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Molten sodium is used as a coolant in some types of fast neutron reactors. It has a low neutron absorption cross section, which is required to achieve a high enough neutron flux, and has excellent thermal conductivity. Its high boiling point allows the reactor to operate at ambient pressure. However, using sodium poses certain challenges. The molten metal will readily burn in air and react violently with water, liberating explosive hydrogen. During reactor operation, a small amount of sodium-24 is formed as a result of neutron activation, making the coolant radioactive.
Sodium leaks and fires were a significant operational problem in the first large sodium-cooled fast reactors, causing extended shutdowns at the Monju Nuclear Power Plant and Beloyarsk Nuclear Power Plant.
Where reactors need to be frequently shut down, as is the case with some research reactors, the alloy of sodium and potassium called NaK is used. It melts at −11 °C, so cooling pipes will not freeze at room temperature. Extra precautions against coolant leaks need to be taken in case of NaK, because molten potassium will spontaneously catch fire when exposed to air.
The phase diagram with potassium shows that the mixtures with potassium are liquid at room temperature in a wide concentration range. A compound Na2K melts at 7 °C. The eutectic mixture with a potassium content of 77 % gives a melting point at −12.6 °C.
Has there been anything published on the effects of salt water cooling for a disintegrating core? Specifically, it would be useful to have some idea of the likely reactions between the fuel oxides and the nuclear reaction products with the chlorine ions in the salt, both dissolved as well as molten. As I remember my chemistry, the chlorine should have no trouble displacing the oxygen under high temperature conditions. Would the resultant chlorides be materially more soluble than the fairly inert oxides? What are the implications for the nature of the airborne emissions from the site and could that help explain the finding of plutonium and neptunium depositions quite a distance from the plant?
Originally posted by thorfourwinds
Our question: Did this 7-inch crack appear 'overnight' in this particular nuclear reactor?
Also, earlier in this thread, we postulated the idea that the borate moderator has reached its lifespan and was probably being inhibited by the saltwater and wouldn't be actually 'operational'...?
It is vitally importance to maintain the stable operation of Nuclear Power Plants now, and well into the future. The discovery of core shroud cracking in the BWR in 1990 led to heightened awareness and enhanced shroud inspection programs worldwide. This inspection initiative revealed that Stress Corrosion Cracking (SCC) of core shroud was becoming an issue for the entire BWR industry.
Extensive cracking of circumferential welds on the core shroud has been discovered in a growing number of U.S. and foreign BWRs. A lateral shift along circumferential cracks at the welds by as little as 1/8 inch can result in the misalignment of the fuel and the inability to insert the control rods coupled with loss of fuel core cooling capability. This scenario can result in a core melt accident. A German utility operating a GE BWR where extensive core shroud cracking was identified estimated the cost of replacement at $65 million dollars. The Wuergassen reactor, Germany's oldest boiling water reactor, was closed in 1995 after wary German nuclear regulators rejected a plan to repair rather than replace the reactor's cracked core shroud.
The crack lines are drawn on the welded portion, however they are actually observed on the shroud body near the welded position. The core shroud is assembled to envelop the whole fuel assembly in the RPV. Therefore, in case of shroud collapse, it is reasonably possible to hypothesize the situation in which reactor control is not possible due to the loss or damage to the steam separators and steam dryers located on the shroud head.
There have never been any safety inspections in Japan that analyze accident simulation assuming cracks in the core shroud. It is not always true that the safety inspection scenario could precisely predict the consequence of an accident resulting from a significant coolant loss accident such as the recirculation pipe rupture in a nuclear power plant with some cracks in its shroud.
According to the NRC report, the fuel rod assemblies in RPV would not be capable of circulating cooling water, because the coolant circulated in the shroud is leaked from cracks in the core shroud, which is also released from the recirculation pipe to the outside of the nuclear reactor. Even if the core shroud is in good condition, being capable of maintaining the circulation of cooling water, cracks in the shroud could ultimately lead to core meltdown, probably the most catastrophic accident that could occur at a nuclear power plant.
The RPV temperature measurements usually measure the temperature from the outside surface of the pressure vessel metal, so if the RPV is intact, its contents should have no effect on the measurement thermocouples.
if the thermocouples were held in place by magnetic recepticles, the steel of the RPV would have lost it's magnetic properties at about 770C, and the thermocouple(s) would have fallen to some position either hanging by their leads or at the bottom of the dry well.
TOKYO (AFP) - Tens of thousands of demonstrators rallied in Tokyo on Monday calling for an end to nuclear energy in Japan after the March 11 disaster that sparked the worst atomic crisis since Chernobyl.
About 60,000 people gathered for the anti-nuclear rally, organisers said, one of the biggest since the earthquake and tsunami and the following disaster at the Fukushima Daiichi power plant.
salt in the (now empty, or mostly empty) rpvs
Sixty thousand protesters gathered in central Tokyo on Monday demanding an end to Japan’s reliance on nuclear power, six month’s after the world’s worst nuclear accident
Tokyo Radiation Exceeds Chernobyl In Some Places … Japanese Government and Experts Discuss Evacuation
The need to evacuate parts of the sprawling capital of 35 million may have once seemed an incredible prospect but some experts say the possibility can no longer be ignored.
In the days immediately after the crisis began at the Fukushima No. 1 nuclear power plant, the government received a report saying 30 million residents in the Tokyo metropolitan area would have to be evacuated in a worst-case scenario, former Prime Minister Naoto Kan revealed in a recent interview.
One of those assessments said everyone residing within 200 to 250 km of the plant — an zone that would encompass half to all of Tokyo and cut clear across Honshu to the Sea of Japan — would have to be evacuated.