Title: Camera Finds Nuclear Plant Crack Summary: BUCHANAN, N.Y. (AP) -- A tiny, remotely controlled device with a video camera has found a crack in a tube that may have been the source of a radioactive leak at the Indian Point 2 nuclear power plant earlier this month, utility officials said.

Source: AP Online Date: 02/29/2000 12:08

LINK TO FULL STORY

-- Dee (T1Colt556@aol.com), February 29, 2000

Answers

Dee, thanks for the info and link.

-- Lurkess (Lurkess@Lurking.XNet), February 29, 2000.

Cracks in steam generator tubes are *unusual* no doubt but not unexpected.

Cracks have three (perhaps four) source of origin.

A crack can originate from a material defect in manufacturing. A "cold fold" can occur which later with corrosion can open and blow out under the higher pressure of the "reactor loop."

A crack can be caused by a foreign object that is carried into the tube by the flow of nuclear coolant. The foreign object can become "jammed" into place and the high velocity flow and resultant flow obstruction can "erode" the tube by electrochemical differences (strips electrons actually) causing a thin section which later blows out under the pressure differential between the "reactor loop" and the steam vessel interior.

A crack can be caused by vibration caused by normal turbulant flow in the tube itself. The turbulance is normal and related flow wise to "von karmen vortex shedding" by a spherical object travelling in any fluid flow. Vibration effects can be made worse by the tubes being not sufficiently "supported" by tube support structures within the steam generator, a possible design defect.

Cracks can also be caused by "embrittlement" caused by chemical activity in deposits that frequently cover the "tube sheets" in the lower sections of steam generators. These deposits are from the water itself (impure water actually) and have been a problem with Westinghouse PWR's in this country. The best solution is better water chemistry control for the "secondary" (non nuclear) water chemistry. An "interim" solution that is frequently done is to "chemically clean" the steam generators using acids or patented processes.

The small amount of radioactivity that escaped probably came from the condenser air removal system (which is the system that removes accumulated air from the turbines and condensers which in turn allows more efficient operation of the "steam cycle." The alarms frequently are wired into plant "trips" which shut down the whole cycle should radioactivity above some pre-set limit be exceeded. At what level the trips are set is usually in the judgement of station management.

The issue certainly was not Y2K related and was probably delt with according to standard operating procedure. An unfortunate occurence, particularly for the owners, stockholders, and any ratepayers who now have to pay for an extended outage for things to cool off and plug the failed tube, but no particular hazard to the public. (at least none more than usual.)

Best regards,

-- Joe (KEITH@neesnet.com), February 29, 2000.

Thank you for your good input Joe!

-- Dee (T1Colt556@aol.com), February 29, 2000.

If that's the failure point - the above explanation is correct.

There are several thousands of these tubes (about 1/2" in diameter each) in each steam generator. If one needs plugging, the process is straight-forward - but expensive and requires some difficult access.

About like having to crawl inside the engine cylinder through the spark plug hole to fix something. There are manholes and access patches, but it isn't comfortable climbing inside the piping and steam generator to get there. Hot work - with little room to move (or even breathe) or move equipment and tools around, radioactive environment, cumbersome clothes and breathing masks....not pleasant at all.

Doesn't take too long to do only one tube repair...the preparation and opening of the steam generator takes longer than the repair will. They may inspect all the rest though while the cover plates are off. Try to identify and fix any that look suspicious before they also break.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), February 29, 2000.

Robert,

Thanks much for your additional comments...very good.

Lurkess...thank you for your kind post. =)

-- Dee (T1Colt556@aol.com), February 29, 2000.