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Tests revealed a stunning 13 047 cracks in Doel 3; and 3 149 cracks in Tihange 2.” (Greenpeace) The largest defect is believed to be 179 mm x 72.3 mm (7 in. x 2.8 in); the smallest 12.3 mm x 13.7 mm (0.48 x .54 in.). These are within the nuclear reactor pressure vessel walls. Doel Tihange Nuclear Reactors in Europe
From Greenpeace:
Thousands of cracks in Belgian reactors, potentially a global nuclear problem, by Kendra Ulrich and Eloi Glorieux, 17 February, 2015

Picture a 33 year-old asphalt road: weathered with time, bearing the cracks and crags of decades of harmless-seeming water trickling into its crevices, freezing, expanding, breaking up the road from within. Most people wouldn’t want to trust their car to the safety of a road like this. And it certainly isn’t the image anyone wants to invoke when talking about critical equipment in nuclear reactors. Yet, on Friday the 13th, two leading materials scientists announced that the Belgian reactors, Doel 3 and Tihange 2, may be experiencing the nuclear equivalent in their reactor pressure vessels; essentially the piece of equipment that contains the highly radioactive nuclear fuel core being comparable to an old, busted up road. Clean Energy Now, Greenpeace, nuclear component Thousands of cracks [1] have been discovered in the pressure vessels of both reactors. This component is required to be integrally sound, with no risk of failure, due to the potentially catastrophic nuclear disaster resulting from the failure of a pressure vessel. As reactors age, the steel of the reactor pressure vessel is damaged – or embrittled – by radiation. According to the scientists, hydrogen from the water in the pressure vessel – which cools the nuclear fuel core – may be corroding the steel by injecting hydrogen atoms into the steel of the vessel itself, where it can accumulate and build up pressure, resulting in the steel blistering – effectively breaking up the pressure vessel from within. Tests revealed a stunning 13 047 cracks in Doel 3; and 3 149 cracks in Tihange 2. [2] After first discovering the problem and shutting down the cracked reactors in 2012, the Belgian Federal Agency for Nuclear Control (FANC), dismissed the issue as a manufacturing problem and okayed the reactor to be start up again in 2013. They did so while acknowledging that they did not to fully understand what was happening inside the reactor steel. However, further testing revealed unexplained and unexpected embrittlement of a test steel sample. Following these findings, both reactors were shut down again since March 24, 2014. But, the announcement of the materials scientists now go one step further: they state that the problem may well be the result of normal reactor operations. This means the cracks may be growing in size, and furthermore, that this could be endemic to the global nuclear fleet. Simply put: the findings in Belgium have serious safety implications for every nuclear reactor on the planet. In response, the Director General of the Belgian nuclear regulator, The Federal Agency for Nuclear Control (FANC), admitted that, “This may be a global problem for the entire nuclear industry. The solution is to implement worldwide, accurate inspections of all 430 nuclear power plants.” When the head of a federal nuclear regulator says that every reactor in the world needs to be inspected for a critical nuclear safety problem, the smart thing for national nuclear regulators to do is take immediate action. Certainly, every reactor needs to be inspected for such cracking at the earliest possible date, but no later than the next maintenance outage. Electrabel, operator of the Belgian reactors, has reacted to the latest news by saying that it may be willing to “sacrifice” one of its crippled reactors to scientific study; meaning they would permanently shut down the reactor and allow destructive testing in the hopes of learning more about this previously ignored or dismissed nuclear safety problem. Given that this phenomenon has not been sufficiently studied and is poorly understood, restarting any reactor in which cracking is found would not only constitute a nuclear experiment, it would place the public at unnecessary and unacceptable risk. There are 1.5 million people living within 30km from the Doel reactor, which is close to the Dutch border. Every reactor needs to be inspected – and before the old, busted up nuclear road leads to yet another catastrophic nuclear disaster. Kendra Ulrich is a Senior Energy Campaigner with Greenpeace Japan. Eloi Glorieux is an Energy Campaigner with Greenpeace Belgium.” http://www.greenpeace.org/international/en/news/Blogs/nuclear-reaction/cracks-in-belgian-nuclear-reactors/blog/52139/ (Emphasis added)


Absent from the recent discussion are the impacts of neutron bombardment, which could cause sudden reactor pressure vessel failure due to embrittlement. Also absent is discussion of previous use of MOX fuel in these reactors. What is the impact of reactor uprates and high burnup fuel?

A detailed study was published on these cracks two years ago, which discusses sources of cracks in nuclear reactors:
2.2.1 Radiation effects During the operation of a nuclear power plant neutrons are emitted from the reactor core and reach the reactor pressure wall. Neutrons (with energies above about 0.5 MeV) cause atomic displacements in the RPV materials, creating interstitials and vacancies (so-called Frenkel defects) that can diffuse through the lattice, recombine or agglomerate forming larger defects. These defects impede dislocation movement causing embrittlement of the material. This radiation embrittlement results in an increase of the ductile-brittle transition temperature (DBTT) to higher temperatures and a reduction of toughness/ductility. The DBTT has to be far below the operational temperatures of the RPV otherwise there is a risk of brittle fracture of the component. Radiation reaching the RPV wall without displacing atoms in the materials lattice structure, can enhance diffusion of impurities by the deposited energy, the so-called radiation-enhanced diffusion (RED). Hydrogen diffusion in the material can also be supported by radiation. ‘The effects of neutron irradiation will lead, in the core area, to an embrittlement of the material and the generation of heat sources by γ-radiation. Heat sources caused by the absorption of γ-radiation are a special type of thermal loading.’ 37 Another effect originating from radiation impact on materials is the radiation-induced segregation (RIS), defined as a radiation-induced redistribution of alloy constituents and impurities at point defect sinks. 38 Radiation effects are complicated processes due to the simultaneous influence of temperature causing thermal diffusion of the produced defects. This diffusion can cause recombination of interstitials and vacancies, but can also induce the formation of vacancy or interstitial clusters. A consequence is for instance a reduced radiation embrittlement at higher irradiation temperatures 39…” (p. 15) “In both Doel 3 and Tihange 2 NPPs MOX 43 fuel elements were used instead of pure UOX 44 -fueling during the 1990ies 45 . The consequence of MOX-fuelled reactor cores is a shift of the neutron spectra and the neutron flux for the impinging neutrons at the RPV wall depending on the core configuration 46. There is not much known on the effect of these changes with respect to radiation embrittlement of the RPV wall materials. … “2.2.3 Fatigue LCF (low-cycle fatigue) of RPV materials is caused by the thermo-mechanical cycling during the startup and shutdown procedures; an influence of the LCF on the microstructure (for instance hydrogen-related defects) and radiation-induced material degradation has to be expected.” (p. 17) From “Flawed Reactor Pressure Vessels in Belgian Nuclear Plants Doel-3 and Tihange-2, Some Comments“, by Ilse Tweer, Materials Scientist, Consultant, January 2013 Commissioned by Rebecca Harms , President of The Greens/EFA Group in the European Parliament http://www.greens-efa.eu/fileadmin/dam/Documents/Studies/Flawed%20Reactor%20Pressure%20Vessels%20in%20Belgian%20Nuclear%20Plants%20Doel-3%20and%20Tihange-2.pdf

Links from the original Greenpeace blog post:
[1] http://www.fanc. be/nl/news/doel-3/tihange-2-new-update/745.aspx
2. Material properties of steel containing hydrogen flakes… In carrying out tests related to theme 2 during the spring of 2014, a fracture toughness test revealed unexpected results, which suggested that the mechanical properties of the material were more strongly influenced by radiation than experts had expected. As a precaution both reactors were immediately shut down again. Electrabel launched a test campaign to find an explanation for the unexpected test results.” (Text from link not at original Greenpeace post; emphasis added.)

[2] http://deredactie. be/cm/vrtnieuws/videozone/programmas/terzake/2.37612

[3] http://www.fanc.fgov. be/GED/00000000/3700/3751.pdf NB: At the Belgium nuclear regulator (fanc) web site, if you click on FR, rather than NL, you tend to get English documents. The deredactie program is a mix of Flemish and English.

Map locations exported from wikipedia: http://en.wikipedia.org/wiki/Doel_Nuclear_Power_Station http://en.wikipedia.org/wiki/Tihange_Nuclear_Power_Station Our

Note [a]: It is a good idea to have at least one month of food and water supplies and be prepared to move in the event of an accident, God only knows where, as the nuclear reactors are now all over, even in the Southern Hemisphere and the two hemispheres are connected… You can never go wrong having extra food and water, however.