fuel rod assemblies were stored at the site. That is about four times as much radioactive material as in the reactor cores combined.
In that same article, the NYT reported that a particular concern was presented by the Spent Fuel Pool in the #4 Reactor building:
Gregory Jaczko, the chairman of the United States Nuclear Regulatory Commission, made the startling assertion on Wednesday that there was little or no water left in another storage pool, the one on top of Reactor No. 4, and expressed grave concern about the radiation that would be released as a result.
The 1,479 spent fuel rod assemblies there include 548 that were removed from the reactor only in November and December to prepare the reactor for maintenance, and these may be emitting more heat than the older assemblies in other storage pools.
A March 21, 2011 accounting of Spent Fuel attempted over at All Things Nuclear pegged the total number of Spent Fuel Assemblies stored at the site as 10,661 and the number of Spent Fuel Assemblies stored in the Spent Fuel Pools at 3,878. That accounting listed the number of Spent Fuel Assemblies as of March 2011 in the Reactor #4 Spent Fuel Pool as 1331. (This obviously is not readily reconcilable with the numbers presented in the NYT article reference above for that Spent Fuel Pool.)
Earlier on, the National Energy Institute(trade group) gave this general description:
Used nuclear fuel at the Fukushima Daiichi plant is stored in seven pools (one at each of the six reactors, plus a shared pool) and in a dry container storage facility (containing nine casks).
Sixty percent of the used fuel on site is stored in the shared pool, in a building separated from the reactor buildings; 34 percent of the used fuel is distributed between the six reactor fuel storage pools, and the remaining six percent is stored in the nine dry storage containers. There are no safety concerns regarding the used fuel in dry storage at Fukushima Daiichi.
So.
To try to get a handle on this, I created the following table based on the International Atomic Energy Agency's 3.22.11 report on fuel (irradiated and un-irradiated) stored in Spent Fuel Pools (individual pools adjacent to the 6 reactors) and the All Things Nuclear reporting of 3.21.11 on the spent fuel stored in those pools as well as in the Shared Pool and the Dry Cask Facility and TEPCO's November 2010 Inspection Report (evidently presented at an industry conference.)
Taken together it appears to show that on the date of the recent earthquake they were maybe within spitting distance of their storage capacity (if their storage capacity was 2,100 tons as stated on page 4 of the TEPCO Inspection Report (2081 tons out of a stated capacity of 2,100 tons.) Even as of March of 2010, that page of the report indicates that the Fukushima Daiichi Nuclear Power Station (NPS) was at 84% of it's storage capacity for spent fuel ("Occupancy").
But a later page (page 9) of that same TEPCO Inspection Report, when describing the storage capacity in terms of Fuel Assemblies, presents a much different picture. It presents figures that would indicate that for the entire plant (all storage locations) Fukushima Daiichi was at only 65% of its storage capacity and for the Spent Fuel Pools they were actually only at 42% of their "capacity".
Curiouser and couriouser.
My own bar-napkinesque calculations (illustrated and explained below) place the Occupancy closer to 99% (using the conservative Capacity limit of 2,100 tons).
So is it 99%, or 84%, or 65% or 42% or less or more than any of these numbers?
Given TEPCO's admitted and repeated shortfalls in honesty-of-reporting and diligence in self-inspection, I have begun to question whether we can even be assured that they had not exceeded their authorized capacity and were storing more spent fuel or more fuel of all kinds in their Spent Fuel Pools or all their storage facilities than was authorized.
The confusion and lack of definitive accounting from TEPCO to the public at any time after the March 11 earthquake might not be as concerning or lead to such doubts or suspicions if recent reports hadn't exhumed the problematic history of TEPCO in maintaining diligent regulatory compliance and practicing basic honesty in reporting to the regulatory bodies, as reported by Reuters on Monday.
The latest incidents add to a record of safety sanctions and misses at Tokyo Electric - more commonly known as TEPCO - that date back a decade and continued into the weeks before the quake.
Less than two weeks before Fukushima Daichi was sent into partial meltdown, the utility had told safety regulators it had failed to inspect 33 pieces of equipment at the plant, including a backup power generator, according to a filing.
So this is what I've been able to collect so far:
Reactor Unit |
Capacity |
Irradiated Fuel Assemblies in Spent Fuel Pool |
Unirradiated Fuel Assemblies in Spent Fuel Pool |
Total Fuel Assemblies in Storage |
Most Recent Additions of Irradiated Fuel - Date |
1 |
900 |
292 |
100 |
392 |
March 2010 |
2 |
1,240 |
587 |
28 |
615 |
Sept 2010 |
3 |
1,220 |
514 |
52 |
566 |
June 2010 |
4 |
1,590 |
1,331 |
204 |
1,535 |
Nov 2010 |
5 |
1,590 |
946 |
48 |
994 |
Jan 2011 |
6 |
1,770 |
876 |
64 |
940 |
Aug 2010 |
Fuel Assemblies in Individual Spent Pools - Total |
8,310 |
4,546 |
496 |
5,042 |
Unknown |
Shared Pool - Total |
6,840 |
6,375* |
xxxx |
6,375 |
Unknown |
Dry Cask - Total |
408 |
408* |
xxxx |
408 |
Unknown |
Fuel Assemblies in All Storage Locations - Total |
15,558 (?? 2,738.2 Tons??) |
11,329 |
496 |
11,825 |
Not Applicable |
* Use of terms "Irradiated" and "Unirradiated" follows usage of
International Atomic Energy Agency's 3.22.11 report also,
Fuel assemblies in Shared Pool and Dry Cask Facility are assumed 100% Irradiated (??). Quantity from All Things Nuclear - More on Spent Fuel Pools at Fukushima 3/21/11
From the All Things Nuclear report on March 17, 2011 it appears that they used an average figure of approximately .1760 tons per fuel assembly for their initial table (4,546** assemblies producing a total of 800 tons for the individual pools.)
If the total number of assemblies stored in all locations at the Fukushima Daiichi plant is as represented above, that would appear to indicate they had fuel stored amounting to approximately 2081 tons.
TEPCO's November 2010 Inspection Report states their Storage Capacity at 2,100 tons.
What confuses me is that the data from the IAEA table (incorporated in my table above) lists capacities for just the individual spent fuel pools at 8,310 Assemblies (the equivalent of 1,462.56 tons). If the current number of assemblies stored in the Shared Pool (6,375) and Dry Cask Facility (408) are converted to capacity of 'tonnage' using that same factor of .1760, in aggregate the Shared Pool and Dry Cask Facility currently hold approximately 1,193.8 tons. (6783 assemblies x .1760)
When that current storage number is added to the individual pool "capacity" (per IAEA) it would result in a total plant capacity of 2,656.36 tons (15,093 assemblies x .1760) , well above the 2,100 ton capacity listed in their inspection report.
Spent Fuel Pool Capacity: 8,310 Assemblies/1,462.56 Tons
Shared Pool Current Storage: 6,375 Assemblies/1,122 Tons
Dry Cask Facility Current Storage: 408 Assemblies/71.8 Tons
Total: 15,093 Assemblies/2,656.36 Tons.
(Not a quote. Blockquoted for formatting only.)
Page 9 of the TEPCO Inspection Report lists total capacity as 15,558 Assemblies, which if translated to Tonnage using the .1760 factor would result in a Capacity of 2,738.2 Tons, (30% higher than the 2,100 listed on Page 4 of the same report.)
It is entirely possible that some basic error exists in the calculations presented above. If so, I would be more than happy to correct it.
It may be that the Assemblies/Tonnage factor of .1760 is grossly incorrect (the factor is an average from the ATN table as it varied slightly from Reactor to Reactor in their numbers - possibly just because of rounding on the Tonnage result) or it may not be uniformly applicable for some technical reason. In an earlier discussion of spent fuel here at dk, Souvarine was coming to a different conclusion on tonnage but in retrospect that may have been based on an assumption of a different capacity based on number of Assemblies (which would be consistent with the TEPCO Inspection Report Page 9, rather than resulting from a different factor .
Could it possibly be (high speculation to follow) that TEPCO increased its capacity for storage in its Spent Fuel Pools by "re-racking" as described on Page 4 of the TEPCO Inspection Report, reflected that increased capacity in their Assemblies figure (pg 9) but not on their Tonnage figure (pg 4)?
If so, does that kind of 're-racking' to increase capacity require governmental approval?
Or is there another problem lurking like different measures of "tons" being used?
Any way you look at, we've got a problem.
If the true Capacity was 2,100 Tons, and they had stored 2,080 Tons at the time of the earthquake, they were pretty much 99% full up (including the non-spent, Un-Irradiated Fuel temporarily stored in the Spent Fuel pools for various reasons.) That's not much wiggle room or room for continued growth in Spent Fuel.
If the true Capacity was closer to 2,800 Tons (15,558 Assemblies), they were only a shade over 60% at capacity (including Spent and 'un-spent' fuel) in their Spent Fuel Pools that are located adjacent to each reactor, within the same building but outside of the reactor's containment vessel. That would mean that another 3000+ spent fuel assemblies could be added to those Spent Fuel Pools before their Capacity was reached.
At this point, reconciling this is beyond me. But it might be worth resolving so we can understand what we're facing with this incident and how similar issues should be handled both in Japan and here in the United States.
For more information on why we should probably be more attentive to Spent Fuel issues, I've collected just a few resources:
here and here, and here, and here.
And for those who are deluded into thinking that in the US "we're different", you might want to start here (we are not immune).
(**Correction Note: This original ATN table appears to have transposed a number for the assemblies in Reactor 6's Spent Fuel Pool as 867, now consistently reported by them and the IAEA report as 876. I included that incorrect number in my previous re-creations of their table.)
UPDATE 1: US Treatment of Re-Racking
In the early 1980s, utilities began looking at options for increasing spent fuel storage capacity. Current regulations permit re-racking (placing fuel rod assemblies closer together in spent fuel pools) and fuel rod consolidation, subject to NRC review and approval, to increase the amount of spent fuel that can be stored in the pool. Both of these methods are constrained by the size of the pool.
http://www.nrc.gov/...
The water-pool option involves storing spent fuel rods under at least 20 feet of water, which provides adequate shielding from the radiation for anyone near the pool. The rods are moved into the water pools from the reactor along the bottom of water canals, so that the spent fuel is always shielded to protect workers.
About one-fourth to one-third of the total fuel load from the pools is spent and removed from the reactor every 12 to 18 months and replaced with fresh fuel.
http://www.nrc.gov/...
Sierra Club v US NRC and Pacific Gas and Electric concerning re-racking (1987) .
The Sierra Club based this contention on a January 1987 draft report commissioned by the NRC and authored by the Brookhaven National Laboratory (BNL). The report was entitled "Severe Accidents in Spent Fuel Pools in Support of Generic Safety Issue 82."4
...
The Brookhaven National Laboratory is one of the national laboratories operated by the federal Department of Energy. The NRC commissioned the Brookhaven laboratory to prepare the report at issue in this case. The report presents the results of an extensive study of the risks posed by severe loss-of-coolant accidents at the spent fuel pools of two facilities that utilize high density storage racks. Using a risk analysis model known as probabilistic risk assessment, the authors analyzed the probability of occurrence for several different accident scenarios that might cause a loss of coolant. Those scenarios included: (1) a loss of cooling capacity; (2) an earthquake; (3) the intrusion of various objects from plane crashes, storms, and mechanical failures; (4) the failure of pool seals; and (5) the dropping of fuel casks during fuel loading. The authors concluded that the probability of such an accident occurring at one of the study plants was equal to or less than 2.6 out of 10,000 per reactor year.
14
Should such an event occur, however, the authors estimated that the likelihood of a zircaloy fire, and a subsequent release of radiation, was as high as 100%. The authors noted that the old-style low density racks have an adequate ventilation space between fuel assemblies to prevent a zircaloy fire in the event of a loss-of-coolant accident, as long as the fuel stored in the racks has been out of the reactor core for at least 50 days. However, because the high density racks used at the study reactors severely restrict ventilation, the authors stated that a loss-of-coolant at those plants could cause a zircaloy fire among fuel assemblies that have been stored in those racks for well over a year. The authors concluded "that the risk estimates are quite uncertain and could potentially (under worst case assumptions) be significant." Accordingly, the authors recommended, inter alia, placing freshly discharged fuel in low density racks as a means to lower the risk.
...
http://ftp.resource.org/...
Severe Accidents in Spent Fuel Pools in Support of Generic Safety Issue 82 Brookhaven National Laboratory (1987)
http://www.osti.gov/...