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.     

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.     

Layout of an internally heated gas generator for the steam gasification of coal

Industrial-scale steam gasification of coal using heat from high temperature reactors requires research and development on allothermal gas generators. Bergbau-Forschung GmbH, Essen, does theoretical and experimental work in this field. The experiments deal with reaction kinetics, heat transfer and material tests. Their significance for the layout of a full-scale gas generator is shown. Including material specifications, the feasibility of a gasifier, characterized by a fluid bed volume of 318 m³ and a heat transferring area of 4000 m², results. The data, now available, are used to determine the gasification throughput from the heat balance, i.e. the equality of heat consumed and heat transferred. Throughputs of about 50 t/hr of coal are possible for a single gas generator, the helium outlet temperature of the HTR being 950°C. Bergbau-Forschung has commissioned a medium-scale pilot plant (200 kg/hr).     

The high temperature gas-cooled reactor as a source of high temperature process heat

The nuclear reactor has established itself as a future major supplier of electrical energy. The industrial market for other forms of energy, however, is almost as large and represents a new potential for the use of nuclear reactors. The high temperature gas-cooled reactor (HTGR) has been developed for commercial application in the electric power generation field. Since the HTGR is capable of delivering process heat in the temperature range of 1000–1500°F, it has many applications that would not be possible at the lower operating temperatures of water-cooled reactors. This paper briefly summarizes the development of the HTGR and outlines its salient technical features. Modifications to the reactor that enable it to be used as a process heat source are discussed. Specific applications are developed for coal gasification, steelmaking, and hydrogen production.     

The HTR and nuclear process heat applications

The High Temperature Reactor HTR offers beside the production of electricity the potential of the production of secondary energy carriers for the fuel and heat market. Therefore the HTR can considerably contribute to solutions of future problems in the energy supply of the Federal Republic of Germany as well as of the world. On the basis of the experiences with the power plants AVR, Fort St. Vrain and THTR-300 new concepts of reactors have been proposed: the medium size reactor HTR 500 and the Modular HTR concept. The high temperature heat application is directed towards the refinement of fossil fuels, the long distance energy system and other applications as e.g. process steam for chemical industry, enhanced oil recovery and water splitting. The research and development program in the projects Prototype Plant Nuclear Process Heat (PNP) and Nuclear Long Distance Energy (NFE) has shown very promising results. These results show that nuclear process heat is technically feasibly and that it is possible to reach a commercial application in the next decades.     

The He/He heat exchanger — Design and semitechnical testing

This is a report on the development of the He/He heat exchanger which is used for high-temperature reactors (HTR) combined with the steam gasification of coal. A concept has been agreed on the basis of the requirements resulting from the application of the HTR. Subsequently those steps, which are required for the development of this component up to construction maturity are described. Simultaneously, questions dealing with material, construction, design, manufacture and related experimental development are taken into consideration.     

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.     

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.     

The application of nuclear process heat for hydrogasification of coal

Hydrogasification is the conversion of coal with hydrogen to methane. Because coal and water only are primarily available for gasification purposes, the hydrogen required for methane production has to be produced by the gasification process. This requires heat at a high temperature level which can be supplied by a high temperature reactor as nuclear process heat. In this paper two process variants are described for hydrogasification of lignite with nuclear process heat. The design data of a draft for commercial-scale plants are given. Also, the pilot plant of Rheinische Braunkohlenwerke AG for hydrogasification of coal in the fluidized bed is described.     

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.     

38. R&D on hydrogen production by high-temperature electrolysis of steam

One of the objectives of the high-temperature engineering test reactor (HTTR) is to demonstrate the effectiveness of high-temperature nuclear heat utilization, which aims to extend the application of nuclear heat to non-electric fields, especially to hydrogen production. As part of the development of the hydrogen production processes, laboratory-scale experiments of a high-temperature electrolysis of steam (HTES) had been carried out with a practical electrolysis tube with 12 solid-oxide cells connected in series. Using this electrolysis tube, hydrogen was produced at the maximum density of 44 N cm³/cm² h at a electrolysis temperature of 950 °C. Thereafter, to improve hydrogen production performance, a self-supporting planar electrolysis cell with a practical size (80 mm × 80 mm of electrolysis area) was fabricated. In the preliminary electrolysis experiment carried out at 850 °C, the planar cell produced hydrogen at the maximum density of 38 N cm³/cm² h, and the energy efficiency was almost as high as that obtained with the electrolysis tube at 950 °C. However, both electrolysis tubes and planar cells did not keep their integrity in one thermal cycle. Durability of the solid-oxide cell against the thermal cycle is one of the key issues of HTES.     

Experiments for combining nuclear heat with the methane steam-reforming process

A high temperature reactor with the cooling gas helium leaving at an average temperature of 950°C offers an interesting possibility for combining nuclear heat with the methane steam-reforming process. However, the incorporation of nuclear heat into this process still requires comprehensive experimental and theoretical studies before an economic and technical optimization of a combined nuclear/chemical plant can be reached. Thus the EVA (single reforming tube, Einzelrohr-Versuchsanlage) pilot plant was set up to examine the methane steam-reforming process in a helium-heated conventional reforming tube. This report describes the plant and specifies some representative experimental results. It follows that convective helium heating is an appropriate method of transferring heat to the reforming tube. In addition, the report describes two accompanying experiments in smaller high pressure test plants and summarizes some of the measured results.     

Thermal response of a modular high temperature reactor during passive cooldown under pressurized and depressurized conditions

The concept of inherent safety features of the modular HTR design with respect to passive decay heat removal through conduction, radiation and natural convection was first introduced in the German HTR-module (pebble fuel) design and subsequently extended to other modular HTR design in recent years, e.g. PBMR (pebble fuel), GT-MHR (prismatic fuel) and the new generation reactor V/HTR (prismatic fuel).This paper presents the numerical simulations of the V/HTR using the thermal-hydraulic code THERMIX which was initially developed for the analysis of HTRs with pebble fuels, verified by experiments, subsequently adopted for applications in the HTRs with prismatic fuels and checked against the results of CRP-3 benchmark problem analyzed by various countries with diverse codes.In this paper, the thermal response of the V/HTR (operating inlet/outlet temperatures 490/1000 °C) during post shutdown passive cooling under pressurized and depressurized primary system conditions has been investigated. Additional investigations have also been carried out to determine the influence of other inlet/outlet operating temperatures (e.g. 490/850, 350/850 or 350/1000 °C) on the maximum fuel and pressure vessel temperature during depressurized cooldown condition. In addition, some sensitivity analyses have also been performed to evaluate the effect of varying the parameters, i.e. decay heat, graphite conductivity, surface emissivity, etc., on the maximum fuel and pressure vessel temperature. The results show that the nominal peak fuel temperatures remain below 1600 °C for all these cases, which is the limiting temperature relating to radioactivity release from the fuel. The analyses presented in this paper demonstrate that the code THERMIX can be successfully applied for the thermal calculation of HTRs with prismatic fuel. The results also provide some fundamental information for the design optimization of V/HTR with respect to its maximum thermal power, operating temperatures, etc.     

Present status of the High Temperature Engineering Test Reactor (HTTR)

In Japan, the research and development on the High Temperature Gas-cooled Reactors (HTGRs) had been carried out for more than fifteen years since 1969 as the multi-purpose Very High Temperature gas-cooled Reactor (VHTR) program for direct utilization of nuclear process heat such as nuclear steel making. Recently, reflecting the change of the social and energy situation and with less incentives for industries to introduce such in the near future, the JAERI changed the program to a more basic ‘HTTR program’ to establish and upgrade the HTGR technology basis.The HTTR is a test reactor with a thermal output of 30 MW and reactor outlet coolant temperature of 950°C, employing a pin-in-block type fuel block, and has the capability to demonstrate nuclear process heat utilization using an intermediate heat exchanger. Since 1986 a detailed design has been made, in which major systems and components are determined in line with the HTTR concept, paying essential considerations into the design for achieving the reactor outlet coolant temperature of 950°C. The safety review of the Government started in February 1989. By request of the Science and Technology Agency the Reactor Safety Research Association reviewed the safety evaluation guideline, general design criteria, design code and design guide for the graphite and the high-temperature structure of the HTTR.The installation permit of the HTTR was issued by the Government in November 1990.     

Materials for coal gasification plants utilizing nuclear process heat generated in a high temperature reactor

In coal gasification plants based on nuclear process heat, materials are subjected to high temperature corrosion in process gas atmosphere at 750 to 900° C. The process gas consists of steam, CO, CH₄, CO₂ and, depending on the gasified coal, low or high H₂S-concentrations. Materials for heat exchangers must be resistant to high temperature corrosion. They should also have adequate creep rupture strength. Therefore the commercial alloy Incoloy 800 and various model alloys were exposed to a process gas atmosphere to determine the corrosion behaviour and also stressed mechanically to investigate the interaction of high temperature creep behaviour and corrosion.

Compared with Incoloy 800, one of the new model alloys (30–32% Ni, 25–27% Cr, and Ce, Fe-balance) exhibits a very good corrosion resistance even when sulphur rich coal is gasified. The creep rupture strength at 900° C is in the range of the creep strength for Incoloy 800.     

Creep rupture strength of heat affected zone for 9Cr ferritic heat resisting steels

This paper describes creep rupture characteristics of weld heat affected zone, HAZ for 9Cr ferritic steels that are promising materials for nuclear energy uses. In general, creep rupture strength in the heat affected zone of peak temperature between 900 and 1000°C is lower than that in the base metal for ferritic steels. Grain refinement and coagulation of carbides for 9Cr–1Mo steels cause decrease in creep rupture strength of the HAZ. The hardness in the simulated HAZ heated to around 1000°C decreases during creep. This seems to be related to weakening of the HAZ at 1000°C. However, substitution of W for Mo is very effective in enhancement of creep rupture strength of the HAZ due to higher stability of carbides and increase in quantity of precipitated carbides during creep rupture test.     

Fuel elements of the high temperature pebble bed reactor

This work is devoted to spherical fuel elements for the high temperature pebble bed reactor, their manufacture and the conditions which they must satisfy for use in a process-heat reactor with an average gas outlet temperature T_{G, out} of 950°C. The positive results known from the operation of the AVR with T_G,out = 950°C and from extensive irradiation tests of the THTR-300 element with BISO coated mixed-oxide particles, even beyond the range of design specifications, and possible damage mechanisms are described in detail. They show that a spherical fuel element already exists, for which only a short-term development is needed to produce a coolant temperature of 950°C in a process-heat reactor. Further developments will be characterized by the use of a pebble bed HTR for high conversion rates (c ≈ 0.95) or for average gas outlet temperatures of more than 950°C. At higher temperatures the increased demands, mainly with regard to the release of fission products, can be fulfilled through the application of TRISO-coated fuel particles and the doping of the fuel kernels with . The reprocessing programme for fuel elements in the Federal Republic of Germany is mentioned briefly.     

Leak rate test of personnel airlock for LWR containment subject to pressures and temperatures beyond design

As part of the U.S. Nuclear Regulatory Commission's (USNRC) Containment Integrity Program, a full-size personnel airlock for a nuclear containment building was subjected to conditions simulating a severe accident.The objective of the test was to characterize the performance of an airlock when subjected to conditions that exceeded design. The gasket tested was a “double dog-ear” configuration made from an elastomer known as EPDM E603. The data obtained from this test will be used by SNL as a benchmark for development of analytical methods.Strain, temperature, displacements, pressure, and leak rate data were measured and recorded from over 330 transducers. The test lasted approximately 60 hours. Data were recorded at regular intervals during heating, pressurization and depressurization.The airlock was originally designed for 340°F and 60 psig. The airlock inner door and bulkhead were exposed to a maximum air temperature of approximately 850°F and a maximum air pressure of 300 psig. Two heating and pressurization cycles were planned; one to heat the air to 400°F and pressurize to 300 psig, and the second to heat to 800°F and pressurize to 300 psig. No significant leakage was recorded during these two cycles. A third cycle was added to the test program. The air temperature was increased to approximately 850°F and held at this temperature for nearly 12 hours. Pressure was increased and the inner door seal failed at a pressure of 150.5 psig. The maximum leak rate recorded past the inner door seal was 706 SCFM. The outer door seal did not fail.