Paks units clear to switch to 15-month fuel cycle

The Hungarian Atomic Energy Authority has authorised the introduction of a 15-month fuel replacement interval at units 1-4 of the Paks nuclear power plant, the plant's owner MVM NPP Ltd announced on 8 December. The move licenses the switch to a new type of fuel assembly with an average enrichment of 4.7%.

The Hungarian Atomic Energy Authority has authorised the introduction of a 15-month fuel replacement interval at units 1-4 of the Paks nuclear power plant, the plant's owner MVM NPP Ltd announced on 8 December. The move licenses the switch to a new type of fuel assembly with an average enrichment of 4.7%.

Hungary's Paks plant (Image: Paks NPP)

The recently issued licence permits the transition to a fuel replacement interval of once every 15 months, instead of once every 12 months, MVM said. "Fuel may only be replaced when reactors are shut down [and] the introduction of a new type of fuel that burns up and loses efficiency over a longer period compared to the previous ones has also become necessary," it said. The new fuel assembly - Gd-2_4.7 - is a "Hungarian innovation" developed through international cooperation and based on the design of the Reactor Physics Section of the Paks plant.

The regulator received no objections to issuing the new licences following a public hearing it held on 23 June.

Among similar types of nuclear power plants, Paks is the first to introduce the 15-month operation interval, MVM said. But the use of operation intervals exceeding 12 months is not unprecedented in the world, it said.

"Due to the economic benefits of implementing extended fuel and outage intervals, the use of fuel intervals other than 12 months has become prevalent in numerous leading countries of the nuclear industry, including the USA and France, and as early as the 1990s," MVM said. In the USA, the average duration of operation intervals increased to 18 months after 2000, while in France the majority of nuclear power plant units operate with fuel intervals of 15, 17 or 18 months, MVM noted. The Krško nuclear power plant in Slovenia switched to an 18-month operation cycle in 2004.

The introduction of the 15-month interval has several economic benefits to both the nuclear power plant and the Hungarian economy, including, most importantly, improvements to safety, MVM said. It reduces the volume of outage-related work, the total occupational exposure to radiation of power plant personnel, and the number of failures due to maintenance risk, it added. Over the entire lifetime of the plant, the number of unit shutdowns and restarts will be lower, which has a positive impact on nuclear safety and the durability of plant systems and components, it said.

In addition, the 15-month operation cycle and the application of a higher enrichment level reduces the volume of used fuel, by 3% on average, the volume of low- and medium-level radioactive waste produced during maintenance work, and also the level of non-radioactive waste.

Moreover, the annual availability of the each unit rises by 2% on average, thus increasing the volume of electricity produced and covering the needs of about 80,000 households - a quarter of a million people. This increase in electricity generation means that Hungary's dependence on energy imports can be reduced by 1%, thus contributing to security of supply.

MVM expects to complete the switch to a 15-month operation cycle at all four Paks units by late 2016.

In accordance with its corporate strategy, MVM Paks NPP Ltd has increased the nominal electric capacity of the units to 108%, received licences to extend the operating lives of units 1 and 2 by 20 years, and applied for similar licences for units 3 and 4. The Paks plant covered 53.6% of total energy output in Hungary last year.

Researched and written
by World Nuclear News