skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Emergency Decay Heat Removal in a GEN-IV Gas-Cooled Fast Reactor

Abstract

A series of transient analyses using the system code RELAP5-3d has been performed to confirm the efficacy of a proposed hybrid active/passive combination approach to the decay heat removal for an advanced 2400 MWt GEN-IV gas-cooled fast reactor. The accident sequence of interest is a station blackout simultaneous with a small break (10 sq.inch/0.645 m{sup 2}) in the reactor vessel. The analyses cover the three phases of decay heat removal in a depressurization accident: (1) forced flow cooling by the power conversion unit (PCU) coast down, (2) active forced flow cooling by a battery powered blower, and (3) passive cooling by natural circulation. The blower is part of an emergency cooling system (ECS) that by design is to sustain passive decay heat removal via natural circulation cooling 24 hours after shutdown. The RELAP5 model includes the helium-cooled reactor, the ECS (primary and secondary side), the PCU with all the rotating machinery (turbine and compressors) and the heat transfer components (recuperator, pre-cooler and inter-cooler), and the guard containment that surrounds the reactor and the PCU. The transient analysis has demonstrated the effectiveness of passive decay heat removal by natural circulation cooling when the guard containment pressure is maintained at or abovemore » 800 kPa. (authors)« less

Authors:
; ;  [1]
  1. Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973-5000 (United States)
Publication Date:
Research Org.:
The ASME Foundation, Inc., Three Park Avenue, New York, NY 10016-5990 (United States)
OSTI Identifier:
20995571
Resource Type:
Conference
Resource Relation:
Conference: 14. international conference on nuclear engineering (ICONE 14), Miami, FL (United States), 17-20 Jul 2006; Other Information: Country of input: France
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; ACCIDENTS; AFTER-HEAT REMOVAL; BLOWERS; COMPRESSORS; CONTAINMENT; CONVERSION; COOLING; COOLING SYSTEMS; DEPRESSURIZATION; DESIGN; FAST REACTORS; HEAT EXCHANGERS; HELIUM COOLED REACTORS; NATURAL CONVECTION; OUTAGES; REACTOR VESSELS; SHUTDOWN; TRANSIENTS; TURBINES

Citation Formats

Cheng, Lap Y., Ludewig, Hans, and Jo, Jae. Emergency Decay Heat Removal in a GEN-IV Gas-Cooled Fast Reactor. United States: N. p., 2006. Web.
Cheng, Lap Y., Ludewig, Hans, & Jo, Jae. Emergency Decay Heat Removal in a GEN-IV Gas-Cooled Fast Reactor. United States.
Cheng, Lap Y., Ludewig, Hans, and Jo, Jae. 2006. "Emergency Decay Heat Removal in a GEN-IV Gas-Cooled Fast Reactor". United States. doi:.
@article{osti_20995571,
title = {Emergency Decay Heat Removal in a GEN-IV Gas-Cooled Fast Reactor},
author = {Cheng, Lap Y. and Ludewig, Hans and Jo, Jae},
abstractNote = {A series of transient analyses using the system code RELAP5-3d has been performed to confirm the efficacy of a proposed hybrid active/passive combination approach to the decay heat removal for an advanced 2400 MWt GEN-IV gas-cooled fast reactor. The accident sequence of interest is a station blackout simultaneous with a small break (10 sq.inch/0.645 m{sup 2}) in the reactor vessel. The analyses cover the three phases of decay heat removal in a depressurization accident: (1) forced flow cooling by the power conversion unit (PCU) coast down, (2) active forced flow cooling by a battery powered blower, and (3) passive cooling by natural circulation. The blower is part of an emergency cooling system (ECS) that by design is to sustain passive decay heat removal via natural circulation cooling 24 hours after shutdown. The RELAP5 model includes the helium-cooled reactor, the ECS (primary and secondary side), the PCU with all the rotating machinery (turbine and compressors) and the heat transfer components (recuperator, pre-cooler and inter-cooler), and the guard containment that surrounds the reactor and the PCU. The transient analysis has demonstrated the effectiveness of passive decay heat removal by natural circulation cooling when the guard containment pressure is maintained at or above 800 kPa. (authors)},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2006,
month = 7
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Increased reliance on passive emergency cooling using natural circulation of gas at elevated pressure is one of the major goals for the Gas-cooled Fast Reactor (GFR). Since GFR cores have high power density and low thermal inertia, the decay heat removal (DHR) in depressurization accidents is a key challenge. Furthermore, due to its high surface heat flux and low velocities under natural circulation in any post-LOCA scenario, three effects impair the capability of turbulent gas flow to remove heat from the GFR core, namely: (1) Acceleration effect (2) Buoyancy effect (3) Properties variation. This paper reviews previous work on heatmore » transfer mechanisms and flow characteristics of the Deteriorated Turbulent Heat Transfer (DTHT) regime. It is shown that the GFR's DHR system has a potential for operating in the DTHT regime by performing a simple analysis. A description of the MIT/INL experimental facility designed and built to investigate the DTHT regime is provided together with the first test results. The first runs were performed in the forced convection regime to verify facility operation against well-established forced convection correlations. The results of the three runs at Reynolds numbers 6700, 8000 and 12800 showed good agreement with the Gnielinsky correlation [4], which is considered the best available heat transfer correlation in the forced convection regime and is valid for a large range of Reynolds and Prandtl numbers. However, even in the forced convection regime, the effect of heat transfer properties variation of the fluid was found to be still significant. (authors)« less
  • A reliability analysis for the decay heat removal system of a 1000-MW--(e) gas-cooled fast breeder reactor (GCFBR) has been carried out. ITT relates only to the GCFBR specific systems required after the maximum depressurization accident, and normal shutdown. Non-GCFBR specific systems such as the electrical supply system and the containment back-pressure system were not included in the analysis. For these analyses, the method of fault trees was used to describe the different failure combinations of the system. The calculations were performed with the system analysis program SAP-1, which combines analytical and simulation methods to find the failure probability and themore » unavailability of the system. The results of the analysis show that the unavailability governs the reliability of the system; a computed value of 3 x 10/sup -4/ was obtained for the unavailability of the system after a maximum depressurization accident, and a value of 4 x 10/sup -8/ was obtained for the unavailability of the system after normal shutdown.« less
  • The gas-cooled fast reactor (GFR) was chosen as one of the Generation IV nuclear reactor systems to be developed based on its excellent potential for sustainability through reduction of the volume and radiotoxicity of both its own fuel and other spent nuclear fuel, and for extending/utilizing uranium resources orders of magnitude beyond what the current open fuel cycle can realize. In addition, energy conversion at high thermal efficiency is possible with the current designs being considered, thus increasing the economic benefit of the GFR. However, research and development challenges include the ability to use passive decay heat removal systems duringmore » accident conditions, survivability of fuels and in-core materials under extreme temperatures and radiation, and economical and efficient fuel cycle processes. This report addresses/discusses the decay heat removal options available to the GFR, and the current solutions. While it is possible to design a GFR with complete passive safety (i.e., reliance solely on conductive and radiative heat transfer for decay heat removal), it has been shown that the low power density results in unacceptable fuel cycle costs for the GFR. However, increasing power density results in higher decay heat rates, and the attendant temperature increase in the fuel and core. Use of active movers, or blowers/fans, is possible during accident conditions, which only requires 3% of nominal flow to remove the decay heat. Unfortunately, this requires reliance on active systems. In order to incorporate passive systems, innovative designs have been studied, and a mix of passive and active systems appears to meet the requirements for decay heat removal during accident conditions.« less
  • Decay heat removal at depressurized shutdown conditions has been regarded as one of the key areas where significant improvement in passive response was targeted for the GEN IV GFR over the GCFR designs of thirty years ago. It has been recognized that the poor heat transfer characteristics of gas coolant at lower pressures needed to be accommodated in the GEN IV design. The design envelope has therefore been extended to include a station blackout sequence simultaneous with a small break/leak. After an exploratory phase of scoping analysis in this project, together with CEA of France, it was decided that naturalmore » convection would be selected as the passive decay heat removal approach of preference. Furthermore, a double vessel/containment option, similar to the double vessel/guard vessel approach of the SFR, was selected as the means of design implementation to reduce the PRA risks of the depressurization accident. However additional calculations in conjunction with CEA showed that there was an economic penalty in terms of decay heat removal system heat exchanger size, elevation heights for thermal centers, and most of all in guard containment back pressure for complete reliance on natural convection only. The back pressure ranges complicated the design requirements for the guard containment. Recognizing that the definition of a loss-of-coolant-accident in the GFR is a misnomer, since gas coolant will always be present, and the availability of some driven blower would reduce fuel temperature transients significantly; it was decided instead to aim for a hybrid active/passive combination approach to the selected BDBA. Complete natural convection only would still be relied on for decay heat removal but only after the first twenty four hours after the initiation of the accident. During the first twenty four hour period an actively powered blower would be relied on to provide the emergency decay power removal. However the power requirements of the active blower/circulators would be kept low by maintaining a pressurized system coolant back pressure of {approx}7-8 bars through the design of the guard containment for such a design pressure. This approach is termed the medium pressure approach by both CEA and the US. Such a containment design pressure is in the range of the LWR experience, both PWRs and BWRs. Both metal containments and concrete guard containments are possible in this pressure range. This approach is then a time-at-risk approach as the power requirements should be low enough that battery/fuel cell banks without diesel generator start-up failure rate issues should be capable of providing the necessary power. Compressed gas sources are another possibility. A companion PRA study is being conducted to survey the reliability of such systems.« less
  • Current research and development on the Gas-Cooled Fast Reactor (GFR) has focused on the design of safety systems that will remove the decay heat during accident conditions, ion irradiations of candidate ceramic materials, joining studies of oxide dispersion strengthened alloys; and within the Advanced Fuel Cycle Initiative (AFCI) the fabrication of carbide fuels and ceramic fuel matrix materials, development of non-halide precursor low density and high density ceramic coatings, and neutron irradiation of candidate ceramic fuel matrix and metallic materials. The vast majority of this work has focused on the reference design for the GFR: a helium-cooled, direct power conversionmore » system that will operate with an outlet temperature of 850ºC at 7 MPa. In addition to the work being performed in the United States, seven international partners under the Generation IV International Forum (GIF) have identified their interest in participating in research related to the development of the GFR. These are Euratom (European Commission), France, Japan, South Africa, South Korea, Switzerland, and the United Kingdom. Of these, Euratom (including the United Kingdom), France, and Japan have active research activities with respect to the GFR. The research includes GFR design and safety, and fuels/in-core materials/fuel cycle projects. This report is a compilation of work performed on decay heat removal systems for a 2400 MWt GFR during this fiscal year (FY05).« less