Wednesday, March 16, 2011
Live Updates about Japan's Nuclear Power Plant after the Earthquake and Tsunami
There are currently 55 operating nuclear power plants in Japan. The ten FEPC member companies own and operate 52 Light Water Reactors (LWR). Three more LWRs are operated by the private company Japan Atomic Power Corporation (JAPC). The Monju Fast Breeder Reactor (a prototype reactor which was taken off line in the 90's but expected to start up again soon) is run by the semi-governmental organization Japan Nuclear Cycle Development Institute (JNC). There are also two more nuclear plants currently under construction, as well as another 11 that are in advanced planning stages. One of those reactors in the planning stage will be owned and operated by another semi-private corporation, The Electric Power Development Co, Inc. (EPDC). Two reactors in Japan, JAPC's Tokai and JNC's Fugen Advanced Thermal Reactor prototype have been permanently closed.
On 11 March 2011, the Japanese government reported to the International
Atomic Energy Agency (IAEA) the explosion of two (2) nuclear power plants in
Fukushima Daiichi following the 8.9 magnitude earthquake that rocked Japan which
affected three (3) nuclear reactors (Units 1, 2 and 4). Unit 1 reactor occurred
outside the primary containment vessel and that the integrity of the vessel remains
intact as confirmed by plant operator of Tokyo Electric Power Company (TEPC).
Fukushima Daiichi is the first nuclear plant constructed and entirely run by TEPC
and one of the 25 largest nuclear power stations in the world.
Japan’s Nuclear and industrial Safety (NISA) confirmed the presence of
radioactive elements cesium-137 and iodine-131 in the vicinity of Fukushima
Daiichi Unit 1. NISA noted that there was an initial increase in levels of radio activity
around the plant but levels lessen in recent hours as observed.
Recognizing that information is still not complete due to the destruction of the communication infrastructure, producing reports that are conflicting, here is our best understanding of the sequence of events at the Fukushima I‐1 power station.
- The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked.
- All external power to the station was lost when the sea water swept away the power lines.
- Diesel generators started to provide backup electrical power to the plant’s backup cooling
system. The backup worked.
- The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply.
- An Isolation condenser was used to remove the decay heat from the shutdown reactor.
- Apparently the plant then experienced a small loss of coolant from the reactor.
- Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery‐supplied control valves lost DC power after the prolonged use.
- DC power from batteries was consumed after approximately 8 hours.
- At that point, the plant experienced a complete blackout (no electric power at all).
- Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure).
- Portable diesel generators were delivered to the plant site.
- AC power was restored allowing for a different backup pumping system to replace inventory in reactor pressure vessel (RPV).
- Pressure in the containment drywell rose as wetwell became hotter.
- The Drywell containment was vented to outside reactor building which surrounds the
- Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building.
- Hydrogen in reactor building exploded causing it to collapse around the containment.
- The containment around the reactor and RPV were reported to be intact.
- The decision was made to inject seawater into the RPV to continue to the cooling process,
another backup system that was designed into the plant from inception.
- Radioactivity releases from operator initiated venting appear to be decreasing.