Safety evaluations of accident scenarios in high temperature gas-cooled reactors

Kroeger, P.G.

doi:10.1016/0029-5493(90)90227-o

Cited by 9 publications

(4 citation statements)

References 1 publication

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“…The results presented here are qualitatively in line with those of Kroeger [30], who performed air ingress calculations for an HTR with prismatic fuel elements assuming air ingress rates dropping within 2 days from 0.2 to 0.06 kg/s.…”

Section: Examples On Accident Estimations For Massive Air Ingresssupporting

confidence: 89%

Phenomenology of Graphite Burning in Air Ingress Accidents of HTRs

Moormann

2011

Science and Technology of Nuclear Installations

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Air ingress with graphite burning belongs to the accident scenarios in HTRs with potentially severe consequences. This paper gives an overview of basic phenomena of graphite burning like ignition conditions and moving reaction fronts. The pioneering graphite burning experiments of Don Schweitzer are successfully reevaluated. Ignition conditions are examined, and it is underlined that burning depends not only on graphite properties but also on the heat balance in the whole graphite arrangement. In graphite-moderated reactors, ignition occurs at about 650°C for small air flow rates: this means that normal operation temperatures in HTRs always allow for ignition. Fuel behaviour in air ingress, as determined in the KORA facility, is discussed: up to about 1300°C modern TRISO fuel is stable in air, but from 1500°C a complete, fast destruction is observed. Exemplary calculations on massive air ingress by chimney draught performed with REACT/THERMIX are outlined. For a hot bottom reflector there is a substantial time span before fuel is attacked. Because severe air ingress in well-designed HTRs belongs to beyond design basis accidents, the knowledge is fairly good. Concerning protecting measures, a more detailed examination of thick SiC layers is proposed.

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Section: Examples On Accident Estimations For Massive Air Ingresssupporting

confidence: 89%

Phenomenology of Graphite Burning in Air Ingress Accidents of HTRs

Moormann

2011

Science and Technology of Nuclear Installations

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“…The SiC layer in TRISO has been demonstrated to be largely resistant to chemical attack and maintains its capability to retain fission products up to 1600°C [21][22][23][24][25]. In analyses of various HTGR accident scenarios, including pressurized loss of forced Ccrculation (equivalent to a loss-of-flow accident in a water-cooled plant), Depressurized loss of forced circulation (D-LOFC, equivalent to a loss-of-coolant accident in a watercooled plant), and reactivity-initiated accidents (including failure to scram), peak fuel temperatures are below this 1600°C limit [18,19,[26][27][28]. The limiting case for peak core temperature is a combination of D-LOFC with failure to scram, but for small HTGR cores the heat transfer to the ground surrounding the reactor cavity is sufficient to keep peak temperatures below 1600°C, even if the RCCS is not functional [27,28].…”

Section: Hypothetical Accident Progressionmentioning

confidence: 99%

“…The postulated sequence of events considered in this PIRT exercise, based upon information available in literature [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], is thus as follows:…”

Section: Hypothetical Accident Progressionmentioning

confidence: 99%

Results of a Phenomena Identification and Ranking Table (Pirt) Exercise for a Severe Accident in a Small Modular High-Temperature Gas-Cooled Reactor

et al. 2019

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Canada has attracted specific interest from developers of nonwater-cooled small modular reactor (SMR) technologies, including concepts based on high-temperature gas-cooled reactors (HTGRs). It is anticipated that some research and development (R&D) will be necessary to support safety analysis and licensing of these reactors in Canada. The Phenomena Identification and Ranking Table (PIRT) process is a formalized method in which a panel of experts identifies which physical phenomena are most relevant to the reactor safety analysis and how well understood these phenomena are. The PIRT process is thus a tool to assess current knowledge levels and (or) predictive capabilities of models, thus providing direction to a focused R&D program. This paper summarizes the results of a PIRT process performed by a panel of experts at Canadian Nuclear Laboratories for a limiting or “worst-case” accident scenario at a generic HTGR-type SMR. Suggestions are given regarding the highest priority R&D items to support severe accidents analysis of these reactors.

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“…During the initial review of the Preliminary Safety Information Document (PSID) of this reactor, various potential accident transients were evaluated (Kroeger, 1989 and1990), primarily using the THATCH computer code and its various sub modules (Kroeger, et al, 1991). The primary focus of these investigations was transients without forced cooling, i.e., with ultimate heat removal by the RCCS.…”

Section: Executive Summarymentioning

confidence: 99%

Safety aspects of forced flow cooldown transients in Modular High Temperature Gas-Cooled Reactors

Kröger¹

1993

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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 report uses the THATCH code to examine whether such restart, during a period of elevated core temperatures, can be accomplished within safe limits for fiiel 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 imscrammed conditions a restart of forced cooling can lead to recriticality, with fuel and metal temperatures significantly exceeding the safety limits.

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Safety evaluations of accident scenarios in high temperature gas-cooled reactors

Cited by 9 publications

References 1 publication

Phenomenology of Graphite Burning in Air Ingress Accidents of HTRs

Phenomenology of Graphite Burning in Air Ingress Accidents of HTRs

Results of a Phenomena Identification and Ranking Table (Pirt) Exercise for a Severe Accident in a Small Modular High-Temperature Gas-Cooled Reactor

Safety aspects of forced flow cooldown transients in Modular High Temperature Gas-Cooled Reactors

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