On March 28 1979, the automatic shutdown system at Three Mile Island PWR 2 was triggered in response to a temperature increase in the primary coolant loop resulting from a minor malfunction in the secondary coolant loop. The reactor was successfully shutdown in less than one second but a relief valve failed to close, resulting in continued loss of coolant in the core. This was not indicated to the controllers because the instrumentation in the control room which showed the status of the relief valve only reported commands, which had been sent to it, and not its actual position. In other words, the valve was shown to be closed in the control room because the close command had been sent even though the valve did not respond. The emergency cooling unit activated as designed and began forcing emergency coolant in the core. However, because the controllers believed the valved had closed as planned, they believed that continued forced cooling would overpressurise the core so they ordered that the emergency cooling system to stop forcing coolant water into the core. The loss of pressure in the core exposed part of the fuel, which began to heat up due to decay of fission products (the fission reaction had already shutdown. The fuel elements were damaged as a third of the fuel melted. By the end of the day, the controllers had re-established forced cooling in the core.
Three Mile Island was the Western version of Chernobyl.
In the fact that there was melting of the fuel, this is true, but in every other way, this is not true. This accident was attributed to poor instrumentation and emergency training, whereas Chernobyl was due to fundamental flaws in reactor design and irresponsible operation. Chernobyl resulted in a large uncontrolled release of radionuclides, whereas TMI resulted only in a controlled venting of a small amount of radioactive material, which was not large enough to be hazardous.
TMI demonstrates that even Western reactors are unsafe.
Figure 1- Car bumper sticker.
For a start, if that were true, it would also apply to the dozens of reactors in service during 1979, which conspicuously did not experience any meltdowns (including the three other units at TMI itself). But in fact TMI demonstrates the safety of Western reactors and the proficiency of the defence-in-depth principle. Despite a failure of primary and emergency coolant and melting of the fuel, only a small amount of material was released into the surroundings in a controlled manner therefore no harm came to any person, apart from those who worried themselves into hypertension due to the scare stories and prophecies of doom from the anti-nuclear camp. Defense-in-depth works.
Radioactive material was released into the surroundings.
The venting was above standard operating limits but did not represent an overly hazardous discharge. It was less than 1mSv at maximum and no more than the equivalent of a chest x-ray on average to those within 10 miles of the plant. This is smaller than the variation in background radiation throughout the United States. There is no evidence of adverse health effects to due to this miniscule increase in radiation exposure despite numerous health studies.
TMI is accepted as the second worst nuclear accident for the industry and it is noteworthy that this second worst accident resulted in no casualties or injuries. How many other industries can make that claim?
A class action suit was filed against TMI by people who said they had suffered adverse health effects as a result of the radiation release.
The case never made it before a jury. When it went before Judge Sylvia Rambo at the District Court of the Middle District of Pennsylvania, it was dismissed on "paucity of evidence".
The parties to the instant action have had nearly two decades to muster evidence in support of their respective cases. As is clear from the preceding discussion, the discrepancies between Defendants, proffer of evidence and that put forth by Plaintiffs in both volume and complexity are vast. The paucity of proof alleged in support of Plaintiffs, case is manifest. The court has searched the record for any and all evidence which construed in a light most favorable to Plaintiffs creates a genuine issue of material fact warranting submission of their claims to a jury. This effort has been in vain.
Unreported hydrogen blowouts caused unreported radiation spikes of intense radiation.
Unsupported speculation on the part of the plaintiffs in the lawsuit. The dosimeter readings were consistent with what was expected from the reported radiation release so there is no evidence of additional radiation release. Even the expert testimony of Dr Lochbaum during the case, which contained speculation about how a blowout may have caused the maladies at the centre of the lawsuit, was followed up by admission that there is no evidence of such an event.
From official court summary:
That is, if Lochbaum's review of the relevant TMI data revealed no conclusive evidence of a blowout, how could his theories regarding how a blowout might have occurred assist a jury? In fact, during the Daubert hearings, Lochbaum went further than stating there was no "conclusive" evidence of a blowout -- he testified that "I did not see any supporting indications that would lead me to believe that there was a blowout . . . . I do not believe that there was evidence of a blowout."
Studies of trees by Professor Shevchenko suggest TMI caused damage on par with Chernobyl.
By his own admission, Professor Shevchenko had not conducted the same level of investigation into the cause of damage to pine trees near TMI, which he had done in areas such as Chernobyl. His conclusion was based on cursory observation of the trees. An as expert witness, he does not have sufficient expertise with regard to other diseases unrelated to radiation, which could also cause the same effect. Therefore, it was concluded that while at first glance, radiation could have caused the damage to the trees, there is not sufficient evidence to accept the damage was caused by radiation from TMI.
From the official court summary:
Both the damaged in tree tops observed by Professor Shevchenko and the chromosome dicentrics are nonspecific effects of radiation exposure. They are classified as nonspecific because the same effects can be caused by things other than radiation. Professor Shevchenko will testify that based solely upon his observation of TMI trees, it is his professional opinion that the trees were damaged as a result of radiation exposure during the TMI accident. Effectively, Professor Shevchenko is asserting that his expertise is so great that he simply knows radiation damage when he sees it. To the extent that Professor Shevchenkols confidence in his abilities is warranted, the record nevertheless reflects that his observations were cursory. Professor Shevchenko testified that he did.not examine the tops of trees from a bucket truck or by having sections cut out and brought down to him for investigation, and that he does not have sufficient expertise to evaluate non-radiation induced diseases in trees. Without disputing his acumen in this area, the court finds that Professor Shevchenko's testimony that selected trees in the TMI area look like trees exposed to radiation at Semipalatinsk, Kyshtym and Chernobyl is simply insufficient to carry the weight of Plaintiffs', entire case. Combining the cytogenetic evidence and the tree evidence likewise fails to carry Plaintiffs' burden. Two nonspecific effects of radiation exposure cannot meld to equal proof of specific exposure to radiation.
Was anything learnt from this?
Of course. Improvements in training and instrumentation resulted from this accident. Thanks to this experience, reactors today are safer than ever. The cost for this lesson was one nuclear reactor but no harm to any person. Quite a bargain.