Finnish Power Plant Research Articles

Novel methodology for functional design chain analysis of a nuclear power plant: A new built Finnish power plant case study

Energized by the fact that nuclear power plants (NPP) have a multidisciplinary character as well as a high degree of coupling and interaction between their elements, regulatory bodies worldwide tend to induce a massive number of requirements to ensure the safety of the plants. Mainly, these requirements aim to apply the defence-in-depth (DiD) safety approach. In Fennovoima Hanhikivi 1 (FH1) NPP, the DiD approach is applied through formalizing functional entities that are responsible for defending various DiD levels and preventing them from failure. Each functional entity consists of safety functions that share common non-functional requirements such as safety classification, failure criterion, diversity, and separation requirements.When investigating the safety functions of any NPP, one concludes that they are significantly interconnected and their processing logics exchange a huge number of signals. Therefore, verifying each safety function independently is not effective because a function may seem to perform its function when it is considered alone, but challenges are found when also the interconnected functions are considered. Thus, it becomes essential to verify the whole functional chain. A functional chain can be defined as a set of safety functions that interact together to guarantee the success of plant systems in case of an initiating event. It should be noted that the functional chain term, defined in this study, is different from the safety group term defined in the IAEA safety glossary. The latter is an assembly of equipment, whereas a functional chain is a group of safety functions. In other words, considering the safety engineering process of the plant life cycle, a functional chain is constructed and defined based on plant-level design down to system-level design, while a safety group is constructed based on system-level design.In this study, a methodology for analysing the functional chain is developed. The methodology mainly targets verifying five aspects of the functional chain which are: measurements, actuators, decision-making processing logic, human–machine interface (HMI), and cabling between various components. The methodology utilizes system engineering approach integrated with a relational database that can be utilized to query the plant design data in order to verify the application of non-functional requirements to the plant design components. Additionally, the study also develops a tool that can assist its users to systematically apply the developed methodology and record its results.Finally, a case study for practically applying the methodology to a NPP design is presented. The application of the methodology succeeded in revealing issues that need to be further clarified with the plant supplier. The main usefulness of applying the developed “functional chain analysis” methodology to a NPP is that it provides an additional as-designed verification approach besides the existing verification methods.

Laboratory scale advection-matrix diffusion experiment in Olkiluoto veined gneiss using H-3 and Cl-36 as tracers

ABSTRACTSpent nuclear fuel from Finnish power plants is planned to be deposited deep in the crystalline bedrock. The bedrock needs to be well characterized to properly assess the risks inherent to the long term safety of the site. In the bedrock the possibly released radionuclides are assumed to be mainly transported by water conducting fractures and their transport is retarded by matrix diffusion and sorption. In this work transport properties of an 80 centimeters long veined gneiss drill core sample from Olkiluoto was studied using an advection-matrix diffusion experiment, which was developed to demonstrate the effect of rock matrix for transport of radionuclides in an advective fracture. The experiment was performed using H-3 and Cl-36 as tracers, and effective diffusion coefficients (De) of (1.7 ± 0.7) × 10-13 m2/s and (1.4 ± 1.0) × 10-14 m2/s and porosities of 1.1 ± 0.3 % and 0.23 ± 0.10 % were determined, respectively. A lower porosity and De for Cl-36 than for H-3 indicates an effect of anion exclusion and the results were found to be in agreement with previous laboratory experiments. However, the comparison to results from a similar in-situ experiment showed that the transport of H-3 and Cl-36 is retarded more in laboratory than in in-situ conditions by matrix diffusion.

Chloride diffusion in pore water in Olkiluoto veined gneiss and pegmatitic granite from a structural perspective

ABSTRACTSpent nuclear fuel from Finnish power plants is planned to be deposited deep in the crystalline bedrock in Olkiluoto, Finland. The bedrock and more specifically the elemental composition of ground water, which is composed of the fracture water and the matrix pore water, needs to be well characterized to assess the risks inherent to the long term safety of the site. To this end, it is valuable to investigate elemental composition of the matrix pore water since it tends to conserve hydrogeological signals for longer time spans compared to open fracture waters.In this study, the chloride concentration of matrix pore water in veined gneiss (VGN) and pegmatitic granite (PGR) samples were investigated. Chloride was out-diffused from the naturally saturated rock cores into deionized water. Chloride pore diffusion coefficients were derived by modelling the chloride breakthrough curves obtained from the out-diffusion experiments. Two component modelling gave best fit to the experimental results. There two diffusion coefficients were (9±2)×10-11 m2/s and (0.5±0.1)×10-11 m2/s for PGR and (2.5±0.5)×10-11 m2/s and (0.4±0.1)×10-11 m2/s for VGN. Porosity distribution and total porosities of the rock samples were studied with the C-14-PMMA autoradiography. Porosity for PGR was found to be 0.6 % with large mineral transecting fissures, and porosity for VGN was found to be 0.7 % with highly porous mineral clusters connected to each other via grain boundaries and intragranular pores. The findings here show that heterogeneity has to be taken into account in modelling to find better agreement with the experimental results. C-14-PMMA autoradiography results indicate dual-component behavior for diffusion in PGR and VGN which were used in the modelling.

Through diffusion study on Olkiluoto veined gneiss and pegmatitic granite from a structural perspective

ABSTRACTSpent nuclear fuel from Finnish power plants is planned to be deposited deep in the crystalline bedrock in Olkiluoto, Finland. The bedrock needs to be well characterized to assess the risks inherent to the long term safety of the site. In the bedrock the possibly released radionuclides are mainly transported by water conducting fractures and their transport is retarded by diffusion and sorption. In porous materials these properties are typically linked to microscopic pore structure (pore size distribution, tortuosity and constrictivity) and chemical nature of the minerals and groundwater.In this work transport properties of veined gneiss (VGN) and pegmatitic granite (PGR) samples from Olkiluoto were studied using various through diffusion experiments and the C-14-PMMA autoradiography. Through diffusion experiments were performed on rock cores using HTO and 36Cl in water phase and He in gas phase as tracers. The effective diffusion coefficients (De) determined for the VGN were found to be dependent on the tracer molecule (De(HTO) < De(He) < De(Cl)) whereas for the PGR such a dependence was not found. The porosity distributions determined by the C-14-PMMA autoradiography revealed the difference in the pore structure between the samples. The porosity of VGN consists mostly of grain boundary pores and pores between biotite lamellae. Due to a high content of nanometer scale pores anion exclusion affected the results of 36Cl and Knudsen diffusion the ones of He for VGN. Furthermore, in the PGR micrometer scale intra- and intergranular fissures form a connected network for diffusive transport and thus all tracers diffuse at the same rate.

Effect of particle size distribution on the self-hardening property of biomass-peat fly ash from a bubbling fluidized bed combustion

An increasing amount of biomass fly ash is produced because of the increased usage of renewable energy sources. Therefore, novel applications in which biomass fly ashes can be utilized efficiently are required. One interesting option is to use biomass fly ashes in hardening applications, such as earth construction. In this study, the self-hardening of ground fly ash from a Finnish power plant with a bubbling fluidized bed boiler that burns forest industry residuals and peat was investigated. Fly ash was ground with three different mills, namely, tumbling ball mill, impact mill, and jet mill, to different particle size distributions. Results showed that the amount of reactive components for ground fly ash samples was more or less the same with the original sample, but the particle size distribution was different. Moreover, the water requirement for self-hardening samples was completely different depending on the grinding mechanism. When particle size distribution was wider (after ball and impact milling), the water requirement was much lower due to the better packing of the particles. A smaller water requirement also led to greater compressive strength even the fly ash samples were chemically and mineralogically the same. After ball milling, obtaining four times higher self-hardening compressive strength, from 5MPa to 20MPa, was possible. For jet milled fly ash, the particle size distribution was narrow due to the classifier in the mill, and the water requirement was high. Therefore, the packing and self-hardening compressive strength of jet milled fly ash was lower than that of impact and ball milled samples.

Studies on the Leaching and Weathering Processes of Coal Ashes

Within the Swedish project Coal-Health-Environment (Kol-Hälsa-Mi1jö) leaching studies were made on several types of coal ashes, fly ashes, bottom ashes and scrubber sludges. Studies were made on the effects of pH, pCl, pCO3. pEDTA and pSO4, in the leaching solution on the leaching of metals from coal ashes. As a model for the leaching system, we studied the leaching of Cr, Co, Ni, tu, Zn, Mo, Se, As, Cd and Pb. The leaching of the metals was found to increase with pH for pH less than 2 and pH greater than 9, and to decrease for 2 > pH > 6. The metal leaching behaviour may in part be explained by the mass-action law. We have also made long-term leaching tests of several coal ashes from Danish and Finnish Power Plants using leaching water of different pH. The dominating crystalline phases in the different coal ashes have been identified by X-ray diffraction technique. The major species in the different coal ashes were found to be mullite (3A12.2SiO2), α-quartz (Sio2) and the iron oxides magnetite and hematite. Leaching and X-ray studies were also made on the magnetic fraction of the fly ashes. Equilibrium analysis were made on the system Me-OH-Cl-CO32− - SO42−, where Me = Cr, Co, Ni, Cu, Zn, Mo, Se, As, Cd and Pb, partly using the computer program HALTAFALL. A model for the metal leaching from a coal ash deposit will be discussed.