Neil -
Quote:
Originally Posted by NeilBlanchard
I had not heard the term PGA before -- it means "peak ground acceleration".
Peak ground acceleration - Wikipedia, the free encyclopedia
I think the Japanese situation shows the urgent need for at least two sets of emergency electric generators; each with different survivability design criteria. In other words, they chose to put the electric generators underground for a particular reason, but didn't take the tsunami into account. So a second set of generators well above the height of a tsunami or other flood. Each set of generators should have enough fuel for several *weeks* of continuous operation.
Also, the design around the cooling pools for the "spent" fuel rods needs a lot more attention: it needs to be seismically robust, and have emergency gravity fed cooling water; maybe from a water tower? Or, the pools should be *on* the ground level? I realize that they have to be moved out of the reactor core and kept under water the whole time -- but when you are working with radiation, you must be taking all precautions.
The news out of Japan has become greatly diminished. What are the long term prospects that they can bring this under (relative) control? |
I hadn't heard of PGA either.
I agree with these ideas, but I think that because the designs were taken from existing USA designs, they were not changed too much beyond seismic reinforcement.
I think the reason that the spent fuel rods being where they are has to do with safety + convenience. You lift them out of the core and into the pool. I would guess that the longer a fuel rod is outside of water, the greater chance of accidents during transition.
I was talking to my Dad and he told me that these nuclear reactors are adapted from nuclear submarine designs. In the case of an accident, the sea water is the "moderator". Flood the reactor and the crisis is averted. A submarine is surrounded by it's safety valve. Depending on the accident you might lose the crew in the process, but at least the accident doesn't have the same scale of long-term problems we are witnessing here.
My Dad also said that the spent fuel rod pool should have been designed to the same standards as the containment vessel. This implies (to me) that the pool would need some kind of (massive?) cover in the case of an accident. Essentially a non-power-generating containment vessel.
Also, I know this may sound silly, but how about "pressure relief" tanks outside of the reactor? Use a reinforced version of the kind that transport high-pressure gases in tanker trucks. In that way, as pressure is building in the containment vessel, the steam could be offloaded into these tanker trucks. The radioactive stearm wouldn't be released to the environment, or at least the *amount* that is released could be mitigated.
Here is what I was expecting to read about. The design didn't take into account the worst-case-scenario :
Japanese Rules for Nuclear Plants Relied on Old Science
http://www.nytimes.com/2011/03/27/wo...nuke.html?_r=1
Quote:
When Japanese engineers began designing their first nuclear power plants more than four decades ago, they turned to the past for clues on how to protect their investment in the energy of the future. Official archives, some centuries old, contained information on how tsunamis had flooded coastal villages, allowing engineers to surmise their height.
So seawalls were erected higher than the highest tsunamis on record. At Fukushima Daiichi, Japan’s fourth oldest nuclear plant, officials at Tokyo Electric used a contemporary tsunami — a 10.5-foot-high wave caused by a 9.5-magnitude earthquake in Chile in 1960 — as a reference point. The 13-foot-high cliff on which the plant was built would serve as a natural seawall, according to Masaru Kobayashi, an expert on quake resistance at the Nuclear and Industrial Safety Agency, Japan’s nuclear regulator.
Eighteen-foot-high offshore breakwaters were built as part of the company’s anti-tsunami strategy, said Jun Oshima, a spokesman for Tokyo Electric. But regulators said the breakwaters — mainly intended to shelter boats — offered some resistance against typhoons, but not tsunamis, Mr. Kobayashi said.
...
Perhaps the saddest observation by scientists outside Japan is that, even through the narrow lens of recorded tsunamis, the potential for easily overtopping the anti-tsunami safeguards at Fukushima should have been recognized. In 1993 a magnitude 7.8 quake produced tsunamis with heights greater than 30 feet off Japan’s western coast, spreading wide devastation, according to scientific studies and reports at the time.
On the hard-hit island of Okushiri, “most of the populated areas worst hit by the tsunami were bounded by tsunami walls” as high as 15 feet, according to a report written by Mr. Yanev. That made the walls a foot or two higher than Fukushima’s bluff.
But in a harbinger of what would happen 18 years later, the walls on Okushiri, Mr. Yanev, the expert in seismic risk assessment, wrote, “may have moderated the overall tsunami effects but were ineffective for higher waves.”
And even the distant past was yielding new information that could have served as fresh warnings.
Two decades after Fukushima Daiichi came online, researchers poring through old records estimated that a quake known as Jogan had actually produced a tsunami that reached nearly one mile inland in an area just north of the plant. That tsunami struck in 869.
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Hindsight is a mute Cassandra,
CarloSW2