An IAEA perspective on Fukushima

I recently had the pleasure to attend a lecture by Randy Beatty (who has been affiliated with the International Atomic Energy Agency [IAEA] for some time), focusing upon the IAEA's perspective on Fukushima, particularly in terms of our current understanding of the sequence of events (which is still evolving) as well as the IAEA's interactions with the government of Japan and TEPCO (the owner of the Fukushima reactors).

Below is a summary of some of the major topics covered, including a more detailed reconstruction of the accident sequence (and particular, both the relatively small timeframe in which most of the damage occurred) as well as a better understanding of how other, secondary complications such as the hydrogen explosions came about. Finally, more precise estimates of the quantities of radiation released and the direction of its spread shed some light on how many were affected and the relative appropriateness of certain evacuation precautions.

Accident sequence

The "main" narrative of the Fukushima incident is relatively understood, summarized as follows:

• Following the 9.0 earthquake, each of the reactors was shut down, halting the fission reaction
• Backup power from diesel generators came online to operate coolant pumps to remove decay heat from the reactor until these were wiped out by the incoming tsunami; 
• Battery backup power came online to operate these pumps until such power was depleted
• Water inside the reactors began to boil away as it heated up.
• As water boiled away, the fuel rods heated up.
• Water interacted with the extremely hot zirconium cladding, producing free hydrogen (which lead to the hydrogen explosions)
• As the fuel rods heated up, the cladding failed, releasing radioactive fission product gasses. The fuel is also believed to have partially melted when it became uncovered by water, releasing more radioactive materials from the core.
• Cooling was restored by injecting seawater into the reactors to quench the decay heat from the rods and prevent further melting.

What has been perhaps less well-understood are issues such as how much fuel melted, how long the core was not covered by water, and the extent of the radioactive release. A great deal of research work is being conducted at the national laboratories presently to reconstruct what was going on inside the reactors in the first few hours (immediately after the rectors were shut down) in order to characterize what exactly happened; thus our understanding on this point will continue to evolve over the next several years.

One of the key issues that seems relevant in much of the accident sequence is the relative speed at which events progressed. While most of the world witnessed the event as a long, drawn-out drama, much of the damage had already occurred in the first few days (and in particular, the several hours the reactors were without power before seawater injection was applied). 

Courtesy of Randy's presentation, here is a good timeline of what occurred at each reactor.

Unit 1

• March 11, 2:46 PM: External power lost, emergency diesel generators begin to supply power
• March 11, 2:52 PM: Emergency cooling systems (isolation condenser) started
• March 11, 3:37 PM: All AC power lost
• March 11, around 5:00 PM: Fuel exposed, core melt begins
• March 12, 5:46 A.M.: Begin of freshwater injection from fire extinguishing line

The fuel was estimated to have been uncovered for about 2.5 hours. Water injection was estimated to have stopped (due to the loss of power) for 14 hours and 9 minutes. 

Unit 2

• March 11, 2:47 PM: External power lost, backup diesel generators start up
• March 11, 2:50 PM: Emergency cooling system (Reactor Core Isolation Cooling system - RCIC) starts up
• March 11, 3:11 PM: All AC power lost
• March 14, 1:25 PM: RCIC operation stops
• March 14, around 6:00 PM: Fuel exposed, core melt begins.
• March 14, 7:54 PM: Seawater injection from a fire extinguishing line begins

Approximately 30% of the core of Unit 2 was estimated to have been exposed in the 6 hours and 29 minutes in which cooling was unavailable.

Unit 3

• March 11, 2:47 PM: Loss of external power, start-up of emergency diesel generators
• March 11, 3:05 PM: Startup of emergency cooling system (RCIC)
• March 11, 3:41 PM: Loss of all AC power
• March 12, 11:36 AM: RCIC stops due to loss of power
• March 12, 12:35 PM: Startup of HPCI (high pressure core injection) system as a backup cooling measure
• March 13, 2:42 AM: Stop of HPCI
• March 13, around 8:00 AM: Fuel exposed, core melt begins
• March 13, 9:25 AM: Startup of freshwater injection into core from a fire extinguisher line

The fuel thus appears to have been exposed from approximately 1.5 hours, with water injection having been unavailable for about 7 hours.

What this means

Several issues are clear from this timeline of events. First, despite an earthquake beyond the design basis for the reactors, emergency systems largely functioned as intended. Were the backup power systems not destroyed by the following tsunami, it is likely the incident would have largely been contained without incident; indeed, it was the "total station blackout" condition which was the root cause of the radioactive releases (i.e., by allowing the fuel to overheat). In this sense, one criticism made of the Japanese government was in its initial reluctance to accept assistance from outside agents such as the United States, which had offered to airlift in replacement generators when the tsunami destroyed the initial generators. Whether this initial refusal was a face-saving measure or something else remains to be seen, but quite clearly this exacerbated the issue.

The loss of emergency diesel power systems was near-total due to the tsunami; a total of twelve diesel generator units were present at Units 1-6, of which all but one at Unit 6 were wiped out. (This remaining unit was elevated above the tsunami.)

Backup systems such as battery backups appear to have mitigated some of the damage, particularly in the case of Unit 3, where Japanese officials report that the battery backups appear to have lasted approximately 50% longer than their design life (around 18 hours, compared to a design life of 12).

Most stark here is the relatively short time period in which most of the damage occurred - in most cases, the fuel was exposed for only a few hours (up to about 6.5 hours for Unit 2, which experienced the most severe fuel damage). Likewise, following the complete loss of power, it took only a few hours for the core to become uncovered due to water boiling from the core.

Complicating the situation at Unit 2 may have been the hydrogen explosion which occurred in the suppression pool (the donut-shaped cavity at the bottom of the reactor, designed to condense steam from the reactor to recirculate coolant and draw off heat). This appears to have accelerated the damage at Unit 2, explaining the extent of damage seen there.

Finally, most of the radioactive release appears to have occurred within the first three days, following the uncovering of the fuel in the cores of Units 1-3. Due to extremely difficult conditions at the reactors from the earthquake and tsunami (i.e., extreme devastation and an overall lack of electricity, with no instrumentation information from inside the reactor buildings), the overall extent and significance of radioactive releases would not be ascertained until later.

Spent fuel pools at Unit 4

Condition of spent fuel in the pool

Unlike Units 1-3, Unit 4 was in a scheduled outage for refueling and maintenance prior to the earthquake. Rather, Unit 4's spent fuel pool contained a mixture of older and newer, more recently-ejected fuel (which is hotter, due to a greater amount of short-lived fission products remaining in the fuel).

The loss of power to Unit 4 produced a similar situation to Units 1-3; even though the fission reaction is "off" in the fuel, short-lived radioactive materials in the fuel continues to decay, generating heat. This heat must be removed from the fuel, thus fuel is stored in deep pools of water, generally kept around room temperature and pressure. (In other words, spent fuel pools are quite similar to very deep swimming pools for spent fuel rods). The water serves a dual purpose; first, the water "wicks" away heat from the rods, keeping them cool, and second the water provides an effective shield from radiation emitted by the spent fuel. 

Heat in the cooling pool must be removed, just as is the case of reactors - thus cooling pumps exist to circulate the cooling water in order to maintain the temperature of the pool (and thus the spent fuel). Thus, should these pumps be disabled (due to a loss of power), this water will begin to heat up as well, eventually boiling. However, spent fuel in the pools is generally much cooler than that from fuel in reactors which have just shut down - recall that decay heat falls off exponentially with time, meaning that after a few weeks, the heat emitted by spent fuel rods is much, much lower than that of a reactor which was just shut down. Thus, the loss of coolant would be much slower than that of Units 1-3.

During the crisis, some speculated based upon limited data (little to no actual instrument data from the pool was available due to the lack of power) that the water levels have precipitously dropped; NRC Chairman Gregory Jaczko even (now infamously) speculated that the pools had gone "completely dry."

However, recent images taken of the spent fuel in Unit 4 by the IAEA indicate that the fuel appears to be intact and undamaged; thus an uncovering of the fuel in Unit 4 appears to be extremely unlikely.

Fuel stored in the spent fuel pool at Fukushima Dai-ichi Unit 4. (Image credit: IAEA) 

In addition, the IAEA has tested for radioactive isotope concentrations in the water within Unit 4's spent fuel pool; in the event that the fuel became uncovered or fuel melted, telltale isotopes would be present to indicate this. Current analysis has failed to find these, further indicating that it is unlikely fuel was damaged at Unit 4. Finally, experts familiar with fuel chemistry indicate that radioactive ruthenium (a chemical in the lanthanide family and a common fission product which tends to travel with water) would have been present outside Unit 4 had fuel melt occurred, which has not been found.

However, the drop in the water level which occurred in Unit 4 is still an unknown (due to the lack of instrument measurements inside the building from the power outage) and difficult to determine; experts are currently attempting to perform back-calculations to estimate this.

Source of the hydrogen explosion

One source of speculation and debate was the hydrogen explosion which occurred at Unit 4, in particular how a hydrogen buildup could have occurred in the outer containment building around the Unit 4 spent fuel cooling pool. The presence of hydrogen is a clearly worrisome sign, implying that a sufficient amount of water has either boiled off or leaked to allow the fuel to become uncovered and grow hot enough to enable the hydrogen production reaction. (Fuel which is covered by water cannot get hot enough to allow the reaction between water and the zirconium clad to occur; therefore, the production of massive amounts of hydrogen would imply an uncovering of the fuel.)

Thus, the hydrogen explosion at Unit 4 lead some (such as Jaczko) to speculate that the spent fuel pool had gone "completely dry." However, no signs of fuel damage were observed, indicating that zirconium hydriding from spent fuel rods in Unit 4's pools was extremely unlikely.

Therefore, where did the hydrogen in Unit 4 come from? The IAEA believes that hydrogen may have been vented from Unit 3 to Unit 4 through a "standby gas treatment system" exhaust pipe; this exhaust tube had joint inputs from Units 3 and 4, thus conceivably allowing hydrogen to travel from Unit 3 (where it was being produced following the core becoming uncovered) to Unit 4 (where it subsequently ignited and exploded).

(Left): Standby pipe from Units 3 and 4; (right) Enlarged view of junction (Image credit: IAEA)

Releases of radioactive materials

Thanks to my colleague Alan's ability to read and speak Japanese, this blog has been following dose data around the plant and surrounding area from early on after the accident. However, the IAEA has helpfully compiled a map of further measurements which were taken by ground stations and measurements by aircraft.

Map of air dose plume release from Fukushima. Red: 9-91 microSv/hr,  Orange: 9.5-19 microSv/hr, Yellow: 3.8-9.5 microSv/hr, Green: 1.9-3.8 microSv/hr, Blue: 1.0-1.9 microSv/hr, Indigo: < 1.0 microSv/hr (Image credit: IAEA)

Air measurements conducted around the area of the plants indicate that much of the plume containing radioactive materials traveled northwest (i.e., due to wind); doses outside the main plume spread to the northwest were found to be relatively negligible. Likewise, with the exception of the plume "tail" in the northwest, nearly all of the elevated dose rates in air were concentrated within a radius of 30 km from the plant, calling into question the logic of NRC Chairman Jazcko's order for Americans within 50 miles (around 80 km) to evacuate.

Evacuation areas around Fukushima. (Image credit: IAEA)

As is clear from the evacuation zone map, the Japanese evacuation order of 20 km with a deliberate evacuation of Iidate and Katsurao prefectures appears to be based upon a sound evaluation of the measured exposure rates. Additional precautions in place (e.g., staying indoors and prophylactic measures such as distributing potassium iodine tablets) were implemented in areas within the 30 km radius.   

Approximately 78,000 people were evacuated from the evacuation area (20 km), with an additional 10,000 evacuated from the "deliberate evacuation area" to the northwest (a smaller number due to the relatively low population density in these areas). Residents in the "Evacuation prepared areas" were informed to stay indoors and prepare for a potential evacuation order in the event of further emergencies (e.g., large measured increases in the exposure rate).

Preventative measures

As a precautionary measure, potassium iodine (KI) tablets were distributed to residents within 50 km of Fukushima prefecture; 1.51 million potassium iodine pills were distributed to approximately 750,000 residents , while 6,100 grams of KI powder was distributed to 120,000-180,000 individuals. 

Potassium iodine is an effective preventative measure for exposure to radioactive iodine (I-129 and I-131) if taken prior to exposure. Iodine is readily taken up by the thyroid; thus, by flooding the body with stable iodine, any radioactive iodine ingested (due to groundwater and air transport) would be excreted out of the body before being absorbed. (Conversely, radioactive iodine is frequently used for the treatment of thyroid disorders, given that the radioactive dose can be easily targeted specifically to the thyroid.)

Evacuations and relative risk 

A point which must be emphasized again in evacuation decisions such as this is in the relative risk averted through evacuation versus the human costs imposed, particularly in light of an epic natural disaster such as this, with tens of thousands dead or missing and over a hundred thousand displaced. Overly conservative evacuations based upon marginal risks (i.e., outside 20-30 km) place an additional burden upon already strained emergency resources (shelters, medical facilities, etc.) while giving little additional benefit. Even under the best of circumstances (which clearly was far from the case here), broad evacuation orders can result in tremendous hardship; the gains from evacuation must therefore be balanced against the additional burdens imposed.

Relative amount of radioactivity released

Based upon calculations made of the measured activity outside the reactors, the IAEA made an estimate of the relative fraction of material released from each core. Nearly all noble fission product gasses (such as xenon and krypton) were released; however, these are of negligible concern, given the fact that they are chemically inert. Approximately 1% of radioactive iodine was released from Unit 1, with about 0.4 to 0.7% of the iodine released from Units 2 and 3. Finally, for other species (including cesium), less than 1% was determined to have been released into the environment; for Units 2 and 3, this was determined to be around 0.3 to 0.6% of the activity in the core.

Estimates as to the total activity released to the atmosphere put the activity of I-131 released around 1.5 to 1.6x10^17 Bq (one becquerel is one atomic decay per second), and around 1.2 to 1.7x10^16 Bq of Cs-137. (Note that not all of this activity was spread inward; large amounts of this release were likely dispersed over the ocean, where they are greatly diluted.)

Presence of transuranic elements 

One rather persistent rumor among media outlets and particular blogs was reports of transuranic elements (i.e., plutonium and other elements above uranium on the periodic table) being found in soil samples outside the plant, indicating a "blowout" of materials from the core similar to Chernobyl. (in the case of Chernobyl, the resulting fire lofted much of the fuel materials into the air, scattering them much farther than they would have otherwise traveled and allowing heavier species, such as plutonium, to escape).

The IAEA did find reports of small amounts of transuranic materials found near the plants from ground monitoring stations and groundwater samples, however these measurements were found to be inconsistent, with little sustained evidence. One difficulty is establishing a source for these materials, which are not necessarily from the plant itself, given the widespread dispersal of radioactive elements around the globe during the time of above-ground atomic testing. Testing for aspects such as the relative abundance of different isotopic species may help to determine the source (i.e., whether the material is older, such as from bomb testing, or newer), however given the relatively scarce amounts found, it has been difficult to establish a source for these materials, given that they conceivably may have precipitated from anywhere in the area.

Worker and resident doses received

Estimating doses for workers was found to be extremely challenging, due both to the lack of instruments at the facility (from the power outage) as well as the flooding, which either swept away or ruined many of the personal dosimetry meters worn by workers or stored at the plants. Of 7800 workers measured, the average worker dose was about 7.7 microSv (well short of the yearly dose limit); 30 were found to have doses greater than 100 milliSv, while 2 workers were found to have equivalent doses to the skin of about 2-3 Sv (due to contact with radioactive water in flooded buildings, causing minor skin burns similar to a sunburn).

Estimation of doses received by the public was measured primarily by the level of surface contamination (i.e., number of radioactive counts per minute). Most of the 195,354 individuals screened were found to be below the 100,000 counts per minute limit; of those who were found to be above this limit, most of these individuals had residual contamination on clothing only and were cleared after changing clothes and vigorously washing their skin.

Accident classification

One question which came up was in the choice (and chronology) of the accident classification of the Fukushima incident, initially placed as a "3" on the INES scale and moved to a "4," then a "5" (similar to Three Mile Island) and then finally upgraded to a "7" (similar to Chernobyl).

INES accident classification scale (Image courtesy of IAEA) 

With respect to the accident classification, the choice of a classification of "7" (the most severe accident category classification) seems somewhat confusing in light of the limited consequences of Fukushima compared to Chernobyl (whose overall total radioactive releases were nearly ten times that of Fukushima). However, the accident classification itself was based upon the total activity of materials released (e.g., very short-lived materials, while quickly going away, will have a higher relative activity rate), including those released into the ocean (where the effect would be relatively dilute). Thus, the application of a "7" rating was a strictly mathematical decision, based on the threshold value for total release.

On the other hand, the sequence of classifications was a more delicate political matter. As evidence surfaced of the situation growing more severe, TEPCO and the Japanese government were continually required to update the accident classifications. (Likewise, there appeared to be a certain reluctance on the part of TEPCO and others to disclose the full significance of the incident). As the situation progressed, it was clear that TEPCO and others would simply need to concede the severity of the conditions, re-classifying the accident as a "7" in order to "get ahead" of the situation, rather than being seen as continually dissembling[?] and delaying. In as much, while the final classification itself was based upon total measurements, in the IAEA's view the chronology of how these ratings were assigned as the accident unfolded were influenced by concerns over public perception.

Plans for improvements

Much of what will occur in the aftermath of Fukushima will be to determine how nuclear operators can plan for and respond better to similar circumstances in the future. Much of the problems encountered at Fukushima came from the total loss of power at the facilities, followed by the destruction of the backup diesel generator units in the tsunami (a condition known as "station blackout," the worst possible circumstance which can occur at a plant).


Thus, many of the IAEA's recommendations fall under these categories. In addition to recommending that operators and plant designers harden facilities against earthquakes and floods, a key area of focus will be in ensuring that reliable backup supplies of power can be maintained in order to operate cooling pumps following an unexpected plant shutdown. This includes hardening backup generators (placing them out of reach of flood waters) and making dedicate contingency plans such as mobile power vehicles to supply power in the case of a generator failure.


Other factors include features such as means to mitigate hydrogen production in circumstances such as this, through the installation of hydrogen "recombiners" (which steadily burn hydrogen rather than allow it to accumulate) and dedicated "blow-out" panels to allow for emergency venting of hydrogen from the outer containment buildings. It was noted that over 300 metric tons of hydrogen was produced in the three reactor units (in other words, over 300,000 kilograms), thus leading to the rather dramatic hydrogen explosions witnessed.


Other recommendations focus upon measures for emergency response, such as procedures for handling nuclear emergencies. A particular complication in the case of Japan was in the widespread devastation beyond the scope of the plants themselves; many workers at the plant were uncertain about the safety of their homes and families, leading to confusion and initial difficulties in maintaining sufficient staff levels to respond to the emergency at the plants.

Proposed safety systems upgrades (click for larger version; image credit: IAEA)

Finally, the IAEA recommends regulatory reforms such as instilling a more thorough safety culture and reinforcing the regulatory safety infrastructure by fostering a greater separation of regulators and utilities, which have been frequently criticized for enjoying too cozy of a relationship in Japan. An additional criticism made was in that preservation of economic assets (e.g., the reactors) was potentially prioritized above safety in the early stages of the response, delaying such measures such as seawater injection (an emergency measure to cool the core which almost certainly would mean a total economic loss for the reactor unit).

Final thoughts

Nuclear safety is a constantly-evolving process; the events at Fukushima will undoubtedly be studied by engineers and scientists for years to come in order to develop better safety features and response techniques to ensure maximum possible safety to the public. To some degree however, there comes a point where one plans against the essentially unpredictable (for example, a record earthquake and tsunami); thus, not every measure can simply be preventative in nature, but rather in how to respond to and mitigate such events. (Examples of this include hardening backup generators and designing robust containment buildings to prevent radioactive releases.)


It likewise is useful to place events like this in context; while it is clear that Fukushima was an extremely serious event in hindsight (it would now appear to be far more serious than Three Mile Island, although less serious than Chernobyl), the consequences must be compared to the risks encountered by the available alternatives. For example, one consequence of the earthquake was the destruction of a hydroelectric dam, destroying over a thousand homes. Liquefied natural gas facilities were also destroyed in the earthquake, leading to further casualties. By comparison, the only person who has died as a result of the Fukushima disaster was not even killed by a radioactive release, but rather was killed by a falling crane.


Risk is an unfortunate fact of life, and in particular of energy production. This applies to all forms of energy production, not just nuclear - each form of energy production comes with equivalent risks and trade-offs, including economics, pollution (for example, the radioactive releases from coal plants in smokestacks are far higher than that of nuclear plants), land utilization (diffuse energy sources such as solar and wind consume enormous land footprints), etc. There is, alas, no "free lunch" when it comes to energy. The best that we can hope for is to understand and minimize risks by constantly striving for better and safer designs and better ways of responding to accidents.


In particular, it is worth noting that the Fukushima plants were of a prior vintage - built in the 1960's and nearing retirement. Newer plants built at Fukushima Dai-ini did not suffer nearly the same consequences as those at Dai-ichi, in part due to enhanced safety features within the designs. Likewise, plant designs being proposed today take advantage of decades of engineering experience, including advances in technology (particularly in advanced computing - perhaps the most amazing thing about much of the existing nuclear fleet is that it was designed with pencils and slide-rules...). New designs such as small modular reactors promise further enhancements in safety.


Ultimately, safety will be an ongoing challenge, one not entirely technical in nature. After Three Mile Island, one of the most radical changes to the U.S. nuclear industry was a focus on human factors - particularly looking at aspects such as instruments in the control room, operator training, and instilling a safety culture. Similar lessons may ultimately have to be internalized in the case of Japan.


It has often been said, "Experience is the harshest teacher, and her lessons the most expensive." For the Japanese, no doubt this case is little different.


A special thanks to Randy Beatty and the IAEA for both presenting and making these resources available to me.

Small Modular Reactors and the Economics of Nuclear

My colleague (and member of my dissertation committee) Dr. David McNelis had an excellent Op-Ed in the Raleigh News and Observer yesterday touting the safety and economics advantages of small modular reactors (SMRs). A snippet:

In contrast to a conventional nuclear plant, SMRs could be added one at a time in a cluster of modules, as the need for electricity rises. The cluster's costs would be paid for over time, softening the financial impact.

The modules could be factory assembled and be delivered by rail to an existing nuclear plant site. In such a configuration, one SMR could be taken out of service for maintenance or repair without affecting operation of the other units.

Most SMRs would be situated beneath the ground to provide better security. Typically they would operate for many years - possibly decades - without refueling and produce far less waste than conventional reactors.

Significantly, almost all of the SMR development is being done with private financing. Companies are using their own resources to develop the small reactors, without government support from mandates or subsidies of the sort that renewable energy sources now require.

As the kids say, do read the whole thing.

SMRs are an interesting, potentially game-changing addition to the nuclear energy market in my opinion, namely due to their ability to overcome one of the chief barriers to the rapid deployment of nuclear energy units right now: high capital costs.

Prohibitively high capital costs (most new reactors are starting with price tags around $4 billion or so) present utilities with a double-whammy of sorts: first in that raising so much capital is in itself a difficult undertaking, particularly compared to the total capitalization of the types of utilities making these investments. (This is where the typical rhetoric about "betting the farm" comes into play, despite the fact that the low fuel and operating costs and very high capacity factors make nuclear units veritable cash cows once electricity begins to flow. Ultimately, such investments require tying up a large portion of an individual utility's assets for several years before any money is generated.) Second, due to the large amounts of money involved and generally long construction times, utilities get hammered on costs by paying interest upon interest; in other words, interest accrues on money they borrow from the moment construction begins, meaning that the "cost of money" is a rather significant factor in nuclear construction. Finally, given both the large amounts of money and extended timelines involved, investors will thus typically demand a "risk premium" - similar to the kind of interest rate premium an ordinary borrower without stellar credit would have to pay on bank loans an credit cards. This too can significantly raise the cost of capital for building new units.

Each of these factors thus conspires to keep many smaller players out of the market. Instead, many have sought to invest in smaller, more scalable alternatives such as natural gas, which has nearly the opposite economics of nuclear: low capital costs (i.e., each unit is of a relatively small capacity and can be built quickly) and relatively high fuel costs as a fraction of the cost of electricity. (While nuclear's fuel cost for electricity is around 10%, natural gas can be around 70-80%). Nor has the price of natural gas ever been historically stable (at least in the last 15 years).

Unless, of course, this is your definition of "historically stable." (Source: EIA)

SMRs have the potential to change the economics of the game by several means. First, many proposed SMR designs are engineered to be mass-produced and pre-fabricated in factories, rather than built on-site. This could tremendously push down prices while also shortening construction times, thus ameliorating what is currently one of nuclear's biggest weaknesses at the moment.

Meanwhile, the "small" in SMRs also may have potentially positive implications for both cost and safety: SMRs can be potentially built into the ground, using the surrounding earth as containment, due to their relatively small size. Given the lower total power and nuclear material within the reactor, it can be said to have a lower overall "radiological footprint," meaning simplified safety planning.

Finally, the "right-size" power of SMR capacity may allow them to be sold in a greater number of markets - places both where a new full-sized reactor is too big for the needs of a community (for example, Fort Calhoun, north of Omaha, is the smallest reactor in the U.S. nuclear fleet, clocking in at only 500 MW; compare this to currently proposed new reactor designs, which begin in the neighborhood of 1000-1100 MW). Likewise, the smaller size means that for utilities only looking to incrementally expand capacity, small reactors may prove to be competitive with alternatives such as natural gas turbines.

One point which I think nuclear advocates tend to allow themselves to be blindsided to at times is in the fact  that above all else, it is economics which will ultimately determine the future of the nation's electricity portfolio. Factors like politics certainly come into play (particularly such issues as energy portfolio mandates, etc.), and likewise factors such as safety can never be understated. Nor should public acceptance ever be ignored, much as it has to the industry's peril in the past. However, those ultimately committing the funds to expand energy sources are the utilities, many of whom answer either directly to shareholders or to ratepayers. In this regard, they have an obligation in either sense to produce power as profitably or affordably as possible.

Thus, the decision for utilities will always ultimately come down to economics, something that nuclear advocates cannot simply ignore. I don't necessarily doubt the assertions of fellow advocates such as Rod Adams, who assert that fossil fuels have a strong interest to defend in continuing to sell their products. (Although I will say that I also don't necessarily buy the idea that those who argue natural gas is currently more economical based on short-term factors are necessarily on the fossil fuel dole, either.) But the fact remains - for nuclear to succeed, it must be able to compete, head to head, dollar for dollar.

Nuclear energy has tremendous advantages to offer, in that is clean, abundant, and easily the most energy-dense source we have available at our disposal. Yet at the end of the day, decisions over energy investments do not necessarily come down to these factors: they come down to economics, and often (regrettably) economic return over the short-term. This may be where SMRs ultimately change the game for nuclear, then - namely, by bringing the advantages of nuclear to bear in a more economically attractive package.

Recent presentations on the events at Fukushima

• Professors from NC State's Department of Nuclear Engineering gave a symposium yesterday on the events at Fukushima, including an analysis of what happened and potential health consequences, as well as a Q&A from the audience. The entire symposium is now available for public viewing (no login required).
• The University of Wisconsin-Madison gave a similar forum, which is also available online.
• MIT's Department of Nuclear Engineering also gave a forum available on the web, although this was earlier in the timeline (and thus the information is likely less up-to-date).

Each of these presentations was designed to engage and inform the general public about the events which have occurred at Fukushima, including a specific explanation of what we understand to have happened so far from the perspective of experts and ultimately what is being done now to bring the situation under control. The advantage of these types of seminars is that the offer the ability to convey more detailed explanations of the specific sequences of events that lead to the current situation which are typically not available in traditional media accounts.

Symposium on Fukushima Daiichi

Several professors from NC State's nuclear engineering department will be discussing the events at Fukushima Daiichi at a public forum this Wednesday; the event will also be live streamed. See below for details.

NC State nuclear engineering experts to discuss events at Japanese power plant

What: Nuclear engineering experts at North Carolina State University will offer insight and analysis during a symposium on the recent events at the Fukushima Daiichi nuclear power plant in Japan. The plant was damaged during the March 11 earthquake and subsequent tsunami resulting in nuclear fuel damage and the release of radioactive material. Media coverage is invited.

Who: A panel of four NC State nuclear engineering faculty members who have been closely following the events in Japan — Drs. John Gilligan, Michael Doster, Paul Turinsky and Man-Sung Yim — will discuss technical issues related to the damage to the plant, as well as challenges officials face as they try to contain the radioactive material. Audience members will have the opportunity to ask questions during the event.

When: 5 p.m. on Wednesday, March 23.

Live stream also available for public viewing of the symposium (no login required).

Where: Park Shops, Room 130, at 101 Current Drive on NC State’s North Campus (map). Parking is available in the Cates Avenue (Coliseum) Parking Deck at 201 Jeter Drive on Central Campus (map). From the deck, visitors should walk north through the tunnel under the railroad tracks to reach North Campus and Park Shops.

Cost: The event is free and open to the public.

Media Contact: Nate DeGraff, Engineering Communications, 919.515.3848

Situation stabilizing at Fukushima

Current reports from TEPCO and NISA indicate that workers have restored off-site power at Units 1 and 2, with plans to restore off-site power to Units 3 and 4 tomorrow (March 21). This is a welcome development, indicating that the situation at the reactors is likely stabilizing. With the restoration of off-site power, cooling pumps can begin to circulate coolant in the reactors and spent fuel cooling pools once more, largely eliminating any further risk of fuel overheating and subsequent inadvertent release of radioactive materials. In addition, holes have been bored into the roofs of Units 5 and 6 as a preventative measure to vent any potential hydrogen buildup as to prevent further explosions of the kind that damaged Units 1 and 3. As off-site power is restored and the radiological levels decline, the damage can be more fully assessed and cleanup work can begin.

Meanwhile, news reports from Japan indicate that through the use of infrared sensors, the surface temperatures at each of the reactors have been verified to be well below 100 C (i.e., the boiling point of water), meaning that water is present at each of the reactor units. It would thus appear that the efforts of workers to restore water to the spent fuel pools and reactors has been successful.

XKCD recently posted a very interesting diagram putting the radiation levels observed in perspective - it's a very useful diagram for directly comparing some of the levels being discussed with levels encountered in everyday settings. This presentation by UCSB physics professor Benjamin Monreal also gives an excellent and concise summary of the likely radiological release consequences of Fukushima as well as past historical incidents (such as Three Mile Island and Chernobyl).

Reports of produce contamination

Now that the situation with the reactors has appeared to have calmed down, much of the media focus now has shifted to reports of radioactive contamination of milk and spinach from areas near the plants. It should be emphasized that the levels of radioactivity found, while above regulatory limits, do not pose any immediate threat to human health.

I will be posting a longer discussion of how radiological contaminaiton gets into the environement (and what we mean by "radiological contamination"), but in the meantime, it is useful to summarize what is going on in this case and the chief areas of concern.

Given the nature of the radioactive release, most the released products fall into the categories of a) Radioactive noble gases (such as krypton, xenon, etc.) and b) Radioactive, chemically active gases such as iodine-131, c) Radioactive isotopes of cesium and strontium.

Noble gases are of little concern, as they do not generally interact with the biosphere (i.e., they don't "stick" to anything, given that they are chemically inert). As a result, these gases will generally travel further into the atmosphere, becoming increasingly diluted (and thus of little concern for human health).

Chemically active species such as iodine are one of the more serious concerns for contamination, as iodine is readily absorbed by the human body (and rapidly taken into the thyroid); this is the basis for using potassium-iodine tablets as a "prophylactic" measure, flooding the thyroid with natural (non-radioactive) iodine such to prevent the uptake of the radioactive species. Iodine in fission products generally falls into two species - iodine-131, which has a half-life of 8 days, and iodine-129, which has a half-life of 15.7 million years. Only iodine-131 is of any serious contamination concern, given the extremely long half-life of iodine-129 (which means the activity from this species is extremely low). (Iodine-129, while being inconsequential to short-term dose, is an isotope of concern for geologic repositories, given its long lifetime and iodine's ease of movement in groundwater.)

Radiological half-life denotes the time in which half of a radioisotope species decays away into a different species. After one half-life, half of the original radioactive species remains; after two half-lives, only a fourth remain, and so on. In some cases, the "daughter" isotope is stable, meaning that no further decays occur. Other times (like with radon), the daughter products are also unstable, leading to a series of decays. (These isotopes can thus be of greater concern - like with radon.)

Iodine-131 decays into Xenon-131, which is stable. Thus, after 8 days, the radiological contamination due to iodine will decrease by approximately half. By three weeks' time, this level will have dropped to an eighth of the original level; by three months' time, the radioactivity from iodine will have virtually disappeared.

Other radioisotopes of concern are strontium-90 and cesium-137, which have half-lives of about 29 and 30 years, respectively. (These two isotopes are incidentally of concern from a waste management perspective, as the heat generated by this pair is a working constraint on repository capacity over the first hundred years.) Because the half-lives of these species are longer, their contributions to dose tends to be extremely small (much of what is ingested would be released by the body before it would decay). Strontium, being of the same element family as calcium, tends to chemically act like calcium in that it is accumulated in the bones; however, the dose levels from strontium would be quite small (far lower than that from natural sources).

Many have pointed to the iodine contamination in the environment (particularly in milk) following Chernobyl as a reason for concern from Fukushima, however the levels of contamination from Chernobyl were far, far greater than those from Fukushima. Unlike Chernobyl, comparatively little radioactive material escaped the reactor, nor was this material lofted high into the air through fires like those found in Chernobyl. As a result, the levels of contamination are far smaller and the effects far more localized. Evidence of this is found in the relative dose estimates based upon monitoring stations around Japan and the plant itself; doses at the plant boundary have been around a few millirem per hour and dropping (particularly as coolant has been restored to spent fuel pools); levels are far lower than this farther away from the plant. 

Beyond reconstruction of the heavily damaged area (both from the earthquake and tsunami), one of the major challenges appears to be in overcoming the stigma of radiological contamination, despite the extremely low levels present (particularly after a few weeks). While any actual long-term health risk from radioactive contamination will be quite minimal after a few weeks (with no immediate-term risk at all), overcoming the stigma of radioactive contamination will take some time. In particular, one of the most pressing challenges will be to further educate the public about both comparative levels of radiation found in nature and the (relative lack of) increased risk from low levels of additional radioactivity.

Update: Alan asked about the nature of emissions from these isotopes of concern and what their subsequent "weighting" factors would be. Cs, Sr, and I are all beta emitters; Cs-137 decays into Ba-137, which has a short-half life and gives off a gamma as it decays. Given this, the weighting factors for each is "1" - so in other words, the conversion from gray/rad is the same value in sievert/rem.

I also found some more resources on maximum recommended contamination levels - the World Health Organization generally recommends contamination levels expressed in units of activity per unit mass - i.e., Becquerels per kilogram (Bq/kg). One Becquerel is one decay per second - so 1000 Bq is 1000 decays per second. (While this sounds large, keep in mind just how many atoms are in even one gram of material - 1000 Bq is actually pretty small.)

The WHO recommends the following limits in foods:

Radioisotope	Max activity (Bq/kg)
I-129, I-131	1000
Cs-137	100
Sr-90	100

This of course is not a comprehensive list (the list is found on page 33 of the above-linked document), however it covers the radioisotopes of concern here.

(For those curious - one can calculate an equivalent dose received by multiplying the following formula: Exposure = Activity [Bq/kg] * Mass consumed [kg] * Age-dependent ngestion coefficient [mSv/Bq]. These ingestion factors are in the above-linked document; I will cover this topic in more detail in a further post.)

CNN is reporting measurements of 965 Bq/kg in tap water in a village in Fukushima prefecture (where the Fukushima Daiichi plants are), compared to a national regulatory limit of 300 Bq/kg. As a result, authorities are advising residents to avoid drinking tap water for the time being.

Again, however, knowing the half-life of I-131 allows us to know when these levels will fall to the safe (conservative) limits; in this case, in about two weeks for an areas closest to the contamination source. While certainly undesirable, in this time frame there are likely other problems with tap water as well beyond radiation, including contamination from biological pathogens, particularly given the tsunami.

Spent fuel pools at Unit 4

Water levels a concern for Unit 4 spent fuel pools

One of the big issues for those following the news right now has been the status of the spent fuel cooling ponds at Fukushima Daiichi Unit 4. Unit 4 was undergoing regular maintenance prior to the earthquake; no fuel was in the reactor. Thus, until now it has not been as serious of a concern as Units 1, 2, and 3.

Reports from the Japan Industrial Atomic Forum (JAIF) indicate low water levels at the spent fuel pool, with damage suspected to the fuel rods. An explosion and fire have also been reported at Unit 4. While some suspect the explosion may have been hydrogen-related, the spent fuel pool was significantly cooler than the reactors at Units 1 and 3, with temperatures reported to be around 85 C (185 F) over the past two days - thus, the explosion remains difficult to understand. Several fires have also broken out over the last two days in the spent fuel storage area - sources indicate that these have been machinery oil fires, which have since been contained. Reports of low water levels at the Unit 4 spent fuel storage pool appear to have begun at least 24 hours ago (as of 19:00 hours on March 15).

It is difficult to determine the current status of the fuel pool, given conflicting accounts. U.S. NRC chairman Gregory Jazcko has indicated that it is his staff's belief that, "there is no water in the spent fuel pool." This was immediately contradicted by a TEPCO spokesperson who indicated "the condition is stable", however no further updates are available at the TEPCO website. However, water levels at the spent fuel pools have been a reported concern for some time, according to both World Nuclear News and NEI.

The Nuclear Industrial Safety Association - Japan's version of the NRC (and part of the Ministry of Economy, Trade, and Industry - METI) - has most recently reported the following:

<Unit 4>

• It was confirmed that a part of wall in the operation area of Unit 4 was damaged. (06:14 March 15th) 

• The fire at Unit 4 occurred. (09:38 March 15th) TEPCO reported that the fire was extinguished spontaneously (11:00 March 15th) 

• The temperature of water in the Spent Fuel Storage Pool at Unit 4 had increased. (84 ℃ at 04:08 March 14th)

• The fire occurred at Unit 4. (5:45 March 15th) TEPCO reported that no fire could be confirmed on the ground.(06:15 March 16th)

• The water injection was stopped. (14:00 March 16th)

CNN and NHK are currently reporting that JSDF helicopters are currently attempting to drop water onto the Unit 4 building in order to add coolant, as well as water cannons (essentially, fire engines) on standby.

Spent fuel pool basics

Unlike the fuel immediately after shutdown like in Units 1 and 3, spent fuel sitting in the cooling pool is considerably cooler, although it still generates enough heat to require water cooling. Spent fuel is generally about 10-13 feet in height; the water covering this fuel is generally at least another 20 feet in height above the fuel itself. This water serves a dual purpose - it both keeps the fuel cool and provides a good measure of radiological shielding; exposure rates immediately above the spent fuel pool are such that workers can generally be in the area without special protective equipment - generally less than 2 millirem per hour (about a fifth of the dose of a chest x-ray).

A spent fuel storage pool (Image courtesy of IEEE spectrum)

The spent fuel storage pool is kept at atmospheric pressure, unlike the reactor. Under normal conditions, pumps will circulate cooling water in order to keep the rods cool, although under emergency conditions, natural circulation is expected to take over (i.e., where warmer water expands and grows less dense, thus rising to the top, while cool water, which is denser, sinks - thus providing a natural "circulation" for heat removal around the rod.) These spent fuel pools tend to be quite robust - a simple failure of pumps or piping would not be able to drain the water level from these pools, which are made of thick concrete and steel.

Generally, the only way significant water level changes could be expected in the spent fuel pool are from evaporation of the water or if a large crack were to develop in the pool itself. Readings over the last two days indicate that the temperatures of the pools were elevated, at around 85 C (185 F) - while certainly warm, well below boiling. (However, one can expect an increased rate of evaporation at this temperature). The IAEA confirms these temperatures for the prior two days, however no data was available for today. If accounts of diminished water levels are to be believed, this would imply that there may be structural damage to the building; this much is unknown at this time.

Reports indicate that there may be fuel damage due to dropping water levels - this would likely be in the form of cladding failures, which have released radioactive fission gases similar to the process in Units 1, 2, and 3. The major concern for workers right now is in personal safety - without the protective layer of water, there is significantly less radiological shielding, making it far more difficult to operate around the spent fuel pool. This would appear to be the reason for using water cannons and helicopter drops in order to supply emergency water, in order to bring radiation levels back down (by providing an adequate layer of water for shielding). 

For those keeping score at home, the radiological source from these spent fuel rods would be deep-penetrating gamma radiation; the danger to workers is that the exposed would be that in the absence of the several feet of water shielding, the spent fuel rods would essentially act as a "gamma flashlight" pointing out of the fuel pool.

Depending upon the age of the fuel rods themselves (which determines the level of decay heat), it seems less likely that any kind of actual fuel melting would occur itself. Rather, the chief issue appears to be in the radiological release from ruptured fuel cladding as well as the higher levels of radioactivity, which make it extremely difficult for workers to get close to the pool in order to refill it with coolant - hence the use of helicopters and water cannons from the ground. 

I will continue to update as I learn more - unfortunately, the news on this appears to be very scarce, and mixed at best.

Update: JAIF confirms helicopters dropping seawater on Units 3 and 4 due to low coolant levels. Private sources have also begun to confirm that water levels are very low at Unit 4.

Fukushima Plant Status as of 7pm March 16th

I've started to come across some other official releases that have been translated into English. I will start with a data sheet outlining the most recent Fukushima plants status.


It seems that the 'time' to start blaming is upon us. The Daiichi plants have suffered damage over the last few days and reports about where to start pointing fingers is now creeping into the recent news reports.

I have witnessed quite a few already saying that there hasn't been enough information coming from official sources; that the government and the company are trying to downplay the situation. I am not in a position to talk about what events happened years ago but I am in a position to speak on what is happening now.

In fact, it is one of the key reasons that I decided to really push any information out in some kind of medium. The events unfolding in Japan are hard to watch and as a nuclear engineer myself I find some small measure of peace explaining what I can to those who care to listen.

The official sources of information are out there. There are enough of them giving updates day in and day out that it's all I can do to try and keep up. Between the three of us, we've found detailed information on the plant status, statements from high levels of Japanese government, our government, nuclear experts, the IAEA, NEI, ANS, NISA, JAIF, TEPCO, .... I mean come on!

We now seem to be transitioning into the next stage where those who have been 'reporting' are now looking how to prolong the story. The uber-hype is probably starting to fall on the deaf ears of the fickle ADHD public.

With that being said, science is a slow, meticulous process that, for some, takes a frustratingly long time. Project time lines are on the order of years. Some spend entire careers chasing for the truth. A physics professor used a saying that, "The more you learn about less and less until you know everything about nothing". In a field like nuclear engineering I couldn't agree more.

It's not that the nuclear engineers didn't do their homework. It's not that the Mark I containment isn't adequate to handle the stresses it was designed to handle. It's that, somehow, at some point in time, someone decided to demand that nuclear energy must operate in the world of absolutes. Is it absolutely safe? Can you guarantee that my child will receive absolutely no radiation dose? Are you absolutely sure? ...Really? This was something that was long established before I was introduced into the industry and I wonder, what will it take to change it?

From the countless hours I have already spent researching the events and keeping up with what's happening over at Fukushima Daiichi I ask what more could people want? These sites are releasing bulletins by the handfuls every day. TEPCO has been releasing updates almost hourly. I guess some expect absolutes. They want to hear that there is no uncertainty; that it is or it isn't. I don't know what to say to this line of thinking other than, "Wake up!" because there are no absolutes.

Science is as science does. Even if there are people to blame or victims to be compensated, none of this will even begin to actually be addressed until the situation at Fukushima is over. Even then, as scientists, we're going to take our thick-rimmed glasses and our pocket protectors and we're going to do our job. Science doesn't require emotion and even if you don't find yourself emotional about science then it's still not hard to understand that the extremely emotional broadcasts don't translate into good science.

When the media gets it right (and wrong)

First, let's talk about some cases where they get it right.

William Saletan at Slate: Nuclear Overreactors. Saletan in a very welcome fashion throws a bit of cold water on the current hyperbole about the Japanese nuclear situation, especially given the current risks we tolerate from other sources of energy (particularly oil, although the same could be said for natural gas extraction as well).

The New York Times has an excellent interactive feature explaining the mechanics involved with the Fukushima reactors in basic terms - it does a very nice job visualizing what's going on here.

WNYC, a New York City NPR affiliate, had an interview with former GE VP for Engineering Quality at GE Nuclear Margaret Harding.

And of course, here's NC State's own Professor Paul Turinsky (who is also on my dissertation committee!) explaining the basics of nuclear reactors on the local news:




Also (perhaps shockingly enough), here's Glenn Beck actually doing a passable job at explaining the issue of defense in depth at reactors like Fukushima with the help of his infamous chalkboard and some M&M's. (He doesn't get quite everything right, but he does do an admirable job compared to many.)

Then, of course, there's the predictable reactions by those who don't really know much about what they're talking about.

First, there's syndicated columnist Anne Applebaum, someone not normally given to fits of hyperbole, with this: If the Japanese can’t build a safe reactor, who can?

Where exactly does one begin with this premise? That somehow, the fact that there is a problem given the fact that these reactors withstood an earthquake well beyond the design basis - one of the largest earthquakes in recorded history - along with a massive tsunami, somehow "demonstrates" that nuclear energy is categorically "unsafe?" (Again, let's see the natural gas facility that can stand up to a similar beating without bursting into flames.)

As they say in the infomercials however, "but wait, there's more!":

Increasingly, nuclear power is also promoted because it safe. Which it is — except, of course, when it is not. Chances of a major disaster are tiny, one in a hundred million. But in the event of a statistically improbable major disaster, the damage could include, say, the destruction of a city or the poisoning of a country. The cost of such a potential catastrophe is partly reflected in the price of plant construction, and it partly explains the cost overruns in Finland: Nobody can risk the tiniest flaw in the concrete or the most minimal reduction in the quality of the steel. 

But as we are about to learn in Japan, the true costs of nuclear power are never reflected even in the very high price of plant construction. Inevitably, the enormous costs of nuclear waste disposal fall to taxpayers, not the nuclear industry. The costs of cleanup, even in the wake of a relatively small accident, are eventually borne by government, too. Health-care costs will also be paid by society at large, one way or another. If there is true nuclear catastrophe in Japan, the entire world will pay the price.

A few problems, here. First, "the destruction of a city or the poisoning of a country?" A reminder that bears repeating: not one single person was killed due to Three Mile Island. None. And so far, the only person killed as a direct result of Japan's reactor accident has been a crane operator - and this was due to the earthquake, not the reactor itself. And why is that? Because nuclear engineers take the job of safety very, very seriously. Reactors are designed with multiple barriers against radioactive release in order to prevent these very dire consequences Applebaum refers to. Every reactor in operation right now in the United States and Japan has multiple systems to prevent radioactive release, unlike the Chernobyl system which undoubtedly Ms. Applebaum refers to.

Furthermore, in the United States at least, the cost of waste disposal is not paid for by the government. Each utility pays a fee ($0.001 per kilowatt-hour of electricity generated) into a waste disposal fund, since the 1980s. This fund has accumulated over $30 billion - of which, only $10 billion has been spent on the (now-defunct) Yucca Mountain repository. One can argue that these costs are picked up by ratepayers, but certainly not taxpayers writ large.

And as for health care costs? Look at the numbers for premature deaths due to every other energy source, particularly for coal, oil, and others. (Even "green" energy sources have their own costs, from toxic waste generated to manufacture semiconductors for solar cells to the environmental impacts to construct and operate wind turbines). The basic story here is simple: there is no "free lunch," and there is certainly no "risk free" form of energy. The best we can do is to weigh the relative risks and benefits appropriately.

Of course, Applebaum's column looks positively benign compared to this piece by Patrick Doherty posted on CNN, originally titled "America needs a path to disaster-free energy." (CNN has since updated the title, although one can catch a hint of the original in the URL.)

Ugh. There's nothing wrong with different points of view, but there is something positively despicable about exploiting tragedy in order to push a particular agenda.