Tuesday, June 10, 2014

The Truth About Nuclear Power - Part 20

Subtitle: Chernobyl Meltdown and Explosion

This article 20 begins five articles on what may be the most serious nuclear plant disasters and near-disasters: Chernobyl, Three Mile Island, Fukushima, San Onofre, and St. Lucie.  Many
Radiation Plume from Chernobyl
credit: BBC
others could be included, from countries around the world.  One reference lists more than 80 serious nuclear power incidents.   The US’ Nuclear Regulatory Commission lists 70 incidents in the past four years in the US alone that required the NRC to send a special investigation team to the plant, or an augmented investigation team.   The Chernobyl article begins with a brief summary or overview of the facts, taken from the NRC's "Report on the Accident at the Chernobyl Nuclear Power Station 1986," then commentary afterward.

Previous articles on The Truth About Nuclear Power emphasized the economic and safety aspects by showing that (one) modern nuclear power plants are uneconomic to operate compared to natural gas and wind energy, (two) they produce preposterous pricing if they are the sole power source for a grid, (three) they cost far too much to construct, (four) use far more water for cooling, 4 times as much, than better alternatives, (five) nuclear fuel makes them difficult to shut down and requires very costly safeguards, (six) they are built to huge scale of 1,000 to 1,600 MWe or greater to attempt to reduce costs via economy of scale, (seven) an all-nuclear grid will lose customers to self-generation, (eight) smaller and modular nuclear plants have no benefits due to reverse economy of scale, (nine) large-scale plants have very long construction schedules even without lawsuits that delay construction, (ten) nuclear plants do not reach 50 or 60 years life because they require costly upgrades after 20 to 30 years that do not always perform as designed, (eleven) France has 85 percent of its electricity produced via nuclear power but it is subsidized, is still almost twice as expensive as prices in the US, and is only viable due to exporting power at night rather than throttling back the plants during low demand, (twelve) nuclear plants cannot provide cheap power on small islands, (thirteen) US nuclear plants are heavily subsidized but still cannot compete, (fourteen), projects are cancelled due to unfavorable economics, reactor vendors are desperate for sales, nuclear advocates tout low operating costs and ignore capital costs, nuclear utilities never ask for a rate decrease when building a new nuclear plant, and high nuclear costs are buried in a large customer base, (fifteen) safety regulations are routinely relaxed to allow the plants to continue operating without spending the funds to bring them into compliance, (sixteen) many, many near-misses occur each year in nuclear power, approximately one every 3 weeks, (seventeen) safety issues with short term, and long-term, storage of spent fuel, (eighteen)  safety hazards of spent fuel reprocessing, (nineteen) health effects on people and other living things, (twenty) nuclear disaster at Chernobyl, (twenty-one) nuclear meltdown at Three Mile Island, (twenty-two)  nuclear meltdowns at Fukushima, (twenty-three) near-disaster at San Onofre, (twenty-four) the looming disaster at St. Lucie, (twenty-five)  the inherently unsafe characteristics of nuclear power plants required government shielding from liability, or subsidy, for the costs of a nuclear accident via the Price-Anderson Act, and (twenty-six) the serious public impacts of large-scale population evacuation and relocation after a major incident, or "extraordinary nuclear occurrence" in the language used by the Price-Anderson Act.  Additional articles will include (twenty-seven) the future of nuclear fusion, (twenty-eight) future of thorium reactors, (twenty-nine) future of high-temperature gas nuclear reactors, and (thirty), a concluding chapter with a world-wide economic analysis of nuclear reactors and why countries build them.  Links to each article in TANP series are included at the end of this article. 

Overview, from NRC Report, Section 4.1 (pg 124)

(quote) “The accident occurred during a test of the turbine generator system.  This test was designed to demonstrate that following a reactor trip, with the resulting loss of onsite power and isolation of the steam supply to the turbine, the rotating inertia of the turbine generator would be sufficient to generate enough electrical power to energize certain safety systems until the diesel generator system could be started and accept the electrical loads.  This test had been performed earlier at similar plants (Russian).  The specific purpose of this test was to determine if a new generator magnetic field regulator would maintain the voltage output from the generator for a longer period.

In the process of establishing the test conditions for the reactor, the operators brought the plant to an unstable operating condition.  However, for a number of reasons, the operators chose to run the test from this unstable condition.  To prevent the reactor from automatically shutting down, the operators purposely bypassed several systems important to safety.  The role of the operator in this accident is discussed in Chapter 5.

With the safety systems bypassed, the plant was in an unstable and vulnerable condition.  The most prominent parameter of this unstable condition was the positive void reactivity coefficient.  This coefficient allowed the reactivity to increase as the volume of steam increased in the core.  Other significant parameters included the low initial power level, low subcooling, low initial steam void fraction in the core, fuel burnup condition, and control system characteristics.  The design characteristics of the Chernobyl plant are detailed in Chapter 2.

The initiation of the test caused the steam volume in the core to increase.  Under the unique test conditions (for which the plant was not designed), and with the safety systems bypassed, a significant insertion [? Increase?] of reactivity resulted.  The resulting power increase produced additional steam voids which added reactivity and further increased the power.  Evaluations to date indicate the reactor was brought to a prompt critical condition.  Assessment of Soviet (and other) analyses also indicates that the energy deposition in the fuel was sufficient to melt some of the fuel.   The analyses to date suggest the following possible sequence of events.  The rapid expansion associated with melting, quickly ruptured the fuel cladding and injected fragmented and molten fuel into the coolant channel.  The interaction of the coolant with the hot fuel fragments produced steam very rapidly.  The high temperatures and rapid production of steam quickly over-pressurized the pressure tubes in the core region.   The pressure tubes then failed and over-pressured the cavity region around the graphite blocks.  Sufficient force was generated to lift the top plate off the reactor and possibly to fail the reactor building and eject core material.  This postulated sequence of events can be associated with the first “explosion” heard by operators at the plant.  A second “explosion” was reported to have occurred approximately 3 seconds after the initial one.

Various speculations on the source of this noise include a second criticality, a hydrogen detonation, or even an echo or reverberation. 

In summary, the event was caused by a combination of procedural and management deficiencies, human errors, and unique design characteristics. “  (end quote)   see link


For the non-technical readers on SLB, a brief deconstruction of the above is in order. The test was to determine if the generators had enough inertia to keep spinning and generate power, even though steam was shut off to the turbine, to keep emergency systems energized until the diesel-powered generators could be started and brought up to speed.  

The plan was to run the reactor at part-load, which would have tripped the existing safety systems into a shut-down.  The safety systems were therefore disabled.  However, the reactor load was far below the planned load.   The reactor went into a mode that had more steam bubbles than normal, which is dangerous because steam does not slow down fission products such as neutrons.  This is the "positive void reactivity coefficient" mentioned above.  Also, the operators pulled the control rods, almost all of them, out of the reactor.   The resulting power surge caused the reactor to go critical, which melted down part of the nuclear fuel and caused not only an explosion, but the graphite parts of the reactor to catch fire.   

Radiation Worldwide

The core explosion, fire, and residual heat from the burning reactor core (that lasted several days) released huge amounts of radioactive materials into the atmosphere.  The plume of airborne particles flew high above the Earth, in a westerly and northerly direction, and tripped radiation monitors in several countries as it circled the globe.   One of the first countries the plume reached was Poland on April 26 and 27, 1986.   Almost all of Europe was impacted with radiation levels many times higher than normal.  The radiation plume eventually reached almost every northern hemisphere country. 

Personally, I was working doing consulting engineering with a contract in West Germany near Dusseldorf.  I finished the initial visit by March 1 of 1986, then returned to the US to do the office work.  A second visit to Germany in July made me quite nervous, particularly in the food we ate while there.  Everyone was very upset over the radiation cloud that rained deadly particles down on the entire continent.  

From a nuclear power plant safety standpoint, the important point is that the nuclear power industry has always insisted that their power plants are safe.  Even after Chernobyl blew up, the argument was “well, that is a Russian design and nobody has any of those.  Besides, the operators went rogue and operated the plant improperly, which made it explode.  That can never happen here.”

The proper response is, “A nuclear plant can never be made fool-proof.  Fools are just too ingenious.”   As shown in part 16 of TANP, operators in western nuclear plants make plenty of mistakes, not only in design but in operation, training, maintenance, parts replacement, security measures, even mundane chores like tightening bolts to the proper torque. 

Health Issues

At Chernobyl, 28 workers died from acute radiation poisoning within 4 months of the explosion.  Many others have died since, but a direct link to Chernobyl radiation exposure is unclear.   The World Health Organization, WHO, estimates 240,000 workers were exposed to high levels of radiation while cleaning up the radioactive debris.  Another 346,000 people were evacuated and relocated away from the radioactive zone near the plant.  see link   

WHO states that greater incidence of thyroid cancer was caused by Chernobyl.   There also is almost a doubling of leukemia cases.    In addition, the radiation caused cataracts in the eyes, increased deaths from cardio-vascular disease, mental health and psychological trauma. 

UPDATE - 6/11/2014 

So much more could be written about the Chernobyl disaster.  In fact, an internet search turns up nearly 5 million websites with the term "Chernobyl."   Hundreds of books about Chernobyl have also been written.   Until the multiple-meltdowns at Fukushima, Japan in 2011, Chernobyl was the greatest nuclear disaster of all-time.  

From an institutional safety standpoint, Chernobyl refutes many of the nuclear proponents' arguments.  First, the plant was subject to regulations in its own country, the USSR.   International regulations apparently were largely ignored.  Who is to say that future nuclear power plant operators will not do something equally devastating, especially as nuclear plants are built in more and more countries?   

Nuclear apologists or proponents are fond of saying that modern plants are secure, have safety systems and backup systems, and have designs that would never allow such an event to happen again.  That is mere talk; as mentioned in the Conclusion below, it is only too easy for operators to disable safety systems or ignore warnings, and run the plant in manual mode.   What is also apparent from the NRC report linked above is the very, very rapid change from quasi-normal operation to reactor criticality, meltdown and explosion.  At Chernobyl, the change required only a few seconds.  Operators tried desperately to insert some of the control rods, but it was too late.  

It is also clear from the NRC even reports that many, if not all nuclear plants in the US run some of their systems in manual mode at times.  Nothing can be made to run forever, as parts degrade and fail and must be replaced or repaired.  A control system normally has an automatic mode and a manual mode, and only well-trained operators should be allowed to run the systems in manual mode.  

What is also apparent from Chernobyl is the industry did not speak out in a timely manner about what happened and the risk to other countries from the radioactive cloud that was headed their way.  It is true that the operators in the plant had more things on their mind right about then, if they were still alive after the explosion.   However, it was radiation detectors in other countries that first gave the alarm internationally.   The extent and magnitude of the event was not known for days.  The psychological impact on billions of people was not small.   What of the parents of small children, who needed to drink milk?  What worries did couples have about future children?  What worries did other people have about radiation sickness, or long-term illnesses such as thyroid cancer and other cancers?    

The next two articles in TANP discuss two more disasters involving core meltdowns: Three Mile Island and Fukushima.  In both instances, like at Chernobyl, a combination of bad design and human error caused major disaster.  Fukushima was a bit more complex because a natural disaster, and earthquake with tsunami initiated the events.  

-- end update


Nuclear power advocates insist that the plants are safe, that modern designs cannot have catastrophic meltdowns.  However, it is clear that human error can easily defeat the best designs, and natural events can overwhelm even the best operators.  Chernobyl operated quite safely until human plans and human errors created the enormous disaster that affected millions of people around the world. 

Previous articles in the Truth About Nuclear Power series are found at the following links.  Additional articles will be linked as they are published. 

Part Twenty - this article

Roger E. Sowell, Esq.
Marina del Rey, California


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