Paks Nuclear Power Plant

Infobox NPP
Picture =
Pic_des =
Country = Hungary
location = Paks
owner = Magyar Villamos Művek Zrt.
operator = Paksi Atomerőmű Zrt.
Built = 1967ndash 1987
Start = December 28, 1982
End =
r_type = VVER-440/V213
r_active = 4
r_active_mw = 1,866
generation = 14,677
for_year = 2007
av_annual_gen = 12,980
net_gen = 305,108
status = O
generators = 8
WEBSITE = http://www.paksiatomeromu.hu
as_of = June 6, 2008

The Paks Nuclear Power Plant, or Paksi Atomerőmű, located 5 km from Paks, central Hungary, is the only operating nuclear power station in Hungary. Altogether, its four reactors produce around 40 percent of the electrical power generated in the country.

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. Once the fuel has been used, which takes four years per reactor, the fuel rods are stored for five years in a cooling pond adjacent to the reactor before being removed from the site for permanent disposal. cite web | url = http://www.npp.hu/index-e.htm | title = Paks Nuclear Power Plan website (English version) | accessdate = 2006-11-25 ]

The nuclear generators is nearly 100 percent owned by state-owned power wholesaler Magyar Villamos Művek (MVM). A few of its 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 it's late development stage.

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 some replacements or refurbishment.

The power generator has done repeated public opinion surveys on lifetime extension and concluded that support for the decision hovered near 70%. [http://www.atomeromu.hu/jovo/uhp_kozertheto.pdf]

Power uprating

Thanks to optimizations, modernizations and new type of fuel 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 the planned upgrades to the remaining two units, the plant's power generation will reach 2000 MWe in 2008. [cite web |url = http://entrac.iaea.org/I-and-C/TM_PRAGUE_2007_05/CD/Papers/Major_paper.pdf | title = Core monitoring system modernization at Paks NPP to serve unit power uprating | month = May | year = 2007 | accessdate = 2008-06-11 |format=PDF]

The 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 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 refuelling and maintenance period on 28 March and its fuel elements removed. [cite web |url = http://www.iaea.org/Publications/Reports/nsr2003.pdf | title = Nuclear safety review for the year 2003 | work = International Atomic Energy Agency | month = August | year = 2003 | accessdate = 2006-11-25 |format=PDF]

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 been 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 in it and its ventilation stack.cite web | title = Report to the Chairman of the Hungarian Atomic Energy Commission on the Authority investigation of the incident at Paks Nuclear Power Plant on 10 April 2003 | url = http://tpc.mingorp.hr/eng/news/paks-report.pdf | work = Technical Support Centre (TPC), Hungarian Ministry of the Economy, Labour and Entrepreneurship | publisher = Hungarian Atomic Energy Agency | date = 23 May 2003 | accessdate=2006-11-25 |format=PDF]

At 02:15 the following morning, the hydraullic 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. 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 so that uranium fuel pellets, containing fission products, had fallen out of them and dropped to 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 through 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 which deprived 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. cite web | title = Report to the Chairman of the Hungarian Atomic Energy Commission on the Authority investigation of the incident at Paks Nuclear Power Plant on 10 April 2003 | url = http://tpc.mingorp.hr/eng/news/paks-report.pdf | work = Technical Support Centre (TPC), Hungarian Ministry of the Economy, Labour and Entrepreneurship | publisher = Hungarian Atomic Energy Agency | date = 23 May 2003 | accessdate=2006-11-26 |format=PDF]

A more realistique interpretation of the core cause of fuel demages is the accepting the fact of zirconium-steam reaction. The drop of 7 cm in the water level gives the amount of water consumed in the reaction with the cladding and structural zirconium alloy. There was no "explosive steam production" and indeed no "thermal shock", but the well known and well investigated zirconium burning in the steam, producing Hydrogen and zirconia.

One of the interesting results of the investigation was that the Hungarian Atomic Agency placed too much trust in the technology and knowledge of the German Framatome Company (currently called Areva), and they did not investigate the drawings provided by the company deeply enough to find out the fatal design flaw in the cleaning equipment (Framatome designed, produced, and used the 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. [cite web |url = http://www.atomeromu.hu/hirek-e/hir040909-e.htm | title = Unit 2 in operation | work = PAKS Nuclear Power Plant Limited press release | date = 2 September 2004 | accessdate = 2006-11-25 ]

External links

*

Footnotes