Pressure Vessel Cracking [Doel & Tihange Follow-up]
In 2012 thousands of defects were discovered in the reactor pressure vessel shells of the NPPs Doel-3 and Tihange-2, Belgium.
The reactor pressure vessel (RPV) is the is the central component of a nuclear reactor, – for safe operation of the nuclear power plant throughout service life RPV failure has to be excluded, because safety systems are not designed to cope with RPV failure
The independent interdisciplinary expertise network, INRAG[1], studied the documents on this issue[2][3], which have been published by the Belgian Regulatory Authority FANC[4]. Based on this study INRAG questions the opinion of the operator – which was accepted by the Regulatory Authority – that these defects were manufacture induced and that these defects did not grow during operation. These defects were not observed during acceptance testing after manufacture.
INRAG is not convinced that the reactor pressure vessel structural integrity assessment using an additional shift for the ductile-brittle transition temperature proposed by the operator[5] is conservative. Experimental testing using non-representative sample material as have been performed by the operator Electrabel cannot eliminate the sets of uncertainties concerning the actual material characteristics of the reactor pressure vessels[6].
INRAG recommended in a letter to FANC that these substantive issues be addressed during the regulatory process, which is now in a decisive stage, relating to the potential restart of these reactors.
Because these issues are potentially generalizable, INRAG strongly recommends inspection of all reactor pressure vessels worldwide for unexpected defects outside the weld regions prescribed in the standards for in service inspection. Therefore INRAG will bring their statement to the attention of the IAEA.
[1] see www.inrag.org
[2] FANC , Doel 3 and Tihange 2 reactor pressure vessels, Provisional evaluation report, January 30, 2013 http://fanc.fgov.be/GED/00000000/3300/3391.pdf
[3] FANC, Doel 3 Tihange reactor pressure vessels, Final evaluation report, May 2013, http://www.fanc.fgov.be/GED/00000000/3400/3429.pdf
[4] FANC: Federal Agency for Nuclear Control
[5] Electrabel, Safety case report: Doel 3 – Reactor Pressure Vessel Assessment, 05/12/2012 http://www.fanc.fgov.be/GED/00000000/3300/3390.pdf
[6] Ilse Tweer, Flawed Reactor Pressure Vessels in Belgian Nuclear Plants Doel-3 and Tihange-2. Some Comments on the FANC Provisional evaluation report (January 30, 2013). March 2013, Commissioned by the Greens/EFA Group in the European Parliament, Brussels, http://www.greens-efa.eu/fileadmin/dam/Documents/Studies/Flawed%20Reactor%20Pressure%20Vessels.pdf