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Introduction
Here
are notes on the BWR Boiling Water type reactors used at Fukushima
@@Specifications and
facts
GE Mark I Containment
- Height of reactor building: 148 ft
- Depth of basement (wetwell):
50 ft
- Length of building: 151: ft
- Height of smokestack/stack tower: 100 meters ~300 ft
- Diameter of containment bulb: 67 ft
- Height of containment 32 meter ~100 ft
- Thickness of concrete containment bulb: 2 meters / 6 ft
- Weight of pressure vessel 441 tons
- Thick of pressure vessel 16 cm
- Diameter of torus (center of tube) 111 ft
- Diameter of vent to torus 81 in
- Height of Reactor 3 explosion: ~1200 ft
- Height of Reactor 1 explosion ~300 ft
- Height of wave splash: 200 ft
- Maximum design fuel cladding temperature: 2200F
- Thickness of bottom of primary containment: 16cm
- Size of hole in containment #1 “a few
centimeters in diameter” based on water leakage
- Radiation released per hour: 10,000 terabecquerels
of iodine-131 after March 11
- Radiation released total: 630,000 terabecquerels
vs 5.2 million for Chernobyl
- Reactor 1 core damage 100% (was est
55% )
- Reactor 2 core damage 100% (was est
25% )
- Reactor 3 core damage 100% (was est
30% )
- Unit 1 is the oldest reactor, scheduled to be taken out
of service this Saturday, March 26th
Reactorsref
Initially to be retired in 2011, but relicense for 10 more years. Damaged
beyond repair,
- Reactor
No. 5: 784 MW power rating, operational (critical) April 18, 1978
- Reactor
No. 6: 1,100 MW power rating, operational (critical) October 24, 1979
- Reactor
No. 7 and 8: planned for 2013-14
Glossary
- Containment
- Primary
containment: Concrete inverted light bulb surrounding steel reactor core
- Secondary
containment: Upper building shell with refueling level, overhead crane
- Upper
containment: Level from bottom of spent fuel pool up to roof
- Lower
containment: Level below spent fuel pool
- Doghouse
- Drywell
- ECCS:
Emergency Core Cooling Sytem
- Wetwell
References
@@Contents
- List of BWR
- Mark I Containment
- Perry Nuclear Generating Station, Ohio
- ReactorCap
- Refueling
- Venting Hydrogen
@@links
@@Generation
@@List of BWR reactors
see
http://en.wikipedia.org/wiki/List_of_boiling_water_reactors
[edit] See also
·
List of nuclear reactors by country
·
List of nuclear power stations
@@Mark I Containment
Summary
The Mark I was the first of 3 containments, and the
weakest design. The Mark II replaces a steel torus with a lined concrete
compartment. Only the Mark III introduces a strong concrete dome over the
reactor like most other reactors, and moves fuel storage into another building.
Some faults of Mark I containment:
·
"Secondary
containment" is just a steel or concrete thin-walled building kept at
slight negative pressure. This was destroyed by hydrogen exposions
in Fukushima Daichi units 1, 3, and 4, along with all
equipment including overhead crane and refueling platform.
·
Destruction of roof
and ducting also destroyed any ability to filter harmful radiation from pool or
vented gases. However it did make it possible to drop air into the pool by
water canon, helicopter and concrete pump as
improvised methods.
·
Hydrogen gases were
vented into upper building rather than up the stack. It is unknown, but
suspected Japanese government did not require that Fukushima units had
installed "hardened" vents designed to vent exposive
gases up the stack through harded ducts. The duct on
reactor 3 was completely severed after the hydrogen explosion. It is possible
power failure deactivated fans and values to properly function.
·
Fuel storage pools
require power to cool and circulate. They are placed above the hot reactor
which can also heat water on top of warm fuel rods which are producing their
own heat. The gates between top of reactor and equipment pool use air-filled
seals which may not work without power, or in earthquake and allow leakage. It
is certain there was a fire in pool unit 4, less certain what happened in Unit
3 which suffered a spectacular explosion sending a dark debris cloud 1000 ft in the air, and probably being the source of pieces of
radioactive debris and plutonium as far as 2 miles away.
Links:
·
2011 NEI Mark I
Containment Report after accident
·
New York times April 6, 2011, 11:54
AM Chemistry 201: Why Is Fukushima So Gassy? By MATTHEW L. WALD
American experts are urging operators of the Fukushima Daiichi plant to fill
the empty space in the primary containment – the area around the reactor
vessel, shown here in red – with inert nitrogen gas to avert explosions.
http://www.gereports.com/how-it-works-white-paper-on-mark-i-containment/
Mark I
Containment Facts and The New York Times
(comment - a whitewash which papers over failings of system
which released a one-tenth scale version of Chernobyl in terms of radiactive releases and building destruction)
·
The torus, which is a large, rounded suppression pool
that sits next to the reactor core, is not the outer containment, it is primary
containment.
·
By design, the outer containment is not a pressure
containing building.
·
The reactor building (secondary containment) is kept
at a slight vacuum to limit radioactivity release during refueling operations
and during certain design scenarios.
·
The design pressures (meaning the pressures that each
containment system is designed to withstand) of a BWR and a PWR primary
containment are similar.
How it Works:
White Paper on Mark I Containment
(comment - this is largely a whitewash of how the GE design
performed so "well")
·
“Coincident long-term loss of both on-site and
off-site power for an extended period of time is a beyond-design-basis event
for the primary containment on any operating nuclear power plant.”
·
“The Mark I containment vessels appeared to have held
pressure to well above the design pressure.”
·
“The response of the reactor pressure vessel and
reactor in general agree with severe accident management studies performed in
the 1980s and early 1990s.”
* Download the full report from the NEI website.
The NEI
website is also providing updates on the situation in Japan.
The Mark I
Containment System in BWR Reactors
The
modifications made to Mark I containments include:
·
Quenchers were installed to distribute the steam
bubbles in order to produce rapid condensation and to reduce loads on the unit.
In a reactor, exhaust steam is piped into a suppression chamber, which is known
as the torus and is a large, rounded suppression pool that sits next to the
reactor core. It is used to remove heat when large quantities of steam are
released from the reactor. In the torus, the steam bubbles go under water. With
the modification to the Mark I, the quenchers, which
are also underwater, make steam bubbles smaller by breaking up the larger
bubbles. This in turn reduces pressure.
·
Another modification is the installation of
deflectors inside the torus. When that steam goes in, the water level rises. The deflectors that were added break up the pressure wave that is
produced and help relieve pressure on the torus.
·
A further modification was made to the saddles on
which the torus sits — basically the series of leg-like structures that support
it. The construction was fortified, as was the steel, to accommodate the loads
that are generated.
A BWR
reactor: The schematic above shows the torus at left, which is doughnut-shaped.
In most BWR designs the spent fuel pool is outside of the
containment building.
Boiling Water Reactor Wikipedia
First series
of production BWRs (BWR/1–BWR/6)
·
1st generation BWR: BWR/1 with Mark I containment.
·
2nd generation BWRs: BWR/2, BWR/3 and some BWR/4 with
Mark I containment. Other BWR/4, and BWR/5 with Mark-II containment.
·
3rd generation BWRs: BWR/6 with Mark-III containment.
Disadvantages
·
Complex calculations for managing
consumption of nuclear fuel during operation due to "two phase (water and
steam) fluid flow" in the upper part of the core. This
requires more instrumentation in the reactor core. The innovation of computers,
however, makes this less of an issue.
·
Much larger pressure vessel than for
a PWR of similar power, with correspondingly higher cost. (However,
the overall cost is reduced because a modern BWR has no main steam generators and
associated piping.)
·
Contamination of the turbine by
short-lived activation products. This means
that shielding and access control around the steam turbine are required during
normal operations due to the radiation levels arising from the steam entering
directly from the reactor core. This is a moderately minor concern, as most of
the radiation flux is due to Nitrogen-16, which has a half-life
measured in seconds, allowing the turbine chamber to be entered into within
minutes of shutdown.
·
Though the present fleet of BWRs are said to be less
likely to suffer core damage from the "1 in 100,000 reactor-year"
limiting fault than the present fleet of PWRs are (due to increased ECCS
robustness and redundancy) there have been concerns raised about the pressure
containment ability of the as-built, unmodified Mark I containment – that such
may be insufficient to contain pressures generated by a limiting fault combined
with complete ECCS failure that results in extremely severe core damage. In
this double failure scenario, assumed to be extremely unlikely prior to the Fukushima I nuclear accidents, an unmodified
Mark I containment can allow some degree of radioactive release to occur. This
is supposed to be mitigated by the modification of the Mark I containment;
namely, the addition of an outgas stack system that, if containment pressure
exceeds critical setpoints, is supposed to allow the
orderly discharge of pressurizing gases after the gases pass through activated
carbon filters designed to trap radionuclides.[7]
·
A BWR requires active cooling for a period of several
hours to several days following shutdown, depending on its power history. Full
insertion of BWRs control rods safely shuts down the primary nuclear reaction.
However, radioactive decay of the fission products in the fuel will continue to
actively generate decay heat at a gradually decreasing rate,
requiring pumping of cooling water for an initial period to prevent overheating
of the fuel. If active cooling fails during this post-shutdown period, the
reactor can still overheat to a temperature high enough that zirconium in the
fuel cladding will react with water and steam, producing hydrogen gas. In this
event there is a high danger of hydrogen explosions, threatening structural
damage to the reactor and/or associated safety systems and/or the exposure of
highly radioactive spent fuel rods that may be stored in the reactor building (approx 15 tons of fuel is replenished each year to maintain
normal BWR operation) as happened with the Fukushima I nuclear accidents.
·
Control rods are inserted from below for current BWR
designs. There are two available hydraulic power sources that can drive the
control rods into the core for a BWR under emergency conditions. There is a
dedicated high pressure hydraulic accumulator and also the pressure inside of
the reactor pressure vessel available to each control rod. Either the dedicated
accumulator (one per rod) or reactor pressure is capable of fully inserting
each rod. Most other reactor types use top entry control rods that are held up
in the withdrawn position by electromagnets, causing them to fall into the
reactor by gravity if power is lost.
@@Mark III Containment
Mark III Containment
http://nuclearstreet.com/nuclear-power-plants/w/nuclear_power_plants/mark-iii-containment.aspx
From:
http://www.nrc.gov/reactors/bwrs.html
Boiling Water Reactors
from
http://www.nrc.gov/reactors/bwrs.html
@@Perry Nuclear Generating Station
Summary: Wikipedia. The Perry Nuclear Power Plant
reactor is a General Electric BWR-6 boiling water reactor design, with a Mark
III containment design. The original core power level of 3,579 megawatts
thermal was increased to 3,758 megawatts thermal in 2000, making Perry one of
the largest BWRs in the United States. Built at a cost of $6 billion, Perry-1
is one of the most expensive power plants ever constructed.[citation needed]
Perry was originally designed as a two-unit installation, but construction on
Unit 2 was suspended in 1985 and formally cancelled in 1994. At the time of
cancellation, all of the major buildings and structures for the second unit
were completed, including the 500-foot-tall (150 m) cooling tower.
Safety problems
from:http://www.fox8.com/news/wjw-perry-nuclear-power-plant-concerns-after-japan-earthquake-txt,0,924650.story
Local Nuclear Plant Shares Traits with One in Japan
Their fuel tanks are above ground, ours are buried and sealed in a vault,"
said Todd Schneider, a spokesman for FirstEnergy. "Our containment
structures are larger and that protects the reactor better," he added.
@@Pictures
Mark I
schematic
http://www.beyondnuclear.org/home/2011/3/12/fukushima-dai-ichi-unit-1-reactor-schematic.html
Fukushima Dai-ichi Unit 1 reactor schematic
Mark II
Reactor Building
http://www.nucleartourist.com/areas/auxbldg.htm
http://www.nucleartourist.com/images/rx-bldg1.jpg
@@Reactor Cap
link Here is
the cap (cap of containment vessel) being lifted by the resident crane, but
this may not be an actual cap of a GE Mark I design:
@@Onagawa
From:
http://en.wikipedia.org/wiki/Onagawa_Nuclear_Power_Plant
[edit] Reactors on Site
[edit] Unit 1
[edit] Unit 2
·
May 2006 it was confirmed that a pipe was leaking due
to debris damage.
·
June 7, 2006 Difficulties with pressure control
prompted further inspections.
·
July 7, 2006 METI and the Nuclear and Industrial Safety Agency
determined that the plant's performance was not satisfactory.[citation needed]
[edit] Unit 3
·
July 7, 2006 Due to pipe integrity concerns the
reactor was shut down.
·
November 25, 2006 Following
repairs the reactor was restarted.
·
March 11, 2011 2011 Tohoku earthquake damaged the
turbines after a fire broke out and was shut down.
[edit] Incidents
[edit] 2001
Small fire in the administrative
offices. Did not affect functioning of the
plant.
[edit] 2005
[edit] 2011
@@Refueling
link Based on the news story this was part
of, this is what things look like during refueling ops of a GE Mark I design
(water level is brought up and a 'water' path made over to the fuel storage
pool so the rods never 'see air'):
picture: 
@@Unit 1
http://sketchup.google.com/3dwarehouse/details?mid=11b70c1651c0b152f0725315050aa28f&prevstart=0
@@Venting
Hydrogen
VENTING
HYDROGEN INTO REACTOR BUILDING A BAD IDEA
http://www.gereports.com/the-mark-i-containment-system-in-bwr-reactors/
Willem Jan Oosterkamp says: April 5, 2011 at 7:54 am
"Venting hydrogen into the reactor building is not a sound technical
solution. I assume that the containment has failed, barring better information
on the Fukushima plants."