Homer Simpson said:
My above points are relating to the TMI event, not Chernobyl.
Homer,
TMI was another case where the accident was initiated by "unthinking" operators.
When I was a student at MIT; Professor Kemeny, who led the investigation of the TMI
accident gave a seminar about the findings of his commission.
At one point in the seminar, Professor Kemeny stated when he toured the TMI control
room, he asked the operators for a "steam table" - a book that gives the equation of state
for water at various conditions and whether the water is in the liquid or gaseous phase or
mixed at the specified conditions.
It took the operators about 30 - 45 minutes to find a steam table!
Professor Kemeny stated that the operators at TMI were absolutely CLUELESS about
what part of phase space of the equation of state for water the reactor coolant was in.
He asked if anyone had read the chronology of the accident in the newspaper. He said
then you know exactly how clueless the operators were.
I knew EXACTLY what he meant. I remember reading the account of the TMI accident
in my morning copy of the Boston Globe. They listed a chronology of events by time.
At one point, the chronology stated that the operators had
stabilized the reactor
at a pressure "X" and temperature "Y".
I wondered how far from boiling conditions they were when they stabilized the reactor.
After all, that's what you are trying to prevent in a PWR like TMI; you don't want the
coolant to boil. It creates regions of vapor that won't cool the fuel properly; and hence
the reactor is subject to meltdown.
I reached for my copy of Keenan & Keyes Steam Tables sitting on the filing cabinet that
adjoined by office desk. When I checked the specified conditions of pressure "X" and
temperature "Y" - I found that those conditions were right ON the saturation line.
The operators hadn't "stabilized" the reactor at all. The pressure and termperature weren't
changing because the coolant was boiling - the condition that the operators should be
attempting to prevent. [ Prof. Kemeny confirmed that was EXACTLY what he was
talking about ].
It was 90 minutes after the onset of the accident, and the operators STILL had NOT
consulted a steam table when they noted vibration of the primary coolant pumps.
The vibration of the pumps was an important CLUE - the pumps were vibrating because
they were pumping a two-phase mixture of steam and water. This two-phase mixture
was cooling the core and preventing a meltdown.
However, the operators didn't realized the significance of this clue - they didn't ask why
the pumps might be vibrating. The operator's response was to shutdown the pumps
without thinking about the implication of what that shutdown might do.
It was when the pumps were shutdown that the fate of the reactor was sealed. Without
the circulation of even the two-phase steam / water mixture - the zirconium cladding
tubes melted - and the reactor core was destroyed, and the accident became the
severe event it was.
The Three Mile Island accident was caused by operators that didn't THINK!
Prior to TMI, the philosophy was that all one had to do was to give the operators the
information they needed on their displays, as well as total command of the system,
including the ability to over-ride any of the automatic systems; and the operators would
do the right thing.
That proved to be a faulty philosophy. We had operators that were reacting, and taking
actions WITHOUT being cognizant of the current state of the system or what the
consequences would be of their actions. They just DID; they didn't THINK!
Yes - there were some mechanical failures at TMI; a sticking pressure relief valve, and
some faulty indicators. However, Professor Kemeny stated that the accident was
recoverable even with these mechanical problems.
According to Professor Kemeny, what turned what should have been a minor accident
into a major calamity were the actions of operators that acted WITHOUT THINKING!
Dr. Gregory Greenman
Physicist
