UPDATE 4 - Third Explosion Reported at Japanese Nuclear Plant, Radiation Readings Rise and Damage to Pressure-Suppression System Feared

UPDATED 8:06 P.M. -- Multiple news agencies on Friday evening reported a third explosion at the Fukushima Daichi nuclear plant, this time at unit 2.

Kyodo News, quoting Japan's Nuclear and Industrial Safety Agency, reported that the reactor's pressure-suppression system may be damaged.

Elevated Radiation readings of 8,217 microsievert per hour were recorded near the plant, per a Tepco announcement reported by Kyodo.


UPDATED 9:18 a.m. -- Tokyo Electric Power confirmed that fuel rods in its Fukushima Daichi unit 2 reactor recently were fully exposed to air, which makes it the the third reactor at the company's plant facing potential core damage.

Tepco reported the reactor's coolant boiled off after a fire pump injecting seawater into the core ran out of diesel, according to Kyodo News. Four of five fire pumps were feared to have been damaged after an explosion at neighboring unit 3 last night.

This morning, Tepco reported it had raised the water level in unit 2 to cover half length of the fuel rods, according to a Reuters report shortly before 9 a.m. The status of water injection into unit 1 and unit 3 remained unclear following the earlier blast, which reports indicated injured 11 but did not damage core containment.


Japan endured not only a magnitude 8.9 earthquake Friday but also emergencies at several reactors over the weekend following station blackouts – one of the most challenging types of emergencies a nuclear plant operator can face.

Fukushima Daichi power plant, Photo: TepcoAs of Sunday night, steam venting and other efforts to cool six reactors at Tokyo Electric Power Company’s Fukushima plants seemed to avert catastrophic core damage or radiation releases.

Japan Atomic Power Company reported a cooling system pump failed at the Tokai No. 2 nuclear plant 75 miles from Tokyo Sunday, but later made assurances that backup cooling systems were operational and core temperatures were receding.

While cautioning that the situation at Fukushima was still “touch and go,” Mark Hibbs of the Carnegie Endowment for International Peace told Reuters that plant operators "appear to be having enough success to have forestalled a definite core melt accident that's difficult to control."

Tepco reported it was pumping seawater and boric acid into reactor units 1 and 3 of the plant (pictured). As officials predicted might happen, an explosion was reported at unit 3 late Sunday similar to the explosion Saturday that damaged unit 1’s reactor building. Both explosions damaged outer buildings at the plant but not primary reactor containment, according to Tepco. Experts surmised the first blast was caused by a buildup of hydrogen created by water contacting damaged fuel cladding. Media reports indicate that fuel rods at both reactors were exposed to air for a period of time, and partial fuel damage remains a possibility for both units.

At the neighboring Fukushima Daini plant (“daichi” means “one,” “daini” means “two”) Tepco said Sunday night that water levels were stable and backup power was available to its reactors. While the plant grappled with earlier power failures, the company indicated it had prepared all four reactors for irradiated steam releases to alleviate coolant pressure.

The reactors in question are all General Electric Boiling Water Reactors (BWRs) brought online between 1971 and 1986. All reactors currently installed at Fukushima Daini are of the BWR-5 design. One reactor at Fukushima Daichi is a BWR-5. Four are BWR-4s. Unit 1, which seems to have sustained the most damage, is a 439-megawatt BWR-3. It is also the oldest reactor at the plant and was scheduled to be taken out of service this Saturday, March 26th.

Fukushima Daichi's reactors feature Mark 1 containment systems (pictured).GE Mark 1 containment, image: NRC

Outside the plant, as many as 210,000 people living within a 20 kilometer radius of Fukushima Daichi were evacuated as a precaution. Radiation levels fluctuated over the weekend, and Kyodo News reported the maximum level of radiation observed near the plant was 1,557.5 microsievert. Normal background radiation exposes most people to about 1,000 microsievert per year.

In a vaguely worded release, Tepco indicated that two workers had been taken to the hospital with injuries directly following the earthquake. Later, one employee and a subcontractor were immobilized for unnamed reasons and taken to the hospital. Radiation readings for a Tepco employee working inside the reactor building exceeded 100 microsievert and he or she was taken to the hospital, while two others working in the control room reported feeling ill. After the explosion at unit 1, four workers were taken to the hospital.

Separately, Tepco reported a crane operator “trapped in the crane operating console of the exhaust stack was transferred to the ground at 5:13PM and confirmed the death at 5:17PM."

Japan's Nuclear and Industrial Safety Agency reported that nine residents evacuated by bus tested positive for elevated radiation levels, and Reuters reported as many as 190 may have been exposed to excess radiation.

 - Read previous Nuclear Street coverage of the Japanese earthquake

- Download the Nuclear Regulatory Commission’s “BWR Systems Reactor Concepts Manual”

- Download TEPCO’s “Tsunami Assessment for Nuclear Power Plants in Japan”

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  • Anonymous

    question as a engineer

    IF the ground acceleration sensors via software are used to automatically put the plant into "shutdown sequence" (insert rods into core etc), why was the excess heat needing to be removed over the next ~3 days not used to run the turbines which can be used to generate the electricity required to run the

    pumps to do the cooling?????? THESE ARE POWER SOURCES...Why does the author (and most articles I've found) suggest "shutdown sequence" (always) means the energy supply to the turbines, then to the generators, then to the pumps, is immediately terminated??? Damage to the "grid" load should not disallow the plant to continue generating electricity to run the pumps to maintain the water circulation critical to cooling the core and keeping the process "under control" until it can be safely shutdown/cooled.

    Note all the subsequent troubles (venting, H2 explosions, etc) would likely not have happened had the cores not been allowed to overheat in the first place.

    Seems pretty silly instead to rely on "backup generators" and batteries (which are obviously not that reliable) to do this (OR using some apparently external energy source to pump seawater through the core to cool it down...which understand renders the reactor unusable) when the heat that can be the source of catastrophe (rod melting) could instead be used as a source of energy to do the cooling required to avoid catastrophe (rod melting).

    Maybe I'm missing something but with all the $ spent on designing these installations and all the "experts" paid to do the system designs (and now talking all over the TV), how is is that nobody apparently has or is even today addressing this fundamental question/option. Obviously, this option would only be practical if the core-turbine coolant loop integrity remained intact but I've not heard anyone yet suggest this has been an issue at any of the plants in/around Sendai.

    Intelligent facts seems to be hard to come by but seems IF I were running one of those plants in the last few days and was faced with what I've been able to piece together, I would have proposed over-riding the turbine shut down and letting the turbines generate the electricity to run the pumps to cool the reactor now needing to be cooled as it "shuts down".

    I tend to believe nuclear will inevitably need to play a major role in our efforts to significantly reduce dependence on fossil fuels HOWEVER I also realize there are significant safety risks that need to be addressed (short term in fission systems and longer term migrating to fusion systems) in smart ways.

    Most of all, since large numbers of people are put at risk by these systems, full and prompt transparency of information (by both private and public sectors) must be mandatory (and has not been happening in Japan nor did it at 3-mile Island nor did it during the BP oil well disaster last summer).

    Rather than the media scaring the crap out of everyone by continually using the term "meltdown" for 3 days (and not chasing down "identified authorities" and really grilling them re facts/options/decision making), I'd appreciate it if the author and anyone else with a real grasp of the facts can help us by explaining why the apparently simple solution response described above was not implemented at these installations immediately after they went into "shutdown sequence".



  • Anonymous

    SteveG, after the reactor is shutdown, power output drops off quickly (3GW to 50MW in an hour, IIRC).  That isn't sufficient to drive the main turbine, and attempting to do so would make the reactor hard to control.  Plus, if the main steam line ruptures from quake damage, you wind up with a big mess that would under most circumstances (ie Diesel backup is working) be unnecessary.  Besides, there is another system, the reactor core isolation cooling (RCIC) that uses decay-heat generated steam to drive a turbine to directly pump coolant.  It is unclear to me (not that I'm an expert) why the RCIC failed or was insufficient on the three reactors that are in trouble (apparently it was working on unit #2 until today).  Probably the pressure was too high, but that doesn't explain how the pressure got out of control in the first place (too much time between loss of diesels and starting up the RCIC?)

    The "unreliable" backup generators are actually pretty reliable as a group--when they are not all simultaneously wiped out by a tsunami.  Apparently the design of the plant assumed a maximum tsunami height, and this quake exceeded it.

  • Anonymous



    Thanks for your reply however several followup questions/commments;

    From your comment understand there IS supposedly a feature designed in (in case of shutdown) to utilize excess heat to generate power to run the cooling pumps (preventing all the subsquent problems due to core over-heating).  In this case appears neither of us has any info as to why this feature did/has not performed as intended.

    Re your comment that upon "shutdown" electrical output dropped, understand when the "grid load" was removed there needs to be an adjustement to the generator apparent load however the generator powered IF still powered by excess core heat via turbines should have plenty of capability to power the pumps in place to recirculate the cooling water for the core.

    From what little I've learned ot this in the last days, seems obvious that one of the critical design paramenters is to assure under any "shutdown" conditions that the system has effective capability to utilize excess core heat to independently get the "core cooled down".  

    In this case for some so far unexplained reason, this did not happen.....a clear failure in either system design OR operating decision-making.

    IF the system design ONLY relied on backup diesel generators, all those responsible failed.

    I'd still like to hear from those "in the know" (obviously the "media" has not been up to the task) to explain how these silly system designs failed to get themselves to a safe cool mode without dependence on "the grid" or silly solutions such as backup generators or backup batteries.

    Think of this:  its only when crises like these occur we can clearly challenge events/decision making.  If when these occur, answers are lacking, incomplete, or don't make sense why should anyone trust our governments to assure common sense considerations and measures are in place (on other OR propsosed new installations).

    On the other hand, IF operator error is the Root Cause, shouldn't we all be aware of that and have the opportunity to assure the right measures are taken going forward to assure it won't happen again????


  • Anonymous

    The RCIC is a pump directly driven by a steam turbine; there isn't any electrical generation in that system.  I assume that there was damage to the RCICs from the tsunami just like the diesels, or possibly the site was so generally messed up (both people and equipment) after the tsunami that it took too long too get them online, and the pressure rose too high for them to be effective.  That is just speculation; we won't know for weeks or months, probably, what the full sequence of events was.

    I'm not sure what is "silly" about the backup generators.  They are redundant, reliable, and would not have been a problem if not for an unanticipated common failure mode--an improbably large tsunami (a failure of site planning).  That said, nobody likes having active components in the safety system, which is why Gen III+ designs feature natural circulation and other enhancements to safety.

    There will be a lot of lessons learned from this, just as there were in prior accidents.  I just hope the industry gets a chance to apply them and isn't shut down by the inevitable (and already beginning) knee-jerk reactions.  Maybe some good will come of this--an accelerated plan to build Gen III+ and Gen IV plants and retire these older designs.

  • Anonymous

    I can only pray for the people of Japan.....such a horrid tragity....one caused by mother nature and the other by man....God help us all

  • Anonymous

    It is understandable to me that some local backup power systems onsite would fail to function after the tsunami.  But I am shocked that plant operators were unable to connect mobile backup generators to their emergency cooling system power grid during the multi-hour grace period provided by the functioning backups (batteries from what I understand).  If the cooling systems really did fail only due to lack of power (and not due to local structural damage), then I think this procedural oversight more than any other should be held responsible for the resulting events.

    The hydrogen gas explosions are also troubling to me.  Hydrogen gas is a known byproduct in these situations, and as such i would have expected a better mechanism to exist for safely venting the volatile gas.  But so far these reactors are 2 for 2 as far as catastrophic hydrogen explosions are concerned.  The first reactor was apparently lucky enough to escape the first explosion without damage to the containment system, but the third reactor does not appear to have been that lucky, and they now think the explosion damaged a piece of the cooling system which may effectively have created a containment breach.  I am surprised at the lack of capability to deal with hydrogen gas byproducts safely.  It appears that the containment system was designed to handle a meltdown, but not hydrogen gas... and therefore the system may handle neither.

  • Anonymous

    Anyone else out there familar with AT&T's Long Lines program and its plans to survive a nuclear attack during the Cold War? Well, they had telecommunications systems buried deep in bunkers designed to withstand a nuclear blast and EMP and I presume, these suckers were also watertight as they were air-tight. Their power sources were large diesel-powered 225 kW generators . . . now, I bring this up because it would seem prudent to have similar generators at all nuclear power plants located in secure areas that were water-tight and otherwise not likely to be affected by tidal waves, floods, and earthquakes. You can make large devices pretty safe against shock by mounting them on springs—this is what these AT&T bunkers had.

    In Katrina, remember a whole hospital lost power because their back-up generators were in the basement and were flooded. Don't people consider when planning aux systems placing these systems in diverse locations around their facility and really securing at least of them?

  • Anonymous



    Again thanks for your prior comments/reply.

    To cover for short term power interruptions (eg, hours) , I can understand the value of redundant diesel generators and batteries.  

    All I meant by "silly" is that when a signficant natural disaster occurs around one of these installations, relying on "short term backup features" such as diesel generators or batteries (vs systems that utilize the residual cooldown head in the core as long as its avaiable) to provide energy to assure cooling to the core is maintained (pumping water, etc) seems "silly".

    I'm sure these generators and batteries are relatively reliable on a short term basis (hours) presuming they aren't subject to incapacitation due to flooding etc (which it appears they were in this case), however to totally depend on them for days to assure the core is safely and reliably returned to ambient temperature it just seems "silly" to me especially when the core itself at the point of "shutdown" holds more than enough energy (in the form of heat) to power a water circulation system long enough to return the core to a safe temperature without huge risk due to running out of diesel fuel etc.

    You seem to acknowledge there WAS an RCIC feature in each of these reactors that SHOULD have avoided the core overheating during the "shutdown" sequence..   The failure to cool the core has caused all the subsequent problems (venting to atmosphere, core damage, H2 explosions, fires, etc.  Obviously, the RCIC feature must be able to reliably function during an "emergency shutdown" (not  dependency on fancy controls sytems etc that can easily be incapacitated during various emergency conditions).

    For whatever reason (I've seen no info on this), seems the RCIC on at least four (4) reactors has failed to function as intended AND the back up to those (the generators and batteries) have also failed to get the job done.

    Somehow those responsible for the these installations need to take much more seriously the responsiblity to assure capability to safely cool the core to ambient after a "shutdown command" is not lost due to natural conditions OR system failures.


  • Anonymous

    One of the issues is that GE BWRs were designed with lots of valve problems.  For example, the safety valve that admits steam to drive auxillary turbines and their attached pumps (intended to put emergency cooling water into the reactor) were found not to open reliably in some cases (by me, actually) due to "hydraulic lock" in the bonnet of the gate valves.  They failed to have a way to remove condensate (water) that collects in the bonnet due to heat transfer while the valve is closed.  When they try to open the valve, the disc cannot move because of the water on the bonnet of the valve.  Simple solution is to drill a hole in the upstream disc for some designs.  That would allow the bonnet to drain.  Testing the valve does not always result in the effect for different reasons, but if one waits long enough between openings or if they remove the thermal insulation on the bonnet, the condensation can be controlling.  So, even if we wish for turbine driven pumps that can use the residual heat/steam from the core, having them work right is another matter, testing and technical specifications not withstanding.

  • Anonymous

    @Charlie Jones


    Sounds like you're got some first hand knowledge of GE BWRs and some of the potential root causes for the present mess at Fukushima Dai-ichi.  Thanks for sharing it.

    Pretty sad to think a situation like this might have been averted by something as simple as more reliable valves.

    Wonder how often the RCIC systems are test or if FMEAs (Failure Modes Effects Analysis) were ever done on the RCIC system for BW nuclear reactors?

    If so, wonder what the records show for the reactors at Fukushima Dai-ichi (bet the public will never know).

    One thing that still amazes me is the fact that there were at least 4reactors running (of the 6?) at this site when the quake occurred that all got out of control simply due to failure of the RCIC system to safely cooldown the core after a "shutdown" command was issued.


    ps_saw some guy on TV tonight that claims he was a Project Manager for GE re BWRs and quit his job re safety concerns he  claimed were being ignored.

  • Anonymous

    Charlie, how big (in terms of power) were the generators needed to feed the emergency cooling system? Do you know? Why didn't they simply replace them? (in a country like Japan finding big generators shouldn't be a problem!!)