Three sources which partially track the performance of the Fukushima Diiachi ECCS

In the previous post I quote the NRC account of the Emergency Core Cooling System controversy of the late 1960s and 1970s. To quote a small but major point from that account: “Once it became apparent (to the AEC) that under some circumstances the containment building might not hold, however, the key to protecting the public from a large release of radiation was to prevent accidents severe enough to threaten containment. And this depended heavily on a properly designed and functioning ECCS.“

And from the NRC technical manual on the BWR Mk 1- 3 in an earlier post, it is seen that the Fukushima Diiachi type reactors are fitted with 2 systems which comprise the ECCS. One of these, at least, uses an integral steam driven turbine to power a pump which provides water to cool the core. The three reactors at Fukushima Diiachi had ECCS systems which were self powered. They did not require any external connection to anything in order to work to keep the core cool. Why then did the ECCS, given the role of protecting the core and hence of protecting and maintaining containment integrity, fail to work? If the AEC determined the role of the ECCS was to ensure containment, then given that containment failed, it follows that the ECCS failed to fulfill its role of ensuring containment integrity. At least within the concepts of the AEC at the time the first Fukushima Diiachi unit was under construction.

The World Nuclear Association has a brief description of the ECCS functioning at its website here:

The ECCS of the reactors are described in a brief account of events, selectively quoted as follows (see the webiste for the full description of that organisation)

Quote: “It appears that no serious damage was done to the reactors by the earthquake, and the operating units 1-3 were automatically shut down in response to it, as designed. At the same time all six external power supply sources were lost due to earthquake damage, so the emergency diesel generators located in the basements of the turbine buildings started up. Initially cooling would have been maintained through the main steam circuit bypassing the turbine and going through the condensers.

Then 41 minutes later the first tsunami wave hit, followed by a second 8 minutes later. These submerged and damaged the seawater pumps for both the main condenser circuits and the auxiliary cooling circuits, notably the Residual Heat Removal (RHR) cooling system. They also drowned the diesel generators and inundated the electrical switchgear and batteries, all located in the basements of the turbine buildings (the one surviving air-cooled generator was serving units 5 & 6). So there was a station blackout, and the reactors were isolated from their ultimate heat sink. The tsunamis also damaged and obstructed roads, making outside access difficult.”

“When the power failed at 3.42 pm, about one hour after shutdown of the fission reactions, the reactor cores would still be producing about 1.5% of their nominal thermal power, from fission product decay – about 22 MW in unit 1 and 33 MW in units 2 & 3. Without heat removal by circulation to an outside heat exchanger, this produced a lot of steam in the reactor pressure vessels housing the cores, and this was released into the dry primary containment (PCV) through safety valves. Later this was accompanied by hydrogen, produced by the interaction of the fuel’s very hot zirconium cladding with steam after the water level dropped.

As pressure started to rise here, the steam was directed into the suppression chamber under the reactor, within the containment, but the internal temperature and pressure nevertheless rose quite rapidly. Water injection commenced, using the various systems provide for this and finally the Emergency Core Cooling System (ECCS). These systems progressively failed over three days, so from early Saturday water injection to the reactor pressure vessel (RPV) was with fire pumps, but this required the internal pressures to be relieved initially by venting into the suppression chamber/ wetwell. ”

“In unit 2, water injection using the steam-driven back-up water injection system failed on Monday 14th, and it was about six hours before a fire pump started injecting seawater into the RPV. Before the fire pump could be used RPV pressure had to be relieved via the wetwell, which required power and nitrogen, hence the delay. Meanwhile the reactor water level dropped rapidly after back-up cooling was lost, so that core damage started about 8 pm, and it is now provisionally understood that much of the fuel then melted and probably fell into the water at the bottom of the RPV about 100 hours after the scram. Pressure was vented on 13th and again on 15th, and meanwhile the blowout panel near the top of the building was opened to avoid a repetition of unit 1 hydrogen explosion. Early on Tuesday 15th, the pressure suppression chamber under the actual reactor seemed to rupture, possibly due to a hydrogen explosion there, and the drywell containment pressure inside dropped. However, subsequent inspection of the suppression chamber did not support the rupture interpretation. Later analysis suggested that a leak of the PCV developed on Tuesday 15th.

In Unit 3, the main back-up water injection system failed at 11 am on Saturday 12th and early on Sunday 13th, water injection using the high pressure system failed also and water levels dropped dramatically. RPV pressure was reduced by venting steam into the wetwell, allowing injection of seawater using a fire pump from just before noon. Early on Sunday venting the suppression chamber and containment was successfully undertaken. It is now understood that core damage started about 9 am and much or all of the fuel melted on the morning of Sunday 13th and possibly fell into the water at the bottom of the RPV, or was retained on the core support plate within the shroud.”

There is then a brief description of functioning ECCS in three of the reactors. The ECCS operated in each reactor for a period and then failed. By some means which is not explained.

As a result of the Ergen Report of 1967, the short form of the AEC’s view might be translated so as to mean this:

“So long as there is a functioning ECCS in a stricken reactor, there is some hope that containment integrity might be contained.” This is how I interpret the decision of the AEC to focus on the ECCS as a means of maintaining containment.

To read that the ECCS did function in all three stricken reactors is heartening until you get to the bit where World Nuclear writes that they all failed. For some undisclosed reason. For the AEC requirement was that the ECCS must remain functioning so long as an emergency need to remove decay heat from the core remains.

The Wikipedia timeline for the disaster provides a detailed listing of the events which took place around and within the reactors.

Again, due to the length, I am taking selected portions only from this site. See the link for the full account.

Friday, 11 March
14:46: A 9.0 magnitude earthquake strikes off the coast of Honshu Island at a depth of about 24 kilometres (15 mi). The Fukushima I power plant’s nuclear reactors 1, 2, and 3 are automatically shut down by the tremor. Nuclear reactors 4, 5, and 6 were undergoing routine maintenance and were not operating, (reactor 4 was defueled in November 2010). The tremor has the additional effect of causing the power plant to be cut off from the Japanese electricity grid, however, backup diesel generators kick in to continue cooling. Tokyo Electric Power Company (TEPCO), the plant’s operator, finds that units 1 and 2 are not operating correctly and notifies the proper officials.[3]
14:52: Reactor 1’s emergency cooling system, which is capable of running without external power, turns on automatically.[4]
15:03: Reactor 1’s emergency cooling system is manually shut down.[4]

15:27: The first tsunami strikes the plant.[5]
15:30: The emergency condenser designed to cool the steam inside the pressure vessel of the No. 1 reactor fails.[6]
15:46 (approximate): A 14-metre (46 ft) tsunami, unleashed by the earthquake, overtops the seawall designed to protect the plant from a tsunami of 5.7 metres (19 ft), inundating the Fukushima facility and disabling the backup diesel generators – all but one of which were housed underground – and washing away their fuel tanks.[7] With the loss of all electrical power supply, the low-pressure core spray, the residual heat removal and low-pressure coolant injection system main pumps, and the automatic depressurization systems all failed (most of the emergency core cooling system). Only the steam-powered pump systems (isolation condenser in reactor 1, high-pressure coolant injection and reactor core isolation cooling system in reactors 2 and 3) remained available. Later, as the temperature rose, a system started that used steam-powered pumps[not in citation given] and battery-powered valves.[8][9]

18:00: The falling water level in reactor 1 reaches the top of the fuel, and the core temperature starts climbing.[13]
18:18: Reactor 1’s emergency cooling system is once again back on.[4

19:30: The fuel in reactor 1 becomes fully exposed above the water surface, and fuel damage in the central core begins soon after.[13]

Saturday, 12 March

Overview map showing evacuation and other zone progression and selected radiation levels.
02:44: Emergency battery power for the high pressure core-flooder system (HPCFS) for reactor 3 runs out.
04:15: Fuel rods in reactor 3 are exposed.

15:36: There is a massive explosion in the outer structure of unit 1. The concrete building surrounding the steel reactor vessel collapses as a result of the explosion; however no damage is believed to have been sustained to the reactor itself. Four workers are injured.
19:00: Sea water injection into reactor 1 is started. TEPCO orders Daiichi to cease seawater injection at 19:25, but Daiichi plant boss Masao Yoshida orders workers to continue with the seawater injection.[13][17]

Sunday, 13 March
02:42: The high pressure coolant injection system for reactor 3 stops and, shortly thereafter, the water level within the reactor starts falling.[18]
07:00 (approximate): The water level in reactor 3 reaches the top of the fuel.[18]
09:00: Core damage starts occurring in reactor 3.[18]
A partial meltdown was reported to be possible at unit 3.[19]

Monday, 14 March
11:01: The unit 3 reactor building explodes, injuring six workers.[23] According to TEPCO there was no release of radioactive material beyond that already being vented, but blast damage affected the water supply to unit 2.[24]
13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.[18]
15:00: A major part of the fuel in reactor 3 drops to the bottom of the reactor pressure vessel.[18]
18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.[18]
20:00: Core damage starts occurring in reactor 2.[18

Tuesday, 15 March
11:00: A second explosion of reactor 3 (according to The World Meteorological Organization report)
20:00: A majority of the fuel in reactor 2 drops to the bottom of the reactor pressure vessel.[18

An explosion in the “pressure suppression room” causes some damage to unit 2’s containment system.[26][27]

end quote.

The third source which mentions the ECCS is IEEE Specturm at

Core Cooling System Working at Two Fukushima Reactors

The relevant quote from this article states: “Yoshinori Moriyama, deputy director-general of the Nuclear and Industrial Safety Agency (NISA) and in charge of nuclear accident measures, told the foreign press on 7 September TEPCO has begun using another cooling system the “core spray line” of the No. 3 reactor to help bring the temperature down in that unit. The core spray line is a part of the Emergency Core Cooling System (ECCS), a collection of sub-systems that can be called on in emergencies to cool a reactor when normal cooling operations are lost. It’s being used is in addition to the feed water line system currently cooling all three reactors.
Until the core spray line was put into operation on 1 September, the reactor’s core was cooled by rising steam from the bottom of the pressure vessel supplied by the feed water line. With the addition of the core spray line, water is now being pumped into the core spray ring header situated above the core causing water droplets to fall onto the core and cool it directly. As it has increased the amount of water pumped through the core spray line, TEPCO has been reducing the amount of water used in the feed water line. Right now, the latter is maintaining a flow of 4 cubic meters and hour, while the core spray line is maintaining a flow of 3 cubic meters/h.
The core spray line could not be used until recently because TEPCO first had to survey the pertinent piping and valves of this subsystem, both inside and outside the reactor building, to see if they were still operable. Given the high radiation in the area, this was difficult, but workers completed the job in July. After the system’s feasibility was confirmed in August, workers attached a temporary hose connection to the core spray line using a make-up water line and began pumping.”

The ECCS for each of the stricken reactors failed by some mean or another. This is in keeping with the radiation fears held by the AEC in 1967.

The mass media has avoided the mention of the ECCS, and while other factors are in play, it is clear that the containment system is related to ECCS. And that the ECCS in place at the time were insufficient to prevent containment breach.

The controversy over the ability of reactor ECCS in the late 1960s and 1970s seems to have resulted in one accurate prediction. Where the ECCS fails or fails to operate, containment follows. The fear first expressed in the commissioning of the Ergen report and later expressed by critics of the AEC and of ECCS design are borne out in the fact that the ECCS of all three reactors had failed by day 3.

The World Nuclear Organisation mentions failure of ultimate heat sink. The requirement of an ECCS is one in which containment is maintained by designed in reliability for as long as required. This failed to happen in March 2011.

The Wikipedia timeline gives the reference which documents the reason for the switch off of the Reactor 1 ECCS as which is “JAIF Earthquake Report No. 91: 18:00, May 24 NHK news regarding status of Fukushima Daiichi nuclear power station yesterday and today.” which states that “The operator of the Fukushima Daiichi nuclear power plant is still unable to
determine how long an emergency cooling system at the Number 1 reactor
remained off after the March 11 earthquake.
Officials of Tokyo Electric Power Company spoke to reporters on Tuesday about
the system, which can function without external sources of power.
Operating records at the plant show that the system turned on automatically 6
minutes after the earthquake, at 2:52 PM, and halted 11 minutes later, at 3:03 PM.
The system was back on more than 3 hours later, at 6:18 PM.
TEPCO says that based on hearing from workers, it has confirmed that the
system was manually shut down at 3:03 PM.
It said this step was made based on a manual, in order to prevent damage to the
reactor, because the temperature of the water to cool the No.1 reactor had
dropped sharply.
TEPCO says the system may have been turned on in the 3 hours until 6:18, but
that it cannot clearly determine the course of events based on studies of circuits
and interviews with workers.
The utility firm says at this point it cannot determine to what extent the
emergency system was functioning, and that it will continue investigating.
The firm also said that data taken in the 30 minutes after the earthquake show no
irregularities in all safety features of the Number 1 to 3 reactors such as
emergency power sources and in major facilities of the plant. ”

In any event, had the ECCS in all units remained operational, no core overheating would have occurred.

But that is not the case. All ECCS failed by the third day. The ECCS is required to function for as long as
needed. The reasons why the ECCS failed needs to be comprehensively explained in plain language.

Had the ECCS worked over the entire period it was required, no core overheating would have occurred, no hydrogen would have been generated, no explosions would have occurred, no massive radionuclide leak and no extraordinary conditions would have threatened the spent fuel pools, for any loss of coolant in them could have been replaced with the hazards posed by the broken reactors. The fire in spent fuel pool 4 would not have occurred. An accurate narrative is required to describe the ECCS failure. The ECCS failure is a threat faced by every nuclear reactor everywhere.

The narrative which relies on the loss of power and the flooding of the diesel generators is insufficent because ECCS does not require external power.

If the failure of the ECCS is related to loss of ultimate heat sink, it needs to be explained clearly. And if that is the case, regulators around the globe need to explain why it is that that the ECCS which is supposed be fully independent and self contained, got knocked out by the same event chain which caused the invocation of the ECCS in the first place. It is totally useless to design and instal an ECCS which is killed by the event which requires ECCS to prevent disaster. Is this is the case, then the whole history of reactor safety design since 1967 has been a crock and mere sales blurb.

One Response to “Three sources which partially track the performance of the Fukushima Diiachi ECCS”

  1. CaptD Says:

    I believe that TEPCO and the other nuclear groups like the IAEA had way too much time to “rig” the logs to make it look like the earth quake did not cause the triple meltdown!

    Consider these articles
    The Loss of Coolant risk in reactors and the urgent call for a “technical fix” that never came.
    Fukushima nuke disaster investigative panel rejects TEPCO tsunami claims

    The final report released by the Diet’s Fukushima nuclear disaster investigative panel has concluded that factors other than the tsunami may have triggered the loss of power at the plant, which aggravated the unprecedented disaster.

    (+ my comment there)
    A Great Article…
    I agree, the Tsunami was not the main reason for Fukushima’s triple meltdown, despite the nuclear industries desire to make it appear that the Tsunami was the problems because to say otherwise would call into question THE SAFETY ALL LAND BASED REACTORS…

    FUKUSHIMA proved that Nature can destroy any land based nuclear reactor, any place anytime 24/7/365!

    THIS IS WHY >90% of the Japanese People are against nuclear, they cannot afford to RISK yet another Fukushima, or having their electric bill go up another 10+% like it recently just has!

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