NORWEGIAN-RUSSIAN COOPERATION IN NUCLEAR LEGACY REGULATION: CONTINUING EXPERIENCE AND LESSONS.

Safe management of nuclear legacies arising from past activities is a critical issue in maintaining confidence for the continuing and future use of radioactive materials. Effective and efficient regulatory supervision of nuclear legacy management is a critical part of that process. The Norwegian Radiation Protection Authority plays an active role in bilateral regulatory cooperation projects with sister authorities in the Russian Federation, as part of Norway's Plan of Action to improve radiation and nuclear safety. Based on this experience and by reference to specific legacy sites and facilities, this study provides an overview of the substantial progress made in remediation at the Site of Temporary Storage for spent fuel and radioactive waste at Andreeva Bay and presents radiation protection issues arising from the experience and lessons learned in this work. It is suggested that this experience can be useful in the further development of international recommendations, standards and guidance on remediation of nuclear legacies.

Biomineralization of calcium disilicide in porous polycaprolactone scaffolds.

The incorporation of CaSi(2) grains within a polycaprolactone (PCL) framework results in bioactive and biodegradable scaffolds which may be used in bone tissue regeneration. Porous PCL scaffolds were prepared via a combination of salt-leaching and microemulsion methods. To provide markedly different structural environments for the inorganic phase, calcium disilicide powder was either added to a mixed-composition porogen during a given scaffold preparation, or alternatively added to pre-formed scaffolds. Selective fluorescent labeling, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis were employed to assess scaffold calcification in vitro. The process of CaSi(2)/PCL scaffold calcification under zero bias, during which calcium phosphate growth is significantly dependent on the structural degradation of CaSi(2) grains, has a similar mechanism as the calcium phosphate growth on bioactive glasses/ceramics. The biomineralization of these scaffolds is initiated solely by the silicide phase and can be accelerated by the degradation of the polymer matrix.

Bias-assisted in vitro calcification of calcium disilicide growth layers on spark-processed silicon.

A dry-etch spark ablation method was used to produce calcium disilicide (CaSi2/Si) layers on silicon (Si) surfaces for the electrochemical growth of apatitic phosphates (calcium phosphate, CaP). CaSi2/Si composite electrodes readily calcify in vitro under the application of a small electric potential, and with proper treatment, the electrodeposition of CaP is localized to the sparked areas. In addition to increasing the local concentration of calcium, interfacial layers of CaSi2 on Si exhibit exceptional site selectivity towards CaP formation under bias due to the difference in conductivity between Si and CaSi2. The proposed mechanism for bias-assisted biomineralization of CaSi2/Si layers on spark-processed Si accounts for the physicochemical properties of deposited CaP films. This work also describes routes to surface modification of calcified composite electrodes with medicinally relevant compounds such as alendronate and norfloxacin. To assess the suitability of this material as a drug-delivery platform, release of the latter compound was also monitored as a function of time.

Mechanism of calcium disilicide-induced calcification of crystalline silicon surfaces in simulated body fluid under zero bias.

A dry-etch spark ablation method was used to produce calcium disilicide (CaSi2/Si) layers on silicon surfaces, and their biomineralization under zero bias was followed by means of scanning electron microscopy, X-ray energy dispersive analysis, and Raman spectroscopy. CaSi2/Si wafers are bioinert at 25 degrees C and bioactive at 37 degrees C. Mechanistic insights regarding biomineralization were derived from an analysis of film growth morphology and chemical composition after various soaking periods in standard simulated body fluid (SBF). Changes in CaSi2/Si calcification behavior as a function of reaction temperature and pH, SBF concentration, and various surface modification processes were also employed for this purpose. During CaSi2/Si calcification under zero bias, calcium phosphate (CaP) growth is strongly dependent on the structural degradation of CaSi2/Si grains. Surface silanol groups, initially present on the as-prepared material, cannot induce CaP nucleation, which begins only upon delamination of CaSi2/Si layers. The calcium phosphate phases, which are present during various growth stages, possibly include a combination of Mg-substituted whitlockite, monetite, and tricalcium phosphate.