An Overview of Non-LWR Vessel Cooling Systems for Passive Decay Heat Removal (Technical Letter Final Report)

Abstract

The following report provides a technical review of various reactor vessel cooling system (VCS) concepts under consideration for decay heat removal (DHR) in non-light water advanced reactor designs. This review focuses on ex-vessel designs, including the Reactor Cavity Cooling System (RCCS), the Reactor Vessel Auxiliary Cooling System (RVACS), and hybrid iterations, using both air and water cooling to achieve their heat removal function. Based on a literature review of publicly available sources published between 1979 and 2021, a technical summary is presented detailing existing and planned VCS design options, their applicability to specific reactor type, and review of authored research and development studies. Following an assessment of the availability of data and modeling tools, an evaluation was performed analyzing their likely performance during normal, degraded, and accident conditions, including reliability, stability, and longevity.With renewed consideration of air-based DHR systems by some US vendors, there is a need to fully understand the complexities inherent to natural circulation systems, and more importantly, how they may influence safety-related heat removal functions and system performance. For DHR systems that rely on air-based mode of cooling, this entails quantification of the impacts of low flow conditions during start-up, relative elevations of inlet and outlet ducts for below-grade installations, effects of the use of multiple parallel chimneys for redundancy, and impact of weather conditions at the plant site. For systems relying on water-based mode cooling, reliance on limited coolant inventory in an event of pipe break or extended duration accident scenarios, sensitivities related to stability of boiling flow and heat transfer conditions, and quantification of full-scale structural vibrations on balance of plant structures are among the complicating factors. Paperwork Reduction Act StatementThis report does not contain information collection requirements and, therefore, is not subject to the requirements of the Paperwork Reduction Act of 1995 (44 United States Code [U.S.C.] 3501 et seq.). Public Protection NotificationThe U.S. Nuclear Regulatory Commission (NRC) may not conduct or sponsor, and a person is not required to respond to, a request for information or an information collection requirement unless the requesting document displays a current valid Office of Management and Budget (OMB) control number.

Preliminary Design of Reactor Cavity Cooling System for a Horizontal Compact HTGR

“…The RCCS is designed to use natural forces and be relatively simple and potential for high levels of performance for the passive safety of HTGR to remove core decay heat during both normal operation and off-normal conditions [3]. Differences between various RCCS designs are mainly in their working fluid and passive mode of operation for the range of the reactor design, for instance, General Atomics (GA) modular high temperature gas-cooled reactor (MHTGR) [4], Next Generation Nuclear Plant (NGNP) [2], and Framatome Steam Cycle -High Temperature Gas Cooled Reactor (SG-HTGR) [5].…”

Semi-Annual Report for Modular Integrated Gas High Temperature Reactor Development during Performance Period October 2021 - March 2022

“…The RCCS is designed to use natural forces and be relatively simple and potential for high levels of performance for the passive safety of HTGR to remove core decay heat during both normal operation and off-normal conditions [2]. Differences between various RCCS designs are mainly in their working fluid and passive mode of operation for the range of the reactor design, for instance, General Atomics (GA) modular high temperature gas-cooled reactor (MHTGR) [3], Next Generation Nuclear Plant (NGNP) [4], and Framatome Steam Cycle -High Temperature Gas Cooled Reactor (SG-HTGR) [5].…”