A friend of mine is friends with a retired nuclear engineer who has considerable experience in building, maintaining and operating plants. He offered the following:
"The primary risk in the short term is radioactive iodine. It has a half life of 8 days, so every 8 days that pass the amount left in the
fuel decreases by 1/2. By moving people away from the plants and giving them iodine tablets to saturate their bodies with iodine
the damage from this source will be significantly reduced.
The reactors in the news are boiling water reactors (BWR, GE design in the US), the Jenkinsville, SC, plant is a pressurized water
reactor (PWR developed by Westinghouse, Combustion Engineering and Babcock & Wilcox in the US). Both are completely
unlike Chernobyl (A large block of graphite full of holes). While we normally consider all the US designs similar in safety there are
significant differences that are important in the current situation. Both PWRs and BWRs contain the core in a large steel pressure
vessel, but things differ from that point.
PWR's keep the primary coolant from boiling in the reactor by maintaining high pressure, the water goes through Steam
Generators (boilers) to make steam for the turbine. As a result the steam going to the turbine does not normally contain any
significant amount of radioactivity and the turbine is located in a separate building. The PWR reactor and steam generators are
located in a containment building designed to contain internal pressures of 50, 60 psi or more.
BWRs boil water as it passes through the reactor and send it directly to the turbine. This probably offers better thermal efficiency
and eliminates the cost of steam generators, but I have always felt if was an inferior design from a safety standpoint. Since BWRs
produce steam that normally contains some radioactivity they put the turbine in a building with the reactor. This requires a large
building. As you could see these are not cylindrical buildings with domed lids like at Jenkinsville, but rectangular buildings that
cannot contain high pressures. To help cool and protect the reactor they were venting steam from the reactor system into the
building, hydrogen built up and eventually led to the explosions seen on TV. The reactor vessel is still intact and they are trying to
cool the core using fire trucks and seawater. This will probably mean the plants are trash in the long run, a financial disaster, but
should prevent a human disaster due to radiation. Every day that passes significantly reduces the amount of volatile radioactive
material that might be released, particularly iodine, the primary short term hazard. Radioiodine has a half life of 8 days so by next
Saturday half of this material will be gone, another 8 days only 1/4 will be left.
All the largest earthquakes from the last century are around the Pacific rim. The faults here are old and generally inactive. It is not
practical to design for every possibility, only for those of reasonable probability. So when Mother Nature decides to get nasty we
suffer. Typically most things are designed for the 100 year flood, or hurricane, not a direct hit by an asteroid. With regard to
earthquakes nuclear plants are designed to what we think is a reasonable earthquake for where each plant is located. From what I
know, even the Japanese plants did not fail due to the earthquake itself, rather external power was lost and the emergency diesel
generators failed, leaving them without operating power to pumps and valves. Control power typically comes from batteries running
inverters, but the power to turn motors comes from the grid or a diesel or gas turbine generator.
The situation is bad, but I suspect in the long run most of the nuclear related problems will be financial. The reactors being cooled
by firetrucks using seawater are in a condition beyond any design accident. However I would like to ask Rudy Mancke how he
envisions a "nuclear volcano" occurring. If the fuel melts it will release materials like iodine into the atmosphere. They know this
and are preparing by evacuating and being ready to give supplemental iodine so your body will be saturated with it. The rest of the
fuel will indeed melt and flow into a lump in the bottom of the reactor vessel and possibly (China Syndrome) melt through into the
concrete or rock underneath where it should encase itself in molten rock which will cool around it. There may be supplemental
cooling for a while, then they will probably just entomb it and build a sealed building over it until the heat load will allow for natural
cooling without melting, years, not eons. Since our government is unable to build a spent fuel repository we now store spent fuel in
containers that are air cooled via natural circulation after ten years or so.
Mancke studied Chernobyl, which is an entirely different animal. The core was a giant carbon block with holes punched through it
for fuel and cooling, plus there was no containment building and little other structure to contain the core in an accident. Once the
carbon ignited it burned (very hotly) and dispersed the materials of the core along with the combustion products.
I expect most, or all deaths, will be related to the tsunami and earthquake. There will be fear of increased cancers and such, but
likely not much to document. I remind people that by moving from Columbia to Denver you would double your annual radiation
dose without any documented increase in cancer. People tend to be irrational about radiation, how else can you explain the fear of
airport security scanners that produce a tiny fraction of the additional radiation you will get from the flight itself.
What should we do? The obvious answer, to me anyway, is to build new plants rather than put everything on hold. The two units
under construction near here are designed to cool themselves in an emergency without any cooling pumps whatsoever. No
emergency cooling pumps, no pump failures. The emphasis on new designs has been to simplify things so there are less things to
fail, less and easier maintenance and passive emergency cooling."
