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Methodology for reference accidents definition for ITER
Fusion Engineering and Design 75–79 (2005) 1103–1107
Methodology for reference accidents definition for ITER T. Pinna a,∗ , S. Raboin b , J. Uzan-Elbez b , N. Taylor c , L. Semeraro a , EISS Team a ENEA Fusion Technologies, Via Enrico Fermi 45, I-00044 Frascati, Rome, Italy ´ Direction de l’Energie Nucl´eaire, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK b
c
Available online 28 July 2005
Abstract The safety assessment of ITER presented in the Rapport Pr´emilinaire de Sˆuret´e (RPrS) for the French Regulator is based on the definition and the study of a limited set of postulated incidental and accidental sequences conservatively selected on deterministic grounds. Ultimate safety margins have also been analysed through hypothetical sequences conservatively extrapolated from the more significant accidents. The rationale for event selection consists firstly of the identification of every radiological source and its confinement barriers; failure of one or several of these barriers may then be presumed and a scenario defined, following a standardized grid; furthermore, the calculations and analysis follow a unique logical scheme to assure consistency and exhaustiveness of the report. Nine accident families have been defined: plasma events, loss of power events, in-vessel events, ex-vessel events, cryostat events, magnet events, maintenance events, tritium plant and fuel events, hot cells events. Calculations with qualified computer codes have shown that the consequences of any postulated accident respect limits defined in the safety guidelines. Moreover, no hypothetical sequence shows any cliff effect, illustrating in this way the robustness of the defence in depth approach used for ITER. It is worth to recall that, in the present status of the ITER project, the only systems subject to the analysis are the tokamak, the tritium plant and the hot cells. © 2005 Elsevier B.V. All rights reserved. Keywords: Preliminary safety report; Accident analysis; Reference events
1. Introduction Safety studies performed for ITER have included extensive analyses of possible off-normal event ∗ Corresponding author. Tel.: +39 06 9400 5820; fax: +39 06 9400 5314. E-mail address: [email protected] (T. Pinna).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.06.030
sequences and of possible potential consequences. Accident analyses are introduced in the “Accident Analysis Guidelines” [1] and “Accident Analysis Specification for GSSR” [2] documents, while the studies are reported in the ITER Generic Site Safety Report (GSSR). Deterministic assessments performed for Reference Events and Ultimate Safety Margins Events are documented in volumes VII [3] and VIII [4],
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T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
respectively; while demonstration that all the possible event initiators and related event sequence scenarios result in consequences that are insignificant or are enveloped by consequences considered deterministically in volumes VII and VIII, is documented in volume X [5]. Such demonstration was done in the manner of probabilistic-like analyses (top-down and bottom-up methods) and was aimed at verifying that (i) the selection of the events studied deterministically is adequate, in so far as they envelope the consequences of all identified events and (ii) every identified event sequence is assessed to ensure that its potential consequences are within the acceptance criteria of the project guidelines. The French Regulator does not assess ITER as a nuclear reactor but as a research facility with radiological and chemical hazards. That imposes for the RPrS the definition and the study of a limited set of incidental and accidental sequences, strictly selected on deterministic grounds, to demonstrate that the acceptance criteria are respected. Therefore, only the GSSR volumes VII and VIII are relevant for the reporting of RPrS volume 2 (i.e. chapter II 2.1, relative to the nuclear risks and dealing with the accidental situations of ITER). Nevertheless, the probabilistic assessments done till July 2001, documented in GSSR, and the assessments performed successively by EFDA Associations will be presented to the French Regulator in an accompanying document to RPrS as background in order to demonstrate the exhaustiveness of the results. Here, in this paper, is reported the methodology used to demonstrate completeness of the set of accidents taken as reference for the RPrS, the parameters considered in the safety assessment and the outcomes of the work in terms of identified radiological hazards. In the present state of the ITER project, the only parts concerned by the analyses are the tokamak building, the tritium plant and the hot cells.
2. Methodology to identify reference events The reference accident scenarios are identified on the basis of the list of radioactive inventories (or source terms) present in the plant and on the basis of confinement barriers dedicated to isolate the inventories from the environment. For each source term the failure of one, or more than one, related confinement barrier has to be postulated. Clearly, the part of the barriers
that could induce, in case of failure, mobilization of radioactive inventories initially confined has to be considered. In defining the reference events, several different kinds of loss of confinement can be identified but to assure that the selected events envelope the overall set of minor events, the most severe failures of confinement barriers have to be considered, typically the ones where the most significant energy sources are involved. For the set of selected reference events to be exhaustive it has to include at least one accident scenario for each source term contained in the plant and, for each accident scenario, the most conservative hypotheses have to be used in defining the parameters needed to study the accident evolutions. Conditions of accident situations are identified with respect to the overall possible states of plant functioning and to their expected likelihood of occurrence: normal operation, incidental situation, accidental situation and hypothetical situation. Normal operation are those plant conditions planned and required for normally operating the plant, including some faults and events, which can occur as a result of the experimental nature of the facility. Incidental situations are not planned but are likely to occur one or more times during the plant life but do not include normal operations. Accidental situations are not likely to occur during the life of the plant but are postulated to assess the safety of the facility. Hypothetical situations are more unlikely to occur than accidental situations and are considered to check sensitivity of the facility in case of postulated extreme accident conditions and to evaluate safety margins.
3. Potential hazards Potential environmental hazards for ITER come from three different sources: - neutronic fluxes, just during plasma operation; - radioactive products, such as tritium, activated materials and dusts, activated corrosion products (ACPs) and activated gas; - chemical materials, toxic and cryogenic ones, such as beryllium, hydrogen, ozone, inert gas, insulator gas, etc.
T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
Risk prevention requires: - confinement of radioactive and toxic materials; - evacuation of decay heat; - limitation of external radiation fields. Thus, safety criteria for ITER can be respected with adequate confinements of source terms and toxic materials able to avoid dispersion of radioactive and toxic materials towards the environment and able to shield radiation fields. Therefore, keeping the prevention of toxic material dispersion in the field of industrial safety and assuming that the design provides enough accuracy in designing appropriate shields to the radiation fields, the safety analyses to be reported to the licensing authority have firstly to demonstrate capability of adopted confinement barriers to avoid the spread of radiological contamination into the environment even in case of accidental situations.
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The radiological source terms can be categorized according to their confinements, in order to better identify sources with similar vulnerability to mobilization in an off-normal event: VVST: Tritium and activated products (mainly dusts) enclosed inside the vacuum vessel (VV) and in primary cooling circuits (T and ACPs). TKST: Tritium and activated products enclosed in the tokamak building, outside the VV. TPST: Tritium, mobilized dusts and activated gas in the tritium plant. HCST: Tritium and activated products contained in the hot cells (HC). The different energies involved in the experiment can be the origin of loss of confinement and of mobilization of the radioactive materials listed above, such in case of loss of energy control. Furthermore, some accidental situations can generate
Table 1 Selected reference events Source terms
Event family
Reference events
Inc/Acc
VVST
Plasma events
Loss of plasma control
I–A
VVST
Electric power events
Loss of off-site power for 1 h Loss of off-site power for 32 h Blackout for 1 h
I A A
VVST
In-vessel events
In-vessel First Wall (FW) cooling loop leak (single pipe break) Multiple FW pipe break Loss of vacuum through one VV/cryostat penetration line
I A A
VVST
Ex-vessel events
Loss of divertor (DV) heat sink Pump trip in DV cooling loop Pump seizure in DV cooling loop Heat Exchanger leakage Heat Exchanger tube rupture Large VV coolant pipe break Large DV ex-vessel coolant pipe break
I I A I A A A
VVST
Maintenance events
Air-leakage into VV during maintenance Stuck DV cassette and failure of transfer cask
A A
TKST and VVST
Cryostat events
TKST and VVST
Magnet events
Cryostat air ingress Water and helium ingress into Cryostat Toroidal field coil short Arc near confinement barrier
A A A A
TPST
Tritium plant events
Tritium process line leakage Accident with transport hydride bed Isotope separation system failure Failure of fuelling line
I A A A
HCST
HC events
Loss of confinement in HC
A
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T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
undesired chemical reactions (e.g. hydrogen explosion) that could aggravate mobilization of radioactive release.
Table 2 Rules for accident analysis Category
Parameters
General
Name of event Objectives Scope of analysis Acceptance criteria Parameter studies
Event sequence
Definition of initiating event, location, etc. Possible transient sequences Aggravating failures Loss of power Linkage to source terms
System assumptions
Process systems assumptions Safety systems assumptions
Confinement assumptions
Overpressure mitigation Mobilization assumption Release from the confinement
Analysis methodology
Scope of modelling Possible codes Source of input data
Results
General Main component temperature H2 generation, if any Cooling system conditions Confinement response in terms of containments challenging and environmental radioactive release
Analysis execution
Work sharing and schedule
4. Identified reference events The analysis of the source terms allocated in the various sections of the plant allows to point out nine different families of events in tokamak building, tritium plant and HC, i.e. plasma, electric power, in-vessel, ex-vessel, maintenance, cryostat, magnet, tritium plant and hot cell events. In Table 1 are listed the 6 incidents (I) and 19 accidents (A) identified. Where more than one initiator was expected to induce similar scenarios, in defining the most representative scenarios, the events that most seriously challenge the confinement functions and that involve the highest energy inventories have been considered.
5. Analysis of reference events All the identified events have been studied by the use of computer codes capable of simulating phenomena related to the accidents. All the accidents have been defined and studied according to the rules listed in Table 2.
6. Evaluation of safety margins 7. Results obtained from accident analyses To show the robustness of the “defence in depth” approach used for ITER and to demonstrate that no cliff edge effects occur, hypothetical accident scenarios have been analysed evaluating ultimate safety margins. Hypothetical sequences have been defined by adding to some of the reference accident sequences aggravating failures, which imply the failure of a safety function. The challenges to confinement functions of the most external barriers (i.e. tokamak and tritium buildings) have been studied in some hypothetical accident situations. Hypothetical maximum production of H2 , risk and possible consequences of H2 and dust explosions, and prolonged loss of decay heat removal function have been considered.
The accident analysis studied the 25 reference events listed in Table 1. The conservative calculations performed led to the conclusion that the potential consequences are within the acceptance criteria of the project guidelines. Maximum external releases in terms of doses are summarized in Table 3 for the 19 accidents. Limits of release in accidental situations, as defined in the project guidelines, are also reported in the last line of Table 3. The study of the ultimate safety margins determined that no cliff edge effect appears to happen and that radiological releases remain under the limit of 10 mSv also in case of hypothetical events.
T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
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Table 3 Environmental releases (in terms of Sv) related to reference accident events Reference events
T (HTO)
AP
ACP
Total dose
Loss of plasma control Loss of off-site power for 32 h Blackout for 1 h Multiple FW pipe break Loss of vacuum through one VV/cryostat penetration line Pump seizure in DV cooling loop Heat exchanger tube rupture Large VV coolant pipe break Large DV ex-vessel cooling pipe break Air-leakage into VV during maintenance Stuck DV cassette and failure of transfer cask Cryostat air ingress Water and helium ingress into cryostat Toroidal field coil short Arc near confinement barrier Accident with transport hydride bed Isotope separation system failure Failure of fuelling line Loss of confinement in HC Project guideline limits
0.026 0 0 0.062 55 0.026 1.8 2.1 150 0.036 11 0 0.0002 0 0 4.5 4.6 17 0.34 10000
0.044 0 0 0.065 26.5 0.044 0 0 3.5 4 1.5 0 0 0 0 0 0 0 35 10000
3.0E-5 0 0 4.2E-6 0 3.3E-4 0.75 5.1 99 0 0 0 5.7 0 0 0 0 0 0 10000
0.07 0 0 0.127 81.5 0.07 2.55 7.2 252.5 ∼4 12.5 0 5.7 0 0 4.5 4.6 17 ∼35 10000
8. Conclusions
References
The application of the above described standardized method, in defining and assessing potential accident sequences, guarantees the homogeneity of the RPrS and gives an exhaustive demonstration of the compliance of ITER with the safety requirements fixed in the design guidelines. Furthermore, results of the calculations are presented in a standardized mode, identifying for each reference event the same items, i.e. nature of the radiological risks, more probable cause of accident, prevention means, survey and detection means, limitation of consequences, sequence of events involved in the accident scenarios, conclusions and remarks.
[1] C. Gordon, et al., Accident Analysis Guidelines for GSSR, G81 RI 4 00-01-27 W0.3, version 3.1, ITER Garching JWS, 21 July 2000. [2] T. Honda, et al., Accident Analysis Specifications for NSSR-2 (AAS-3), G 81 RI 3 00-02-29 W 0.1, version 3.2, ITER Garching JWS, 07 July 2000. [3] GSSR vol. VII (Generic Site Safety Report), G 84 RI 6 01-06-27 R1.0, ITER Garching July 2001. [4] GSSR vol. VIII (Generic Site Safety Report), G 84 RI 7 01-06-27 R1.0, ITER Garching, July 2001. [5] GSSR vol. X (Generic Site Safety Report), G 84 RI 9 01-06-27 R1.0, ITER Garching, July 2001.
Methodology for reference accidents definition for ITER T. Pinna a,∗ , S. Raboin b , J. Uzan-Elbez b , N. Taylor c , L. Semeraro a , EISS Team a ENEA Fusion Technologies, Via Enrico Fermi 45, I-00044 Frascati, Rome, Italy ´ Direction de l’Energie Nucl´eaire, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK b
c
Available online 28 July 2005
Abstract The safety assessment of ITER presented in the Rapport Pr´emilinaire de Sˆuret´e (RPrS) for the French Regulator is based on the definition and the study of a limited set of postulated incidental and accidental sequences conservatively selected on deterministic grounds. Ultimate safety margins have also been analysed through hypothetical sequences conservatively extrapolated from the more significant accidents. The rationale for event selection consists firstly of the identification of every radiological source and its confinement barriers; failure of one or several of these barriers may then be presumed and a scenario defined, following a standardized grid; furthermore, the calculations and analysis follow a unique logical scheme to assure consistency and exhaustiveness of the report. Nine accident families have been defined: plasma events, loss of power events, in-vessel events, ex-vessel events, cryostat events, magnet events, maintenance events, tritium plant and fuel events, hot cells events. Calculations with qualified computer codes have shown that the consequences of any postulated accident respect limits defined in the safety guidelines. Moreover, no hypothetical sequence shows any cliff effect, illustrating in this way the robustness of the defence in depth approach used for ITER. It is worth to recall that, in the present status of the ITER project, the only systems subject to the analysis are the tokamak, the tritium plant and the hot cells. © 2005 Elsevier B.V. All rights reserved. Keywords: Preliminary safety report; Accident analysis; Reference events
1. Introduction Safety studies performed for ITER have included extensive analyses of possible off-normal event ∗ Corresponding author. Tel.: +39 06 9400 5820; fax: +39 06 9400 5314. E-mail address: [email protected] (T. Pinna).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.06.030
sequences and of possible potential consequences. Accident analyses are introduced in the “Accident Analysis Guidelines” [1] and “Accident Analysis Specification for GSSR” [2] documents, while the studies are reported in the ITER Generic Site Safety Report (GSSR). Deterministic assessments performed for Reference Events and Ultimate Safety Margins Events are documented in volumes VII [3] and VIII [4],
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T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
respectively; while demonstration that all the possible event initiators and related event sequence scenarios result in consequences that are insignificant or are enveloped by consequences considered deterministically in volumes VII and VIII, is documented in volume X [5]. Such demonstration was done in the manner of probabilistic-like analyses (top-down and bottom-up methods) and was aimed at verifying that (i) the selection of the events studied deterministically is adequate, in so far as they envelope the consequences of all identified events and (ii) every identified event sequence is assessed to ensure that its potential consequences are within the acceptance criteria of the project guidelines. The French Regulator does not assess ITER as a nuclear reactor but as a research facility with radiological and chemical hazards. That imposes for the RPrS the definition and the study of a limited set of incidental and accidental sequences, strictly selected on deterministic grounds, to demonstrate that the acceptance criteria are respected. Therefore, only the GSSR volumes VII and VIII are relevant for the reporting of RPrS volume 2 (i.e. chapter II 2.1, relative to the nuclear risks and dealing with the accidental situations of ITER). Nevertheless, the probabilistic assessments done till July 2001, documented in GSSR, and the assessments performed successively by EFDA Associations will be presented to the French Regulator in an accompanying document to RPrS as background in order to demonstrate the exhaustiveness of the results. Here, in this paper, is reported the methodology used to demonstrate completeness of the set of accidents taken as reference for the RPrS, the parameters considered in the safety assessment and the outcomes of the work in terms of identified radiological hazards. In the present state of the ITER project, the only parts concerned by the analyses are the tokamak building, the tritium plant and the hot cells.
2. Methodology to identify reference events The reference accident scenarios are identified on the basis of the list of radioactive inventories (or source terms) present in the plant and on the basis of confinement barriers dedicated to isolate the inventories from the environment. For each source term the failure of one, or more than one, related confinement barrier has to be postulated. Clearly, the part of the barriers
that could induce, in case of failure, mobilization of radioactive inventories initially confined has to be considered. In defining the reference events, several different kinds of loss of confinement can be identified but to assure that the selected events envelope the overall set of minor events, the most severe failures of confinement barriers have to be considered, typically the ones where the most significant energy sources are involved. For the set of selected reference events to be exhaustive it has to include at least one accident scenario for each source term contained in the plant and, for each accident scenario, the most conservative hypotheses have to be used in defining the parameters needed to study the accident evolutions. Conditions of accident situations are identified with respect to the overall possible states of plant functioning and to their expected likelihood of occurrence: normal operation, incidental situation, accidental situation and hypothetical situation. Normal operation are those plant conditions planned and required for normally operating the plant, including some faults and events, which can occur as a result of the experimental nature of the facility. Incidental situations are not planned but are likely to occur one or more times during the plant life but do not include normal operations. Accidental situations are not likely to occur during the life of the plant but are postulated to assess the safety of the facility. Hypothetical situations are more unlikely to occur than accidental situations and are considered to check sensitivity of the facility in case of postulated extreme accident conditions and to evaluate safety margins.
3. Potential hazards Potential environmental hazards for ITER come from three different sources: - neutronic fluxes, just during plasma operation; - radioactive products, such as tritium, activated materials and dusts, activated corrosion products (ACPs) and activated gas; - chemical materials, toxic and cryogenic ones, such as beryllium, hydrogen, ozone, inert gas, insulator gas, etc.
T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
Risk prevention requires: - confinement of radioactive and toxic materials; - evacuation of decay heat; - limitation of external radiation fields. Thus, safety criteria for ITER can be respected with adequate confinements of source terms and toxic materials able to avoid dispersion of radioactive and toxic materials towards the environment and able to shield radiation fields. Therefore, keeping the prevention of toxic material dispersion in the field of industrial safety and assuming that the design provides enough accuracy in designing appropriate shields to the radiation fields, the safety analyses to be reported to the licensing authority have firstly to demonstrate capability of adopted confinement barriers to avoid the spread of radiological contamination into the environment even in case of accidental situations.
1105
The radiological source terms can be categorized according to their confinements, in order to better identify sources with similar vulnerability to mobilization in an off-normal event: VVST: Tritium and activated products (mainly dusts) enclosed inside the vacuum vessel (VV) and in primary cooling circuits (T and ACPs). TKST: Tritium and activated products enclosed in the tokamak building, outside the VV. TPST: Tritium, mobilized dusts and activated gas in the tritium plant. HCST: Tritium and activated products contained in the hot cells (HC). The different energies involved in the experiment can be the origin of loss of confinement and of mobilization of the radioactive materials listed above, such in case of loss of energy control. Furthermore, some accidental situations can generate
Table 1 Selected reference events Source terms
Event family
Reference events
Inc/Acc
VVST
Plasma events
Loss of plasma control
I–A
VVST
Electric power events
Loss of off-site power for 1 h Loss of off-site power for 32 h Blackout for 1 h
I A A
VVST
In-vessel events
In-vessel First Wall (FW) cooling loop leak (single pipe break) Multiple FW pipe break Loss of vacuum through one VV/cryostat penetration line
I A A
VVST
Ex-vessel events
Loss of divertor (DV) heat sink Pump trip in DV cooling loop Pump seizure in DV cooling loop Heat Exchanger leakage Heat Exchanger tube rupture Large VV coolant pipe break Large DV ex-vessel coolant pipe break
I I A I A A A
VVST
Maintenance events
Air-leakage into VV during maintenance Stuck DV cassette and failure of transfer cask
A A
TKST and VVST
Cryostat events
TKST and VVST
Magnet events
Cryostat air ingress Water and helium ingress into Cryostat Toroidal field coil short Arc near confinement barrier
A A A A
TPST
Tritium plant events
Tritium process line leakage Accident with transport hydride bed Isotope separation system failure Failure of fuelling line
I A A A
HCST
HC events
Loss of confinement in HC
A
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T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
undesired chemical reactions (e.g. hydrogen explosion) that could aggravate mobilization of radioactive release.
Table 2 Rules for accident analysis Category
Parameters
General
Name of event Objectives Scope of analysis Acceptance criteria Parameter studies
Event sequence
Definition of initiating event, location, etc. Possible transient sequences Aggravating failures Loss of power Linkage to source terms
System assumptions
Process systems assumptions Safety systems assumptions
Confinement assumptions
Overpressure mitigation Mobilization assumption Release from the confinement
Analysis methodology
Scope of modelling Possible codes Source of input data
Results
General Main component temperature H2 generation, if any Cooling system conditions Confinement response in terms of containments challenging and environmental radioactive release
Analysis execution
Work sharing and schedule
4. Identified reference events The analysis of the source terms allocated in the various sections of the plant allows to point out nine different families of events in tokamak building, tritium plant and HC, i.e. plasma, electric power, in-vessel, ex-vessel, maintenance, cryostat, magnet, tritium plant and hot cell events. In Table 1 are listed the 6 incidents (I) and 19 accidents (A) identified. Where more than one initiator was expected to induce similar scenarios, in defining the most representative scenarios, the events that most seriously challenge the confinement functions and that involve the highest energy inventories have been considered.
5. Analysis of reference events All the identified events have been studied by the use of computer codes capable of simulating phenomena related to the accidents. All the accidents have been defined and studied according to the rules listed in Table 2.
6. Evaluation of safety margins 7. Results obtained from accident analyses To show the robustness of the “defence in depth” approach used for ITER and to demonstrate that no cliff edge effects occur, hypothetical accident scenarios have been analysed evaluating ultimate safety margins. Hypothetical sequences have been defined by adding to some of the reference accident sequences aggravating failures, which imply the failure of a safety function. The challenges to confinement functions of the most external barriers (i.e. tokamak and tritium buildings) have been studied in some hypothetical accident situations. Hypothetical maximum production of H2 , risk and possible consequences of H2 and dust explosions, and prolonged loss of decay heat removal function have been considered.
The accident analysis studied the 25 reference events listed in Table 1. The conservative calculations performed led to the conclusion that the potential consequences are within the acceptance criteria of the project guidelines. Maximum external releases in terms of doses are summarized in Table 3 for the 19 accidents. Limits of release in accidental situations, as defined in the project guidelines, are also reported in the last line of Table 3. The study of the ultimate safety margins determined that no cliff edge effect appears to happen and that radiological releases remain under the limit of 10 mSv also in case of hypothetical events.
T. Pinna et al. / Fusion Engineering and Design 75–79 (2005) 1103–1107
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Table 3 Environmental releases (in terms of Sv) related to reference accident events Reference events
T (HTO)
AP
ACP
Total dose
Loss of plasma control Loss of off-site power for 32 h Blackout for 1 h Multiple FW pipe break Loss of vacuum through one VV/cryostat penetration line Pump seizure in DV cooling loop Heat exchanger tube rupture Large VV coolant pipe break Large DV ex-vessel cooling pipe break Air-leakage into VV during maintenance Stuck DV cassette and failure of transfer cask Cryostat air ingress Water and helium ingress into cryostat Toroidal field coil short Arc near confinement barrier Accident with transport hydride bed Isotope separation system failure Failure of fuelling line Loss of confinement in HC Project guideline limits
0.026 0 0 0.062 55 0.026 1.8 2.1 150 0.036 11 0 0.0002 0 0 4.5 4.6 17 0.34 10000
0.044 0 0 0.065 26.5 0.044 0 0 3.5 4 1.5 0 0 0 0 0 0 0 35 10000
3.0E-5 0 0 4.2E-6 0 3.3E-4 0.75 5.1 99 0 0 0 5.7 0 0 0 0 0 0 10000
0.07 0 0 0.127 81.5 0.07 2.55 7.2 252.5 ∼4 12.5 0 5.7 0 0 4.5 4.6 17 ∼35 10000
8. Conclusions
References
The application of the above described standardized method, in defining and assessing potential accident sequences, guarantees the homogeneity of the RPrS and gives an exhaustive demonstration of the compliance of ITER with the safety requirements fixed in the design guidelines. Furthermore, results of the calculations are presented in a standardized mode, identifying for each reference event the same items, i.e. nature of the radiological risks, more probable cause of accident, prevention means, survey and detection means, limitation of consequences, sequence of events involved in the accident scenarios, conclusions and remarks.
[1] C. Gordon, et al., Accident Analysis Guidelines for GSSR, G81 RI 4 00-01-27 W0.3, version 3.1, ITER Garching JWS, 21 July 2000. [2] T. Honda, et al., Accident Analysis Specifications for NSSR-2 (AAS-3), G 81 RI 3 00-02-29 W 0.1, version 3.2, ITER Garching JWS, 07 July 2000. [3] GSSR vol. VII (Generic Site Safety Report), G 84 RI 6 01-06-27 R1.0, ITER Garching July 2001. [4] GSSR vol. VIII (Generic Site Safety Report), G 84 RI 7 01-06-27 R1.0, ITER Garching, July 2001. [5] GSSR vol. X (Generic Site Safety Report), G 84 RI 9 01-06-27 R1.0, ITER Garching, July 2001.