July-August 2019 NPJ

SPECIAL ADVERTISING SECTION The increase of solar and wind power in the energy mix is impacting overall electricity generation which is good in terms of reducing carbon. However, the variable output of these renewable sources creates challenges for utilities. Implementing operational flexibility for nuclear power plants through a variety of mechanisms is a viable solution. We asked two experts, one from Framatome and one from EDF, a few questions about flexible operations. What is flexible operations? Flexible operations is the ability of nuclear power plants to adjust core thermal power to match electrical demand and control frequency of the electrical system. Flexible operations is typically thought of in terms of four grid operating modes: daily load maneuvers, primary and secondary frequency control, response to unexpected grid upsets and extended low power operation. How long has EDF been using flexible operations within its French fleet? The EDF nuclear fleet has operated in fl exi bl e mo de sin ce the early 1980s. Nu clear gene rates ab out 75 per ce nt of F re nc h electricity and ha s to adapt to periods of lo w consumption at night or on weekends. The fleet also pr ov ides a large part of the frequency regu lati on required by the grid op er at or. Th an ks to grey control rods to lev el the fl u x sh ap e in the c ore of the re ac tor, w e re du c e l iq uid wa ste Advertorial Can flexible operations be the key to achieving low-carbon energy generation? generation when the load varies, but load following is possible with black control rods. Every day, each reactor receives the load program for the day after, according to grid needs, consumption, renewable generation, and exports. Our reactors can make variations twice a day, going down to 20 percent of nominal power in only half an hour, and returning to full power at the same pace. Control room operators are trained to prepare and realize the load variations. What is an example of successful flexible operations? A successful load variation is made on schedule, in a safe manner, by monitoring core temperature, control rod positions, flux shape, chemistry, and waste generation. Some units, chosen for economic reasons, make about 100 load variations in a year, without any noticeable impact to safety and equipment reliability. Being flexible avoids using gas or coal to adjust the overall generation. It allows an electricity mix composed mainly of nuclear and renewable sources, with very low carbon emissions. Is this a common way of operating the fleet in the U.S.? No, but the dr iver s for fl exible oper at ions a re c ha ngin g in the U.S. T od ay , mo re and more U. S. ut ilit ies are either evalu atin g the tr an si tion to fle xible op er atio ns o r ar e ac t ively pur su in g im plem enta tion of fl e xi bl e op e r at io ns. Why should a U.S. utility consider flexible operations? A utility might consider implementing flexible operations for a myriad of reasons, but the most common are economics and carbon reduction efforts. In de-regulated markets where over-generation and transmission constraints can lead to negative prices, flexible operations can provide cost avoidance. A plant might also consider flexible operations to maximize use of non- carbon emitting sources and further lower its overall carbon footprint. What should a utility consider when exploring flexible operations? A utility must determine how flexible each nuclear generating asset needs to be. This will depend on the inherent design limits of the plant (e.g., allowable maneuvering rates), as well as the desired grid operating modes. Higher degrees of flexibility can result in greater implementation costs. For this reason, Framatome recommends that a feasibility study be performed which should evaluate the impact of flexible operations on all plant systems, structures, components and programs from the reactor core to the grid. This will provide a holistic assessment and avoid potentially costly surprises. A utility must consider h o w soon it wan ts to implemen t flexi ble op er ations. If plant modifications ar e required, th is cou ld require a tw o- to four -year implementation sc hedu le dep en ding on the types of m odifi c ations . Fi na lly , a u ti li ty m us t ch oose an im pl ementati on partner . Ch oo sing an i mp le m entation pa rt ne r th at has ex pe rien ce in fl p er atio ns e xibl e o tudies , to per form feasibil i ty s an d pl an t engine erin g ev alua ti on s m at ome, with up gr ad e s i s critical. Fr a g exper ie nce th e d eca de s of o pe ra ti n of the E DF fl deal choi c e. eet , is a n i www.framatome.com