Since the Fukushima accident, the abbreviation IC, which had commonly referred to transistor integrated circuits, has come to be also used to indicate the emergency core cooling equipment.

IC comes from the first letters of the term “isolation condenser.” This structure cools steam travelling through tubes from the reactor with water in a tank outside the containment vessel. The steam is reverted back to water form and returns to the reactor. This is safety equipment that utilizes a natural effect and was employed on the initial BWRs.

Its shortcoming is that the equipment is not capable of actively cooling steam on account of the process of natural circulation, and it has become obsolete as safety designs have become more sophisticated.

The IC was even fitted on the Japan Power Demonstration Reactor (JPDR) of the Japan Atomic Energy Research Institute. The manner in which it initially cooled was intense with the cooling rate said to be several times the limiting value.

At Fukushima as well, the cooling status immediately after the IC began operating exceeded the limiting value, so it was turned on and off manually. This suspension has been blamed in the media as the cause of the failure of emergency cooling, but this criticism is inappropriate.

Immediately after the IC starts operating, the temperature inside the tank is low, so the IC is able to provide considerable cooling. In addition, there is some amount of condensation inside the tubes to begin with, so cool water is injected all at once, exceeding the cooling limit rate for the pressure vessel.

Parenthetically, the temperature of the reactor pressure vessel is almost the same as that of the steam, approximately 300 degrees Celsius. When a cool water mass enters, parts of the vessel are rapidly cooled. The cooled surface attempts to contract, but the entire warm vessel is not able to, so a discrepancy (force) arises here. When this force is considerable, cracks or fractures form on the thick vessel. This is intolerable, so a limiting rate has been set to cool the pressure vessel slowly.

Right after the earthquake, no one imagined that a huge tsunami would hit and an accident would occur. At the startup of the IC, it is not surprising then that the cooling rate would be monitored and the valve operated.

The problem arose later, after the tsunami struck. The valve, which was designed to be failsafe, closed automatically when its power source was lost, disabling IC cooling.

According to the interim report of the government’s Investigation Committee on the Accident, DC power was temporarily restored at around 18:00. The shift operator realized that IC operation was possible and opened the valve. However, since the cooling function was weak, the valve was closed once again. By contrast, Emergency Headquarters, which was in a separate building, mistakenly assumed that the IC continued to operate.

Perhaps this difference in perception concerning the IC was considered a factor delaying implementation of alternative coolant injection and venting, which led to an escalation of the accident at the Unit 1 reactor, as the report devotes 34 pages on the matter.

Differences in understanding were likely to exist under such circumstances. However, the principal causes of the venting delay were the verification of resident evacuation status and the visit to the site by former Prime MinisterKan. On top of that, alternative cooling is handled by different personnel. The report goes too far in shifting the question toward the IC. This shift has resulted in a lack of balance overall in the review of the accident and irregularities observed in the investigation. In addition, there is insufficient understanding of the actual situation on site where the disaster occurred and a slight distortion toward armchair judgments.

On site, there was literally nothing to work with as the station had been overrun by tsunami and had fallen into a severe state with total darkness, nonexistent signals, reoccurring aftershocks, scattered debris and a loss of electric power. In such a situation, could anything have been accomplished flawlessly?

TEPCO workers who were on site do not talk about that time of their accident management for fear of being singled out for inconsistencies in their testimony or lapses in memory. They are afraid of being criticized for making false statements. People involved in nuclear power such as myself have been excluded at the will of Prime MinisterKan and are not able to lend a helping hand. The result has been annoyance that the inquiry into the cause of the accident has not proceeded in a perspicuous manner as hoped.

The line “the horses do not stir, the men do not speak” from the poem by General Nogi recollects the desperate battle at Lushun (Port Arthur) which lacked any fundamental perspective of the entire situation. I hope that the investigation into the accident focuses on a bigger picture so that all Japanese technology is not twisted around and disparaged as being “hills, river, grass, trees, truly desolate, a ten mile stretch” with nothing that can be done for nuclear power as it stands “in the slanted rays of the setting sun.”

Returning to the topic, why was the IC shut down a failsafe measure? If the tubes break, steam carrying radiation would be released. The isolation valve closed so as to prevent that from happening. When the valve closes, cooling is lost.

Between such conflicting demands, closing the valve was prioritized. The hope of keeping a radiological accident from happening in Japan with its limited land space was too obstinate.

Although it is a difficult issue, “confining” should come after “cooling”. One could say that the failure was the result of the hope to prevent radiation release being held too strongly and prioritized over engineering logic.