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

Title: Assessments of Water Ingress Accidents in a Modular High-Temperature Gas-Cooled Reactor

Abstract

Severe water ingress accidents in the 200-MW HTR-module were assessed to determine the safety margins of modular pebble-bed high-temperature gas-cooled reactors (HTR-module). The 200-MW HTR-module was designed by Siemens under the criteria that no active safety protection systems were necessary because of its inherent safe nature. For simulating the behavior of the HTR-module during severe water ingress accidents, a water, steam, and helium multiphase cavity model was developed and implemented in the dynamic simulator for nuclear power plants (DSNP) simulation system. Comparisons of the DSNP simulations incorporating these models with experiments and with calculations using the time-dependent neutronics and temperature dynamics code were made to validate the simulation. The analysis of the primary circuit showed that the maximum water concentration increase in the reactor core was <0.3 kg/(m{sup 3}s). The water vaporization in the steam generator and characteristics of water transport from the steam generator to the reactor core would reduce the rate of water ingress into the reactor core. The analysis of a full cavitation of the feedwater pump showed that if the secondary circuit could be depressurized, the feedwater pump would be stopped by the full cavitation. This limits the water transported from the deaerator to the steammore » generator. A comprehensive simulation of the HTR-module power plant showed that the water inventory in the primary circuit was limited to {approx}3000 kg. The nuclear reactivity increase caused by the water ingress would lead to a fast power excursion, which would be inherently counterbalanced by negative feedback effects. The integrity of the fuel elements, because the safety-relevant temperature limit of 1600 deg. C is not reached in any case, is not challenged.« less

Authors:
 [1];  [1];  [2]
  1. Tsinghua University (China)
  2. Forschungszentrum Juelich (Germany)
Publication Date:
OSTI Identifier:
20840245
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Technology; Journal Volume: 149; Journal Issue: 3; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; CAVITIES; EXCURSIONS; FEEDBACK; FEEDWATER; FUEL ELEMENTS; HELIUM; HTGR TYPE REACTORS; NUCLEAR POWER PLANTS; REACTIVITY; REACTOR CORES; SAFETY MARGINS; SIMULATION; SIMULATORS; STEAM; STEAM GENERATORS; TIME DEPENDENCE

Citation Formats

Zhang Zuoyi, Dong Yujie, and Scherer, Winfried. Assessments of Water Ingress Accidents in a Modular High-Temperature Gas-Cooled Reactor. United States: N. p., 2005. Web.
Zhang Zuoyi, Dong Yujie, & Scherer, Winfried. Assessments of Water Ingress Accidents in a Modular High-Temperature Gas-Cooled Reactor. United States.
Zhang Zuoyi, Dong Yujie, and Scherer, Winfried. Tue . "Assessments of Water Ingress Accidents in a Modular High-Temperature Gas-Cooled Reactor". United States. doi:.
@article{osti_20840245,
title = {Assessments of Water Ingress Accidents in a Modular High-Temperature Gas-Cooled Reactor},
author = {Zhang Zuoyi and Dong Yujie and Scherer, Winfried},
abstractNote = {Severe water ingress accidents in the 200-MW HTR-module were assessed to determine the safety margins of modular pebble-bed high-temperature gas-cooled reactors (HTR-module). The 200-MW HTR-module was designed by Siemens under the criteria that no active safety protection systems were necessary because of its inherent safe nature. For simulating the behavior of the HTR-module during severe water ingress accidents, a water, steam, and helium multiphase cavity model was developed and implemented in the dynamic simulator for nuclear power plants (DSNP) simulation system. Comparisons of the DSNP simulations incorporating these models with experiments and with calculations using the time-dependent neutronics and temperature dynamics code were made to validate the simulation. The analysis of the primary circuit showed that the maximum water concentration increase in the reactor core was <0.3 kg/(m{sup 3}s). The water vaporization in the steam generator and characteristics of water transport from the steam generator to the reactor core would reduce the rate of water ingress into the reactor core. The analysis of a full cavitation of the feedwater pump showed that if the secondary circuit could be depressurized, the feedwater pump would be stopped by the full cavitation. This limits the water transported from the deaerator to the steam generator. A comprehensive simulation of the HTR-module power plant showed that the water inventory in the primary circuit was limited to {approx}3000 kg. The nuclear reactivity increase caused by the water ingress would lead to a fast power excursion, which would be inherently counterbalanced by negative feedback effects. The integrity of the fuel elements, because the safety-relevant temperature limit of 1600 deg. C is not reached in any case, is not challenged.},
doi = {},
journal = {Nuclear Technology},
number = 3,
volume = 149,
place = {United States},
year = {Tue Mar 15 00:00:00 EST 2005},
month = {Tue Mar 15 00:00:00 EST 2005}
}
  • For light water reactors, loss of coolant is an important point in safety analysis, whereas for gas-cooled reactors the ingress of water into the core region is an incident of safety relevance. The applicability of the computer code system GAMTEREX to pebble beds of spherical high-temperature gas-cooled reactor fuel elements with simulated water ingress is verified by experiment. The measurements were performed at a Siemens-Argonaut reactor, using its ring core as a driver zone for a pebble-bed core in the center of the reactor.
  • Experiments in a subcritical assembly with pebble-bed high-temperature gas-cooled reactor fuel and hydrogen ranging between 0 and 14.4 vol percent were carried out to study the effects of water ingress in reactivity and to test the accuracy of diffusion-code calculations for small subcritical systems. Special emphasis is given to an adequate description of the influence of the water ingress on the diffusion properties of the pebble-bed system. The agreement between experimental and theoretical results is in all cases better than +-0.01 in k/sub eff/.(auth)
  • A rapid water ingress transient, resulting from steam generator tube or tube-sheet failures, could lead to a reactivity insertion and core heatup in the Modular High Temperature Gas-Cooled Reactors. This paper considers the effect of hypothetical rapid and severe water ingress scenarios of extremely low probability, and assesses the effect of such transients on potentially excessive fuel temperatures and subsequent fuel failures. The results indicate that for the worst postulated scenarios the conservatively set limiting fuel temperature of 1600{degree}C is indeed exceeded, but only for a few seconds, and then only in a small fraction of the core. Therefore, itmore » appears that even the most severe and rapid water ingress transients would not lead to significant fuel failures. Parametric variations of the key variables indicate that the reactivity worth of water and the fuel thermal properties must be established with high confidence as the design progresses. 7 refs., 11 figs., 3 tabs.« less
  • 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 suchmore » 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.« less
  • The transient which involved a steam-generator tube leak and the ingress of moisture into the primary coolant system of the standard Modular Modular High Temperature Gas-Cooled Reactor (MHTGR) is analyzed by using the MINET (Momentum Integral NETwork) computer code. The analysis provides detailed information on the effect of power excursion on transient system pressures and temperatures. It is concluded that during the short term transient period the moisture ingress presents no threat to the integrity of the fuel elements and does not lead to pressures which would cause relief valve opening and fission product release.