Coal gasification with heat from high temperature reactors: Objectives and status of the project “Prototype Plant for Nuclear Process Heat (PNP)”

It is by now fairly widely known that the high temperature reactor (HTR) is a unique nuclear energy source which can supply heat at temperatures up to 1000°C for application in chemical processes, for which previously exclusively combustion heat sources have been used. With the HTR, it is possible to apply nuclear energy not only for electrical power production but also for the synthesis of liquid or gaseous energy carriers. Nuclear coal gasification appears most promising as the first step for the demonstration and industrial application of nuclear process heat technology in the Federal Republic of Germany. Reactor manufacturers and coal mining companies in co-operation with the Nuclear Research Center at Jülich established a joint project in 1975 for the development of an HTR with a coolant outlet temperature of 950°C, for the development and testing of nuclear coal gasification, for the detailed engineering of a prototype plant consisting of an HTR and gasification plant and finally for the construction and operation of this prototype plant for nuclear process heat (PNP). This contribution describes the status of the PNP-Project and the scope for future development.     

High and very high temperature reactor research for multipurpose energy applications

Ten years ago, the European High Temperature Reactor (HTR) Technology Network (HTR-TN) launched a programme for developing HTR Technology, which expanded so far through 4 successive Euratom Framework Programmes. Many projects have been performed - in particular the RAPHAEL project in the 6th Euratom Framework Programme and presently ARCHER in the 7th - in line with the Network strategy that identified cogeneration of process heat and power as the main specific mission of HTR. HTR can indeed address the growing energy needs of industry presently fully relying on fossil fuel combustion with a CO₂-lean generation technology, thanks to its high operating temperature and to its unique flexibility obtained from its large thermal inertia and its low power.Relying on the legacy of the former European leadership in HTR technology, this programme has addressed specific developments required for industrial process heat applications and for increasing HTR performances (higher temperatures and fuel burn-up). Decisive achievements have been obtained concerning fuel manufacturing and irradiation behaviour, key components and their materials, safety, computer code validation and specific HTR waste (fuel and graphite) management. Key experiments have been performed or are still ongoing: irradiation of graphite, fuel and vessel materials and the corresponding post-irradiation examinations, safety tests and isotopic analyses; thermal-hydraulic tests of an Intermediate Heat Exchanger mock-up in helium; air ingress experiments for a block type core, etc. Through Euratom participation in the Generation IV International Forum (GIF), these achievements contribute to international cooperation.HTR-TN strategy has been recently integrated by the “Sustainable Nuclear Energy Technology Platform” (SNE-TP) as one of the 3 “pillars” of its global nuclear strategy. It is also in line with the orientations and the timing of the “Strategic Energy Technology Plan (SET-Plan)” for the development of CO₂-lean energy technologies, and thus strengthens the nuclear option in a future European energy mix.Nuclear cogeneration for industrial process heat applications is a major innovation and a major challenge, requiring large-scale demonstration to prove its industrial viability. To enable demonstration, it is necessary not only to develop an appropriate nuclear heat source, but also to develop coupling technologies and to adapt industrial processes to the coupling with a HTR. This requires a close partnership between the conventional and the nuclear technology holders as the base of a Nuclear Cogeneration Industrial Initiative.Recently the project EUROPAIRS initiated by HTR-TN together with process heat user industries has set the bases of such a strategic partnership.     

Nuclear Process heat—application to fuels and chemical production

Synthesis gas, a mixture of CO and H₂, produced from coal and a HTR nuclear source can be an economic feedstock for synthetic fuel and chemicals production. Such chemicals as hydrogen, ammonia, methanol, steel, can be readily produced from synthesis gas and other raw feedstocks by standard chemical engineering practice. Direct coal liquefaction is accomplished by adding H₂ to a pressurized coal slurry or solution. The use of the HTR to provide both the synthesis gas (using its high temperature capability) and steam or electricity for chemical process application (using its steam bottoming cycle capability) gives substantial conservation advantages in the use of coal compared to the non-nuclear equivalent processes. The desirability of efficiently using both the high and low temperature sources of the HTR requires a coupling between two or more chemical processes and the HTR (in a ‘Chemplex’) if a match is to be made between the high temperature and steam cycles of the HTR and the needs of the chemical processes.     

The HTR for process heat application according to the BBC/HRB-concept

The development of the High-Temperature Reactor (HTR) for the generation of nuclear process heat for coal gasification applying temperatures up to 950°C is one of the most important long-term HTR-development objectives pursued within the German PNP-project. The HTR for nuclear process heat generation according to the concept of BBC/HRB is part of the commercialization strategy of the HTR-line, which is based on the preceding AVR experimental reactor, the THTR-300 MW_c prototype plant and the HTR-500 MW_c plant. This strategy permits an optimum utilization of the development of the nuclear heat supply system of the THTR-300 and HTR-500 and represents a consequent continuation of the German HTR development pursued up to now. It will result in the lowest possible cost and time expenditure on the commercialization of the HTR for all applications. A new reactor development is not required with this concept. The earliest possible realization of a first-of-its-kind nuclear process heat plant will be determined by the development of the gasification processes.     

Motivation for and possibilities of using nuclear process heat

A reduction in the use of fossil energy carriers on the energy supply sector will be made possible by a more efficient utilization of energy and the commercial application of nuclear energy. The resources of fossil energy carriers will be saved and the long-term supply of raw materials for the chemical industry will be ensured. High temperature reactors (HTRs) with spherical fuel elements are not only characterized by high conversion rates reducing uranium requirements to a minimum, but they also supply heat at a high temperature level. Besides electricity supply, this will also open up the much larger heat market to nuclear energy. Nuclear process heat can be used for heating purposes by way of energy transported over long distances or by district heating; it may also be used to cover the heat requirements in refining plants. This is shown by means of a supply strategy for the Federal Republic of Germany using secondary energy carriers. Profitability studies have shown that nuclear process heat has a number of economic advantages over conventional heat generation, which are still supplemented by ecological benefits (e.g. reduction in waste heat, SO₂ and CO₂ emissions). The ecological aspect will, no doubt, be of particular significance in the future, since even today some of the man-induced rates are reaching the levels of natural rates of mobilization of materials.     

Nuclear process heat—application to coal gasification

The high temperature gas cooled reactor has achieved peak coolant temperatures from 775 to 950°C, depending on the core design. These temperatures are sufficiently high to consider the HTR as a source of heat for several large industrial processes. In this article the application is to a coal gasification process which produces a mixture of carbon monoxide and hydrogen as the key product. The gasifier system itself is coupled to the HTR via a catalyzed fluidized bed coal gasifier operating at 700°C and producing methane. The feed to this gasifier is a mixture of carbon monoxide, hydrogen and steam with the stoichiometry chosen to effect an overall athermal reaction so that no heat is directly transferred into the gasifier. Its hydrogen supply is generated by steam reforming the methane produced using the direct HTR heat. This indirect system has advantages in terms of its final product, indirect heat transfer and ultimately in the savings of approximately 40% of the coal which would otherwise have been assumed in an all-coal process producing the same final product.     

Gasification of coal with steam using heat from HTRs

In existing coal gasification processes a substantial part of the coal is used to provide the heat for the reaction, for the generation and superheating of steam and for the production of oxygen. By using heat from HTRs to substitute this part, the coal is then completely used as raw material for gas production. This offers the following advantages compared with the existing processes: a saving of coal, less CO₂ emission and, in countries with high coal costs, lower gas production costs. A survey is given of the state of the project, discussing the first design of a commercial gasifier, the influence of the helium outlet temperature of the HTR, kinds of products, and the overall efficiency of the plant. The aim of the development is to demonstrate the use of heat from an HTR for full scale coal gasification, starting in 1985.     

Absorbed dose estimation using LET dependence in glow curve of thermoluminescent phosphor Li3B7O12:Cu in therapeutic carbon beams

A high temperature ratio (HTR) method has been proposed to correct the linear energy transfer (LET) dependence of thermoluminescent (TL) efficiency. To realize the use of the slab-type thermoluminescence detector (TLD) that based on the phosphor Li₃B₇O₁₂:Cu for heavy charged particle beam, the HTR method has been considered. To improve the reproducibility of HTR, the slow heating rate method is introduced in this report and the coefficient variations of HTR decreased from 10%–20% to 8%. The relation between TL-efficiency, HTR, and LET for Li₃B₇O₁₂:Cu was manifested and the TL-efficiency as a function of HTR was derived in an attempt to measure the absorbed dose without LET information. The feasibility of the HTR method in therapeutic carbon beams was evaluated by comparing the dose estimated by Li₃B₇O₁₂:Cu and by an ionization chamber. The accuracy of dose estimation in carbon beams was improved by using the HTR method, but there is room for further improvement. The use of Li₃B₇O₁₂:Cu in heavy charged particle beams can be materialized with further improvement of HTR sensitivity.     

Role of heat exchangers in helium liquefaction cycles: Simulation studies using Collins cycle

Energy efficiency of large-scale helium liquefiers generally employed in fusion reactors and accelerators is determined by the performance of their constituting components. Simulation with Aspen HYSYS^® V7.0, a commercial process simulator, helps to understand the effects of heat exchanger parameters on the performance of a helium liquefier. Effective UA (product of overall heat transfer coefficient U, heat transfer surface area A and deterioration factor F) has been taken as an independent parameter, which takes into account all thermal irreversibilities and configuration effects. Nondimensionalization of parameters makes the results applicable to plants of any capacity. Rate of liquefaction is found to increase linearly with the effectiveness of heat exchangers. Performance of those heat exchangers that determine the inlet temperatures to expanders have more influence on the liquid production. Variation of sizes of heat exchangers does not affect the optimum rate of flow through expanders. Increasing UA improves the rate of liquid production; however, the improvement saturates at limiting UA. Maximum benefit in liquefaction is obtained when the available heat transfer surface area is distributed in such a way that the effectiveness remains equal for all heat exchangers. Conclusions from this study may be utilized in analyzing and designing large helium plants.     

The high temperature reactor - an important tool in meeting the challenge of world energy supply

A growing and, in its majority, poor mankind will need increasing amounts of energy at moderate prices. At the same time, ecological stresses on our environment, on the forests of the Third World (firewood crisis), and on the climate must be limited. The High Temperature Reactor (HTR) is a well-suited answer to all challenges, as it can supply eletricity safely and economically, be built close to process steam and district heat consumers, procure more hydrocarbons from coal relative to a given release of CO₂, and has the potential of splitting water with high efficiency. At times of affluent fossile fuels, however, and not yet apparent need to restrict their use for reasons of climate, individual companies cannot bear the development and introduction of HTRs all by themselves. Therefore governments are called upon for support.     

Transport of nuclear heat by means of chemical energy (nuclear long-distance energy)

Nuclear long-distance energy, i.e. the transportation of chemically bound energy, represents a potential application for process heat plants in which the endothermic reaction takes place at the heat source (high temperature reactor) whereas the exothermic back reaction occurs at the region of heat utilization (consumer). Due to the following criteria, i.e. reversibility of the chemical reaction, sufficiently large reaction enthalpy, favourable temperature region for the forward and back reactions, and the available technology, a combination of the methods of endothermic steam reforming of methane and exothermic methanation is chosen. As well as supplying household and industrial consumers with heating, process steam and electrical energy, an interconnected system with synthesis gas consumers (e.g. methanol production and iron ore reduction plants) is possible. It is shown that the amount of reactor heat which is convertible into long-distance energy depends considerably on the helium temperatures in the high temperature reactor and lies between 60 and 73% of the reactor power. Conceivable circuit schemes for the nuclear steam-reforming plants and the methanation plants are described. Finally, it is demonstrated, with the help of a simple model for cost estimations, that the nuclear long-distance energy system can make heating for households available in competition with oil heating and that due to the lower specific transport costs, for distances larger than 50 km it is also more economical than the hot water supply from the thermal power coupling of steam turbine plants using light water reactors (LWRs) or high temperature reactors (HTRs).     

Latest achievements of CEA and AREVA NP on HTR fuel fabrication

Extensive research and development programs on the (Very) High Temperature gas cooled Reactor (V/HTR) are being conducted by many countries mainly promoted by the attractiveness of this concept and its capability for other applications than electricity production, such as high temperature process heat and cogeneration. In this international context, the Commissariat à l’Energie Atomique (CEA) and AREVA NP through its project called ANTARES (Areva New Technology for Advanced Reactor Energy Supply) conduct a V/HTR fuel development and qualification program, among which one major activity is dedicated to the mastering of the nuclear fuel fabrication technology. The fuel concept selected for this project is the compact design based on UO₂ kernels and SiC coating.First laboratory-scale experiments were performed to recover the know-how of HTR-coated particles and fuel element manufacturing. The different stages of UO₂ kernel fabrication by the Gel Supported Precipitation (GSP) process were reviewed and improved. Experimental conditions for the Chemical Vapour Deposition (CVD) of coatings have been defined on dummy kernels supported by a modelling approach of the CVD process. The compacting processes formerly used at CERCA were reviewed and updated.In order to support a future industrial manufacturing factory and to meet the next short-term challenge, which is the fabrication of coated particle batches that will be compacted for the first irradiation test scheduled in OSIRIS, a lab-scale experimental manufacturing facility, named CAPRI (CEA and AREVA PRoduction Integrated) line has been set up and is in operation since early 2005. The CAPRI line is composed of a manufacturing line for TRISO particles, named GAIA, located at CEA Cadarache, and a compacting line for fuel elements based at CERCA, AREVA NP Subsidiary, Romans.Since early 2005, many tests have been performed leading to a better understanding and optimization of coating particle and compact manufacturing processes.In support to this fuel fabrication tool, development of accurate characterization methods were carried out to supply products meeting the specifications and to provide feed-back information to enhance fuel production quality.     

Methane from synthesis gas and operation of high-temperature methanation

The methanation process is an important unit in generating substitute natural gas (SNG) from coal and in providing heat in the Long-Distance Nuclear Energy Transport (NFE) system. Procedures for methanizing synthesis gases containing CO, CO₂ and H₂ have been developed and tested at the Kernforschungsanlage Jülich GmbH (KFA - Federal Republic of Germany) since 1976. This is being carried out together with the partner in the NFE Project, Rheinische Braunkohlenwerke AG, Cologne (FRG).It has been demonstrated in several thousand operating hours at the KFA since 1979 that the procedures and components developed, as well as the catalysts employed satisfy the demands made by high-temperature methanation in the three-stage methanation plants ADAM I and ADAM II with a SNG gas production of 200 or 3300 m³ (STP)h⁻¹ and a useful heat capacity of 300 kJ/s or 5.8 MJ/s.In 1981 a single-stage pilot plant was put into operation at the KFA in which one reactor with cooled stepped reaction tubes and catalytic fixed beds was utilized. The test operation of 1100 hours shows that at a high gas load on the reaction tubes, thermodynamic equilibrium with a high methane content in the product gas can be achieved with simultaneous steam production at 100 bar.     

Radiation doses to the public from the nuclear industry

Section 1: It is shown that the dangers arising from power production in the past were greater than those arising from any form of power production today. Section 2: The specific ways in which radiation injures both the present and future generations are described. Section 3: The routine risks arising from nuclear power production are compared with those arising from other modern sources; first the risks to those employed in power production and then the risks to the general public, including the risks arising from efforts to conserve energy. Section 4: The risks to the public arising from major accidents are explained. Section 5: The radiation risks incurred by the public in the course of medical diagnosis and treatment are described and discussed. Section 6: Conclusion. It is pointed out that the dangers of nuclear energy are considerably less than those of all other sources other than directly piped natural gas; and that the reduction of the specific risks due to ionizing radiation arising from medical uses and from domestic heat conservation could save about a hundred times as many lives as would the complete elimination of the radiation arising from the production of nuclear power.     

HTR's role in process heat applications

Advanced high-temperature nuclear reactors create a number of new opportunities for nuclear process heat applications. These opportunities are based on the high-temperature heat available, smaller reactor sizes, and enhanced safety features that allow siting close to process plants. Major sources of value include the displacement of premium fuels and the elimination of CO₂ emissions from combustion of conventional fuels and their use to produce hydrogen. High value applications include steam production and cogeneration, steam methane reforming, and water splitting. Market entry by advanced high-temperature reactor technology is challenged by the evolution of nuclear licensing requirements in countries targeted for early applications, by the development of a customer base not familiar with nuclear technology and related issues, by convergence of oil industry and nuclear industry risk management, by development of public and government policy support, by resolution of nuclear waste and proliferation concerns, and by the development of new business entities and business models to support commercialization. New HTR designs may see a larger opportunity in process heat niche applications than in power given competition from larger advanced light water reactors. Technology development is required in many areas to enable these new applications, including the commercialization of new heat exchangers capable of operating at high temperatures and pressures, convective process reactors and suitable catalysts, water splitting system and component designs, and other process-side requirements. Key forces that will shape these markets include future fuel availability and pricing, implementation and monetization of CO₂ emission limits, and the formation of international energy and environmental policy that will support initiatives to provide the nuclear licensing frameworks and risk distribution needed to support private investment. This paper was developed based on a plenary session presentation at HTR-2006 which won Best Paper.     

Update of the French R&D strategy on gas-cooled reactors

Gas-cooled reactors take up a strong second role in France's R&D strategy on future nuclear energy systems as priority was given in 2005 to fast neutron reactors with multiple-recycle for their potential to optimally use uranium resource and minimize the long term burden of radioactive waste. Owing to the European past experience on sodium-cooled fast reactors (SFRs), this reactor type was logically selected as reference for a new generation fast neutron reactor intended to be tested as a prototype in the 2020s and be ready for industrial deployment around 2040. At the same time, the potential merits of a gas fast reactor (GFR) with ceramic clad fuel for a safe management of cooling accident are acknowledged for the potential of this reactor type to resolve critical issues of liquid fast reactors (safety, operability and reparability). A pre-feasibility report on a first concept of GFR was issued in 2007 that summed-up results of a 5-year international R&D effort on GFR fuel technology, reactor design and operating transient analyses. This report established a global confidence in the feasibility of this concept and its potential for attractive performances. Furthermore, it suggested directions of R&D to generate by 2012 an updated concept with improved performances and taking better benefit from GFR specific technologies.A second activity on gas-cooled reactors originates from the current interest of CEA's industrial partner AREVA in high or very high temperature reactors (V/HTR) for supplying hydrogen, synthetic hydrocarbon fuels and process heat for the industry. This activity currently encompasses R&D on V/HTR key technologies such as particle fuel fabrication, high temperature compact heat exchangers and coupling technologies to various power conversion systems. R&D on V/HTR and GFR are synergistic in various respects. The GFR can be viewed as a more sustainable version of the VHTR and synergies exist in research on heat resisting materials, helium system technology and power conversion systems. Both reactors require active research in materials and spur developments of new metallic alloys and ceramics applicable to other advanced nuclear systems.     

Model of cladding failure estimation for a cycling nuclear unit

Nuclear reactor operating modes under multiple cyclic power changes have been promoted recently, and fuel element cladding behavior under the multiple cyclic power changes has been widely known as a key issue in terms of rod design and reliability. A model of nuclear reactor fuel rod cladding failure estimation under multiple cyclic power changes is proposed. The model is built on the basis of the following admissions of the energy version of creep theory: processes of cladding creep and destruction proceed together and affect each other, intensity of creep process is estimated by specific dispersion power W(τ), while intensity of destruction—by specific dispersion energy A(τ) accumulated during time τ. Having calculated the equivalent stress and the rate of equivalent creep strain, the condition of fuel rod cladding failure used on the basis of the energy version of the theory of creep gives us a criterion to decide if a multiple cyclic power change operating mode is permissible for a given variant of power history and coolant conditions.     

Development of probabilistic models to estimate fire-induced cable damage at nuclear power plants

Numerous Probabilistic Risk Assessments (PRAs) have shown that fire is a major contributor to Nuclear Power Plant (NPP) risks. However, prediction and estimation of the likelihood of fire-induced damage to electrical cables and circuits and their potential effects on the safety of the NPPs are still a practical challenge, particularly because of the lack of physics-based models with which to perform consistent and objective assessments.This paper contains a discussion of two models - the heat transfer and the IR “K-factor” models - to estimate the likelihood of fire-induced cable damage given a specified fire profile. The results of this research will help to (1) develop a consistent framework to estimate the likelihood of fire-induced cable failure modes, and (2) develop some guidance to evaluate and/or reduce the risks associated with these failure modes in existing and new NPPs.The models are developed (i.e., their parameters are estimated) based on the test data from various fire damage tests sponsored by the nuclear industry and the U.S. Nuclear Regulatory Commission (NRC). Among the models evaluated, the physics-based heat transfer model is promising because it takes into account the properties and characteristics of the cables and cable materials and the characteristics of the thermal insult. This model can be used to estimate the probability of cable damage (P_CD) under different thermal conditions.