Fukushima: Lessons Learned (Part Three)

Flying Blind

The incoming tsunamis, much larger than planned for, had destroyed back-up electrical generation capability when the diesel generators were swamped and electrical switch gear wetted.  Electricity was vital in order to monitor the conditions within the reactor vessels and to take actions to prevent a catastrophic event.

Plant personnel were now faced with an extremely complex set of variables related to the requirement to control the heat associated with the nuclear fuel.  Water was used to control the temperature but the loss of electricity meant that the ability to replenish or circulate that water was severely hampered.  Monitoring the level of the water to ensure that fuel remained covered was difficult and spotty.  The heated water would eventually vaporize into steam creating escalating pressures in the vessels which could lead to an uncontrolled release of radioactive gases to the reactor containment structure.  Since the reactor vessel and containment structures had pressure limitations, failure to control rising pressures caused by escalating temperatures could also cause a catastrophic event.

Complete boiling off or loss of all water surrounding the fuel rods would result in their degradation, eventual melting and the potential release of very high amounts of radiation if the containment systems failed.

A potential also existed for the steam being created by high temperatures to react with zirconium in the vessel material to create large amounts of hydrogen, an extremely explosive gas. Such an explosion would also result in the release of radioactive gases and the potential dissemination of highly radioactive debris across a wide area.

These scenarios were true for each of the three operating reactors and there were concerns, as well, about the integrity of the stored spent fuel cooling systems.

Plant battery systems also failed because of flooding and grounding.  Critical temperatures and pressures were spiking.  Complicating an already complex scenario was the fact that the plant was effectively isolated and a much larger area was attempting to deal with its own overlapping emergencies.  Outside help, if it arrived at all, would be slow in coming.

Workers moved into an improvisation mindset as they attempted to control the reactors through “unorthodox” methods.  They were forced to rely on “creativity” and work experience as they derived solutions that were “unique” and completely outside of design guidance. They swept the administration building for design documents, plans and drawings and created a work center to brainstorm methods for injecting vital cooling water into the reactors. At one point they were reduced to scavenging auto and truck batteries and cables and bringing them to the control rooms in order to supply enough DC power to monitor reactor water levels.

They looked to fire control systems (stationary pumps and fire apparatus) as a means to inject water into the vessels to control temperature.  Neither scenario proved easy.  Of the three fire engines on site, one was damaged by the tsunami; another was blocked by an oil tank and a de-energized security gate, leaving just one for the initial attempt.

The tsunamis had strewn the site with debris, blown off manhole covers and generally created an extremely hazardous working area.  Building interiors were pitch black, often flooded and there was effectively no monitoring of radiation available.

Controlling reactor temperature and pressure would mean finding reliable water sources and successfully locating and manipulating a complicated series of valves using whatever was at hand. Water would have to be introduced and pressure controlled and released.  Crews would be learning as they went as they determined that key valves were either air or electrically activated and that they all must be operated properly in order to achieve the desired result.

Tomorrow:  Part Four, Explosions

1 Comment

  • Larry Osborne says:

    “They were forced to rely on “creativity” and work experience….”(Pargraph 7). Therein is at least one lesson for state and local governments, as they hire, train, and retain fire and rescue, and other emergency service personnel.

    The quality of those responders, as well as the potential loss of “work experience” caused by excessive turnover, including that caused by successively different private providers, can have a significant and perhaps disasterous effect during these rare but catastrophic events.

    Two books regarding the Challenger disaster, “Major Malfunction”, and “Prescription For Disaster” could illustrate the same points.

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