Searching for a Sarcophagus solution- Could EKOR fill the gap?1 February 1998
The Chernobyl authorities have given the go-ahead to the US company, Eurotech Ltd, to proceed with the construction of industrial scale equipment for on-site manufacturing of EKOR, a compound that will be used to fill the space in the Sarcophagus to immobilise the radioactive dust inside. This radiation resistant material was developed at the Kurchatov Institute. While it won’t solve all the problems of the destroyed reactor, it may ensure that there is little risk that the dust inside the Sarcophagus will ever be released into the atmosphere. But what is this “stuff” called EKOR?
The Sarcophagus covering the ruins of reactor 4 at Chernobyl is deteriorating much faster than expected. This has led to a growing concern that the 15-40 t of radioactive dust inside could escape into the atmosphere creating another environmental disaster. Until a permanent enclosure or decommissioning can be accomplished, there is an urgent need for an effective way of suppressing this dust.
For over a decade, scientists at the Kurchatov Institute have been developing a proprietary silicon-organic foam-type elastomer, called EKOR, that is radiation and fire resistant and appears to be the ideal dust suppressant for use within the Sarcophagus. This material could be used to fill most spaces no matter how inaccessible they are. The completion of the development programme was the result of the joint efforts of Kurchatov, the Euro-Asian Physical Society (EAPS) and Eurotech Ltd (see Panel).
By July 1996 the material had successfully completed accelerated-life and environmental testing under simulated Chernobyl radiation conditions. In February 1997 Eurotech completed the assembly of the equipment required to mix, pump, deliver, and spray the EKOR material under field application conditions. The assembly was carried out by Chimmash – a design and manufacturing facility for nuclear and chemical equipment in the Urals. Several successful demonstrations applying EKOR were carried out during May in order to prove its efficacy on an industrial scale.
The success of these demonstrations has led to the signing of an agreement by Eurotech, the Chernobyl plant and Ukrstroj (the Ukrainian State Construction Company) to begin an application project using EKOR. This agreement has been ratified by the Chernobyl Administration, the Kurchatov Institute, and ERBC Holdings Ltd, a European merchant bank and founding shareholder in Eurotech. Chernobyl authorities have told Eurotech to forego the planned construction of test manufacture and application equipment and proceed directly with the construction of industrial scale equipment capable of continuous supply of EKOR at the destroyed reactor. This work has commenced and the equipment is scheduled for delivery to the site in the first quarter of 1998.
Although this will not be an ultimate solution to the waste problem, EKOR will suppress the radioactivity in the Sarcophagus and also assist the work to stabilise and dismantle the whole structure. The developers make the point that even should the Alliance plan to build a second shell around the Sarcophagus be given the go-ahead, in their opinion, reducing radiation levels by filling the spaces with EKOR will help complete any assembly work more safely. The material strength of EKOR will also help to support the structure. According to their estimates, the necessary volume to fill could be about 35 000 m3.*
TESTING AND PRODUCTION
Full-scale testing of EKOR’s properties has been carried out in a programme known as Cocoon.
Testing was done under the anticipated extreme environmental conditions at Chernobyl. Results showed that EKOR will keep its structural integrity under the very intense radiation levels for extended periods of time – up to 10 billion rads of exposure (350 rads being a lethal dose for any human) without emitting combustible gases. Accelerated-life testing has shown that exposed to radiation levels at Chernobyl, EKOR could last between 200 to 300 years without any significant change in properties. Furthermore, EKOR, unlike normal hydrocarbon-based industrial foam materials, does not suffer from hydrogen emission under intense radiation that could cause an explosion and fire under the existing radiation levels at Chernobyl. In addition, the material will not burn in an open flame.
EKOR is easily produced in a variety of forms (flexibile, rigid and as a film) and densities. The basic formulation is a closed cell flexible foam material that can be formulated to produce a relatively wide range of densities: from a low density foam of 0.1 - 0.7 gm/cm3 to a high density film of 1.5 gm/cm3.
The material maintains good structural stability, preserving its structural properties under radiation up to an absorbed dose of 100 MGy, transforming finally into a foam-ceramic with a good mechanical compression capabilty. For applications where structural strength is required, EKOR can be formulated to produce a hard foam with a mechanical bearing strength of 6.3 kg/cm2.
EKOR is hydrophobic, completely water proof and in a modified form will cure underwater. With aggressive adhesive properties, EKOR will adhere to almost any surface including wood, concrete, glass, and rusted material as well as underwater surfaces without the need for a primer. This capability is particularly important for suppressing or containing radioactive dust particles that may stick to walls, floors, ceilings, air conditioning ducts etc, as a result of accidents at, for example, fuel processing plants or power stations. EKOR can resist corrosion caused by decimolar solutions of acids, alkalis and organic solvents. More importantly, EKOR does not become radioactive itself and can be easily extracted after a long period of irradiation; it is ecologically clean – it does not practically absorb actinides nor fission products – and can be easily handled after use. In its final form, after usage, EKOR becomes a simple SiO2 powder.
The basic EKOR material can be produced with a wide variation of density, plasticity, foam formation time and other properties depending on the application requirements. For example, the time for foam formation could be changed from several minutes to several hours. Mechanical properties can also be changed from an easily compressible foam-type elastomer to a quasi-ceramic light foam. Any special additives (eg boron) can easily be accommodated.
Material synthesis is simple and can be done on-site by mixing of prepared components. Polymerisation proceeds spontaneously at natural temperature.
OTHER NUCLEAR APPLICATION
The use of EKOR is not limited to the control and containment of contaminated material from accidents, but can be used as a safe radiation resistant material in the storage, transport, and disposal of nuclear fuel and waste in a variety of ways, for example:
• Cushioning and protecting nuclear fuel rods during transport.
• Lining storage barrels and casks for intermediate storage.
• Encapsulating low level medical radwastes for permanent burial.
• Filling abandoned uranium mines to prevent water borne seepage or radioactivity.
• Covering uranium mill tailling piles.
Eurotech sees the managing of waste from nuclear power plants providing a very large potential market for EKOR. As the company points out, the main methods used to fix radwaste involve bitumen, cement and glass, all of which have disadvantages. Bitumen is flammable, cement due to its water content is corrosive and generates hydrogen by radiolysis and chemical decomposition of water, glass only incorporates 10-15% of waste and needs for production an expensive high temperature melting process. Therefore, there is an opportunity for a good multi-purpose material such as EKOR which can contain a wide variety of radwaste without many of the problems associated with the standard methods.
Eurotech also sees a market for non-nuclear applications of this material.
A less expensive (non-radiation resistant) form of EKOR has been developed showing great promise for applications in the transport industry. EKOR’s excellent fire resistant and insulation properties makes it ideal for use in the components of walls and partition structures of submarines, ships and tankers, aircraft, automobiles and railroad cars. Like its radiation resistant form, this type of EKOR material is non-combustible and can tolerate temperatures between -60°C and +300°C before undergoing any significant property changes, turning into sand at around 1500°C. EKOR also remains non-toxic under the impact of flame.