TEPCO has posted an English translation of the hand-written records kept by the control room operators at Fukushima during the first few days of the emergency, from the March 11 until the unit #3 hydrogen explosion on March 15. We received a copy of the “TEPCO Fukushima Timeline” through another nuclear website (Nuclear Street). The “timeline” for each unit differs from the rest only in the duration of each report. To explain…the record for unit #1 ends at 4pm on March 12, an hour after it’s hydrogen explosion. The other three affected reactor plants have reports that continue until just after the hydrogen explosion on #3 refueling deck on March 15. While we do not have the complete record through the re-establishment of electronic record-keeping on March 19, we can at least begin to find definitive answers for some questions and resolve some misinformation.
- Did the earthquake cause any of the safety systems to malfunction, or in any way place the three operating reactor fuel cells in an unsafe condition?No! All three operating reactor systems had an automatic chain-reaction stoppage (SCRAM) within 1 minute of the earthquake tremors starting. All sets of emergency diesels for all units started automatically and were supplying power to their respective emergency systems. It seems the earthquake did knock out the transmission lines connecting the plants to the nationwide grid, thus there was a wide blackout outside of the Power complex. The diesels were kept the plant site electrified. All three operating reactors were being supplied with water using their Reactor Core Isolation Cooling (RCIC) systems. Control room records verify what we have postulated for months…the 9.0 earthquake did not cause the accident at Fukushima Daiichi.
- Did the operators shut off any of the emergency cooling systems before the tsunami hit, as reported by the news media, TEPCO, and the government?No. This was perhaps the first instance of poor, easily misunderstood communication with the world-at-large. Unit #1’s Isolation Cooling system was cycled on and off, by procedure, until the tsunami hit. The RCIC systems automatically shut down on units #2 and 3 because of high water level inside the RPVs. This was a design function of the system and occurred without operator action. The operators quickly restarted the systems on both units.
- If not the earthquake, what caused the Fukushima accident?The cause of the accident was a 45 ft. high tsunami inundating the operating diesel generators for units #1 through 4, resulting in a complete loss of all electrical power. A total station blackout, which the entire Japanese nuclear community thought to be impossible. The reactor core cooling systems all needed electrical power to operate. Even the high pressure, steam-driven coolant injection systems required power to operate the valves supplying steam to them. The Isolation Condensers (I/C), which turn the depleted steam from the pumps back into water, lost their sea water cooling flows. Plus, there was total darkness inside each power plant, making manual operations to get RPV cooling systems restarted extremely difficult. Control room operators used flashlights to monitor RPV conditions until emergency lighting, operated off the un-flooded batteries, was energized a few hours after the blackout began. There are no windows on reactor buildings, so they remained in total darkness.
With decay heat at the level of more than 20 megawatts inside each RPV when the tsunami hit, and severely limited capabilities to remove that heat, the RPVs rapidly heated and pressures went up. Some initial creative efforts to control the pressure build-up using battery power to get steam to high pressure pumps were successful in units #2 and 3. Unit #1 however, soon heated its I/C condenser to maximum, lost the ability to further cool the RPV and it’s pressure began to rise steadily. It was nearly two days before unmitigated pressure increases occurred in units #2 & 3. Regardless, the inability to stop the temperature and pressure increases in all three caused high pressure safety relief valves to open and dump steam into their respective suppression chambers (S/C)/torus. With inadequate injection systems to replenish the water lost to the relief valves being open, eventually the fuel cells inside the RPVs were no longer covered with water and melting of fuel ensued. The time-lines for each RPV were quite different, however.
- When did the reactor fuel cells become uncovered?Unit #1 records show that at 10pm (~6 hrs. post-tsunami) the water level in the reactor was more than 2 feet above the top of the fuel cell. Unfortunately, there are no further water level reports in the unit #1 operator records there-after, but it can be assumed that unit #1 fuel was uncovered a few hours later. Unit #2‘s water level dropped to the top of its fuel cell on March 14, at 5:17 pm. This was more than 70 hours into the actual tsunami-caused blackout. Complete uncovery and the onset of fuel meltage probably occurred after that. There was still a lot of decay heat, but many times less severe than was the case with unit #1, who’s core was probably uncovered ~10 hours after the full blackout began. Unit #3‘s RPV water level dropped to the top of the fuel cell on March 13, at 4:15 am. This was about 37 hours after the tsunami, with a decay heat level of more than 10 megawatts. Not as much heat production as unit#1 when it’s core began to uncover, but still enough heat to dry the fuel cell and begin meltage faster than with unit #2. Thus we see that unit#1 probably melted first, unit #3 second, and unit #2 last. It only follows that meltdown severity ought to be in the same order. Why TEPCO and NISA still say that unit #2 had the worst meltdown remains a mystery.
- Why didn’t the operators do something to keep the cores covered with water?They tried to keep the cores covered, but inadequate emergency power design and increasing radiation levels in the plant locations where operators could possibly get water to the core, prevented them from keeping the fuel cells covered. They did all they could, and some operating employees even allowed themselves to be over-exposed to radiation in the valiant attempt to recover reactor water level control.
- Valiant operators? What about all the news reports of the operators fleeing the plant property? What about all the reports of operator evacuations?This is yet another example of poor TEPCO and governmental communications. Here’s what actually happened. Each nuclear power plant complex in Japan has an “anti-earthquake” structure built to withstand all possible temblors. Plant staffs are trained to immediately, but calmly, proceed to the structure when an earthquake begins. This includes aftershocks and tsunami warnings. However, this does not apply to essential personnel who are operating plant systems. Only non-essential personnel are to proceed to the anti-earthquake building. As it turns out, essential control room and plant operating staff remained at their posts while all non-essential personnel went to the anti-earthquake building. There was no panic. There was no wild, full-scale evacuation of the power complex. Why TEPCO and the government agencies used the term “evacuation” is a bizarre mystery. No such thing happened at Fukushima!
- Why didn’t the operators vent (relieve the high internal pressures) sooner and perhaps avoid the disastrous hydrogen explosions?This aspect begins with unit #1, which was severely over-pressurized long before units #2 and 3. The plant manager ordered the operating staff to prepare for venting just after midnight on March 12, but the venting operation could not be started until it was confirmed that all residents within 3 km of the power complex had evacuated. The Prime Minister was advised of the necessity of evacuation by 9pm the previous evening, and the order for evacuation was issued soon there-after. By procedure, the high pressure could not be reduced by venting before evacuation had been confirmed! So, they prepared to vent unit #1, but had to wait. At 12:30 am, the government said evacuation of the 3km radius was complete. This was confirmed by the government at 1:45am. At 1:30am, the Prime Minister gave the plant manager permission to start venting after a press conference to announce the venting had occurred. The press conference was held at 3:06 am. However, some off-duty operators arrived at the Fukushima power complex and reported they had seen people in the town of Okuma. The government assurance of the evacuation was wrong! The plant manager could not begin venting until the entire 3km radius was abandoned, and that no longer seemed to be the case. The Prime Minister arrived at the nearby emergency center at 7am, demanding to know why venting had yet to occur. When told there were still a few people in the 3 km radius, he calmed down but ordered venting to begin as soon as evacuation was certain. At 9:03am, final confirmation of Okuma’s evacuation was verified, and at 9:15am the venting of unit #1 began.
Too little, too late. The above procedural delays had allowed pressures inside the Primary and Secondary Containments to raise way too high, and leaks occurred which sent considerable fission product contamination and hydrogen gas into the outer spaces of the reactor building. When the venting eventually began, it seems some of the gasses did not leave the system through the outside exhaust stack, but rather accelerated the leakage into the reactor building’s interior. The unit #1 hydrogen explosion occurred at 3:36pm.
Unit 2 and 3 operators found ways to temporarily cool their RPVs for dozens of hours after the unit #1 explosion, avoiding the need to vent. Damage caused by flying debris from the unit #1 explosion and resulting increases in radiation levels inside the #2 & 3 reactor buildings made preparations for venting units #2&3 considerably more difficult, after the need to relieve internal pressures was recognized.
We feel the seven answered questions above are the most important, at this point. We will share more in subsequent updates, but there is one item of current importance that begs immediate coverage…
- NHK World reports Prefectural governors across Japan have severely criticized the government’s proposal for administering “stress tests” on the idled nuclear power plants, and Prime Minister Kan immediately making the tests mandatory before considering restarts. NISA says the testing will follow the recent proposal made by the IAEA, but could give no details on what the tests will entail or how they might be administered. The Nuclear Safety Commission says they might have details for everyone in a week, but distrust among the governors abounds. The governors basically don’t trust the government’s sudden announcement. Saga Governor Furukawa says he cannot understand why the government made its proposal just when he was about to decide on restarting Genkai units #2&3. The governor’s criticism seems to imply that the “stress test” announcement may be a poorly-planned political ploy.