VGB PowerTech - Autorenexemplar - © 2017 1 VGB PowerTech 5 l 2017 Editorial 1 For some components even the need for replacement could be waived. Proactive action is of great importance for safe and economic long term operation of any NPP taking into account flexible operation. Overall, today almost 25 per- cent of the NPPs worldwide are flexible, providing hun- dreds of reactor years of op- erational experience. The larg- est wealth of experience comes from the French and German fleets. France, with 58 NPPs, has a strong need for flexibility due to the high nuclear share of its energy portfolio. Also one of the Swiss NPPs is now in the final stage of the flexible operation modernization project for reactor control considering addition- ally heat and steam extraction for external purposes. In the USA, EPRI initiated a technical advisory group to support utilities mov- ing from base load to flexible power operation. Growing renew- able energy and strong competition from low-priced carbon fuel required in some American states to promote flexible operation of NPPs. In Spain, with Europe’s second largest wind power capac- ity and with currently decreasing overall demand, NPPs have be- gun last year to perform a limited number of slow power ramps. Also for countries using VVER-type NPPs, the grid requirements are changing, e. g. in Russia with respect to primary regulation. Ukraine is considering replacing the control reserve service in fu- ture, provided until now by aged fossil fired plants, with existing NPPs. Chinese NPP operators are analysing various flexible op- eration scenarios and some of them are facing seasonal part load operation due to the grid requirement, e. g. during the rainfall period. For all new builds worldwide, advanced flexibility is an important design requirement anyway. IAEA is close to release a detailed guideline for non-base load operation of NPPs, consider- ing both new builds and existing plants. What about the current market situation for reserve and bal- ancing energy? The European markets are growing together through cross-border trading. However, the prices are decreas- ing due to growing competition. In the medium term, the con- trol reserve price is still considered attractive due to the further planned growth of renewables. Offer and demand will deter- mine the price level. Hereby, further development of various new technologies such as the large scale battery storages have to be borne in mind. In summary, flexible operation is needed to meet the current and future grid requirements and at the same time to ensure profitabil- ity for NPPs. In the future, every power plant is expected to become capable of flexible operation, and NPPs will be no exception! The motivation for going flexible for a Nuclear Power Plant (NPP) can vary significantly according to the regional context. For some NPPs, several relevant measures for flexible operation are imple- mented and well-proven. For others, flexible operation is still not preferable and some actions are even not authorized, e. g. remote secondary control by the grid dispatcher. The German power plant operators have been demonstrating ad- vanced, safe and reliable flexible operation for many years. NPPs are among the most flexible plants in the grid. Load following op- eration is typically performed with a power gradient of 2 percent per minute in the range from 40 to 100 percent generator power. The design margin could even allow greater values. NPPs of the predecessor company of today’s AREVA NP, German KWU, had been already designed for enhanced load-following, primary, secondary and tertiary power regulation capability. Over a long time these capabilities were however only occasionally used to cope with some grid-related events, whilst NPP Unter - weser already systematically experienced dynamic power adjust- ments during the warm months due to the cooling temperature limitations of the river Weser. The need for frequent flexible operation appeared recently in or - der to compensate fluctuating, annually increasing power gener - ated by renewable energy sources and lead to first modernization projects related to the improvement of the turbine instrumenta- tion & control (I&C) systems. Since 2008, the German electricity market allows negative elec- tricity prices. On the one hand, the annual volume of electricity sold at negative prices is worth millions of Euros. On the other hand, the reserve and balancing markets together with redis- patching and intraday trading allows new price models. Hence various German operators of pressurized water reactors decided on full automation of plant operation to achieve maximal flexibility, also with respect to the core loading. The introduction of the digital technology in the field of I&C was very beneficial for the needed upgrade of reactor control, including introduction of the World Association of Nuclear Operators (WANO)-favored reactivity management. This allowed the power level ranges for the control reserve to be increased incrementally, including the necessary prequalification procedure, which created more com- mercial opportunities on the spot market. The first plant to begin with this modernization of reactor con- trol was Philippsburg-2 in 2008, achieving the world record in primary power regulation. Further NPPs followed in 2014/2015, introducing remote controlled secondary power regulation in the worldwide leading range from 60 and 100 percent of generator power. Various feasibility studies were carried out to evaluate the impact of flexible operation on I&C, NSSS and Fuel performance. There- by, items like power plant chemistry, lifetime of components and power maneuvering/pellet cladding interaction (PCI) – guide- lines were stated to be of particular importance. Developed tools and the existing operational experience related to fatigue, flow-accelerated corrosion (FAC), vibration phenomena etc. are also beneficial for non-nuclear plants in flexible operation (e. g. fatigue monitoring systems). Related new evaluation meth- ods based on local temperature measurements and corresponding realistic loads are being implemented. In this way, fatigue margins can recover with respect to flexible operation as well as other new requirements such as Environmentally Assisted Fatigue (EAF). Flexible operation of nuclear power plants – first steps for paradigm change worldwide? Dr.-Ing. Tatiana Salnikova Project Manager, Products and Projects AREVA GmbH
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VGB PowerTech 5 l 2017 Editorial
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For some components even the need for replacement could be waived. Proactive action is of great importance for safe and economic long term operation of any NPP taking into account flexible operation. Overall, today almost 25 per-cent of the NPPs worldwide are flexible, providing hun-dreds of reactor years of op-erational experience. The larg-est wealth of experience comes from the French and German fleets. France, with 58 NPPs, has a strong need for flexibility due to the high nuclear share of its energy portfolio. Also one of the Swiss NPPs is now in the final stage of the flexible operation modernization project for reactor control considering addition-ally heat and steam extraction for external purposes. In the USA, EPRI initiated a technical advisory group to support utilities mov-ing from base load to flexible power operation. Growing renew-able energy and strong competition from low-priced carbon fuel required in some American states to promote flexible operation of NPPs. In Spain, with Europe’s second largest wind power capac-ity and with currently decreasing overall demand, NPPs have be-gun last year to perform a limited number of slow power ramps. Also for countries using VVER-type NPPs, the grid requirements are changing, e. g. in Russia with respect to primary regulation. Ukraine is considering replacing the control reserve service in fu-ture, provided until now by aged fossil fired plants, with existing NPPs. Chinese NPP operators are analysing various flexible op-eration scenarios and some of them are facing seasonal part load operation due to the grid requirement, e. g. during the rainfall period. For all new builds worldwide, advanced flexibility is an important design requirement anyway. IAEA is close to release a detailed guideline for non-base load operation of NPPs, consider-ing both new builds and existing plants. What about the current market situation for reserve and bal-ancing energy? The European markets are growing together through cross-border trading. However, the prices are decreas-ing due to growing competition. In the medium term, the con-trol reserve price is still considered attractive due to the further planned growth of renewables. Offer and demand will deter-mine the price level. Hereby, further development of various new technologies such as the large scale battery storages have to be borne in mind. In summary, flexible operation is needed to meet the current and future grid requirements and at the same time to ensure profitabil-ity for NPPs. In the future, every power plant is expected to become capable of flexible operation, and NPPs will be no exception!
The motivation for going flexible for a Nuclear Power Plant (NPP) can vary significantly according to the regional context. For some NPPs, several relevant measures for flexible operation are imple-mented and well-proven. For others, flexible operation is still not preferable and some actions are even not authorized, e. g. remote secondary control by the grid dispatcher.The German power plant operators have been demonstrating ad-vanced, safe and reliable flexible operation for many years. NPPs are among the most flexible plants in the grid. Load following op-eration is typically performed with a power gradient of 2 percent per minute in the range from 40 to 100 percent generator power. The design margin could even allow greater values.NPPs of the predecessor company of today’s AREVA NP, German KWU, had been already designed for enhanced load-following, primary, secondary and tertiary power regulation capability. Over a long time these capabilities were however only occasionally used to cope with some grid-related events, whilst NPP Unter-weser already systematically experienced dynamic power adjust-ments during the warm months due to the cooling temperature limitations of the river Weser. The need for frequent flexible operation appeared recently in or-der to compensate fluctuating, annually increasing power gener-ated by renewable energy sources and lead to first modernization projects related to the improvement of the turbine instrumenta-tion & control (I&C) systems. Since 2008, the German electricity market allows negative elec-tricity prices. On the one hand, the annual volume of electricity sold at negative prices is worth millions of Euros. On the other hand, the reserve and balancing markets together with redis-patching and intraday trading allows new price models.
Hence various German operators of pressurized water reactors decided on full automation of plant operation to achieve maximal flexibility, also with respect to the core loading. The introduction of the digital technology in the field of I&C was very beneficial for the needed upgrade of reactor control, including introduction of the World Association of Nuclear Operators (WANO)-favored reactivity management. This allowed the power level ranges for the control reserve to be increased incrementally, including the necessary prequalification procedure, which created more com-mercial opportunities on the spot market.
The first plant to begin with this modernization of reactor con-trol was Philippsburg-2 in 2008, achieving the world record in primary power regulation. Further NPPs followed in 2014/2015, introducing remote controlled secondary power regulation in the worldwide leading range from 60 and 100 percent of generator power.
Various feasibility studies were carried out to evaluate the impact of flexible operation on I&C, NSSS and Fuel performance. There-by, items like power plant chemistry, lifetime of components and power maneuvering/pellet cladding interaction (PCI) – guide-lines were stated to be of particular importance.
Developed tools and the existing operational experience related to fatigue, flow-accelerated corrosion (FAC), vibration phenomena etc. are also beneficial for non-nuclear plants in flexible operation (e. g. fatigue monitoring systems). Related new evaluation meth-ods based on local temperature measurements and corresponding realistic loads are being implemented. In this way, fatigue margins can recover with respect to flexible operation as well as other new requirements such as Environmentally Assisted Fatigue (EAF).
Flexible operation of nuclear power plants – first steps for paradigm change worldwide?
Dr.-Ing. Tatiana SalnikovaProject Manager, Products and ProjectsAREVA GmbH
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Editorial VGB PowerTech 5 l 2017
2
Für die Ertüchtigung zum Lastwechselbetrieb von Kernkraftwer-ken (KKW) gibt es je nach nationalem Kontext unterschiedliche Gründe. Für manche KKW sind vielfältige Einrichtungen für den Lastwechselbetrieb umgesetzt und betriebserprobt. Für andere ist dies noch nicht erwünscht oder Maßnahmen sind nicht geneh-migt, z. B. ferngesteuerte Sekundärregelung durch den Netzbe-treiber.
Die deutschen Betreiber zeigen in der Betriebspraxis einen fortgeschrittenen, sicheren und verlässlichen Lastwechselbe-trieb seit mehreren Jahren. KKW gehören zu den lastwech-selfähigsten Kraftwerken im deutschen Netz. Beim typischen Lastfolgebetrieb variieren sie ihre Leistung um etwa 2 Prozent pro Minute im Regelband zwischen 40 und 100 Prozent der Generatorleis tung. Die Flexibilität des Anlagendesigns könnte sogar höhere Werte erlauben.
Anlagen des AREVA NP-Vorgängerunternehmens KWU waren von vornherein für erweiterten Lastfolgebetrieb, Primär- und Sekun-därregelung sowie Minutenreserve ausgelegt. Viele Jahre erfolgte der Einsatz dieser Fähigkeiten jedoch nur gelegentlich zum Ge-gensteuern bei netzrelevanten Ereignissen. Nur die Leistung der Anlage Unterweser wurde in warmen Monaten bereits regelmäßig an Vorgaben für die Maximalwassertemperatur des Flusses Weser dynamisch mit sehr großen Leistungsänderungen angepasst.
Die später stark zunehmende Stromerzeugung aus fluktuierenden erneuerbaren Energiequellen brachte eine verstärkte Nachfrage nach Kraftwerksflexibilität mit sich; erste Modernisierungspro-jekte betrafen die Ertüchtigung der Turbinenregelung.
Seit 2008 werden auf dem Elektrizitätsmarkt in Deutschland negative Strompreise zugelassen. Einerseits geht das Handels-volumen mit negativen Strompreisen in die Millionen Euro, an-dererseits bieten zuverlässige Bereitstellung der Reserve- und Regelleistung zusammen mit Redispatch-Maßnahmen und Intra-day-Handel neue Einnahmequellen.
Daher entschieden sich mehrere deutsche Betreiber von Druck-wasserreaktoren für die vollständige Automatisierung des Be-triebes zum Zweck der maximalen Flexibilität auch bezüglich der Kernbeladung. Die Einführung der digitalen Technologie im Bereich der Leittechnik hat die dafür notwendige Modernisie-rungen der Reaktorregelung wesentlich erleichtert. Dabei wurde auch das von WANO (World Association of Nuclear Operators) favorisierte Reaktivitätsmanagement eingeführt. Somit konnte das Leistungsband für die Regelleistung inklusive notwendiger Pr-äqualifikation und damit auch die kommerziellen Möglichkeiten auf dem Spotmarkt stufenweise erweitert werden.
Als erste Anlage setzte Philippsburg-2 im Jahre 2008 eine solche Modernisierung der Reaktorregelung um und erzielte den Welt-rekord im erreichten Leistungsband der Primärregelung. In den Jahren 2014/2015 haben weitere Anlagen nachgezogen und den ferngesteuerten Sekundärregelbetrieb in einem weltweit führen-den Regelband zwischen 60 und 100 Prozent der Generatorleis-tung ermöglicht.
In vielfältigen Studien wurde die Wechselwirkung des dynami-schen Anlagenbetriebs mit Leit- und Verfahrenstechnik sowie dem Brennelementverhalten untersucht. Besonderes Augenmerk wurde u.a. auf die Anlagenchemie, die Lebensdauer von Kom-ponenten und Festlegung der Fahrregeln (pellet cladding inter-action (PCI)-Guidelines) gelegt.
Die dafür entwickelten Tools und existierenden Erfahrungen im Bereich Ermüdung, Erosionskorrosion, Vibration usw. kommen auch beim Lastwechselbetrieb nichtnuklearer Anlagen zum Einsatz (z. B. Ermüdungsüberwachungssysteme). Dazu gehört auch die Anwendung neuer, auf lokalen Temperaturmessungen und daraus ermittelten realistischen Belastungsdaten basierender Auswer-
temethoden. Das ermöglicht die Ermittlung von Margen bezüglich flexibler Fahrweisen und neuer Anforderungen, wie z. B. bezüglich der Berücksich-tigung des Mediums-Einflus-ses. Für einige Komponenten erübrigt sich sogar ein sonst ggf. notwendiger Austausch. Dieses vorausschauende Han-deln ist von großer Bedeutung für den sicheren und profitab-len Langzeitbetrieb unter Be-rücksichtigung von Lastwech-selvorgängen.Heutzutage sind circa 25 Pro-zent der KKW weltweit flexibel mit einer gesamten Betriebser-fahrung von mehreren hundert Reaktorjahren im Einsatz. Die größten Erfahrungen existieren in Frankreich und Deutschland. Frankreich hat mit 58 KKW starke Flexibilitätsanforderungen durch den hohen Nuklearanteil am Energiemix. In der Schweiz geht eine entsprechende Nachrüstung für die Reaktorregelung in Kürze in Betrieb. Dabei wird die Wärme- und Dampfauskopp-lung für externe Zwecke mitberücksichtigt. In den USA wurde von EPRI eine technische Arbeitsgruppe initiiert, um den Über-gang der KKW zum Lastwechselbetrieb zu unterstützen. In man-chen US-Staaten waren die wachsenden erneuerbaren Energien und die Konkurrenz durch billige fossile Brennstoffe der Grund, den Lastfolgebetrieb mit KKW voranzutreiben. In Spanien, mit der zweitgrößten Windproduktion in Europa und mit sinkender Stromnachfrage, fahren KKW seit dem letzten Jahr in begrenz-tem Ausmaß langsame Lastwechselvorgänge. Auch bei den Kern-kraftwerken im russischen WWER- Design ändern sich die Net-zanforderungen, beispielsweise bezüglich der Primärregelung in Russland. In der Ukraine wird untersucht, wie die bisher von älteren Kohlekraftwerken bereitgestellte Regelleistung zukünftig durch existierende KKW ersetzt werden kann. Chinesische KKW analysieren den Lastwechselbetrieb und mehrere Anlagen fahren heute vom Lastverteiler geforderten saisonalen Teillastbetrieb, beispielsweise während der Regenzeit. Für alle neuen KKW ist die erweiterte Lastwechselfähigkeit weltweit eine wichtige De-sign-Anforderung. Die IAEA wird in Kürze eine Leitlinie zum Last-wechselbetrieb in neuen und bestehenden KKW herausgeben. Was ist mit dem heutigen Markt für flexible Leistung? In Euro-pa gibt es eine starke Tendenz zum Wachsen, bedingt durch den grenzüberschreitenden Handel. Jedoch sinken die Preise durch wachsende Konkurrenz. Mittelfristig darf man – aufgrund des ge-planten weiteren Ausbaus der Erneuerbaren Energien – dennoch von attraktiven Regelleistungspreisen ausgehen. Angebot und Nachfrageleistung werden dafür entscheidend sein. Zahlreiche neue Technologien – unter anderem die Batteriespeicher – könn-ten hier zukünftig eine noch wichtigere Rolle spielen.Zusammenfassend ist der Lastwechselbetrieb für KKW notwen-dig, um die Netzanforderungen von heute und morgen zu erfüllen und auch gleichzeitig die Profitabilität der KKW zu erhöhen. Je-der Stromerzeuger wird zukünftig lastwechselfähig sein müssen und KKW werden dabei keine Ausnahme bilden können!
Lastwechselbetrieb mit Kernkraftwerken – erste Schritte zu einem weltweiten Paradigmenwechsel?
Dr.-Ing. Tatiana SalnikovaProject Manager, Products and ProjectsAREVA GmbH
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