New problems of salt, smoke, and cooling failure at Japanese nuclear plant
It is likely to be an even bigger problem when the water inside the reactor is much more radioactive than usual and is under extremely high pressure, as it has been in all three reactors at the Fukushima Daiichi plant
New Problems Arise at Japanese Nuclear Plant, NYTimes.comBy KEITH BRADSHER March 23, 2011 “……..nuclear engineers say some of the most difficult and dangerous tasks are still ahead — and time is not necessarily on the side of the repair teams.The tasks include manually draining hundreds of gallons of radioactive water and venting radioactive gas from the pumps and piping of the emergency cooling systems, which are located diagonally underneath the overheated reactor vessels. The health warning that infants should not drink tap water — even in Tokyo, far from the stricken plant — raised alarms about extensive contamination.
Western nuclear engineers have become increasingly concerned about a separate problem that may be putting pressure on the Japanese technicians to work faster: salt buildup inside the reactors, which could cause them to heat up more and, in the worst case, cause the uranium to melt, releasing a range of radioactive material.
Richard T. Lahey Jr., who was General Electric’s chief of safety research for boiling-water reactors when the company installed them at the Fukushima Daiichi plant, said that as seawater was pumped into the reactors and boiled away, it left more and more salt behind.
He estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds apiece in Reactors No. 2 and 3, which are larger.
The big question is how much of that salt is still mixed with water and how much now forms a crust on the reactors’ uranium fuel rods. Chemical crusts on uranium fuel rods have been a problem for years at nuclear plants.
Crusts insulate the rods from the water and allow them to heat up. If the crusts are thick enough, they can block water from circulating between the fuel rods at all. As the rods heat up, their zirconium cladding can ignite, which may cause the uranium inside to melt and release radioactive material.
Some of the salt might be settling to the bottom of the reactor vessel rather than sticking to the fuel rods. But just as a heating element repeatedly used to warm tea in a mug tends to become encrusted in cities where the tap water is rich with minerals, boiling seawater is likely to leave salt mainly on the fuel rods, Mr. Lahey said……..
The water in the pipes tends to become radioactively contaminated because the valves that separate it from the reactor are never entirely tight.
It is likely to be an even bigger problem when the water inside the reactor is much more radioactive than usual and is under extremely high pressure, as it has been in all three reactors at the Fukushima Daiichi plant at various times since the earthquake and tsunami….
Fukushima Daiichi’s Reactor No. 3 began belching black smoke for an hour late in the afternoon, leading its operator, Tokyo Electric Power Company, to evacuate workers.. No. 3 is considered one of the most dangerous of the reactors because of its fuel — mixed oxides, or mox, which contain a mixture of uranium and plutonium and can produce a more dangerous radioactive plume if scattered by fire or explosions. The cooling system at Reactor No. 5, which was shut down at the time of the earthquake and has shown few problems since, also abruptly stopped working on Wednesday afternoon, said Hiro Hasegawa, a spokesman for Tokyo Electric…..
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