Paks Nuclear Power Plant

The Paks Nuclear Power Plant (Hungarian: Paksi Atomerőmű), located 5 kilometres (3.1 mi) from Paks, central Hungary, is the first and only operating nuclear power station in Hungary. Altogether, its four reactors produce more than 40 percent of the electrical power generated in the country.

Technical parameters

VVER is the Soviet designation for a pressurized water reactor. The number following VVER, in this case 440, represents the power output of the original design. The VVER-440 Model V213, was a product of the first uniform safety requirements drawn up by the Soviet designers. This model includes added emergency core cooling and auxiliary feedwater systems as well as upgraded accident localization systems.

Each reactor contains 42 tons of slightly enriched uranium dioxide fuel. Fuel takes on average three years to be used (or "burned") in the reactors; after this the fuel rods are stored for five years in an adjacent cooling pond before being removed from the site for permanent disposal.

The power plant is nearly 100% owned by state-owned power wholesaler Magyar Villamos Művek (MVM). A few shares are held by local municipalities, while a voting preference or "golden" share is held by the Hungarian government. The government is planning to partially privatize MVM but has said that due to security concerns, the Paks nuclear power generator will be kept fully state owned.

One brand-new reactor was bought from Poland after the Żarnowiec Nuclear Power Plant project was abandoned in its late development stage.

On the 30th of March 2009 the National Assembly of Hungary gave its principal consent by votes 330 for, 6 against and 10 abstained to the preparation works of the possible new units. On 26th of February 2010 the owner state company MVM Group decided the expansion with about 2000 billion Hungarian Forints price. On the 17th of January 2011 Tamás Fellegi, the National Developmental Minister of Hungary discussed with Sergey Kiriyenko (Rosatom) and Deputy Finance Minister of Russia Dmitriy Pankin in Moscow about Paks Nuclear Power Plant expansion.

Lifetime extension

The original 30-year lifetime of the four blocs will begin to run out in 2012. As Hungary lacks energy resources and relies heavily on the power plant, it has committed to a 20-year lifetime extension.

In 2000, the Paks Nuclear Power Plant commissioned a feasibility study which concluded that the plant may remain in operation for another 20 years. The study was updated in 2005 with similar conclusions.

In November 2005, Hungary's Parliament passed a resolution with overwhelming bipartisan majority to support the lifetime extension.

The feasibility study concluded that the non-replaceable parts are in sufficient condition to remain in operation for another 20 years while a minority of replaceable parts needed replacement or refurbishment.

The power generator made repeated surveys of public opinion on the lifetime extension and concluded that support for the decision hovered near 70%.

Following the Fukushima I nuclear accidents in March 2011, Hungary's government said it would conduct a stress test on the Paks Nuclear Power Plant to assess safety, but it would not abandon plans for lifetime extension and it would also go ahead with plans for its expansion.

Power uprating

Thanks to optimizations, modernization and fuel upgrades it was possible to safely increase the output power of the Unit 4 reactor to 500 MWe in 2006, followed by Unit 1 in 2007. With upgrades to the remaining two units the plant's power generation reached 2000 MWe in 2009.

2003 incident

An INES level 3 event ("serious incident") occurred on 10 April 2003 at the Unit 2 reactor. The incident occurred in the fuel rod cleaning system located under 10 metres (33 ft) of water in a cleaning tank next to the spent fuel cooling pond, located adjacent to the reactor in the reactor hall. The reactor had been shut down for its annual refueling and maintenance period on 28 March and its fuel elements removed.

The cleaning system had been installed to remove dirt and corrosion from fuel elements and control rods during shutdown, as there had previously been problems with magnetite corrosion products from the steam generators being deposited on the fuel elements which affected the flow of coolant. The sixth set of thirty partially spent elements were in the tank having been cleaned, the cleaning having finished at 16:00. At 21:50, radiation alarms mounted on the cleaning system detected a sudden increase in the amount of krypton-85. The suspicion was that one of the fuel rod assemblies was leaking. At 22:30, the reactor hall was evacuated because of elevated radiation levels both there and in the ventilation stack.

At 02:15 the following morning, the hydraulic lock of the cleaning vessel lid was released, and immediately the dose rate increased significantly (6-12 millisieverts/hour) around the spent fuel pond and the pool containing the cleaning machine, and the water level dropped for a short time, by about 7 cm (2.8 in). Water samples from the pond showed contamination due to damaged fuel rods. The lid on the cleaning machine was winched up at 04:20, but one of the three lifting cables attached to it broke; and it was not finally removed until 16 April.

The incident was initially given an INES rating of 2 ("incident"). However a video examination of the damaged fuel elements following the successful removal of the lid caused the rating to be raised to 3 ("serious incident"). This revealed that cladding on the majority of the 30 fuel elements had been broken, with radioactive spent uranium fuel pellets spilling from the elements into the bottom of the cleaning tank. Apart from the release of radioactive material, a concern was that the accumulation of a compact mass of fuel pellets could lead to a criticality accident, as the pellets were in a tank of neutron moderating water. Water containing neutron absorbing boric acid was added into the tank to raise its concentration to 16 g/kg to prevent this. Ammonia and hydrazine were also added to the water to help with the removal of radioactive iodine-131.

An investigation by the Hungarian Atomic Energy Agency concluded that the cause of the incident was inadequate cooling of the fuel elements, which were heated due to the radioactive decay of short-lived fission products. These were kept cool by water circulated by a submerged water pump. However the cooling was inadequate, leading to the damage to some elements through a build-up of steam around them, depriving them of most of their cooling. The investigation proposed that the severe damage probably occurred when the lid was released, causing thermal shock to cladding because of the sudden entry of cool water into the system, and explosive steam production.

One of the interesting results of the investigation was that the Hungarian Atomic Agency had placed too much trust in the technology and knowledge of the French Framatome Company (now Areva). The agency did not investigate documentation provided by the company deeply enough, missing a fatal design flaw in the Framatome-designed, produced, and operated cleaning equipment.

The discharge of radioactive gases through the stack continued for several days after the incident, although the Hungarian Atomic Energy Agency determined that the radiation levels adjacent to the plant were only about 10% above normal. However, the reactor remained out of service for over a year, finally resuming commercial electricity production in September 2004.

2009 outage incident

A self-powered neutron detector (SPND) was dropped when the wire rope holding it broke during an outage on 4 May 2009. The event was rated as INES 2. All staff were evacuated, but no member was exposed to the permitted daily radiation dose.