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Radiation Shielding Concrete with Depleted Uranium Dioxide

#3732


Production and Testing of High-strength Concretes Including Depleted Uranium Dioxide Concerning their Use as Shielding Materials in Construction of Casks for Spent Nuclear Fuel. Stage 2

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
3 Approved without Funding

Registration date
05.04.2007

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow

Collaborators

  • Oak Ridge National Laboratory, USA, TN, Oak Ridge

Project summary

This is a proposal to extend ISTC Project #2691 by two years at $100K per year. ISTC Project #2691 has been unusually successful. A depleted uranium dioxide concrete (DUCRETE) material has been defined that provides shielding for both gamma radiation and neutrons. A patent ahs been applied for. An extension of this work is requested because: 1) funding is needed to bridge the gap between laboratory studies and pre-commercialization of DUCRETE - an Initiative for Proliferation Prevention (IPP) contract will be sought to design, fabricate and test a prototype DUCRETE cask, and, 2) perform experiments that were not done by the U.S. collaborator, Oak Ridge National Laboratory (ORNL). About 50kgs of material was manufacture for testing at ORNL as part of the original work

It is the objective of the Project to further study characteristics of high-strength concrete with aggregate based on depleted uranium dioxide as applied to its use in casks design developed for spent nuclear fuel storage and transportation. This project continues ISTC Project #2691. The aggregate and high-strength concrete were developed under ISTC project #2691 1-6.

The USA and Russia have accumulated vast amount of depleted uranium wastes (~ 106 tons) in the form of chemical compounds: uranium hexafluoride (UF6) and uranium tetrafluoride (UF4). These compounds are minor products of uranium enrichment process and they have not been used yet. The stock of these compounds is still increasing. This results in great ecological problems and requires increasing expenses for their storage and maintenance.

One of the potential ways to address the ecological problem related to UF6 and UF4 utilization is production of depleted uranium dioxide (DUO2) from these compounds and its use as an aggregate for special concrete. This special concrete can be used as structural and shielding material in casks for SNF and high-level wastes storage and disposal.

A new type of concrete consists of ceramics (DUAGG) based on UO2, which substitutes traditional aggregate used in standard concrete. DUAGG is produced by pressing powdered UO2 into briquettes following by their crashing, dispersion of the crushed material by fractions and sintering of the obtained particles. Then DUAGG is mixed with Portland cement and water, and as a result we obtain high-strength concrete called DUCRETE.

As a result of work performed under ISTC Project #2691 we have fabricated DUAGG with compressive strength of 2800 kg/cm2 (280 MPa) and density close to steel density: 7,85-7,90 g/cm3 1-5.

Due to uranium content in a new material, the application of DUCRETE in casks will provide effective reduction of -radiation. Moreover use of DUCRETE may result in moderation (slowing) of fast neutrons due to high level of oxygen in DUO2 (1.3 g/cm3). This allows their capture by thermal neutrons absorbers. This quality is a unique one for high-strength shielding materials.

The adavantage of DUCRETE use in casks design for SNF storage includes the following items:

  1. Maximal capacity for SNF under given mass-dimensional parameters of the cask;
  2. Increase of protection level of spent nuclear fuel compared with pool storage of SNF;
  3. Reduction of consequences effect under beyond-the- credible accidents (including terrorist acts).

On April 23-30, 2006 in Oak Ridge, TN, USA there was a meeting of Russian and American scientists on research and development in the field of beneficial use of depleted uranium. At the meeting it was stated that perspective use of the new concrete required thorough studies of its features and adaptation of its characteristics as applied to environment of the material in casks for SNF storage and transportation. Necessity in additional testing of DUCRETE is caused by the following factors:

1) Standard extra-strong concretes with high density are fragile and relatively low tensile, bending strength and chipping strength as compared with other materials. Such concretes are also characterized with low resistance to dynamic and explosive impacts. This means that under sudden deformation resulting from high-energy impact (for instance, terrorist missile attack) the SNF transportation and storage concrete cask may be crushed that will result in generation of cask parts with high energy, which can be transferred to another cask component and damage them.

There is the possibility to improve concrete resistance due to disperse reinforcement. This means that thin short fibers are introduced into concrete mixture that provides micro-reinforcement of concrete and increases in several times its resistance to tension stresses and energy intensity under dynamic impacts. Another advantage of disperse reinforcement is the possibility to reduce or to eliminate the necessity to reinforce concrete with rebar that results in reduction of production cost.

2) Concrete in the cask will be subjected to long-term impact of ionizing irradiation.

This impact will be accompanied with water radiolysis and oxygen and hydrogen generation.

Availability of oxygen in concrete massive may cause oxidation of a part of UO2 to U2O3. Some data are available that establish theoretical possibility to suppress UO2 oxidation by introducing special additives into concrete composition.

Use of such additives allows reducing or eliminating the following parameters:

  • Generation of internal stresses due to reduction of U3O8 content that has lower density than UO2,
  • Hydrogen release from DUCRETE.

3) There is the possibility to improve DUCRETE strength by increasing size of DUAGG particles and optimization of its grain composition. DUCRETE samples used in the experiments performed under ISTC Project #2691 were fabricated using the aggregate, which maximum size did not exceed 10mm. It is reasonable to study the impact of increase of DUAGG particles size onto mechanical characteristics of DUCRETE, and based on the results of the study to recommend its optimal grain composition.

The performed work will enable us to get enough information for successful use of DUCRETE in casks for SNF storage and transportation.

The Project implementation will be based on scientific-technical potential and vast experience of highly skilled specialists from VNIIEF and VNIINM in the field of uranium and its compounds material science, development of technologies to produce uranium materials and fabrication of different items from such materials including shielding casks, and testing of nuclear-physical, chemical, mechanical and other uranium features and materials based on uranium.

Skills and experience of the specialists allow performing the planned studies in full scope and by the time fixed. The extension of this project will enable keeping the established team of concrete experts together while new pre-commercialization, e.g. IPP, contracts of DUCRETE are put into place.

Work under the Project will be carried out using the available design-theoretical, design, production and experimental bases using certified software packages, measurement-inspection equipment and facilities, and experimental methods that meet advanced scientific-technical requirements and approaches to address the Project tasks.

This Project is suggested by Oak Ridge National Laboratory, which is involved into activities related to civil use of depleted uranium wastes.

This Project provides great interest for all countries with atomic energy, which are addressing the problems of SNF and HLW management.

The scope of research will be discussed and agreed with foreign collaborators.

Exchange of the information obtained under the Project will be carried out in the following way:

  • Provide collabarotors with comments to the technical reports submitted by ISTC Project particiapnts;
  • Annual joint seminars where collaborators can discuss the results obtained under the Project performance.

In addition collaborators can participate in technical audits of the Project performed by ISTC staff.

References

  1. Study of concrete aggregate characteristics based on depleted uranium dioxide. Report on task 2 under ISTC Project # 2691, 2005.
  2. Optimization of high-strength concrete composition with aggregate based on ceramics from uranium dioxide. Report on task 4 under ISTC Project #2691, 2005.
  3. Optimization of composition and production technology for high-strength concrete with ceramic aggregate based on depleted uranium dioxide. Paper for the 9th International Conference «Environmental Remediation and Radioactive Waste Management», 4 – 8 September 2005, Glasgow, Scotland,VNIIEF (Russia), VNIINM (Russia), ORNL (USA)
  4. High-strength concrete with ceramics based on depleted uranium dioxide. Presentation for the International Conference on Radioactive Wastes management «Global Progress Towards Safe Disposal», 2 – 6 May 2006, Las-Vegas, NevadaVNIIEF (Russia), VNIINM (Russia), ORNL (USA)
  5. Patent application # 2006101614 of 23.01.2006
  6. High-density concrete with ceramic aggregate based on depleted uranium dioxide used as structural and radiation-shielded material for SNF storage and transportation casks, Paper for IX INTERNATIONAL CONFERNCE «SAFETY OF NUCLEAR TECHNOLOGIES: TRANSPORTATION OF RADIOACTIVE MATERIALS - ATOMTRANS- 2006», St. Petersburg 25-29 September 2006


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