Jon,
some time ago I was CET of a large research plant where we had a small
GE reactor, specialized for production of radiation, not power. We also
used other radiation sources like gamma sources (cobalt), accelerators,
lasers and aside from that, ultrasonic generators. Several hundreds of
my collegues worked on the effect of ionizing radiation on biology. Some
of my fellow scientists worked in international organizations on nuclear
affairs. That was the preface.
A friend of mine, Dieter, worked for IAEA (Int. Atomic Energy Ass.) as
an expert for radiation on human tissue. He told me, right after the
Fukushima catastrophy had happened, that he had visited that site
shortly before for a conference. During the noon break, at fair weather,
he took a walk out to the molehead with some other participants.
Suddenly, a wave occurred, higher than the usual ones, so that they had
to run back to dry grounds, but all of them got we pants. He wondered
why that nuclear plant was built so close to the sea, considering the
fact that even without any catastrophic event the water raised up to the
very walls of the facility. We discussed what had happened later and
Dieter's comment was: no wonder at all to me. And that seemed to be the
opinion of many others of the expert team, too.
The plant had been placed where it is now only under the aspect of
economy (safety being put aside) since the pumps für cooling water would
need much more power if the reactors would have been placed higher up or
farther away from the coast. I am sure that everybody dealing with the
question of locating these reactors has the same opinion.
By the way: The laboratory building where the little reactor of my
facility was housed, producing only max. 1 MW thermal power, was
equipped with a 630 kW Diesel generator and a large NiFe battery for
emergency lighting, and 5 more generators are distributed around the
campus, plus 2 Saturn gas turbines in the main energy building, so in
case of failure of the public energy system we would be able to keep up
full service al least for several days.
If all the nuclear power plants in the world would be constructed under
the aspect of safety instead of economy and if this safety status would
be maintained, i.e. adapted to technical progress, there would be no
need for emission of any harmful substances for electric power
production. And as we saw in Chernobyl, plutonium production is harmful
even without applying it to the environment by means of bombs.
Peter
Am 10.03.2019 um 17:51 schrieb Jon Elson:
Am 10.03.2019 um 17:51 schrieb Jon Elson:
On Saturday 09 March 2019 23:43:26 Gregg Eshelman via Emc-users wrote:
The one problem I see as being really troublesome with the design of
Fukushima is that it apparently was incapable of being fully self
powering of all its systems at any time.
No, not true. They had at least SEVEN Diesel generators. Crazily,
many of them were in the basement of the buildings, where they could
get flooded. Also, a number of them were sea-water cooled, and when
the tsunami hit, the first thing it did was submerge the giant sea
water pump motor and short it out. So, they lost all their sea water
cooling.
Who designs a power plant
able to run for 25 years or so, producing electricity, without needing
to be refueled, that does not tap its own power generation to run all
of its electronics, pumps etc?
The problem is the turbines, alternators and their exciters are not
designed to run over a 1000:1 power range. This was what caused the
big mess at Chernobyl. In the US, we require a UPS on the most
critical items such as primary coolant circulating pumps. Then, we
back that up with fast-start Diesel generators that can be on line at
full power in under six seconds. This stuff is REALLY expensive,
especially a UPS that will run FOUR 1000 Hp pumps. The Russians
didn;t want to pay for that, so they came up with the idea they could
run the critical loads off the inertia of the turbine-alternator set
for a minute while the Diesels came on line. This did require the
alternator exciter to be able to regulate the alternator's output
voltage basically down to zero current. Well, after making the mods
to the exciter, they had to test it. Doing a test like this on an
actual, operating reactor requires extremely careful planning, and
training of all personnel in exactly what to do, when, and what to do
if anything diverges from the plan.
So, they scheduled this test to be done right before a refueling
shutdown. But, somebody didn't get the word, and shut down the
reactor. Uranium reactors build up a huge amount of radioactive
iodine as a fission daughter product, and it is a strong neutron
absorber. So, right after you shut down the reactor, the iodine
builds up, and poisons the reaction, It can take a whole DAY for the
reaction to build back up and "burn off" the iodine. Well, they
needed the reactor to be above some power level to run the test, so
they pulled all the control rods ALL the way out, to try to get some
reaction going again. Now, when ready for refueling, the reactor is
full of Plutonium, which is more reactive than uranium. (Note, the
Chernobyl RBMK-1000 reactor is identical to a graphite pile Plutonium
production reactor they used for their weapons program, so it is
ENGINEERED to make Plutonium, it isn't an unwanted byproduct like
commercial power reactors.) So, when refueling is needed, the reactor
is quite unstable with all that Plutonium, and pulling the control
rods all the way out makes it worse. So, they cut over from grid
power to their own alternator, and as the station ran off the inertia
of the alternator, the alternator SLOWED DOWN! This meant the
frequency decreased, and any pumps running off that power began to
slow down. Now, the next horror of the RBMK-1000 is that it has a
"positive void coefficient". That means that if the cooling water
boils, it INCREASES the nuclear reaction rate!
This is due to the graphite being the neutron moderator, and the water
being a neutron absorber. It isn't clear exactly what the next chain
of events and actions were, but at some point they canceled the test
and scrammed the reactor. Another odd feature of the control rods of
that reactor is the bottom half meter of them has a big graphite
plug. The control rods sit in the middle of the cooling water pipes
of the reactor (the RBMK-1000 is not immersed in water like most other
reactors). So, driving dozens of control rods inward opposed the flow
of the cooling water, the water started to boil, the slugs of graphite
entering the core increased the reactivity, and the reaction ran away
very quickly.
This insane test, of course, should have NEVER been done on a fueled
reactor. But, that's Russia for you.
No nuclear power plant should require
an external electricity supply for anything as long as at least one
reactor is 'hot' and one turbine is running.
Well, that's why they have BANKS of Diesel generators!
IMHO, an ideal
multi-reactor power plant should have one small
reactor/turbine/generator set for powering everything in the facility.
No, you have to have massive amounts of electrical power to even begin
to start a small reactor.
The Callaway County plant is a pressurized water reactor, and has FOUR
1000 Hp circulating pumps. In fact, the bring-up procedure after a
shutdown is to use the pumps to warm the reactor to near operating
temperature, as the reactor itself would raise the temperature too
quickly.
One the size of what's used in a nuclear submarine. Under normal
conditions its output would be added to what the big reactors and
generators produce, but in an emergency where the big reactors are
shut down, the little one would stay up and running, in its well
armored and isolated, flood proof, building, supported on isolating
springs.
Diesel generators can be started in seconds when needed, a reactor
takes hours or DAYS to be started safely.
When the earthquake hit, Fukushima went to automatic shutdown.
Apparently the external power supply also went down so the diesel
generators kicked in. That's where the trouble began. The tsunami took
out the generators, which shut down the cooling pumps. Since there
wasn't any other way to get power to the pumps to cool down the
reactor cores, they heated up to the point where the water in the
vessels split into hydrogen and oxygen, which then caused explosions.
Well, not exactly right. The various items in the reactor core must
not absorb neutrons or the reactor won't work. With a limited choice
of material, it is practice to make the fuel rod cladding from
Zirconium. Hot Zirconium in water is kind of like pouring water on
burning Magnesium, it splits the water to get the Oxygen. This can
start as soon as the reactor core is uncovered, and the Zirconium
burns fine in pressurized steam. From a neutron perspective,
Zirconium is ideal, from all other perspectives, it is one of the
worst things to use.
Better protected generators, and more of them, plus modern control
systems with the ability to quickly self test for damage and get back
online after a SCRAM initiated by the earthquake sensors - might have
gotten one core back online and the facility back under self power in
the time between the quake and the tsunami hitting. But that couldn't
happen because Fukushima was forced to be frozen in the technological
past.
Is Japan still keeping all their nuclear plants idle?
No, they have restarted a few of their better-engineered plants.
Of course, the concept of placing the oldest plants RIGHT on the ocean
in the country that has known about the tsunami phenomenon for
thousands of years was just insane. They DO have a problem that the
government is under the thumb of industry there.
(My apologies for a very long answer to an off-topic thread.)
Jon
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