ANALYSIS: Hungary eager to shed Russian-origin SNF: the story behind one damaged batch, and what to do with it

Венгерская АЭС Пакш

Publish date: April 5, 2013

Written by: Andrey Ozharovsky

MOSCOW – Hungary may repatriate spent nuclear fuel (SNF) from its Paks plant to Russia as soon as 2014, the country’s nuclear authority said in late January, triggering a wave of concern from Hungarian environmentalists, who believe the decision to export the dangerous material – which was severely damaged during chemical treatment in 2003 – is irresponsible and threatens risks to public health and the environment

Hungary readying to send Paks spent fuel to Russia

The announcement of expected repatriation of spent fuel from Paks Nuclear Power Plant (NPP) to Russia came in an official January 28, 2013 statement (in Hungarian) by the Hungarian Atomic Energy Authority (Országos Atomenergia Hivatal, HAEA), which said that the damaged fuel  was expected to be “finally removed.” The old fuel assemblies, which contain over four tons of spent fuel, are currently stored in the cooling pond of the plant’s Reactor Unit 2.

The “final removal” implies sending the damaged fuel to Russia. “After a series of tests, [and] the appropriate technological and administrative steps, the damaged fuel is expected in 2014 [to be] returned to Russia,” the HAEA’s statement read (in Google Translate automatic translation).

The fuel assemblies that contain the SNF came under severe damage and were partially destroyed during an accident in April 2003. An assessment of just how extensive the damage must be can be obtained from the results of a simulation experiment that retraced the scenario of the 2003 accident, described in a 2007 paper by researchers at the Hungarian Academy of Sciences KFKI Atomic Energy Research Institute

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One of the photographs picturing the results of the modeling experiment shows that the fuel rods did not simply sustain loss of seal, but were shattered, crumbling into fragments. One of the safety barriers – the zirconium cladding that the fuel composition is enclosed in – was simply disintegrated.

Fuel rods that have sustained such extensive damage present special hazard and, though spent fuel is not treated as waste by Russian law, these would certainly merit re-classification as such. Hungary’s desire to get rid of this dangerous waste, sending the spent fuel rods back to Russia – the country where they were originally produced – and the Russian State Atomic Energy Corporation Rosatom’s willingness to receive it, may fall in line with what continued to be a more or less traditional practice Russia inherited from the Soviet Union, of having spent nuclear fuel used in a country to which it was originally supplied repatriated back to Russia for subsequent reprocessing (with the resulting radioactive waste sent back to the client state for disposal).

But questions remain, and the chief of them is: What exactly is Russia planning to do with the destroyed SNF when it has arrived? Is reprocessing an option, and if so, using what kind of technology and equipment? And will Russia send back to Hungary the radioactive waste that is necessarily generated when spent nuclear fuel undergoes reprocessing?

When reached for details about the upcoming delivery, Rosatom could not immediately respond to Bellona’s request for comment.

Europe taking out nuclear trash

An addendum on importation to Russia of spent nuclear fuel from Hungary’s Paks NPP was signed in Moscow on April 29, 2004 – a mere two days before Hungary was to officially become a member of the European Union. The document is entitled “Protocol on the Agreement between the Government of the Union of Soviet Socialist Republics and the Revolutionary Worker-Peasant Government of the People’s Republic of Hungary on Cooperation in the Construction of a Nuclear Power Plant in the People’s Republic of Hungary, of December 28, 1966.”

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Article 2 of the Protocol reads: “The Hungarian Side delivers, and the Russian Side accepts for temporary technological storage, and subsequent reprocessing, all irradiated nuclear reactor fuel assemblies manufactured in the Russian Federation and used at Paks NPP, after their cooling period in the Hungarian Republic of no less than five years.”

“All” is the key word here. Russia has agreed to accept all spent fuel assemblies, and that would include the damaged ones – the ones that were practically destroyed during the 2003 accident. Notably, at the time of the signing of the protocol, in 2004, it was also known that at least some of the fuel assemblies from 2003 had sustained severe damage and that their storage in Hungary was a costly and hazardous process. It is possible that the European Union may have wanted Hungary to offer some guarantee that the problem of the damaged fuel assemblies would be dealt with. It appears, however, that the solution has been found in merely relocating the problem – from Hungary to Russia.

The 2003 accident: a cleaning fiasco

One way to look at the 2003 event at Paks NPP is as an example of an all-too-frequent scenario – a case study in how experimental work at a nuclear power plant devolves into a contingency event and, subsequently, an accident or even a disaster.

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The VVER-440 reactor operated at Paks NPP’s Reactor Unit 2 was built by the Soviet Union in 1984. The Soviet Union – and, following the breakup of the USSR, Russia, via Rosatom – has also supplied the unit with reactor fuel, produced by Rosatom’s Elektrostal-based nuclear fuel manufacturer Mashinostroitelny Zavod.

A fuel assembly for a VVER-440 reactor consists of 126 fuel rods (see, for instance, this brochure from Paks NPP). A fuel rod is a sealed zirconium tube with a diameter of 9.1 millimeters filled with fuel pellets (uranium dioxide). One fuel assembly holds 137 kilograms of enriched uranium. As nuclear fuel is burned in a reactor, generating energy, dangerous radionuclides are gradually accumulated in the fuel rods – fission products and plutonium. 

Thirty fuel assemblies holding spent reactor fuel came under severe damage in April 2003 during a chemical treatment procedure, when the assemblies, which had been removed from the reactor of Reactor Unit 2, were undergoing cleaning. The area and the equipment in it were contaminated. The accident – which a story on the nuclear news website Atominfo.Ru (in Russian) described as one of the mysteries of the global nuclear energy lore – was classified as a “serious incident,” or Level 3 event, on the International Nuclear Event Scale (INES). (The International Atomic Energy Agency (IAEA) INES scale provides this general description of impacts of a Level 3 event on the people and environment and radiological barriers and control: “exposure in excess of ten times the statutory annual limit for workers; non-lethal deterministic health effect (e.g., burns) from radiation; exposure rates of more than 1 [sievert per hour] in an operating area; severe contamination in an area not expected by design, with a low probability of significant public exposure”). Eighteen months were needed after the incident at Paks to restore the conditions at the reactor unit to those suitable to resume operations.

The anatomy of an accident

The chemical cleaning process used was a technology proposed, according to the Atominfo.Ru story, by the French firm Framatome ANP (now, AREVA NP). The cleaning was undertaken to scrub the surface of the fuel rods free of accumulated corrosion products. This corrosion-caused crud on the fuel rods’ surfaces hindered heat removal and proper coolant circulation, which could affect the reactor unit’s economic performance as well as potentially lead to an accident. 

Experimental cleaning with an acidic solution took place in a specially built cleaning tank designed to hold thirty fuel assemblies and placed at the bottom of a special pit under 13 meters of water, said the 2007 paper describing the Hungarian incident simulation experiment. Acidic solution was applied for the chemical removal of crud, at high liquid flow in a closed circulation loop. After the completion of crud removal, the solution was changed for clean water of the spent fuel storage pool and circulation was established in an open loop.

The Hungarian paper – authored by Péter Windberg and Zoltán Hózer of the Hungarian Academy of Sciences KFKI Atomic Energy Research Institute and entitled “CODEX-CT-1 and CT-2 Integral Tests: Two Possible Scenarios of the Paks-2 Incident” – says: “Due to design problems the cooling of the fuel was insufficient and the decay heat resulted in the heat-up, oxidation and embrittlement of the zirconium components. The opening of the cleaning tank and the water inflow from the spent fuel storage pool led to the fragmentation of fuel assemblies and to the release of radioactive fission products.”

Before the cleaning procedure, the fuel assemblies had been operated in the reactor for a period of between six and 30 months. During the cleaning, no criticality occurred, but the decay heat was quite significant. It was this decay heat that caused the rising temperature and subsequent degradation of the fuel assembly cladding and may have under different circumstances led to a meltdown.

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The CODEX-CT test scenarios were of three phases – formation of water level and steam volume in the tank, seven hours’ oxidation in high temperature steam, and final reflood of brittle fuel assemblies, the paper said, concluding that “[t]he thermal and mechanical loads resulted in the fragmentation of many fuel rods.”

Under the first phase, because of design deficiencies that prevented sufficient flow through the assemblies to remove the decay heat, the temperature in the upper part started to increase. When the saturation temperature was reached, the formation of a steam volume took place in short time. This period lasted about 2.5 hours, the Hungarian paper said.

Continuous temperature increase – compounded by very low heat removal to the surrounding water, on account of the double wall system isolating the tank – led to the increase of pressure inside the fuel rods, the paper explained.

“At 800-900 [degrees Celsius], the internal pressure could reach 30-40 bars. In this range of pressure and temperature plastic deformation of the cladding can take place and the ballooning can lead to burst and activity release from the fuel. It is very probable that this type of fuel failure was responsible for the activity release measured by the […] detectors,” said the paper.

The further increase of temperature – the maximum cladding temperature reached 1200-1300 degrees Celsius – accelerated the oxidation of zirconium components. This period lasted for seven hours, the paper said, adding that the bottom part was cooled by water and suffered no significant changes.

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Finally, the opening of the hydraulic locks created a small gap between the cover and the tank, and pressure in the tank likely decreased, precipitating increased injection of cold water from the cooling pond. Intense steam production took place when the cold water evaporated on the hot surface of the fuel, the paper said, probably pushing the fuel assemblies upward, and further rising the cover and widening the gap between the cover and the vessel – which resulted in water from the cooling pond flooding the tank and causing defragmentation of the fuel rods and escape of radioactivity.

“After the [2003] incident detailed visual examination was carried out with the help of video cameras,” Windberg and Hózer write in their 2007 paper. “The examination indicated that most of the fuel assemblies suffered damage. Brittle failure and fragmentation of fuel assemblies was observed. Many assemblies were broken and fragmented below the upper plate, too. Some assemblies were fractured in their entirety. Fuel rod fragments and shroud pieces accumulated on the lower plate between the assemblies. Some fuel pellets were fallen out of fuel rods, their form remained mainly intact. Heavy oxidation of the zirconium components was identified.”

These destroyed fuel assemblies are now being prepared for transportation to Russia.

An “irresponsible” solution

Bellona has obtained a comment for this story from András Perger, an expert with Energiaklub, a Hungarian organization working, as it says in one of its publications, toward rational and clean production and use of energy. Perger spoke in an email correspondence of the prospect of the fuel’s repatriation to Russia and the risks involved in the delivery and subsequent reprocessing.

“We […] believe that this solution is irresponsible, as it means an implicit danger for the Russian environment and the Russian people – beyond the dangers of transporting the damaged fuel,” Perger said. “We also believe that the earlier transports of SNF in the 1990s contributed to the pollution of the environment of Russia, and endangered the people living around the reprocessing facilities, and the transport routes.”

According to Perger, the original five-year license for storing the containers with the damaged fuel in the cooling pond was extended until 2018, and work was done on the interim storage at Paks to prepare the facility to accommodate the casks.

“It seems,” Perger wrote, “that Hungary wants to get rid of this kind of nuclear waste, even though the [issue of] interim storage of […] the damaged fuel has been solved.”

Perger also spoke of the difficulty with obtaining access to information both about the incident and the plans on further management of the fuel.

“We do not know too much about the issue. The information we have we gained through a court case,” Perger said, explaining that in 2006, the Hungarian nuclear authority ordered Paks to prepare a strategy on the long-term handling of the damaged fuel as a condition of the removal of the fuel from the cleaning tank. “We asked [the] HAEA to release the strategy. The[y] denied [us] access to it, so we went to […] court. We won the case in 2009.”

The documents that Energiaklub obtained revealed that work was under development with a Russian partner to deliver the damaged fuel to Russia, Perger said.

But, wrote Perger, “[the] biggest problem about the issue is the transparency of it. We do not know what is being done, and what is planned to be done. We do not know technical details and there is no clear information on [the] schedule.”

Hungary-Russia nuclear waste export: The safety and legal concerns

Meanwhile, Paks NPP said in a January 28, 2013 statement on its website (in Hungarian, retrieved with Google Translate automatic translation) that the damaged fuel was being prepared for drying and repacking for subsequent transportation to Russia. Special equipment had been put together in Russia, and around twenty Russian specialists were involved in works at the site.

But with the preparations apparently in progress, there are still issues that remain unresolved.

“Legally, we do not fully understand the situation yet, but we see some problems, [both] in the European legislation (which does not permit [sending] nuclear waste to third country if the environmental standards of that country are below the European standards), and […] in the Russian legislation (which orders to send the waste of reprocessing back to the origin country of the nuclear waste),” Energiaklub’s Perger explained in his email correspondence with Bellona.

According to Perger, it was the latter that proved to be a problem for Hungary in the 1990s, and, coupled with the rising reprocessing prices, may have been a factor in why Hungary stopped sending its SNF to Russia.

Legal intricacies aside, the fate of a batch of damaged spent nuclear fuel – in desperate need, as it is, of special handling – would warrant special worry.

According to Perger: “As we do not [know] the technology, we do not know what are the risks of the process. However, it seems that as it is not normal SNF, the process poses more risks for everyone involved in the project.”