Belgian Doel-3 and Tihange-2 Back in the News

Tihange Nuclear Plant, Belgium.  Courtesy Electrabel.

Tihange Nuclear Plant, Belgium. Courtesy Electrabel.

By Will Davis

The years-long saga surrounding the reactor pressure vessels at the Doel-3 nuclear power plant and Tihange-2 NPP in Belgium has taken another turn, pushing these units back into the broader news cycle and renewing calls from some (uninformed) quarters for further worldwide action and/or permanent shutdowns.

The saga began in mid-2012 when Electrabel, owner-operator of Belgian nuclear plants, discovered anomalies in the reactor vessel of Doel-3 while using a new ultrasonic examination method (originally devised to assess the quality of welding the cladding to the pressure vessel, but which had apparently detected underlying flaws in the pressure vessel itself.) This led to a flurry of examinations both materially and archivally worldwide as various regulators and owners looked into the metallurgical records for pressure vessels manufactured in part or in whole by the long-defunct Rotterdam Dockyard concern. The eventual result in the United States was the determination that only nine nuclear plants had either sections or whole vessels made by Rotterdam, and that records and present analysis were quite sufficient to ensure that no integrity, and thus safety, issues existed. (See link in text above for extensive detail on this, previously on ANS Nuclear Cafe by this author.) These results were essentially duplicated worldwide with the exception of course of Doel-3 and eventually Tihange-2. Electrabel was required to submit a restart plan to Belgium’s FANC (Federal Agency for Nuclear Control).

Doel Reactor Pressure Vessel

Reactor vessel of the type used at Doel-3, Tihange-2. Barrel or body section comprised of forged rings, welded together to form vessel. Inclusion of hydrogen during manufacture produces localized high pressure areas that crack circumferentially, which are called “flakes.” Now, irradiation damage coupled with these inclusions is thought to be causing more rapid vessel embrittlement than predicted. Illustration courtesy FANC.

After some extensive analysis, FANC allowed Electrabel to restart these two units in May 2013, but provided a number of longer-term requirements that Electrabel would have to meet in order to keep the units in service.

Unfortunately for Electrabel, in August 2014 a number of reactor vessel steel samples that had been irradiated for testing were actually destructively tested, and showed a marked decrease in their mechanical properties—in a word, embrittlement, or for a more general term, a weakening under some extreme conditions. While the plants had been operating with much more restrictive heatup and cooldown rates for the reactor vessels (to reduce stress on them) the decision was made to shut both down immediately in a case of extreme prudence, in expectation of further analytical result.

The call for another session by FANC’s consultant panel on reactor pressure vessel issues has, however, led to a re-igniting of the issue in the press and a further call to action by FANC’s director. This worldwide analysis of vessels has been done before, as was detailed in a previous article on ANS Nuclear Cafe, but it may be that FANC would like to doubly assure its conviction that material properties of hydrogen flaked pressure vessel steels of the type and composition used in Doel-3 and Tihange-2 might be degrading more quickly under irradiation than previously assumed. (This, however, essentially ignores many years’ worth of study in the United States and in Russia concerning pressure vessel welds, defects, and embrittlement conducted by national labs as well as the Atomic Energy Commission [now the Nuclear Regulatory Commission] and which is a condition that is continuously monitored and evaluated.) This “call to action” by FANC as a matter of prudence has unfortunately been picked up by such ‘advocates’ as Greenpeace, which is calling for extreme actions in the name of safety, without apparently understanding the deep pool of knowledge existing in this field.

Doel Nuclear Power Plant.  Courtesy Electrabel.

Doel Nuclear Power Plant. Courtesy Electrabel.

For now, the path forward for these two units is far less clear than it is for any other units worldwide that have part or whole vessels manufactured by Rotterdam Dockyard. Globally, operators have already conducted examinations sufficient to ensure integrity of these vessels in the near term. WENRA (Western European Nuclear Regulators Association) also completed in December 2014 the first phase of a Europe-wide analysis and feedback on the integrity of reactor vessels of plants of any type or origin using forged ring type vessels, and this investigation and feedback process continues. (Vessels fabricated from plates, which typically are large boiling water reactor vessels, are not as prone to hydrogen inclusion driven flaking due to the smaller size of the original ingots and due to the rolling process deforming the material, according to WENRA.)

For Doel-3 and Tihange-2, the spotlight is on; it is impossible to predict that these units have any percentage of chance of restarting if FANC’s expert panel finds that the reduction in strength of the irradiated samples (and thus by association the vessels installed in the plants) is increasing at a rate that puts the absolute operational limits for these vessels’ lives in any sort of near time frame.

For more information:

WENRA Report – Activities in WENRA countries following the recommendation regarding flaw indications found in Belgian reactors.


DavisWill Davis is Communications Director, historian, newsletter editor and board member for the N/S Savannah Association, Inc. He is a consultant to the Global America Business Institute, a contributing author for Fuel Cycle Week, and writes his own popular blog Atomic Power Review. Davis is also a consultant and writer for the American Nuclear Society, and serves on the ANS Communications Committee. He is a former US Navy reactor operator, qualified on S8G and S5W plants.

7 thoughts on “Belgian Doel-3 and Tihange-2 Back in the News

  1. Josep Rey

    Hi all!

    I recently heard about a rumor saying that problems with reactors at Thiange and Doel are because the light water coolant flowing in the primary circuit is making the steel vessel very weak.

    Considering that a 80% of the reactors worldwide use water as a primary coolant, this problem would also be found in all those reactors, meaning that the probabiliy of a loss of coolant accident is getting higher every day. Is it true? Or it is just a design flaw in Belgium?

  2. L. Mascow

    Considering that a 80% of the reactors worldwide use water as a primary coolant, this problem would also be found in all those reactors, meaning that the probabiliy of a loss of coolant accident is getting higher every day.

    Think they would’ve found that out long ago with lots of decommed reactors, so there’s no need to fret every day. Worst case nightmares are always worst than the fizzled reality coming true, a’la TMI and Fukushima.

  3. Will Davis

    Hello, Josep;

    The reactor vessels are clad internally with stainless steel, and the primary coolant chemistry is closely controlled so that corrosion of either the stainless steel vessel clad (lining) or the vessel itself due to water is a non-existent over life of the plant.

    The problems here are the potential weakening of the material of the pressure vessel itself due to first the inclusion of hydrogen causing ‘hydrogen flaking,’ and second the cumulative effect of intensive irradiation of the vessel steel which leads to increasing embrittlement. The plants are of course designed with the knowledge that embrittlement will occur over the life of the plant — and it’s often this factor that determines life extension. The vessels are normally designed with more than enough reserve of strength to make up for a reduction of strength over the lifetime of the plant. What the key issue for FANC and Electrabel deals with is whether or not this hydrogen flaking in the vessel itself highly compounds or exacerbates the reduction of ductility of the vessel, and/or is likely to allow for failure in a case of extreme thermal shock. These issues will have to be analyzed by FANC, its expert panel and Electrabel before FANC allows these two units to continue to operate.

    All of the other reactor vessels in the world which were made by Rotterdam Dockyard in whole or in part have, to my knowledge, been cleared of any further issues. No other comparable issues exist with other vessels made by other manufacturers to my knowledge.

  4. northcoast

    The ASME Boiler and Pressure Vessel Code design requirements for nuclear pressure vessels was developed around a “leak before break” objective. Given that no pressure vessel can be crack free, testing requirements and allowable crack size are designed to provide safety margins against catastrophic crack growth as predicted by fracture mechanics analysis.

    The steel in these vessels is brittle at very low temperatures and more ductile at operating temperature.
    There is concern about operating safety whenever the steel ductility may be below design requirements.

  5. David Gaeddert

    Dear people,

    I have experience in steel and chemical industries from ’66 to ’12. I’ve known about hydrogen embrittlement, but nothing as extreme as what is apparently being reported in nuclear pressure vessels now. One speculation has been about “proton migration” from cooling water into pressure vessel steel. steel.

    I wish to introduce my “lonely neutron” hypothesis for consideration. A neutron, left alone, will decompose into a proton and electron–a hydrogen atom. With the neutron flux in an operating reactor, there is plenty of opportunity for stray neutrons to decompose into hydrogen atoms and cause problems in the steel. It is easy to imagine how a crack in a pressure vessel weld or plate would flood containment with hot, radioactive steam. If cooling of core could not maintained, results could be bad.

  6. Will Davis

    Your theory is rather interesting to me. Keep in mind of course that in some pressurized water reactors we actually inject hydrogen into the primary coolant to suppress radiolytically generated oxygen, whose presence would (needless to explain to you) be bad. This has been done for many years, and that effect is quantified and accounted for.

    My guess here is that what’s happening isn’t revelation of a wholly lower margin of safety than we’d previously assumed. Instead, we’re seeing that the materials used in vessels have defects we had not seen before because we weren’t able. (Everyone to whom I’ve spoken about this Belgian “witch hunt” for the last couple of years feels the way I do about this, at least for now.) Now, the big question here is why the irradiated samples tested in Belgium showed what they thought was a marked decrease in ductility. We also don’t know the expected ductility they used as their baseline. I think a lot more work will occur there, and I think we need to be able to better see how Belgium’s pressure vessel standards and measurements compare to ours.

  7. mjd

    @David Gaeddert March 19, 2015 at 13:13
    “A neutron, left alone, will decompose into a proton and electron–a hydrogen atom.”
    I’m having trouble seeing this is true, or even possible. The part about ending up with a H atom. The most probable decay results in 3 particles, all with KE which moves them apart. A proton, an electron, and an electron anti neutrino. The decay energy total is ~.08MEV, mass lost as energy. To get back to a H atom something will have to “fuse” the p and e back together. That takes energy, converted back to mass. I can’t see that happening inside the vessel metal. But willing to listen