Nuclear Engineering

This article examines how 'safety case' experts working on Finland’s nuclear waste repository project at Olkiluoto summoned, conjured, or channeled memories of Seppo—a deceased colleague whose ‘specter,’ as some put it, still ‘haunts’ their scientific community. For some, Seppo’s postmortem presence manifested as gaps in knowledge left behind by an expert often reluctant to document the methodological assumptions underlying his knowledge-practices. For others, it manifested as anecdotes about Seppo’s stubbornness, irritability, and intellectual intensity as well as his more jovial demeanor during sauna nights, workplace parties, or trips abroad. Still others caught themselves asking ‘What Would Seppo Do?’ while troubleshooting at work. Inspired by anthropological and philosophical work on ancestors and haunting, the article unpacks how the multi-millennial time horizons of nuclear waste risk, the intergenerational time horizons of expert succession, and the everyday time horizons of a single expert life-course shared entwined fates. It focuses less on what knowledge disappeared when an expert’s body died – or how it could have been preventatively backed-up or managed – and more on what has lived on of the expert in and through surviving colleagues. Analysis of 'afterlives of expertise' like these can, it concludes, provide insights for a current moment of intergenerational transition in nuclear energy sectors in Europe, North America, and beyond.

Nuclear and thermonuclear weapons have been an anxiety factor for people for decades and generations. This paper's purpose is to reduce this anxiety by reducing the effect and efficiency of thermonuclear weapons by discussing on a possible projectile and to trigger new ideas on that subject. To achieve this objective, it is determined that thermonuclear weapons' efficiency could be reduce by capturing fast neutrons which are causing the fusion reaction. To benefit from previous studies, FNRs has been selected to search on their fast neutron capturing technologies. Investigated materials are 151 Eu, 157 Gd, 164 Dy, 186 W and 178 Hf. These materials' cross-sections, their special features and properties has been compared. Most proper material that has been identified is 151 Eu due to its high and reliable neutron capture cross-section and ability to create a neutron capture chain reaction. It is proposed, the most efficient compound of 151 Eu would be Eu2O3, in powder form. Other helpful materials and their usages has been specified. Projectile's inner mechanism and design has been given and one of the possible casing material of the projectile has been defined as tungsten carbide (WC).

The proton exchange membrane fuel cell (PEMFC) is a prominent environmentally friendly alternative candidate to internal combustion engines in automotive applications. The recovery of the waste heat of light-duty diesel engines has been investigated recently, which is similarly relevant for PEMFCs. Thermoelectric generators (TEG) applied on the stack’s walls have been already proposed and tested as a cooling method for small scale applications of the PEMFC. For the medium scale usages of the PEMFC stack, TEG technology may be further used to recover heat lost through the cooling water required for stack thermal management, which was the focus of the present study. Using an agglomerate model for the PEMFC and a computational fluid dynamic (CFD) thermal model for the TEG heat exchanger unit, the operation and performance of the PEMFC stack and heat recovery unit were simulated, respectively. After validation, results indicated that the transferred heat from the PEMFC to the cooling ch...

We derive a microscopic version of the successful phenomenological hydrodynamic model of Bohr-Davydov-Faessler-Greiner for collective rotation-vibration motion of an axially symmetric deformed nucleus. The derivation is not limited to small oscillation amplitude. The nuclear Schrodinger equation is canonically transformed the to collective co-ordinates, which is then linearized using a constrained variational method. The associated constraints are imposed on the wavefunction rather than on the particle co-ordinates. The approach yields three self-consistent, time-reversal invariant, cranking-type Schrodinger equations for the rotation-vibration and intrinsic motions, and a self-consistency equation. For harmonic oscillator mean-field potentials, these equations are solved in closed forms and applied to the ground-state rotational bands in some axially-symmetric nuclei. The results are compared with the measured data.

Nuclear Power plants can be designed to withstand the strongest shaking in earthquakes but engineers need to know what these accelerations might be.  Eight lines of investigation are identified for testing the seismic capability of the Vijaydurg Fault,  which has the largest fault scarp in southern India, and which passes offshore within 10 km of the planned Jaitapur power station.

This contribution demonstrates how the deposition rates from a flowing stream of coagulation-aged 'polydispersed' aggregated aerosols can be accurately predicted by systematically correcting results calculated for the hypothetical case of 'monodispersed' dense spheres in the same carrier gas environment, using information on: a) the size- and morphology-dependence of individual particle transport properties, b) the spreads (sigma_g) of aggregate size distribution functions due to Brownian coagulation in the Knudsen (Kn_p >>1) and continuum regimes (Kn_p <<1), and c) the fractal properties (exponent Df) of the constituent aggregates. In addition, the implications of restructuring the fractal aggregates on aerosol deposition rates are also discussed since aggregated particle populations can change not only due to coagulation but also due to finite-rate restructuring processes such as those brought on by sintering at high temperatures or aggregate-induced steam condensation. Saturated or near saturated steam (can be considered as an inactive material) that condenses on pre-existing suspended aggregates increased their mass and removal rate.

Author to whom correspondence should be addressed:
Professor Yehia Khalil, email: yehia.khalil@yale.edu
Office: M8
Chemical Engineering Teaching Laboratory: M228
Mason Laboratory
Yale University 9 Hillhouse Avenue, New Haven, CT 06520, USA

Nuclear industry is in crisis and innovation is the central theme of its survival in future. Artificial intelligence has made a quantum leap in last few years. This paper comprehensively analyses recent advancement in artificial intelligence for its applications in nuclear power industry. A brief background of machine learning techniques researched and proposed in this domain is outlined. A critical assessment of various nuances of artificial intelligence for nuclear industry is provided. Lack of operational data from real power plant especially for transients and accident scenario is a major concern regarding the accuracy of intelligent systems. There is no universally agreed opinion among researchers for selecting the best artificial intelligence techniques for a specific purpose as intelligent systems developed by various researchers are based on different data set. Interlaboratory work frame or round-robin programme to develop the artificial intelligent tool for any specific purpose, based on the same data base, can be crucial in claiming the accuracy and thus the best technique. The black box nature of artificial techniques also poses a serious challenge for its implementation in nuclear industry, as it makes them prone to fooling.

This brief paper is to explain one of my ideas relating to deep space propulsion. This paper explains what I call the "Nuclear Thermal Pulsejet Engine" and how we can use vacuum of space to cool a small nuclear reactor down for future nuclear powered spacecraft.

INVAP uses computational tools to predict the behavior of the reactor to be built. Every
new reactor needs increasingly detailed analysis from different points of view, as nuclear safety and
fulfillment of user requirements (flux and production levels, spectra requirements, perturbations, etc).
Furthermore, this analysis must be modeled with a consistent level of detail from all the engineering
variables. INVAP has been on continuous development of the calculation system used for design and
optimization of nuclear reactors. The calculation codes have been polished and enhanced with new
capabilities as they were needed for the reactor design, improving its safety, fuel economy and
performance. Nowadays, this calculation line is divided in two main codes: Cell (CONDOR) and Core
(CITVAP) codes. The homogenized and condensed macroscopic Cross Section (XS) is one of the
main parameters used as interface between both codes; which are calculated by the Cell code and they
are used as input by the Core code.
The present work summarizes the different theories, algorithms and numerical approaches used by
CONDOR to generate the required parameters. The description covers all the calculation stages from
the geometrical input up to the generation of the output parameters, describing the different methods
used in the different stages.

The history of humanity is closely intertwined with energy developments, from taming fire to splitting atoms, and few would argue against the centrality of electricity to modern life. However, despite the fact that pressures on achieving sustainable and carbon-neutral energy continues to mount, the fossil fuel-based energy system remains firmly in place, with over 80% of total primary energy supplied by oil, coal and natural gas. Energy production by means of nuclear energy is increasingly framed as a major policy tool for rapid decarbonisation and prevention of energy pollution deaths. However, despite extensive reframing efforts, global nuclear generation is falling, due to a combination of closures outpacing new build and the low costs and ease of deployment of fossil fuels.
This has prompted headlines such as “Nuclear power is dying. Can radical innovation save it?” and “Can sodium save nuclear power?”, with innovation being a common theme in discourse around the absence of a nuclear renaissance as well as in response to public concerns around safety, waste and proliferation. This innovation frame stretches beyond advanced fission concepts, with fusion being pitched as a safer and a less controversial alternative. However, despite this extensive focus on innovation, only limited work has been done on path dependencies acting as barriers for nuclear innovation. This article will set out some of the implications of path dependency in regards to nuclear innovation, as well as an opportunity to reflect on lessons for future nuclear innovation.

The flow contraction through sharp-edged short orifices respectively the narrowest flow cross-section or the vena contracta has been measured for water, air and air/water mixture. The results demonstrate that the contraction in the case of subcritical single-phase flow is restricted to values between 0.62 and one, while in the two-phase flow it is limited to very narrow ranges of air mass flow qualities where the flow regime is specified as bubbly or spray.

• Atmospheric dispersion modeling for two credible accidents of the TRIGA Mark II research reactor in Kinshasa (TRICO II) was performed. • Radiological safety analysis after the postulated initiating events (PIE) was also carried out. • The Karlsruhe KORIGEN and the HotSpot Health Physics codes were used to achieve the objectives of this study. • All the values of effective dose obtained following the accident scenarios were below the regulatory limits for reactor staff members and the public, respectively. a b s t r a c t The source term from the 1 MW TRIGA Mark II research reactor core of the Democratic Republic of the Congo was derived in this study. An atmospheric dispersion modeling followed by radiation dose calculation were performed based on two possible postulated accident scenarios. This derivation was made from an inventory of peak radioisotope activities released in the core by using the Karlsruhe version of isotope generation code KORIGEN. The atmospheric dispersion modeling was performed with HotSpot code, and its application yielded to radiation dose profile around the site using meteorological parameters specific to the area under study. The two accident scenarios were picked from possible accident analyses for TRIGA and TRIGA-fueled reactors, involving the case of destruction of the fuel element with highest activity release and a plane crash on the reactor building as the worst case scenario. Deterministic effects of these scenarios are used to update the Safety Analysis Report (SAR) of the reactor, and for its current version, these scenarios are not yet incorporated. Site-specific meteorological conditions were collected from two meteorological stations: one installed within the Atomic Energy Commission and another at the National Meteorological Agency (METTELSAT), which is not far from the site. Results show that in both accident scenarios, radiation doses remain within the limits, far below the recommended maximum effective (whole body) dose of 20 mSv/year for workers and 1 mSv/year for the general public in the IAEA Basic Safety Standards 115 and demonstrate the radiation safety of this reactor. This guarantees the safety of workers and the population around the plant site.

Via decrement of mass of planets, we can send the entire planets to far space orbital allocations. We can convert physical matter into energy, it can either get irradiated to outer space, get transmitted back to Earth's potential energy, get used as a self-propellant, or it can get used in a complex model of these systems; it decreases the mass of the planet. By conversion of the matter to energy, Earth will lose some mass that decreases the gravitational fields for Earth; the formulas of the current research are deduced to control the movements of the planets. Celestial bodies, like any other mechanical systems which follow, and are based on, the physical laws of mechanics and dynamical systems, follow these laws. So since the celestial object “A” exerts the “F” force on the celestial object “B”, the celestial object “B” exerts an interactive force “F” on the celestial object “A” also. All celestial objects exert gravitational influences on each other. Scientists believe, once upon a time, the Sun would be much hotter than what it is today. By that point, this high temperature leads to extinction of the entire existence of life on Earth. When the gravitational force changes, a space particle may either get departed from the other particle or come closer to the other particle.

Диссертации "Моделирование процессов перелома кинетики окисления и переориентации гидридов в циркониевых оболочках твэлов". Диссертация на соискание кандидата технических наук по специальности 05.14.03 "Ядерные энергетические установки, включая проектирование, эксплуатация и вывод из эксплуатации" была представлена к защите 18 сентября 2018 в НИЦ "Курчатовский институт".

PhD thesis (in Russian) Modeling of oxidation kinetic transition and hydrides reorientation in zirconium claddings of fuel rods

This article extends previous efforts on genetic algorithms (GAs) applied to a core design optimization problem. We introduce the application of a new Niching Genetic Algorithm (NGA) to this problem and compare its performance to these previous works. The optimization problem consists in adjusting several reactor cell parameters, such as dimensions, enrichment and materials, in order to minimize the average peak-factor in a three-enrichment zone reactor, considering restrictions on the average thermal flux, criticality and sub-moderation. After exhaustive experiments we observed that our new niching method performs better than the conventional GA due to a greater exploration of the search space.

Nuclear transmutation is a process in which conversion of one isotope into another isotope takes place as product of nuclear reactions. PyNE is nuclear engineering toolkit for python. In this paper simulation of transmutation is shown using PyNE in python. Initially PyNE was installed in python to access all the library files. PyNE has all the library file within itself, which has been imported and then simulation has been done. In this paper transmutation of Fe-56 is given. All the stages of transmutation are simulated and at the end total time required for transmutation is also given. Transmutation of any material can be performed using this toolkit under defined circumstances.

Many different reactor systems have been proposed and some of these have been developed to prototype and commercial scale. Six types of reactor (Magnox, AGR, PWR, BWR, CANDU and RBMK) have emerged as the designs used to produce commercial electricity around the world. A further reactor type, the so-called fast reactor, has been developed to full-scale demonstration stage. These various reactor types will now be described, together with current developments and some prototype designs.

The Advanced Lead Fast Reactor European Demonstrator (ALFRED) is the 300 MWth pool-type reactor aimed at proving the feasibility of the design concept adopted for the European Lead-cooled Fast Reactor (ELFR) of Generation-IV, whose preliminary design has been proposed within the LEADER (Lead Cooled European Advanced Demonstration Reactor) EURATOM Project.In the frame of investigating different options to optimize the conceptual fuel pin design of ALFRED, the fuel performance analysis of the reactor core is carried out by means of the TRANSURANUS code, which is presented in this paper. Results of the average and the hottest reactor conditions are discussed concerning both fuel and cladding performance on the basis of indicative design limits. A sensitivity analysis is performed in order to assess the impact of models and parameters affected by a larger uncertainty, and to identify a “worst case” scenario. This strategy allows identifying some design parameters which could be modified to improve the fuel pin behaviour, in order to gain benefits mainly in terms of maximum fuel temperature. The results of the present work are useful for giving feedback to the conceptual design of the ALFRED reactor and, in perspective, to improve the safety-by-design characteristics of the LFR systems.

The polar γ-ray radiography method was studied extensively, Gamma-ray from Ir-192 source was used to detect weld defects in the main gas pipeline extending from Khoms to Tripoli. Gamma-ray radiographic inspections were carried out according to the ASTM(1) standards, and the radiographs were analyzed according to the quality specifications API(2) standard-1104. The polar γ-ray mode has been applied to specimens of weld joints of pipes used in this pipeline in the regions [the kilometer 118(3)] and [the kilometer 123], and weld joints in the SLR 7 station in the region [the kilometer 125]. The results obtained from Gamma-rays have been discussed and analyzed

What happened, in the years leading up to Valentine's Day 2014, that made a canister of nuclear waste burst open and spew out fire underground at a US facility for the long-term disposal of radioactive military waste? According to one widely publicized scenario, a simple run-of-the-mill typo led to organic kitty litter mistakenly being used to soak up liquid in the drum instead of another kind of absorbent material. This ultimately led to a reaction that made heat and pressure build up in the drum, causing it to erupt. But was that "simple" clerical error symptomatic of a much deeper, system-wide problem-- involving a US Energy Department plan to rush the pace of nuclear waste disposal? What were the political, social, and financial elements involved in making Los Alamos' waste drum #68660 erupt that February night? What can be done to prevent similar accidents – which can have price tags of hundreds of millions of dollars or more – from happening again in the future? A cultural anthropologist spent 10 weeks onsite after the event, logging 43 interviews and trying to answer these questions. Here is what he found.

PARAGON is Westinghouse's state-of-the-art code for two-dimensional lattice calculations. It is based on collision probability with interface current method and written entirely in FORTRAN 90/95 with dynamic memory allocation. As such, PARAGON provides great flexibility in increasing the problem size, mesh structure, and number of energy groups, hence the solution accuracy with respect to standard lattice codes. The purpose of this paper is to demonstrate the applicability of PARAGON to whole core simulations and to validate its theoretical models. A two-dimensional PWR core model has been developed and studies have been performed, investigating the effects of the coupling order of the interface current method. Results have been compared to those from continuous energy MCNP calculations, showing excellent agreement in both core reactivity and pin-and assembly-power distributions.

This study provides an independent, outside-in estimate of the cost and schedule risks of nuclear waste storage projects. Based on a reference class of 216 past, comparable projects, risk of cost overrun was found to be 202% or less, with 80% certainty, i.e., 20% risk of an overrun above 202%. Based on a reference class of 200 past, comparable projects, risk of schedule overrun was found to be 104% or less, with 80% certainty, i.e., 20% risk of overrun above 104%. Cost risk and schedule risk are both substantial for nuclear waste storage projects.

In this paper, an attempt has been made to systematically organize the research investigations conducted on clad tube failure, so far. Before presenting the review on the clad failure studies, an introduction to different clad materials has been added, in which the effect of alloying elements on the material properties have been presented. The literature on clad failure has been broadly categorized under the headings LOCA and RIA. The failure mechanisms like creep, corrosion and pellet–clad interaction have been discussed in details. Each subsection of the review has been provided with summary table, in which the studies are arranged in the chronological order. A small section on acceptance criteria for ECCS has also been included. The last section of the review has been dedicated to the core-degradation phenomena.

Analytical Study of Stuxnet Attacks on Iranian nuclear reactors .
1. Physical Weakness  in industrial control systems in Iranian nuclear Bases.
2.  Software Weakness and security in  industrial control systems in Natanz nuclear Bases .
3. What is Stuxnet .
4. Reverse engineering of Stuxnet .

Niebotyczne koszty cywilnej energetyki jądrowej nie powinny odżegnywać od inwestycji w bloki jądrowe w Polce. Kluczem do ich zrealizowania może być skorzystanie z dodatkowych, nieoczywistych źródeł finansowania. Największą ciekawostką jest to, że wpływ na powodzenie energetyki jądrowej w Polsce będzie miał sposób finansowania i uregulowania… odpadów radioaktywnych oraz terenów pogórniczych.

In the first decades of space exploration several concepts appeared for utilizing nuclear energy in space. However, only a few of them were developed into actual instruments. Radioisotope powered batteries and heating units have been regularly used in automatized space probes since then. Small nuclear reactors were also launched into space in the Cold War era, but the hazards finally proved to be too great compared to the benefits. Nuclear propulsion systems were also developed in the USA (NERVA) and in the USSR (RD 0410) but never actually used in a launched spacecraft. The concept of a radioisotope powered thermal rocket engine also existed, but the initial experiments revealed several problems, so the concept was set aside. Nuclear energy in space Cascade decaying isotopes Outline of a possible implementation of the THOR engine (Thorium-228 isotope powered thermal rocket engine). The body of the engine could be made of tantalum-hafnium carbide ceramic, which has a melting point at 4260 K-this material allows high working temperatures (3300-3600 K) while effectively absorbing the radiation of the source. The hydrogen propellant leaves the nozzle at a speed of 10 km/sec at this temperature. Adding a small amount of hydrocarbons to the propellant material prevents the chemical wear of the engine parts by the hot hydrogen gas flowing through them.

An Internal Flood PRA involves scenarios in which a pipe rupture can result in the release of a large volume of water over a short period of time.  Given the size of the flow rate and the available space available for water accumulation, the rise in water height as a function of time is necessary to be computed in order to determine the time available for operator intervention before extensive damage is experienced.  To determine the available time before a critical water height is achieved, it is desired that a simplified, yet consistent, approach be used to help determine the height of water rise as a function of time due to water inflow and outflow.  Accounting for area drainage and propagation of water from one adjoining compartment to another must also be taken into account in order to realistically model a given internal flood scenario. 

A mathematical model using mass balance relationships can be used to model flow of water into and out of multiple adjoining areas subject to an internal flood event using a set of linked differential equations that define the change in water height as a function of time for each affected space.  Various restrictions and openings that exist between compartments and allow propagation of water from one area to another can be modeled using a consistent set of empirical relationships to estimate flow rates and simulate the postulated scenario as a function of time.  An example showing the use of such empirical relationships for a given pipe rupture is presented to best show how a simplistic model can be created to estimate water height versus time for various rooms connected via propagation flowpaths.  The use of such information can yield the available time for operator mitigation before the equipment in affected rooms is damaged due to water submergence.

W hile it is unmistakable that climate change mitigation must occur, it is less clear which particular strategies, infrastructures and practices offer the greatest potential in the energy sector. Pacala and Socolow argued more than a decade ago that a series of 'stabilization wedges' would enable humanity to maintain quality of life while avoiding catastrophic climate change 1. They discussed more than a dozen such potential wedges ranging from energy efficiency and fuel switching from coal to natural gas to the advanced deployment of renewable electricity, nuclear power, and carbon capture and storage 1. Other studies similarly note the importance of renewable energy and nuclear power in climate miti-gation pathways and/or for achieving energy systems with net-zero emissions 2-5. As we near three decades of dedicated climate protection interventions in many countries' energy strategies, we closely examine in this paper the extent to which scales of national attachments to either nuclear power or renewables associate with each other, and with effective aggregate reductions in national carbon emissions. Despite many contingencies and complexities, this offers a first-order test of conventional background assumptions that each strategy is comparably effective, and without notable opportunity costs or antagonistic effects on other strategies. Accordingly, this paper uses regression analyses to interrogate relevant and consistent global datasets extending over 25 years and 123 countries, and to test interconnected hypotheses related to carbon emissions reduction with nuclear power and renewable energy, as well as one about crowding out and technological lock-in. One core finding is that countries with nuclear power attachments do not tend to have significantly lower levels of national carbon emissions. A second core finding is that lower levels of carbon emissions do associate more strongly with the relative scales of national attachments to renewable energy than with nuclear attachments. In other words, it is renewable (more than nuclear) attachments that tend to be associated in practice with significantly lower levels of carbon emissions. This is in line with recent work such as that of Jin and Kim, who find, using data from a sample of 30 countries, that "nuclear energy does not contribute to carbon reduction unlike renewable energy" 6. A third core finding is that the scales of nuclear and renewable attachments tend to vary negatively with each other. This is broadly consistent with a finding that nuclear and renewables commitments crowd each other out. We then rigorously test and seek to validate these findings through further multiple regression analyses as well as an investigation of possible moderating effects. Note that the carbon-emission trends observed may not occur because of the choice between renewable or nuclear energy; the choice might be one result of a broader policy programme that leads to less carbon emissions (or does not). The nuclear climate mitigation hypothesis Emphasizing the widely discussed carbon emissions abatement potential of nuclear power, the nuclear climate mitigation hypothesis holds that the relative scale of national attachments to nuclear electricity production will vary negatively with carbon emissions. In simpler terms, emissions are expected to decline the more a country adopts nuclear electricity supply. Elements of this proposition are prominent in both energy policy and the academic literature 7-12. For instance, the International Energy Agency includes nuclear power as one of its select 'low-carbon technologies' and argues that if the world is to see a 50% drop in energy-related CO 2 emissions, then nuclear energy must expand rapidly to where it reaches 1,200 gigawatt electrical (GWe) of installed capacity in 2050, when it also becomes the single largest source of electricity that year 13. Achieving this level of nuclear capacity would require about US$4 trillion of additional investment, larger than any other source of electricity 13. Two of the most widely emphasized contenders for carbon emissions reduction in the electricity sector are nuclear power and renewable energy. While scenarios regularly question the potential impacts of adoption of various technology mixes in the future, it is less clear which technology has been associated with greater historical emission reductions. Here, we use multiple regression analyses on global datasets of national carbon emissions and renewable and nuclear electricity production across 123 countries over 25 years to examine systematically patterns in how countries variously using nuclear power and renew-ables contrastingly show higher or lower carbon emissions. We find that larger-scale national nuclear attachments do not tend to associate with significantly lower carbon emissions while renewables do. We also find a negative association between the scales of national nuclear and renewables attachments. This suggests nuclear and renewables attachments tend to crowd each other out. NATure eNerGy | www.nature.com/natureenergy

Thorium fuel cycle requires innovative, remote controlled and maintenance-free technologies due to the presence of 232 U and other hard γ-emitting isotopes with its main fissile constituent 233 U. Microwave heating, due to interaction-absorption and volumetric in nature is material specific. It has an effect on the process and the quality of the product as well. Use of microwave heating has shown promising outcomes for many processing steps like pyrohydrolysis and vitrification in thorium fuel cycle. Microwave applicators can be adapted for use in glove-boxes and hot-cells. This paper presents an overview of the application of microwave heating in thorium based fuel cycle.

ABSTRACT Interest in evaluation of reactor response and off-site consequences following beyond design basis accidents has significantly increased after Fukushima. MELCOR is an advanced computational aid that has been widely used and adapted to various reactor designs for severe core damage analyses. This paper summarizes the core thermal hydraulic response for a hypothetical severe accident caused by station blackout with failure of the steam generator safety relief valve at a Chinese pressurized reactor 1000-MW power plant – CPR1000 using MELCOR. Analytical results for a) temperature distribution of the fuel pellets, b) the fuel cladding, c) flow rate of the coolant, and, d) hydrogen mass changing over time are presented. The analyses are focused on safety assessment of the reactor core for severe accidents and are part of the overall evaluation of safety features of the CPR1000 reactor for residual risk posed by severe accidents.

Water chemistry of the Primary Heat Transport System (PHT) of CANDU – Pressurised Heavy Water Reactors profoundly influences the transport of corrosion products around the
Heat Transport System (HTS), where they can be deposited as crud on steam generators, feeder pipes and on the fuel. Fuel cladding can be covered with deposits which have precipitated from the coolant as a result of temperature changes or non-optimal coolant pH. Precipitation of deposits in-core must be avoided as far as possible, as it leads to fouling of the fuel, loss of heat transfer efficiency, and increased radiation fields.
In the recent years a Canadian NPP experienced increased instances of black deposits being observed on fuel bundles discharged from one of the units. The black deposits were
initially observed in 2008 during in-bay fuel inspections. Since then it has been determined that all the discharged fuel bundles have black deposits on them and that observed deposits have been increasing in size (thickness and surface area). This negative trend has persisted through to 2012, when one of fuel bundles was observed with significantly larger
deposit than previously seen. Initial analysis of the deposit indicated it to be iron oxide (magnetite). Flow Accelerated Corrosion (FAC) of carbon steel feeder pipes is the primary
source of iron, which deposits as magnetite on HTS surfaces. . The black deposits have predominantly been located immediately downstream of the bearing pads of the fuel bundle. Deposits have also tended to form on the bottom-downstream quadrant of the fuel bundles.
The deposits were most prevalent in low power channels, but some deposits have been observed on high power channels.
It was reported by the utility that the PHT system chemistry has been maintained in specification for most of the time during normal operation but the chemistry control during outages was inadequate. Due to design constraints, purification circuit was not available during outages and ion-exchange columns and filters could not be utilized. pH control was also less than optimal due to air ingress during outages.
Canadian Nuclear Safety Commission (CNSC) imposed a 3% derating on the power to maintain the safety margins. The utility implemented changes to the chemistry specifications
and is operating the unit at a slightly higher pH range. The utility has also since implemented design changes to permit purification and filtration of PHT system during outages.
CNSC has been closely monitoring the situation and recommended additional monitoring and reporting requirements to the utility. This paper will describe the chemistry optimization, improvements to the filtration system and other efforts undertaken by the utility to reduce
crud deposit on the fuel.