Posted on 04/18/2003 6:23:25 PM PDT by Paleo Conservative
WASHINGTON, April 18 — A nuclear reactor in Texas is leaking cooling water from the bottom of its giant reactor vessel, a development that experts view with concern because they have never seen it before, the Nuclear Regulatory Commission said today.
Technicians at the South Texas Nuclear Project, about 90 miles southwest of Houston, have found residues indicating that cooling water leaked from the vessel through two penetrations where instruments are inserted into the core, according to the company that operates the plant. Operators at all 103 commercial nuclear reactors have been giving closer attention to their reactor vessels since the discovery last year of extensive leaks in the vessel head at another plant, Davis-Besse, near Toledo, Ohio.
The Texas plant, South Texas 1, shows much smaller signs of leakage than the Ohio plant. In both cases, technicians found deposits of boron, a chemical added to the water to control the nuclear reaction, which remains after the water evaporates. At Davis-Besse, technicians cleaned out boron with shovels; in Texas, technicians found an amount about half the volume of an aspirin tablet, according to Ed Halpin, the plant general manager.
No corrosion is visible but no one is sure what is underneath. At Davis-Besse, the steel of the vessel was so corroded that a metal part on the head flopped over like a mailbox that was no longer stuck properly into the front lawn. At that plant, workers have replaced the vessel head, a part that was intended to last for the lifetime of the reactor. Davis-Besse has remained closed since the leak was discovered, 13 months ago.
The South Texas leak is unexpected and, so far, unexplained. "This is the first time it's been seen, either here or abroad," said Victor Dricks, a spokesman for the Nuclear Regulatory Commission. Representatives of two national nuclear industry groups are at the plant to study the problem, and plant managers have promised to keep the reactor shut until they find the cause and fix it to the commission's satisfaction, he said. The plant is currently shut for re-fueling.
The vessel is 14.4 feet wide and 46 feet high, made of steel about six inches thick. Its bottom has 58 penetrations, where instruments can be inserted to measure the flow of neutrons, the subatomic particles that sustain the chain reaction. There are leaks at two of the penetrations, although the volume of water was apparently small, Mr. Dricks said.
At plants around the country, cracks of some metal parts have been traced to stresses created in construction. Others have been caused by a phenomenon called intergranular stress corrosion cracking, which occurs in some metals when they are under stress at high temperature. But Mr. Halpin said he would not speculate about the cause of the South Texas leak.
Water inside the vessel is at a temperature of more than 500 degrees and a pressure of more than 2,000 pounds per square inch, so even a small hole could release large volumes of radioactive water into the containment building. Mr. Dricks said, however, that the pumps in the plant's emergency core cooling system could inject water faster than it could leak through a hole the size of the penetration, so that the nuclear core would stay covered. The design is for contamination in such cases to stay within the containment dome.
A problem for repair is that the radiation field under the reactor is about 500 millirem per hour, Mr. Halpin said. At that rate, a worker would absorb in four hours the radiation dose that most reactor operators set as a limit for a full year. Repair work in such high fields is usually carried out by large teams of workers, each spending only a short period at work.
South Texas 1 is one of the youngest plants in the country. It went on line in August 1988. South Texas 2, which is adjacent, followed in June 1989. It shows no sign of leakage. The two reactors are owned by the cities of Austin and San Antonio, a subsidiary of American Electric Power, and Texas Genco LP, a generating company.
You don't want steam in a reactor vessel, you need liquid coolant. I assume that you are checking saturation tables. Water at saturation temperature is borderline steam. You want a pressure that will prevent steam from occurring in the core and removing the cooling effect of the water. So 500 degrees and 2000 lbs is a perfectly acceptable combination.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.