Part 1. Operated nuclear power plants
The first mention of the dangers of using nickel alloys for the production of equipment of western nuclear power plants was done by H Coriou et al., 3-eme Colloque de Metallurgie sur la Corrosion, Saclay North Holland Publ. Co., Amsterdam, Holland, p. 161, 1959.
The safest reactors in the world can be shut down because of the increased danger. Independent experts investigating an accident at the nuclear power plant, "Davis Besse", given the conclusion of the feasibility of stopping all 69 units with PWR reactors in the United States. U.S. regulator does not hide his anger …. But with time to calm down and continue the process of extending the operation of nuclear power plants, because new nuclear power plants under construction with the AP-1000 reaktoromi problems seem even more.
Alloy 600 is actively used earlier light-water projects in the western Uzbekistan. At first, seemed the best one, this material created as a result of one of the biggest crises in the history of the reactors.
In 1971 he had recorded the first leak in the steam generators of PWR, caused by corrosion of Alloy 600. Then, in block number 3 of NPP "San Onofre" PWR reactor corroded pipe for instrumentation equipment on the volume compensator. In 1987 he ran down the sleeve of the same expansion joint on the block with PWR in Arkansas. And in 1989, the first information about the corrosion of PWSCC on French units. Yet two years later, the first cases were detected corrosion damage pipes for entry control rod drive on the covers of Western pressurized reactors. Nowadays there are leaks measuring sensors in the reactor bottom and cracks in the butt joints (butt weld). Well, it all started already in 1971 with a leak in the steam generators.
These and other incidents are well documented and collected in the aforementioned report, NUREG-1823, or other known document MRP-111 (Materials Reliability Program Resistance to Primary Water Stress Corrosion Cracking of Alloys 690, 52, and 152 in Pressurized Water Reactors).
As you can see, no one has ever put information about problems with the alloy 600 "under the bar." U.S. laws simply do not allow it. But what is absolutely right, Vladimir Rychin — all relevant publications are mainly in the highly specialized trade press, not getting to the pages of popular publications and, especially, newspapers and magazines for a mass audience. Western companies are trying to strictly observe their way of designers, manufacturers and owners of the safest in the world of atomic technology.
Not faced with the problem of alloy 600 only Russian VVER reactors modifications and German PWR. In Germany, after the known issues at the plant "Obrigaym» (Obrigheim), it was decided to abandon the alloy 600 in favor Incolloy 800, which allowed local nuclear industry to remain bystanders in the subsequent epic changes coming down the primary circuit equipment.
Anyone who is trying to figure the problem of Alloy 600, it is important to understand — the main difficulty stems from the fact that this material is too often used by Western designers in various elements of power. If you look at the chart the major western projects to ensure that the unusually high prevalence of this alloy.
Diagram PWR reactor project "Westinghouse" (red labeled cells using Alloy 600)
Alloy 600 in most western plants made all bushings, fittings, sleeves, which provide input to the measuring vessel and pipes, sensors, actuators, heaters, and environments. American designers used the elements of the alloy in the field piping connections nozzles containers of different materials. These adapters in the English-language literature as safe end, but ironically, the "safe ends" or the safety features found in the western projects real sources of danger.
And in addition we should not forget that not only corrode the elements of the alloy 600, but also created on the basis of its consumables Alloy 82 and Alloy 182.
The most famous incident, but luckily not turned-human casualties occurred at the nuclear power plant, "Davis Besse" in the U.S. state of Ohio. Corrosion destroyed sleeve pipe to enter the drive control rod, and then started for the cover of carbon steel.
February 16, 2002 the U.S. nuclear power plants, "Davis-Besse" in the state of Ohio with one reactor PWR-900 was stopped due to unplanned intensive clogging filters boron. Careful examination showed that station is on the verge of disaster.
It should be noted that the material covers unstable corrosion. For their protection in the projects envisaged sleeve. Such a sleeve just been destroyed by "Davis Besse." Stop the corrosion process could welding of stainless steel with a thickness less than a centimeter. If cladding would also be damaged, hot radioactive water from the body to be pulled out of the reactor space, with clear consequences.
A diagram schematically showing a corrosion reactor lid.
In 2014, the station had to be put new reactor lid, the manufacture of which does not use an alloy 600. But following an incident in 2010, also associated with a corrosive degradation, company owner has decided on the early acquisition covers the group AREVA. In October 2011, work began on its installation, but were stopped on October 10 after the discovery of cracks in the facade of decorative concrete containment. Start the unit after the completion of the replacement of the cover was originally scheduled for late November 2011. The station is licensed to operate until 2017, but plans to seek an extension until 2037.
However, the regional office of the Nuclear Regulatory Commission (NRC) in Chicago argue that the station did not receive permission to run as long as it is confirmed — found during the outage cracks in the concrete containment does not affect safety.
Meanwhile, small fire, what occurred at the station on Wednesday, regulators do not attach importance. Ignition occurred after the leakage of oil from one of the valves.
After the incident at the plant, "Davis-Besse" from the project unit with the AP-1000 reactor was hastily removed material I600MA. Thus, the American designer actually admitted — in the PWR technology allowed inside critical error. In other words, the error in the reactor DNA.
Comparison with the DNA is not accidental. Following the United States, I600MA been involved in projects of almost all of these PWR-reactor in the world, with the exception of Russia. If the new light installations dubious material may try to replace with more suitable, then at existing plants to prevent sudden catastrophe will be possible only through organizational measures, such as a deeper and more frequent inspections.
The degree of severity of the error can be judged by designers panic Throwing the AP-1000. All elements of the new unit is "almost a third generation" Variation proposed replacement material I600MA. This indicates, first of all, the designer of the uncertainty about the reliability of the child.
And finally, one small but very typical observation. One of the candidates to replace the discredited I600MA called material I690TT. And it would be an alternative suspiciously familiar to many Russian nuclear scientists — it is stainless steel SS316L. For those who understand — this steel, which is close in composition to steels, has been successfully used in the Russian VVER reactors.
It is natural that this situation has been very beneficial to a number of companies. Errors of American designers are bringing additional profits, the French group AREVA. Such a conclusion can be reached after reading the report submitted by the members of the group (S.Sills, H.Gloagen and R.Tevene) at the International Conference ICAPP-2007, held in Nice in May 2007.
Replacement of the basic equipment of the primary circuit of PWR and its derivatives began in the early 80's due to stress corrosion cracking (PWSCC) of Alloy 600, reminiscent of the authors of the report. First in line to replace the steam generators were (80th year), followed by followed by the cover of reactors and other equipment (90s onwards).
The report notes that replacing the western blocks and other elements are subject, in particular, expansion of the segments of the primary circuit piping and internal parts of the body. The growth of replacement equipment caused by the appearance, in addition to PWSCC, stress corrosion cracking of the second circuit (IGSCC).
The diagram covers replacement reactors, made in France AREVA group (blue), the U.S. (brown) and other countries (in yellow)
According to the report, with the further spread of the problem of Alloy 600 at the plant of western projects, the owners of the stations will wake up the question of finding ways to save money when replacing damaged by corrosion of the equipment. The way out of this situation may be the simultaneous replacement of a large number of elements (such as steam generators and reactor head). However, against the background of saving money — in particular, due to the smaller number of autopsies containment — simultaneous replacement will require more careful planning and well-coordinated work of many professionals. Otherwise, the owners of nuclear power plants may face delays and disruption of the schedule changes.
The authors believe that a single solution for replacement of equipment suitable for all types of reactors PWR, do not exist, and each unit should be considered separately.
Dismantled equipment belongs to the category of radioactive waste, and handling is necessary to develop a strategy beforehand. Some companies prefer to place the captured equipment in temporary storage (mausoleums) directly on the site or in the immediate vicinity. This allows you to save on transportation and also provides easy access to the equipment for taking samples and conducting other research.
But the construction of the mausoleum does not eliminate the problem in principle — that is, over time, this equipment will have to take out a specialized store. An alternative approach involves removal once the old equipment in the interim or permanent storage.
Mausoleums dismantled steam generators in France (left) and the U.S.
Corrosion PWSCC has become an indispensable companion Western reactors. All the materials of the first circuit on your station will degrade. You need to know the answers to the following questions:
What equipment leaks show up?
Where and when will it happen?
Will continue to use the unit until the end of his term of service with the discovery of the defect?
This pessimistic conclusion reached in 2004 by specialists of the Institute of Nuclear Energy (NEI), the Western companies that own the reactors PWR American-made or built by U.S. licenses may choose as their unofficial guide to action.
Prepared according to the site
Over the past 33 years in the United States are not built a single new nuclear power plant
The degradation of the nuclear industry in the U.S.