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Options for treating high-temperature gas-cooled reactor fuel for repository disposal

Description: This report describes the options that can reasonably be considered for disposal of high-temperature gas-cooled reactor (HTGR) fuel in a repository. The options include whole-block disposal, disposal with removal of graphite (either mechanically or by burning), and reprocessing of spent fuel to separate the fuel and fission products. The report summarizes what is known about the options without extensively projecting or analyzing actual performance of waste forms in a repository. The report also summarizes the processes involved in convert spent HTGR fuel into the various waste forms and projects relative schedules and costs for deployment of the various options. Fort St. Vrain Reactor fuel, which utilizes highly-enriched {sup 235}U (plus thorium) and is contained in a prismatic graphite block geometry, was used as the baseline for evaluation, but the major conclusions would not be significantly different for low- or medium-enriched {sup 235}U (without thorium) or for the German pebble-bed fuel. Future US HTGRs will be based on the Fort St. Vrain (FSV) fuel form. The whole block appears to be a satisfactory waste form for disposal in a repository and may perform better than light-water reactor (LWR) spent fuel. From the standpoint of process cost and schedule (not considering repository cost or value of fuel that might be recycled), the options are ranked as follows in order of increased cost and longer schedule to perform the option: (1) whole block, (2a) physical separation, (2b) chemical separation, and (3) complete chemical processing.
Date: February 1, 1992
Creator: Lotts, A.L.; Bond, W.D.; Forsberg, C.W.; Glass, R.W.; Harrington, F.E.; Micheals, G.E. et al.
Partner: UNT Libraries Government Documents Department

Innovative safety features of the modular HTGR

Description: The Modular High Temperature Gas-Cooled Reactor (MHTGR) is an advanced reactor concept under development through a cooperative program involving the US Government, the nuclear industry, and the utilities. Near-term development is focused on electricity generation. The top-level safety requirement is that the plant's operation not disturb the normal day-to-day activities of the public. Quantitatively, this requires that the design meet the US Environmental Protection Agency's Protective Action Guides at the site boundary and hence preclude the need for sheltering or evacuation of the public. To meet these stringent safety requirements and at the same time provide a cost competitive design requires the innovative use of the basic high temperature gas-cooled reactor features of ceramic fuel, helium coolant, and a graphite moderator. The specific fuel composition and core size and configuration have been selected to the use the natural characteristics of these materials to develop significantly higher margins of safety. In this document the innovative safety features of the MHTGR are reviewed by examining the safety response to events challenging the functions relied on to retain radionuclides within the coated fuel particles. A broad range of challenges to core heat removal are examined, including a loss of helium pressure of a simultaneous loss of forced cooling of the core. The challenges to control of heat generation consider not only the failure to insert the reactivity control systems but also the withdrawal of control rods. Finally, challenges to control of chemical attack of the ceramic-coated fuel are considered, including catastrophic failure of the steam generator, which allows water ingress, or failure of the pressure vessels, which allows air ingress. The plant's response to these extreme challenges is not dependent on operator action, and the events considered encompass conceivable operator errors.
Date: January 1, 1992
Creator: Silady, F.A. & Simon, W.A.
Partner: UNT Libraries Government Documents Department

Licensed operating reactors: Status summary report data as of December 31, 1991. Volume 16

Description: The Nuclear Regulatory Commission`s annual summary of licensed nuclear power reactor data is based primarily on the report of operating data submitted by licensees for each unit for the month of December because that report contains data for the month of December, the year to date (in this case calendar year 1991) and cumulative data, usually from the date of commercial operation. The data is not independently verified, but various computer checks are made. The report is divided into two sections. The first contains summary highlights and the second contains data on each individual unit in commercial operation. Section 1 capacity and availability factors are simple arithmetic averages. Section 2 items in the cumulative column are generally as reported by the licensee and notes as to the use of weighted averages and starting dates other than commercial operation are provided.
Date: March 1, 1992
Partner: UNT Libraries Government Documents Department

MHTGR thermal performance envelopes: Reliability by design

Description: This document discusses thermal performance envelopes which are used to specify steady-state design requirements for the systems of the Modular High Temperature Gas-Cooled Reactor to maximize plant performance reliability with optimized design. The thermal performance envelopes are constructed around the expected operating point accounting for uncertainties in actual plant as-built parameters and plant operation. The components are then designed to perform successfully at all points within the envelope. As a result, plant reliability is maximized by accounting for component thermal performance variation in the design. The design is optimized by providing a means to determine required margins in a disciplined and visible fashion.
Date: May 1, 1992
Creator: Etzel, K.T.; Howard, W.W. & Zgliczynski, J.B.
Partner: UNT Libraries Government Documents Department

Continuous improvement of the MHTGR safety and competitive performance

Description: An increase in reactor module power from 350 to 450 MW(t) would markedly improve the economics of the Modular High Temperature Gas-Cooled Reactor (MHTGR). The higher power level was recommended as the result of an in-depth cost reduction study undertaken to compete with the declining price of fossil fuel. The safety assessment confirms that the high level of safety, which relies on inherent characteristics and passive features, is maintained at the elevated power level. Preliminary systems, nuclear, and safety performance results are discussed for the recommended 450 MW(t) design. Optimization of plant parameters and design modifications accommodated the operation of the steam generator and circulator at the higher power level. Events in which forced cooling is lost, designated as conduction cooldowns are described in detail. For the depressurized conduction cooldown, without full helium inventory, peak fuel temperatures are significantly lowered. A more negative temperature coefficient of reactivity was achieved while maintaining an adequate fuel cycle and reactivity control. Continual improvement of the MHTGR delivers competitive performance without relinquishing the high safety margins demanded of the next generation of power plants.
Date: May 1, 1992
Creator: Eichenberg, T.W.; Etzel, K.T.; Mascaro, L.L. & Rucker, R.A.
Partner: UNT Libraries Government Documents Department

Assessment of engineering plant analyzer with Peach Bottom 2 stability tests

Description: Engineering Plant Analyzer (EPA) has been developed to simulate plant transients for Boiling Water Reactor (BWR). Recently, this code has been used to simulate LaSalle-2 instability event which was initiated by a failure in the feed water heater. The simulation was performed for the scram conditions and for the postulated failure in the scram. In order to assess the capability of the EPA to simulate oscillatory flows as observed in the LaSalle event, EPA has been benchmarked with the available data from the Peach Bottom 2 (PB2) Instability tests PT1, PT2, and PT4. This document provides a description of these tests.
Date: January 1, 1992
Creator: Rohatgi, U.S.; Mallen, A.N.; Cheng, H.S. & Wulff, W.
Partner: UNT Libraries Government Documents Department

Innovative safety features of the modular HTGR

Description: In this document the innovative safety features of the MHTGR are reviewed by examining the safety response to events challenging the functions relied on to retain radionuclides within the coated fuel particles. A broad range of challenges to core heat removal are examined, including a loss of helium pressure and a simultaneous loss of forced cool of the core.
Date: April 1, 1992
Creator: Silady, F.A. & Simon, W.A.
Partner: UNT Libraries Government Documents Department

Characteristics of potential repository wastes

Description: The LWR spent fuels discussed in Volume 1 of this report comprise about 99% of all domestic non-reprocessed spent fuel. In this report we discuss other types of spent fuels which, although small in relative quantity, consist of a number of diverse types, sizes, and compositions. Many of these fuels are candidates for repository disposal. Some non-LWR spent fuels are currently reprocessed or are scheduled for reprocessing in DOE facilities at the Savannah River Site, Hanford Site, and the Idaho National Engineering Laboratory. It appears likely that the reprocessing of fuels that have been reprocessed in the past will continue and that the resulting high-level wastes will become part of defense HLW. However, it is not entirely clear in some cases whether a given fuel will be reprocessed, especially in cases where pretreatment may be needed before reprocessing, or where the enrichment is not high enough to make reprocessing attractive. Some fuels may be canistered, while others may require special means of disposal. The major categories covered in this chapter include HTGR spent fuel from the Fort St. Vrain and Peach Bottom-1 reactors, research and test reactor fuels, and miscellaneous fuels, and wastes generated from the decommissioning of facilities.
Date: July 1, 1992
Partner: UNT Libraries Government Documents Department

Modular High Temperature Gas-Cooled Reactor heat source for coal conversion

Description: In the industrial nations, transportable fuels in the form of natural gas and petroleum derivatives constitute a primary energy source nearly equivalent to that consumed for generating electric power. Nations with large coal deposits have the option of coal conversion to meet their transportable fuel demands. But these processes themselves consume huge amounts of energy and produce undesirable combustion by-products. Therefore, this represents a major opportunity to apply nuclear energy for both the environmental and energy conservation reasons. Because the most desirable coal conversion processes take place at 800[degree]C or higher, only the High Temperature Gas-Cooled Reactors (HTGRs) have the potential to be adapted to coal conversion processes. This report provides a discussion of this utilization of HTGR reactors.
Date: September 1, 1992
Creator: Schleicher, R.W. Jr. & Lewis, A.C.
Partner: UNT Libraries Government Documents Department

Strategies for denaturing the weapons-grade plutonium stockpile

Description: In the next few years, approximately 50 metric tons of weapons-grade plutonium and 150 metric tons of highly-enriched uranium (HEU) may be removed from nuclear weapons in the US and declared excess. These materials represent a significant energy resource that could substantially contribute to our national energy requirements. HEU can be used as fuel in naval reactors, or diluted with depleted uranium for use as fuel in commercial reactors. This paper proposes to use the weapons-grade plutonium as fuel in light water reactors. The first such reactor would demonstrate the dual objectives of producing electrical power and denaturing the plutonium to prevent use in nuclear weapons.
Date: October 1, 1992
Creator: Buckner, M.R. & Parks, P.B.
Partner: UNT Libraries Government Documents Department

Nuclear Reactors and Technology

Description: This publication Nuclear Reactors and Technology (NRT) announces on a monthly basis the current worldwide information available from the open literature on nuclear reactors and technology, including all aspects of power reactors, components and accessories, fuel elements, control systems, and materials. This publication contains the abstracts of DOE reports, journal articles, conference papers, patents, theses, and monographs added to the Energy Science and Technology Database during the past month. Also included are US information obtained through acquisition programs or interagency agreements and international information obtained through the International Energy Agency`s Energy Technology Data Exchange or government-to-government agreements. The digests in NRT and other citations to information on nuclear reactors back to 1948 are available for online searching and retrieval on the Energy Science and Technology Database and Nuclear Science Abstracts (NSA) database. Current information, added daily to the Energy Science and Technology Database, is available to DOE and its contractors through the DOE Integrated Technical Information System. Customized profiles can be developed to provide current information to meet each user`s needs.
Date: January 1, 1992
Creator: Cason, D. L. & Hicks, S. C.
Partner: UNT Libraries Government Documents Department

Potential applications of high temperature helium

Description: This paper discusses the DOE MHTGR-SC program's recent activity to improve the economics of the MHTGR without sacrificing safety performance and two potential applications of high temperature helium, the MHTGR gas turbine plant and a process heat application for methanol production from coal.
Date: September 1, 1992
Creator: Schleicher, R.W. Jr. & Kennedy, A.J.
Partner: UNT Libraries Government Documents Department

Magnitude and reactivity consequences of moisture ingress into the modular High-Temperature Gas-Cooled Reactor core

Description: Inadvertent admission of moisture into the primary system of a modular high-temperature gas-cooled reactor has been identified in US Department of Energy-sponsored studies as an important safety concern. The work described here develops an analytical methodology to quantify the pressure and reactivity consequences of steam-generator tube rupture and other moisture-ingress-related incidents. Important neutronic and thermohydraulic processes are coupled with reactivity feedback and safety and control system responses. The rate and magnitude of steam buildup are found to be dominated by major system features such as break size compared with safety valve capacity and reliability and less sensitive to factors such as heat transfer coefficients. The results indicate that ingress transients progress at a slower pace than previously predicted by bounding analyses, with milder power overshoots and more time for operator or automatic corrective actions.
Date: December 1, 1992
Creator: Smith, O.L. (Oak Ridge National Lab., TN (United States))
Partner: UNT Libraries Government Documents Department

Nuclear reactors built, being built, or planned, 1991

Description: This document contains unclassified information about facilities built, being built, or planned in the United States for domestic use or export as of December 31, 1991. The book is divided into three major sections: Section 1 consists of a reactor locator map and reactor tables; Section 2 includes nuclear reactors that are operating, being built, or planned; and Section 3 includes reactors that have been shut down permanently or dismantled. Sections 2 and 3 contain the following classification of reactors: Civilian, Production, Military, Export, and Critical Assembly. Export reactor refers to a reactor for which the principal nuclear contractor is an American company -- working either independently or in cooperation with a foreign company (Part 4, in each section). Critical assembly refers to an assembly of fuel and assembly of fuel and moderator that requires an external source of neutrons to initiate and maintain fission. A critical assembly is used for experimental measurements (Part 5).
Date: July 1, 1992
Creator: Simpson, B.
Partner: UNT Libraries Government Documents Department

Continuous improvement of the MHTGR safety and competitive performance

Description: An increase in reactor module power from 350 to 450 MW(t) would markedly improve the economics of the Modular High Temperature Gas-Cooled Reactor (MHTGR). The higher power level was recommended as the result of an in-depth cost reduction study undertaken to compete with the declining price of fossil fuel. The safety assessment confirms that the high level of safety, which relies on inherent characteristics and passive features, is maintained at the elevated power level. Preliminary systems, nuclear, and safety performance results are discussed for the recommended 450 MW(t) design. Optimization of plant parameters and design modifications accommodated the operation of the steam generator and circulator at the higher power level. Events in which forced cooling is lost, designated as conduction cooldowns are described in detail. For the depressurized conduction cooldown, without full helium inventory, peak fuel temperatures are significantly lowered. A more negative temperature coefficient of reactivity was achieved while maintaining an adequate fuel cycle and reactivity control. Continual improvement of the MHTGR delivers competitive performance without relinquishing the high safety margins demanded of the next generation of power plants.
Date: May 1, 1992
Creator: Eichenberg, T. W.; Etzel, K. T.; Mascaro, L. L. & Rucker, R. A.
Partner: UNT Libraries Government Documents Department

Innovative safety features of the modular HTGR

Description: The Modular High Temperature Gas-Cooled Reactor (MHTGR) is an advanced reactor concept under development through a cooperative program involving the US Government, the nuclear industry, and the utilities. Near-term development is focused on electricity generation. The top-level safety requirement is that the plant`s operation not disturb the normal day-to-day activities of the public. Quantitatively, this requires that the design meet the US Environmental Protection Agency`s Protective Action Guides at the site boundary and hence preclude the need for sheltering or evacuation of the public. To meet these stringent safety requirements and at the same time provide a cost competitive design requires the innovative use of the basic high temperature gas-cooled reactor features of ceramic fuel, helium coolant, and a graphite moderator. The specific fuel composition and core size and configuration have been selected to the use the natural characteristics of these materials to develop significantly higher margins of safety. In this document the innovative safety features of the MHTGR are reviewed by examining the safety response to events challenging the functions relied on to retain radionuclides within the coated fuel particles. A broad range of challenges to core heat removal are examined, including a loss of helium pressure of a simultaneous loss of forced cooling of the core. The challenges to control of heat generation consider not only the failure to insert the reactivity control systems but also the withdrawal of control rods. Finally, challenges to control of chemical attack of the ceramic-coated fuel are considered, including catastrophic failure of the steam generator, which allows water ingress, or failure of the pressure vessels, which allows air ingress. The plant`s response to these extreme challenges is not dependent on operator action, and the events considered encompass conceivable operator errors.
Date: January 1, 1992
Creator: Silady, F. A. & Simon, W. A.
Partner: UNT Libraries Government Documents Department

Innovative safety features of the modular HTGR. Revision 1

Description: In this document the innovative safety features of the MHTGR are reviewed by examining the safety response to events challenging the functions relied on to retain radionuclides within the coated fuel particles. A broad range of challenges to core heat removal are examined, including a loss of helium pressure and a simultaneous loss of forced cool of the core.
Date: April 1, 1992
Creator: Silady, F. A. & Simon, W. A.
Partner: UNT Libraries Government Documents Department

Strategies for denaturing the weapons-grade plutonium stockpile

Description: In the next few years, approximately 50 metric tons of weapons-grade plutonium and 150 metric tons of highly-enriched uranium (HEU) may be removed from nuclear weapons in the US and declared excess. These materials represent a significant energy resource that could substantially contribute to our national energy requirements. HEU can be used as fuel in naval reactors, or diluted with depleted uranium for use as fuel in commercial reactors. This paper proposes to use the weapons-grade plutonium as fuel in light water reactors. The first such reactor would demonstrate the dual objectives of producing electrical power and denaturing the plutonium to prevent use in nuclear weapons.
Date: October 1, 1992
Creator: Buckner, M. R. & Parks, P. B.
Partner: UNT Libraries Government Documents Department

Options for treating high-temperature gas-cooled reactor fuel for repository disposal

Description: This report describes the options that can reasonably be considered for disposal of high-temperature gas-cooled reactor (HTGR) fuel in a repository. The options include whole-block disposal, disposal with removal of graphite (either mechanically or by burning), and reprocessing of spent fuel to separate the fuel and fission products. The report summarizes what is known about the options without extensively projecting or analyzing actual performance of waste forms in a repository. The report also summarizes the processes involved in convert spent HTGR fuel into the various waste forms and projects relative schedules and costs for deployment of the various options. Fort St. Vrain Reactor fuel, which utilizes highly-enriched {sup 235}U (plus thorium) and is contained in a prismatic graphite block geometry, was used as the baseline for evaluation, but the major conclusions would not be significantly different for low- or medium-enriched {sup 235}U (without thorium) or for the German pebble-bed fuel. Future US HTGRs will be based on the Fort St. Vrain (FSV) fuel form. The whole block appears to be a satisfactory waste form for disposal in a repository and may perform better than light-water reactor (LWR) spent fuel. From the standpoint of process cost and schedule (not considering repository cost or value of fuel that might be recycled), the options are ranked as follows in order of increased cost and longer schedule to perform the option: (1) whole block, (2a) physical separation, (2b) chemical separation, and (3) complete chemical processing.
Date: February 1, 1992
Creator: Lotts, A. L.; Bond, W. D.; Forsberg, C. W.; Glass, R. W.; Harrington, F. E.; Micheals, G. E. et al.
Partner: UNT Libraries Government Documents Department

Safety aspects of forced flow cooldown transients in modular high temperature gas-cooled reactors

Description: During some of the design basis accidents in Modular High Temperature Gas Cooled Reactors (MHTGRs) the main Heat Transport System (HTS) and the Shutdown Cooling System (SCS), are assumed to have failed. Decay heat is then removed by the passive Reactor Cavity Cooling System (RCCS) only. If either forced flow cooling system becomes available during such a transient, its restart could significantly reduce the down-time. This paper uses the THATCH code to examine whether such restart, during a period of elevated core temperatures, can be accomplished within safe limits for fuel and metal component temperatures. If the reactor is scrammed, either system can apparently be restarted at any time, without exceeding any safe limits. However, under unscrammed conditions a restart of forced cooling can lead to recriticality, with fuel and metal temperatures significantly exceeding the safety limits.
Date: September 1, 1992
Creator: Kroeger, P. G.
Partner: UNT Libraries Government Documents Department

Evaluation of MHTGR fuel reliability

Description: Modular High-Temperature Gas-Cooled Reactor (MHTGR) concepts that house the reactor vessel in a tight but unsealed reactor building place heightened importance on the reliability of the fuel particle coatings as fission product barriers. Though accident consequence analyses continue to show favorable results, the increased dependence on one type of barrier, in addition to a number of other factors, has caused the Nuclear Regulatory Commission (NRC) to consider conservative assumptions regarding fuel behavior. For this purpose, the concept termed ``weak fuel`` has been proposed on an interim basis. ``Weak fuel`` is a penalty imposed on consequence analyses whereby the fuel is assumed to respond less favorably to environmental conditions than predicted by behavioral models. The rationale for adopting this penalty, as well as conditions that would permit its reduction or elimination, are examined in this report. The evaluation includes an examination of possible fuel-manufacturing defects, quality-control procedures for defect detection, and the mechanisms by which fuel defects may lead to failure.
Date: July 1, 1992
Creator: Wichner, R. P. & Barthold, W. P.
Partner: UNT Libraries Government Documents Department

MHTGR thermal performance envelopes: Reliability by design

Description: This document discusses thermal performance envelopes which are used to specify steady-state design requirements for the systems of the Modular High Temperature Gas-Cooled Reactor to maximize plant performance reliability with optimized design. The thermal performance envelopes are constructed around the expected operating point accounting for uncertainties in actual plant as-built parameters and plant operation. The components are then designed to perform successfully at all points within the envelope. As a result, plant reliability is maximized by accounting for component thermal performance variation in the design. The design is optimized by providing a means to determine required margins in a disciplined and visible fashion.
Date: May 1, 1992
Creator: Etzel, K. T.; Howard, W. W. & Zgliczynski, J. B.
Partner: UNT Libraries Government Documents Department

Impact of increasing MHTGR power on passive heat removal

Description: In 1990 a cost reduction study recommended that the reference US MHTGR module design be changed to an 84-column, 450 MW(t) annular reactor core to attain improved economics with the same high level of safety as the previous reference 66-column, 350 MW(t) MHTGR module. The objective of this paper is to report on a recently completed core configuration trade study that reviewed the basis for that recommendation with more detailed assessments. The trade study examined alternate core configurations in terms of the size, shape, and power level. Core configurations at 450 MW(t), an alterative at higher power, and one at lower power were considered. These alternatives represented the maximum achievable power for fuel element for two different reactor vessel sizes. Fuel, reactor internal and vessel temperatures during pressurized and depressurized conduction cooldown transients are presented and compared to limits. Based on the need to improve economics without sacrificing the MHTGR`s high level of safety, the trade study confirmed that the previously selected 84-column, 450 MW(t) annular design remains the preferable configuration.
Date: July 1, 1992
Creator: Dunn, T. D.; Schwartz, A. A. & Silady, F. A.
Partner: UNT Libraries Government Documents Department

Non-isotropic thermal behavior of an MHTGR fuel block: Impact upon reactivity feedback

Description: This report discusses lumped parameter and detailed multi-dimensional thermal analyses of a New Production Modular High Temperature Gas Cooled Reactor (NP-MHTGR) fuel block were conducted that indicated that during a power transient, the target temperature would rise significantly later than the fuel temperature. This behavior, which is due to radiative, convective and conductive heat transport phenomena within the fuel block coupled with the significantly different thermal physical properties of the fuel block materials, leads to the potential for a delayed positive contribution to the temperature coefficient of reactivity of the NP-MHTGR core during TOP events. These results have indicated the need for additional experimental and analytical studies in order to more fully assess the design, operational and safety implications of this phenomenon. In addition, experiments in the TREAT facility are planned to provide additional data to assist in the capabilities to predict the reactivity feedback characteristics of the NP-MHTGR core. These studies will be the subject of a future paper.
Date: September 1, 1992
Creator: Delpech, M.; Singer, R. M. & Finck, P. J.
Partner: UNT Libraries Government Documents Department