atw - March 2015

NucNet

Ziel des Eagle-Projektes sind die Ermittlung sowie Vermittlung geeigneter Vorgehensweisen für die Information und Kommunikation von Themen in Zusammenhang mit ionisierender Strahlung. Im Rahmen des Projektes wurden dazu u.a. Meinungsumfragen in Europa durchgeführt.

Geneviève Baumont, Sachkundiger der French Expert Commission, und Marie-Hélène Eljammal, Mitautorin einer vom französischen Institute for Radiological Protection and Nuclear Safety durchgeführten Umfrage, stellten sich den Fragen zu Projekt und Ergebnissen von NucNet.

Mariana Jockenhövel-Barttfeld, Ola Bäckström, Jan-Erik Holmberg, Markus Porthin, Andre Taurines and Tero Tyrväinen

Digital instrumentation and control (I&C) systems appear as upgrades in existing nuclear power plants (NPPs) and in new plant designs. In order to assess the impact of digital system failures, quantifiable reliability models are needed along with data for digital systems that are compatible with existing probabilistic safety assessments (PSA).

The paper focuses on the modelling of software failures of digital I&C systems in probabilistic assessments. An analysis of software faults, failures and effects is presented to derive relevant failure modes of system and application software for the PSA. The estimations of software failure probabilities are based on an analysis of the operating experience of TELEPERM® XS (TXS). For the assessment of application software failures the analysis combines the use of the TXS operating experience at an application function level combined with conservative engineering judgments. Failure probabilities to actuate on demand and of spurious actuation of typical reactor protection application are estimated. Moreover, the paper gives guidelines for the modelling of software failures in the PSA. The strategy presented in this paper is generic and can be applied to different software platforms and their applications.

Stefan Fricke and Michael Braun

For more than 30 years TÜV NORD is a competent consultant in nuclear safety is-sues giving expert third party opinion to our clients. According to the German regulations the safety against brittle fracture has to be proved for the reactor pressure vessel (RPV) and with a new level of knowledge the proof has to be continuously updated with the development in international codes and standards like ASME, BS and RCC-M.

The load of the RPV is a very complex transient pressure and temperature situation. Today these loading conditions can be modeled by thermal hydraulic calculations and new experimental results much more detailed than in the construction phase of German Nuclear Power Plants in the 1980s. Therefore, the proof against brittle fracture from the construction phase had to be updated for all German Nuclear Power Plants with the new findings of the loading conditions especially for a postulated small leakage in the main coolant line.

The RPV consists of ferritic base material (about 250 mm) and austenitic cladding (about 6 mm) at the inner side. The base material and the cladding have different physical properties which have to be considered temperature dependently in the cal-culations. Radiation-embrittlement effects on the material are to be respected in the fracture mechanics assessment. The regions of the RPV of special interest are the core weld, the inlet and outlet nozzle region and the flange connecting weld zone.

The fracture mechanics assessment is performed for normal and abnormal operating conditions and for accidents like LOCA (Loss of Coolant Accident).

In this paper the German approach to fracture mechanics assessment to brittle fracture will be discussed from the point of view of a third party organization.

Miguel Peinador Veira, Samir El Kanbi, Jean-Luc Stephan and Johannes Martens

Nach dem Auftreten von Ereignissen in Kernkraftwerken im Stillstandsbetrieb in den 1980er-Jahren und auf Grundlage von probabilistischen Sicherheitsanalysen in den 1990er-Jahren wurde deutlich, dass Risiken bei diesem Betriebszustand nicht zu vernachlässigen sind und entsprechende Vorsorgeprogramme getroffen werden müssen.

Eine umfassende Prüfung und Begutachtung der zugehörigen Betriebserfahrungen aus den letzten 10 Jahren wurde von der Gemeinsamen Forschungsstelle (Joint Research Centre) durchgeführt. Ziel der Untersuchung ist es, gewonnene Erkenntnisse und abgeleitete Empfehlungen den Betreibern und Aufsichtbehörden zur Verfügung zu stellen.

Im vorliegenden Beitrag wird dargestellt, welche Aufgaben im Verlauf einer Kernkraftwerksrevision anstehen, welche komplexen Zusammenhänge zu berücksichtigen sind und wie sichergestellt werden kann, dass alle Systeme beim Wiederanfahren zuverlässig verfügbar sind.

Die Studie unterstreicht die Bedeutung genauer Informationen zum Anlagenstatus im Kontrollraum. Viele lessons learned beziehen sich auf Form und Umfang von Alarmmeldungen und dem Umgang mit Betriebshandbüchern. Die Ergebnisse dieser Analyse stehen allen Beteiligten für Anwendung und Umsetzung zur Erhöhung der Sicherheit zur Verfügung.

Jong Woon Park

A realistic evaluation methodology has been licensed to the large break loss of coolant accident (LBLOCA) analysis for Westinghouse design 3 loop plants and OPR1000 plants. As an effort to extend the methodology to Kori Unit 1 which was under life extension stage and equipped with upper plenum injection (UPI), benchmarking of the method is performed for the UPI test of UPTF. Throughout benchmarking, UPI model was developed based on the assessment for the UPTF test 20. The predicted results using this model are found to agree well with the test data. LBLOCA analysis results for Kori Unit 1 showed that present method well predicted the important UPI phenomena, which include breakthrough area, down-flow rate into the core, hot leg water carryover rate, and liquid level in upper plenum.

Ulrike Feldmann

With its decision taken on 21. October 2014 (Az.: 2 BvE 5/11) the Federal Constitutional Court (BVerfG) decided during court proceedings between administrative bodies on the scope and limits of the parliamentary right of information. Even though the proceeding did not deal with nuclear exports but arm exports, foreign trade law, however, does not only designate an export licence obligation for military weapons but also for so called dual-use goods meaning goods, which can be used both for friendly as well as for military purposes.

The export of these goods requires according to the so-called Dual-Use Regulation (EG) 428/2009 a licence. Annex I category 0 of the regulation (EG) 428/2009 lists a variety of nuclear materials, plants and equipment items for which this licence applies. In the same manner as arm exports, also exports of nuclear dual-use goods are being discussed in a special cabinet committee, the Federal Security Council (BSR), which shall coordinate cross-departmentally the German security and defence policy under consideration of economic interests and which categorises its results, according to the rules of procedure, as confidential.

Also legally not regulated but common “preliminary enquiries” at the responsible Federal Ministry or rather Federal Office of Economics and Export Control by companies which plan an export and want to affirm the general approval for their export business prior to conclusion of contract take not only place for arm exports but also for nuclear dual-use goods.

The decision by the Federal Constitutional Court can be applied to consultations about the authorisation of nuclear dual-use goods.

Michael Kirst, Ulf Benjaminsson and Carina Önneby

There are a total of 33 VVER active reactors in the EU and Ukraine, accounting for the largest percentage of the total electricity supply in the countries operating these. The responsible governments and utilities operating these units want too see an increased diversification of the nuclear fuel supply. Westinghouse is the only nuclear fuel producer outside Russia, which has taken the major steps to develop, qualify and manufacture VVER fuel designs – both for VVER-440 and VVER-1000 reactors. The company has delivered reloads of VVER-440 fuel to Loviisa 2 in Finland, VVER-1000 fuel for both the initial core and follow-on regions to Temelin 1-2 in the Czech Republic and more recently reloads of VVER-1000 fuel to South Ukraine 2-3.

Technical challenges in form of mechanical interference with the resident fuel have been encountered in Ukraine, but innovative solutions have been developed and successfully implemented and today Ukraine has, for the first time in its history, a viable VVER-1000 fuel design alternative, representing a tremendous lever in energy security for the country.

Gunhyo Jung and Moosung Jae

The System-Integrated Modular Advanced Reactor (SMART) that has been recently designed in KOREA and has acquired standard design certification from the nuclear power regulatory body (NSSC) is an integral type reactor with 330MW thermal power. It is a small sized reactor in which the core, steam generator, pressurizer, and reactor coolant pump that are in existing pressurized light water reactors are designed to be within a pressure vessel without any separate pipe connection. In addition, this reactor has much different design characteristics from existing pressurized light water reactors such as the adoption of a passive residual heat removal system and a cavity flooding system. Therefore, the safety of the SMART against severe accidents should be checked through severe accident analysis reflecting the design characteristics of the SMART. For severe accident analysis, an analysis model has been developed reflecting the design information presented in the standard design safety analysis report. The severe accident analysis model has been developed using the MELCOR code that is widely used to evaluate pressurized LWR severe accidents. The steady state accident analysis model for the SMART has been simulated. According to the analysis results, the developed model reflecting the design of the SMART is found to be appropriate. Severe accident analysis has been performed for the representative accident scenarios that lead to core damage to check the appropriateness of the severe accident management plan for the SMART. The SMART has been shown to be safe enough to prevent severe accidents by utilizing severe accident management systems such as a containment spray system, a passive hydrogen recombiner, and a cavity flooding system. In addition, the SMART is judged to have been technically improved remarkably compared to existing PWRs. The SMART has been designed to have a larger reactor coolant inventory compared to its core’s thermal power, a large surface area in the lower hemisphere of the reactor pressure vessel assembly, and a large free volume in the containment building.

Lisa Diener

Threshold values affect our daily lives. Whether it concerns traffic or noise regulations, we all experience thresholds on a regular basis. But how are such values generated? The conference “Determine Thres-hold Values in Radiation Protection”, taking place on January 27th 2015 in Braunschweig, focused on this question. The conference was undertaken in the context of the BMBF-funded interdisciplinary research project “ENTRIA – Disposal Options for Radioactive Residues”. It aimed to stimulate a cross-disciplinary discussion. Spea-kers from different disciplinary backgrounds talked about topics like procedures of setting threshold values, standards for evaluating dosages, and public participation in the standardization of threshold values. Two major theses emerged: First, setting threshold values always requires considering contexts and protection targets. Second, existing uncertainties must be communicated in and with the public. Altogether, the conference offered lots of input and issues for discussion. In addition, it raised interesting and important questions for further and ongoing work in the research project ENTRIA.

Siegfried Balke

The European Atomic Energy Community (EAG-EURATOM), which was organisationally established on 1st January 1958, is not to the same degree part of an economic discussion as the European Economic Community. The EAG has a strongly accentuated technical-scientific character and is often economically considered as appendix of major economic integration efforts within Europe.

Still it would be wrong not to suspect economical effective components within the European Atomic Energy Community. The opposite is already recognisable as the EAG needs to integrate itself into a system of international organisations and institutions, which are already existent in the field of a friendly exploitation of nuclear power and which embrace a larger geographical field as the six – member-states of the EURATOM, the European Economic Community and the European Coal and Steel Community.

One advantage of the treaty on establishing the European community is that it considers the Atomic Energy Community as an important but not independent branch from general economic activity. The organisational bracket for all three European Treaties of Integration will be the common Parliament and – what is to be expected, in its practical impact a -not to be underestimated- joint headquarters for all three institutions.

John Shepherd

Germany’s so-called “energy transition” (“Energiewende”) is increasingly drawing the intention of the international community – but it seems for all the wrong reasons.

US Senator Lamar Alexander said recently that German energy policy is one of the reasons the US should not abandon nuclear, but actually encourage increased investment in nuclear power plants. Alexander’s remarks were made in an article published by the US Nuclear Energy Institute, in which he outlined his reasons why the US should not follow Germany’s lead.

Alexander rightly pointed out that the cost of attempting to replace nuclear power with wind, solar, and accompanying infrastructure is estimated by the German government at some 1.2 trillion US dollars (about 1 trillion euros).

The senator also made the point that Germany “does not produce enough reliable, baseload energy for an important manufacturing economy”. He also expressed concern at Germany’s reliance on buying natural gas from Russia.

While Germany has been forcing the closure of nuclear power plants others, including the oil-rich United Arab Emirates (UAE), have been investing in new nuclear, Alexander said.

Judging from Alexander’s remarks, it seems that Germany’s energy transition experience will, after all, have a long-lasting legacy. That legacy will be a valuable lesson to other major industrialised nations in why they should not follow Germany’s lead in abandoning a sensible energy mix, if they wish to maintain and develop economic and industrial productivity while keeping to international commitments to tackle climate change.