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Title: Use of DRACS to Enhance HTGRs Passive Safety and Economy

Abstract

This paper discusses the use of DRACS to Enhance HTGRs Passive Safety and Economy. One of the important requirements for Gen. IV High Temperature Gas Cooled Reactors (HTGR) is passive safety. Currently all the HTGR designs use Reactor Vessel Auxiliary Cooling System (RVACS) for passive decay heat removal. [1] The decay heat first is transferred to core barrel by conduction and radiation, and then to reactor vessel by thermal radiation and convection; finally the decay heat is transferred to natural circulated air or water systems. RVACS can be characterized as a surface based decay heat removal system. Similar concepts have been widely used in sodium cooled fast reactor (SFR) designs, advanced light water reactors like AP1000. The RVACS is especially suitable for smaller power reactors since small systems have relatively larger surface area. RVACS tends to be less expensive. However, it limits the largest achievable power level for modular HTGRs due to the mismatch between the reactor power (proportional to volume) and decay heat removal capability (proportional to surface). When the relative decay heat removal capability is reduced, the peak fuel temperature increases, even close to the design limit. Annual designs with internal reflector can mitigate this effect therefore furthermore » increase the power. Another way to increase power is to increase power density. However, it is also limited by the decay heat removal capability. Besides safety, HTGRs also need to be economical in order to compete with other reactor designs. The limit of decay heat removal capability set by using RVACS has affected the economy of HTGRs. Forsberg [2] pointed out other disadvantages of using RVACS such as conflicting functional requirements for the reactor vessel and scaling distortion for integral effect test of the system performance. A potential alternative solution is to use a volume based passive decay removal system, call Direct Reactor Auxiliary Cooling Systems (DRACS), to remove or mitigate the limitation on decay heat removal capability. DRACS has been widely used in SFR designs and in liquid salt cooled high temperature reactors. The containment cooling system in BWR is another example of volume based decay removal systems. DRACS composes of natural circulation loops with two sets of heat exchangers, one in reactor side and another is in environment side. DRACS has the benefits of increasing the power as needed (scalability) and modularity. This paper introduces the concept of using DRACS to enhance HTGRs passive safety and economy.« less

Authors:
; ;
Publication Date:
Research Org.:
Idaho National Laboratory (INL)
Sponsoring Org.:
DOE - NE
OSTI Identifier:
1027897
Report Number(s):
INL/CON-11-20766
TRN: US1105295
DOE Contract Number:  
DE-AC07-05ID14517
Resource Type:
Conference
Resource Relation:
Conference: ANS 2011 Annual Meeting,Hollywood, FL,06/26/2011,06/30/2011
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 22 GENERAL STUDIES OF NUCLEAR REACTORS; AFTER-HEAT REMOVAL; CONTAINMENT; CONVECTION; COOLING SYSTEMS; DECAY; DRILLING EQUIPMENT; FAST REACTORS; FUNCTIONALS; GAS COOLED REACTORS; HEAT EXCHANGERS; NATURAL CONVECTION; POWER DENSITY; POWER REACTORS; REACTOR VESSELS; REMOVAL; SAFETY; SODIUM; SURFACE AREA; THERMAL RADIATION; DRACS

Citation Formats

Haihua Zhao, Hongbin Zhang, and Ling Zou. Use of DRACS to Enhance HTGRs Passive Safety and Economy. United States: N. p., 2011. Web.
Haihua Zhao, Hongbin Zhang, & Ling Zou. Use of DRACS to Enhance HTGRs Passive Safety and Economy. United States.
Haihua Zhao, Hongbin Zhang, and Ling Zou. Wed . "Use of DRACS to Enhance HTGRs Passive Safety and Economy". United States. https://www.osti.gov/servlets/purl/1027897.
@article{osti_1027897,
title = {Use of DRACS to Enhance HTGRs Passive Safety and Economy},
author = {Haihua Zhao and Hongbin Zhang and Ling Zou},
abstractNote = {This paper discusses the use of DRACS to Enhance HTGRs Passive Safety and Economy. One of the important requirements for Gen. IV High Temperature Gas Cooled Reactors (HTGR) is passive safety. Currently all the HTGR designs use Reactor Vessel Auxiliary Cooling System (RVACS) for passive decay heat removal. [1] The decay heat first is transferred to core barrel by conduction and radiation, and then to reactor vessel by thermal radiation and convection; finally the decay heat is transferred to natural circulated air or water systems. RVACS can be characterized as a surface based decay heat removal system. Similar concepts have been widely used in sodium cooled fast reactor (SFR) designs, advanced light water reactors like AP1000. The RVACS is especially suitable for smaller power reactors since small systems have relatively larger surface area. RVACS tends to be less expensive. However, it limits the largest achievable power level for modular HTGRs due to the mismatch between the reactor power (proportional to volume) and decay heat removal capability (proportional to surface). When the relative decay heat removal capability is reduced, the peak fuel temperature increases, even close to the design limit. Annual designs with internal reflector can mitigate this effect therefore further increase the power. Another way to increase power is to increase power density. However, it is also limited by the decay heat removal capability. Besides safety, HTGRs also need to be economical in order to compete with other reactor designs. The limit of decay heat removal capability set by using RVACS has affected the economy of HTGRs. Forsberg [2] pointed out other disadvantages of using RVACS such as conflicting functional requirements for the reactor vessel and scaling distortion for integral effect test of the system performance. A potential alternative solution is to use a volume based passive decay removal system, call Direct Reactor Auxiliary Cooling Systems (DRACS), to remove or mitigate the limitation on decay heat removal capability. DRACS has been widely used in SFR designs and in liquid salt cooled high temperature reactors. The containment cooling system in BWR is another example of volume based decay removal systems. DRACS composes of natural circulation loops with two sets of heat exchangers, one in reactor side and another is in environment side. DRACS has the benefits of increasing the power as needed (scalability) and modularity. This paper introduces the concept of using DRACS to enhance HTGRs passive safety and economy.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2011},
month = {6}
}

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