Statement by Scientists and Engineers Concerning Fukushima Daiichi Nuclear Power Plant

March 23, 2011

Our Views of the Accidents at the Fukushima Nuclear Plants after the Earthquake

From: The Group of Concerned Scientists and Engineers Calling for the Closure of the Kashiwazaki-Kariwa Nuclear Power Plant
Toda Building, 4th Floor, 1-21 Yotsuya, Shinjuku, Tokyo 160-0004

Over ten days have passed since the Tohoku Pacific Offshore Earthquake hit the Fukushima Daiichi (No.1) Nuclear Power Plant on March 11, 2011. The progress of cooling the reactor cores is slow. The situation remains serious, and we do not yet know how this catastrophic accident will end.

The current situation clearly demonstrates the high vulnerability of nuclear plants throughout Japan to earthquakes and tsunamis. If a similar scale of earthquake hits other nuclear plants, it is quite possible that one or more accidents of a similar catastrophic scale may occur. Two nuclear plants in Japan are of particular concern to us: the Kashiwazaki-Kariwa Nuclear Plant, which was damaged by the 2007 Niigata Chuetsu Offshore Earthquake, and the Hamaoka Nuclear Plant, which is located on top of the potential source fault of the expected “Tokai Earthquake.” We suggest that the possibility of another large-scale accident similar to the one at Fukushima Daiichi should not be underestimated.

We, the members of The Group of Concerned Scientists and Engineers Calling for the Closure of the Kashiwazaki-Kariwa Nuclear Power Plant, have discussed how the current situation should be evaluated, and what kinds of demands need to be made to the electric power companies and the government. The following is the summary of our views.

As of today, the amount of information that has been released is too limited and inadequate to fully evaluate the progress of this accident over the past 10 days. Furthermore, given that many of the measuring instruments (thermometers, etc.) within the reactors seem to have been broken, we may never know the details of this accident. With these limitations in mind, our current view is as follows.

At the time of the earthquake, Units 1, 2 and 3 of the Fukushima Daiichi Plant were in operation. Units 4, 5 and 6 were not in operation because of periodic inspections. All four units of the Fukushima Daini (No.2) Plant were in operation. When the earthquake hit, the control rods of the four reactors of Fukushima Daini were automatically inserted, and this terminated the nuclear fission reaction of the fuel. At Fukushima Daiichi, however, the external power supply was cut off, the emergency diesel generators also failed, and the fuel tank for the generators seems to have been swept away by the tsunami. As a result of these problems, it became impossible to cool down the reactor cores, a critical procedure that should have occurred right after the nuclear reactors stopped working.

The Pressure Vessel and the Containment Vessel of Nuclear Reactors
Within Units 1, 2 and 3 of the Fukushima Daiichi Nuclear Plant, once the cooling water became unavailable, the water in the reactor core evaporated as a result of the decay heat from the fission products causing a drop in the water level. This resulted in the exposure of the fuel rods above the water level. When this condition continued, the melting of the fuel rods was inevitable.

TEPCO (Tokyo Electric Power Company) first attempted to connect an external fire pump to the plumbing in order to pour water into the nuclear reactor. This attempt was not successful, presumably because the water was not supplied from the water tank normally used to provide water to the reactor. As a result, the water level within the reactor continued to drop. When this condition occurred at Unit 1, it is said that TEPCO discussed the possibility of cooling the reactor using sea water, but that they decided not to do this immediately because, at that point, they still wanted to avoid decommissioning. The decision to use sea water was made later after the hydrogen explosion occurred at Unit 1. Because of this delay, the situation deteriorated very quickly.

The nuclear reactor is designed so that when the water within the pressure vessel evaporates and the pressure within the vessel increases, a safety relief valve opens to lower the pressure. When this happens, the vapor within the pressure vessel is sent to the suppression chamber of the containment vessel. Releasing the vapor causes the water level within the pressure vessel to drop further. If the safety valve is continuously open, the fuel rods become exposed above the water. Without enough cooling water, the temperature of the fuel rods increases, and eventually temperatures reach the point where the zircaloy cladding tubes of the fuel rods react chemically with water vapor, to produce hydrogen.

We believe that hydrogen in the containment vessel was the cause of the explosions at Units 1, 2 and 3. It is important to note that hydrogen explosions occurred in the upper part of the building shells of Units 1 and 3. On the other hand, the explosion at Unit 2 occurred in the lower section in the suppression chamber. It is important to understand why these two different patterns occurred. It is likely that the suppression chamber of Unit 2, as well as the reactors and pipework of all the units, were already damaged by the earthquake.

Storage Pool for Spent Fuel Rods
On March 15, a hydrogen explosion occurred at the storage pool for the spent fuel rods of Unit 4. On March 16, another explosion was reported at Unit 3. It is likely that spent fuel rods that were taken out of the reactors and kept in the storage pools were exposed to air, because the water level decreased within the pools. The exposed fuel rods must have reacted chemically with the water vapor producing hydrogen, which then chemically reacted explosively with oxygen.

Exposure of the spent fuel rods may have been caused not only by the evaporation of water but also by the loss of water within the storage pool due to sloshing (spillage) during the earthquake.

As a temporary measure, fire trucks discharged seawater into the fuel pools of Units 3 and 4. Ultimately, it will be necessary to restore electricity so that the water pump can be restarted to circulate the cooling water.

The large amount of water discharged from Units 3 and 4 has increased the possibility that water contaminated by radioactive materials may flow into the sea and ground water. In fact, high levels of radioactive iodine, cesium and other elements have been detected. The amount of these elements is greater than the standards considered safe by the government (reported by TEPCO on March 22).

Possibility of Further Crises at the Daiichi Plant
On March 21, an external power supply was connected to the Fukushima Daiichi Plant. As of the morning of March 23, however, electrical power is not connected to various instruments. We still do not know when the circulation of the cooling water will be restored. Although the amount of heat resulting from radioactive decay will decrease over time, it is possible that the delicate balance between the heat release and the cooling may be lost. There is still a danger that molten fuel deposited at the bottom of the pressure vessel, or the containment vessel could melt through the bottom of these vessels. Alternatively, the cores of one or more reactors could go critical.

According to TEPCO, neutron radiation was observed on March 14 and 15. This might be an indication that nuclear fission, or “criticality” occurred. Criticality can occur not only within the reactors but also in the fuel storage pools. For example, if the earthquake damaged the storage racks which separate individual fuel rods (e.g., cranes, manipulators or other instruments may have fallen onto the racks), criticality could occur because the fuel rods would become too close to each other.


Radioactive materials are being released into the air from the Fukushima Daiichi Plant. High levels of contamination have been observed in the vicinity of the nuclear plant. Radioactive materials that originated from the plant have also been reported in many parts of northeastern Japan. On March 21, contamination of agricultural products (including milk and spinach) above the level of the temporary standards set by the Food Sanitation Act were reported in Fukushima Prefecture as well as in several prefectures in the Kanto Region. Contamination of the sea water near the nuclear plant has also been reported. This may affect marine products.

How should we evaluate the level of radioactive contamination? Should we evacuate? Is it safe to eat agricultural products? Our view is the following.

Currently, a major problem is that TEPCO has not made any official announcements about the amounts of the discharged radioactive materials. As a result, it is extremely difficult to grasp the complete picture of the radiation contamination. Reports of radiation measurements at various observation stations are also limited. As of March 23, we still do not have full access to the radiation measurements from each prefecture. No results of the simulation of the dispersal patterns of radioactive materials have been published either. Given these limitations, it is difficult to make a conclusive statement about the levels and range of radioactive contamination.

When judging the contamination levels and taking actions to deal with the situation, it is important to distinguish between external radiation exposure and internal exposure. Radiation exposure within or above the nuclear plant site mainly comes directly from the exposed fuel rods. On the other hand, radiation exposure in the vicinity of the plant as well as in the areas further away from the plant comes from radioactive materials that were discharged into the air. In the latter case, radiation exposure can occur not only to the outside of the body but also inside the body if radioactive materials are ingested.

Because alpha particles and the beta particles emitted from the radioactive materials inside the body only penetrate a short distance, they destroy the structure of cells nearby in an intensive manner. This results in a high incidence of cancer. Given this, some scholars suggest that the legal upper limit for radiation exposure should be lower than the standard set by the report of ICRP (International Commission on Radiological Protection).

Workers’ Radiation Exposure at the Nuclear Plant Site
Monitors within and above the nuclear plant site indicate that high levels of radiation above 100mSv/hr have been observed. As a result, workers’ activities had to be frequently interrupted. Although the stabilization of the reactors to avoid critical dangers is an urgent matter, it is also important to ensure the safety of workers, including those from TEPCO, contracted companies, firefighters, and members of the Self Defense Forces. These people should not be exposed to high levels of radiation. The Health, Labor and Welfare Ministry has raised the upper legal limit of safe radiation exposure from 100mSv to 250 mSv. This change should not lead to an underestimation of radiation doses. Nor should it result in coercion of workers to force them to work in areas where they could be exposed to radiation.

Necessity to Evacuate from the 30km Zone
According to the standard set by the Disaster Prevention Guideline of the Nuclear Safety Commission, evacuation is in order when the estimate of the cumulative radiation level is above 50mSv, and staying inside is in order when the radiation level is above 10mSv . It is not clear on what kinds of data the evacuation order for the 20km zone from Fukushima Daiichi and the order to stay inside for the 30km zone were issued. It is likely that the seriousness of the situation has been underestimated. Furthermore, people who are staying indoors within the 30km zone are suffering from scarcity of supplies, partly because some transport companies are not willing to send their workers into this zone. An immediate evacuation order from this zone should be issued.

Evacuation from the 80km Zone Recommended by the US and Others
The United States government announced that they had told their citizens to evacuate from the zone 80km around the Fukushima Daiichi Nuclear Plant. Several other countries have taken similar actions. It is reasonable to assume that these countries had reasons for taking these actions, and that Japanese nationals living within this zone may also be in danger.

The decision to evacuate or not should be made on the basis of multiple factors, including one’s living environment, relations with other people, and the possibility of finding a secure evacuation place. However, the evacuation of pregnant women (and babies in the womb), infants, and children should be a priority.

Areas within the 200km Zone, including the Tokyo Metropolitan District
There are reports that the radiation level within the 200km zone is as high as 1 micro Sv/hr. If a person keeps receiving this amount of radiation for one year (8,760 hours), the cumulative amount will be 8.76mSv. This is above the legal limit for members of the public to be exposed to radiation (1mSv/yr). Critics may say that this amount is not much larger than the level of natural radiation, which is 1.2mSv/yrÅDGiven the risk of additional internal exposure, however, the continuous exposure to this level of radiation may not be desirable.

The critical issue here is how long it will take for this emergency situation to end. It is necessary to closely monitor what happens next at the nuclear plant site and how the radiation measurements change.

Impacts on Agricultural Products
Food contamination by radioactive iodine and/or cesium in amounts that are above the temporary legal limits set by the Food Sanitation Act has been reported from tests on milk from Fukushima and from tests on vegetables (spinach etc.) from multiple prefectures in the Kanto Region. Food safety is being threatened. Following the regulation of the Act on Special Measures Concerning Nuclear Emergency Preparedness, the government suspended the shipment of certain vegetables from several prefectures. As a result, farmers had to discard their products. The government and TEPCO are responsible for compensation to the producers. Depending on the duration of this emergency status, agricultural production from various parts of Japan may be heavily damaged. To prevent further damage, it is critical that the release of further radioactivity be stopped and the cooling function of the nuclear reactors and fuel storage pools be restored as soon as possible.

It is clear that the past accident at the Kashiwazaki-Kariwa Nuclear Power Plant, which narrowly escaped turning into a major accident, was a warning about Japanese nuclear plant policies. For the past four years, we have been making this point. Unfortunately, the Japanese government and TEPCO did not learn the lesson from the Kashiwazaki-Kariwa accident. We are angry and extremely disappointed by this.

Underestimation of the Possible Size of Earthquakes and Tsunamis
Many people who previously denied the possibility of any nuclear power plant accidents state that the scale of the earthquake, M9.0, and the size of the resultant tsunamis were beyond their expectation. It should be pointed out, however, that the scale of the Sumatra Earthquake on December 26, 2004 was also M.9.0 and that it was associated with large tsunamis. The assumed level of tsunamis (a phenomenon commonly associated with earthquakes) at the Fukushima Daiichi Plant was inadequate. For example, the fuel tanks for the generators of Unit 1, which seem to have been swept away by the tsunami, were located near sea level, and were not protected from a large tsunami.

Delay of the Use of Sea Water to Cool the Reactors
As stated above, sources report that TEPCO discussed the possibility of cooling the reactor of Unit 1 using sea water as early as the morning of March 12, the day after the earthquake. Unfortunately, the decision to use the sea water was delayed until the evening of the same day, when the Prime Minister ordered TEPCO to do so after a hydrogen explosion occurred at Unit 1. The decisions to use sea water for the other two reactors were further delayed. Use of seawater did not occur until March 13 for Unit 3 and March 14 for Unit 2. The fuel pools were not filled with sea water until March 15, when an explosion and fire occurred at Unit 4. Because of these delays, the scale of the accident was amplified.

It is said that TEPCO initially did not want to use sea water, because the decision to use sea water would result in having to decommission the units. If this is true, it implies that TEPCO made profits their priority rather than the safety of people, and that NISA (Nuclear and Industrial Safety Agency) and associated bureaucrats and scholars supported TEPCO’s decision. This structure of decision-making is similar to the one used during the safety review about resuming the operation of the Kashiwazaki-Kariwa Nuclear Plant.

Delay in Public Information Disclosure
TEPCO has been slow in disclosing information about damage to various instruments within the nuclear plant. Disclosure of data about various parameters, which are critical to understanding the conditions of the reactors, has also been slow. To date, it still is not possible to obtain such information on a real-time basis. Disclosure of relevant information is extremely important not only for the people living in the affected areas but also for concerned scholars and engineers who can help predict what will happen and who can make relevant suggestions. For example, scholars could have advised that sea water be used at an earlier stage if the relevant information had been adequately disclosed.

Information about the amount of radioactive materials emitted is also limited. To date, no concrete estimate of the total amount of radioactive materials emitted has been published. Radiation measurements at the monitoring posts within the nuclear power plant site are not available on a real-time basis. Additional monitoring posts have not been set up. No permanent surveillance video cameras are available. The government should disclose the radiation measurement data at various monitoring posts inside and outside of Fukushima Prefecture, and simulate the results to predict the dispersal patterns of radioactive materials. As of today, this has not occurred.

Three local groups that are against the Kashiwazaki-Kariwa Nuclear Plant, as well as the Prefectural Residents’ Group to Protect Peoples’ Lives and Hometowns from the Nuclear Power Plant (Genpatsu kara Inochi to Furusato o Mamoru Kenmin no Kai) have requested that the governor of Niigata Prefecture, the mayors of Kashiwazaki City and Kariwa Village, and the president of TEPCO listen to their call to immediately stop the four units of the Kashiwazaki-Kariwa Nuclear Plant. We strongly support their demand.

We also support their claim that scholars who previously denied the possibility of nuclear power accidents should not be in charge of the safety review as members of the Prefectural Technical Committee. It is necessary to reorganize this committee and appoint new members. The new committee should consist of scholars who have raised concerns about the safety of nuclear power plants, engineers who are familiar with nuclear plants, and representatives of prefectural residents.

The Nuclear and Industrial Safety Agency and the Nuclear Safety Commission, both of whom have been in charge of the safety reviews of nuclear plants in Japan, are responsible for the current situation. The Japanese review system is inferior to the review systems of other countries, such as the US Nuclear Regulatory Commission. Since the scale of the earthquake that struck the Kashiwazaki-Kariwa Plant was much larger than originally assumed, the Japanese government carried out a review of all the nuclear plants within the country, including the Fukushima Nuclear Plants. The current “nuclear earthquake disaster” (genpatsu shinsai) at the Fukushima Plants revealed that the review was not thorough enough.

Scholars and Engineers of The Group of Concerned Scientists and Engineers Calling for the Closure of the Kashiwazaki-Kariwa Nuclear Power Plant have been working closely with local residents to examine the reliability of “seismic ground motion evaluation” and “seismic safety evaluation” of equipment. “Seismic ground motion evaluation”, which deals with natural phenomena, is not always reliable. Furthermore, “seismic safety evaluation” of human-made instruments is also unreliable due to many unknown factors. Using “the judgment of engineers,” the government and the electric power company dismissed the possibility of severe damage from an earthquake as unlikely, and resumed the operation of the Kashiwazaki-Kariwa Nuclear Plant. We have voiced our opinion that this decision was a mistake. The current “nuclear earthquake disaster” at the Fukushima Plants revealed that our concern was justified.

We will continue our efforts to prevent any future “nuclear earthquake disaster” in Japan.


Statement by Scientists and Engineers Concerning Fukushima Daiichi Nuclear Power Plant (no.2) (April 7, 2011)

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