Ukrainian reactors need two years to adjust to load-following

Ukraine's Energoatom has said it would need at least two years and extra funds to introduce load-following at the 15 VVER units it operates. The Cabinet of Ministers requires the country's reactors to be adapted to load-following mode by the end of this year, according to its Action Plan for 2016.

A load-following power plant adjusts its electricity output as demand fluctuates throughout the day.

At a round table discussion held last week, representatives from Energoatom and the State Nuclear Regulatory Inspectorate of Ukraine discussed how the government's target could be achieved.

According to a statement issued by the company on 8 April, Energoatom director Yuriy Sheyko said during the meeting that adapting Ukraine's VVER-type reactors to load-following was "technically possible, but would take at least two years of thorough preparation".

Energoatom has to date performed 21 loading and unloading cycles at unit 2 of the Khmelnitsky nuclear power plant, as authorised by the regulator, Sheyko said. "The unit's power was reduced from 100% of nominal capacity to 75% and then increased back to 100%," he said.

During this process, the company was able to identify items of equipment that would need to be upgraded to enable the change to load-following mode. A detailed report on this and other recommendations has been sent to the regulator, he said.

Sheyko noted that, in order to test a unit's suitability for load-following, a reactor would need to undergo 200 loading/unloading cycles. This means the company would need at least two years to adapt all of the country's reactors.

The head of the regulatory authority, Serhiy Bozhko, said shifting to load-following was "conventionally accepted best practice" among nuclear plant operators.

"A lot of countries have already adjusted their nuclear power plants that were originally designed for baseload operation to load-following," he said, adding that France had been following the practice since the mid-1970s.

Konstyantyn Yschapovskyy, the prime minister's deputy, said daily control of power output was technically feasible, but requires "long-term and comprehensive tests". Energoatom would need to take in account, Yschapovskyy said, the cost of new equipment and labour required for the work.

"These will require additional financing and Energoatom would need to be compensated for expenses associated with load-following operation." At this stage, neither the technical requirements nor the related expenses have been worked out, he added.

Oleh Hodun, Energoatom's head of design safety and fuel utilisation, stressed that analysis of the technical requirements of load-following was not an "experiment", but "implementation of a program with due regard for stringent safety requirements".

But Ivan Plachkov, chairman of the Ukrainian Energy Assembly and a former energy minister, noted that Ukraine had already been working for ten years on an analysis of load-following for its reactors. The fact the government has set a target date, of 31 December 2016, is misleading as it suggests Energoatom is hastily preparing a program in response to this, he said. Plachkov also said that the country's regulator is respected among its peers in other countries and would, "I am sure, rule out any experiments or abnormal operations at Ukrainian nuclear power plants".

Normally, baseload generating plants, with high capital cost and low operating cost, are run continuously, since this is the most economic mode. But also it is technically the simplest way, since nuclear and coal-fired plants cannot readily alter power output, compared with gas or hydro plants. The high reliance on nuclear power in France has meant the reactors collectively need to be used in load-following mode.

All of France's nuclear capacity is from pressurized reactor (PWR) units, for which there are two ways of varying power output - control rods and boron addition to the primary cooling water. For the last 25 years EDF has used in each PWR some less absorptive "grey" control rods which weigh less from a neutronic point of view than ordinary control rods and they allow sustained variation in power output. This means that grid operator RTE can depend on flexible load-following from the nuclear fleet to contribute to regulation in three respects. These are primary power regulation for system stability (when frequency varies, power must be automatically adjusted by the turbine); secondary power regulation related to trading contracts; and adjusting power in response to demand (decreasing from 100% during the day to 50% or less during the night, etc.).

Established in 1996, state-run Energoatom operates all of Ukraine's 15 Russia-built pressurised water reactors, which are at four sites - Khmelnitsky, Rovno, South Ukraine and Zaporozhe.

Researched and written
by World Nuclear News