Radek Škoda

Burnable Absorber Comparison Between VVER, PWR and SFR With UWB1 and SERPENT Codes

Research of fuel depletion aims at development and introduction of advanced types of burnable absorbers (BA) in nuclear fuel. BAs compensate for the initial reactivity excess and consequently allow for lower power peaking factors and longer fuel cycles with higher fuel enrichments.The paper describes the comparison of selected BA elements (Gd, Eu, Er) for 3 different nuclear fuel types (VVER, PWR and SFR). The effect of harder VVER spectra and the effect of thermal vs fast neutron spectra is evaluated and commented. Uniformly distributed BAs in the fuel were assumed.Comparison calculations were performed with the newly developed UWB1 fast fuel depletion code and with the SERPENT Monte Carlo code. The comparison of UWB1 and SERPENT codes is included in the analysis. Next steps of improving the UWB1 code are suggested.Copyright

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake: Nuclear fuel durability enhancement

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020.

Assessment of Small Modular Reactor Fuel Cost

Small Modular Reactors (SMRs) offer to the nuclear industry a simple, standardized, and safe option for new reactor builds as they are factory built, requiring smaller initial capital investment with shorter construction times. SMRs also promise competitive economy when compared with the current fleet. Construction cost estimates for a majority of the projects, which are mostly in their design stages, are proprietary, but fuel configuration, fuel enrichment, average burn-up, and thermal efficiency are publicly available for most SMR projects. This paper calculates the fuel cost when generating electricity, for selected SMR plants, including optimal tails depletion. The results are compared between one another and with current Light Water Reactors (LWR), providing a rough comparison of a long-term economics once the capital investment is amortized.Copyright

ASSESSMENT OF BURNABLE ABSORBER FUEL DESIGN BY UWB1 DEPLETION CODE

U W B1 depletion code is being developed as a fast computational tool for the study of burnable absorbers in University of West Bohemia in Pilsen, Czech Republic. Research of fuel depletion aims at development and introduction of advanced types of burnable absorbers in nuclear fuel. Burnable absorbers compensate for the initial excess reactivity and consequently allow for lower power peaking factors and longer fuel cycles with higher fuel enrichments. The paper describes the depletion calculations of CANDU, PWR and SFR nuclear fuel doped with rare earth oxides as burnable absorber. Uniform distribution of burnable absorber in the fuel is assumed. Based on performed depletion calculations, rare earth oxides are divided into two groups, suitable burnable absorbers and poisoning absorbers. Moreover, basic economic comparison is performed based on actual stock prices.

AGN-201M: Using Low Power Training Reactors in Education

The AGN reactor type was supposed to be a workhorse of nuclear education in the sixties, with dozens of units being produced and sold around the USA and overseas. However, nowadays only 4 units are fully operational, the rest has been mothballed or decommissioned. In 2010 Texas A&M University made the AGN-201M again part of its education program, after years of reactor inactivity. This very recent practical experience from Texas A&M shows that AGN-201M can be successfully used for undergraduate and graduate nuclear education and new educational methods can be implemented on the reactor. The paper demonstrates new experimental classes developed for the reactor and may serve as an idea for other mothballed AGNs or training reactors worldwide.Copyright

Small Modular Reactor and Large Nuclear Reactor Fuel Cost Comparison

Small modular reactors (SMRs) offer simple, standardized, and safe modular designs for new nuclear reactor construction. Factory built SMRs promise competitive economy when compared with the current reactor fleet. Construction cost of a majority of the projects, which are mostly in their design stages, is not publicly available, but variable costs can be determined from fuel enrichment, average burn-up, and plant thermal efficiency, which are published design parameters for many near-term SMR projects. This paper gives a simulation of the fuel cost of electricity generation for selected SMRs and large reactors, including calculation of optimal tails assay in the uranium enrichment process. The fuel costs of several SMR designs are compared between one another and with current generation large reactor designs providing a rough comparison of the long-term economics of a new nuclear reactor project. SMRs are predicted to have higher fuel costs than large reactors. Particularly, integral pressurized water reactors (iPWRs) are shown to have from 15% to 60% higher fuel costs than large reactors. Fuel cost sensitivities to reactor design parameters are presented.Copyright

Zirconium Dioxide as a Protective Layer of Zirconium Fuel Cladding

Zirconium is important because of its mechanical and neutronics properties combined with its extraordinary resistance against corrosion. It’s mainly usage in nuclear engineering is as a nuclear fuel cladding. Even though Zr layers are very resistant to neutron fluence at reactor operating temperatures, high pressure and high radiation doses, exothermic Zr oxidation in accident scenario still occurs. Hydrogen, and a newly created layer of zirconium dioxide, are undesirable products of the high temperature steam oxidation. ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces large stresses and these stresses cause ZrO2 to crack upon cooling from high temperatures. To stabilize ZrO2 other oxides may be added. Therefore ZrO2 with its high ionic conductivity makes it one of the most promising ceramics to protect fuel cladding and the paper focuses on properties of ZrO2 used on Zr fuel cladding of common power reactors.Copyright

Burnable Absorber Selection With UWB1 Depletion Code

Research of nuclear reactor fuel depletion aims at development and introduction of advanced types of burnable absorbers (BA) applied within nuclear fuel. BAs compensate for the initial reactivity excess and consequently may allow for lower power peaking factors and longer fuel cycles with higher fuel enrichments.Modern computer codes for nuclear fuel depletion calculation require a substantial amount of computational time. Therefore, any parametric calculations for BA selection need to be carried out only with a fast depletion code. The main purpose of the newly developed UWB1 code is a rapid calculation of nuclear fuel depletion, which is achieved by the approximations in the equations describing transport part of fuel depletion. Microscopic cross sections are assumed to be constant through depletion calculation steps.The paper describes the first step of analysis using a new version of UWB1, that was accomplished with the assumption of uniformly distributed BA in fuel. BA elements, nuclides and nuclide mixtures were compared and their performance was consequently evaluated based on multiplication coefficient behavior during depletion.Copyright

Polycrystalline Diamond Films as Protection of Zircaloy Fuel Cladding

Polycrystalline diamond coating is a promising possibility for prevention, or reduction of high temperature oxidation of zirconium alloys. Zirconium alloys are used as cladding material in almost all types of nuclear reactors, where creates a barrier between nuclear fuel and cooling water in the primary circuit. Hydrogen and considerable amount of heat is released during steam oxidation that may occur in an eventual accident. In this paper Zircaloy-2 alloy was covered by polycrystalline diamond layer using Plasma Enhanced Linear Antennas Microwave Chemical Vapor Deposition system reactor. X-Ray Diffraction and Raman spectroscopy measurements confirmed coverage of the surface area with crystalline and amorphous carbon layer. Characterizations were done for zirconium alloy covered with diamond layer before and after corrosion and irradiation tests - ion beam irradiation tests and high temperature steam exposure.Copyright

Cost Saving When Using Enhanced Conductivity Nuclear Fuel Containing BeO in WWER-1000 Reactors

Current pressurized water reactors utilize sintered UO2 that has a number of advantages and disadvantages. Uranium Dioxide’s low thermal conductivity results in a large thermal gradient within the fuel pellet corresponding to higher centerline temperatures compared to other potential fuel forms. These gradients result in non-uniform thermal expansion leading to large internal stresses resulting in cracking of the pellet and fuel-clad interaction, which can lead to loss of the integrity of the fuel pin. Higher fuel temperatures also increase the release of fission gases. Fuels with higher thermal conductivity may alleviate or reduce the severity of these adverse conditions. It is shown that higher thermal conductivity can be obtained by adding BeO to the basic UO2 matrix. This paper focuses on WWER1000 hexagonal fuel geometry. Improvements when using 10% of BeO, as proposed in this paper, reduce the centerline nuclear fuel temperature by 234°C and improve the fuel economy while reducing its cost by 7%. The study was done for NPP Temelin which has two units WWER1000/320.Copyright