Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Design Basis Accidents (DBA) M. T. Porfiri – ENEA UTFUS-TECN (Frascati)

Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015

Design Basis Accidents (DBA)

M. T. Porfiri – ENEA UTFUS-TECN (Frascati)

Seminar – Safety in Nuclear Fusion Plants

La Sapienza University Rome – 24 April 2015


Outline

Safety Analysis “Course”: Deterministic Assessment

DBA: definition

General Safety Objectives: ITER case

Project Environmental Release Guidelines: ITER case

DBAs: ITER case

Release fraction in incidents: ITER case

Release fraction in accidents: ITER case

Example: LOCA in Divertor cooling loop

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Glossary

ACP Activated Corrosion ProductsDBA Design Basis AccidentDCF Dose Conversion FactorDV DivertorEPR European Pressurized ReactorEST Environmental Source TermFW First WallFMEA Failure Mode and Effects AnalysisISS Isotope Separation SystemITER International Tokamak Experimental ReactorHTS Heat Transfer SystemHX Heat ExchangeLOOP Loss Of Offsite PowerPFC Plasma Facing ComponentPIE Postulated Initiating EventPST Process Source TermTF Toroidal FieldVV Vacuum Vessel

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(Courtesy of S. Ciattaglia)

Safety Analysis “Course”: Deterministic Assessment

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SOURCE

TERMS ASSESSMENT

Normal working conditions Occupational dose

IEAS

Thermodynamic transients Aerosols and H3 transport

Containments Release from the plant DCF

Overall Plant AnalysisFFMEA

Radioactive waste Operational&Decomm wasteIdentification&classification

Management•On-site•Recycling•Final disosal

Effluents

PST

PST EST

DCF

man*Sv/y

dose/sequence to MEI

frequency*dose

Quantity and waste categories

mSv/y

SOURCE

TERMS

Normal working conditions Occupational dose

PIE Thermodynamic transients

Aerosols and H3 transport

Confinements Release from the plant DCF

Overall Plant Safety AnalysisFMEA

Radioactive waste Operational&Decomm waste

Identification&classification

Management• On site• Recycling• Final disposal

Effluents

PST

PST EST

DCF

person*Sv/y

dose/sequence to Public

frequency*dose

Quantity and waste categories

mSv/y


DBA: definition

A Design Basis Accident is a postulated accident that a nuclear facility must be designed and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety [NRC].

They are classified as incidents and

accidents, according to the frequency of occurrency.

The methodologies to be used for the DBAs analysis must be conservative. That means they use pessimistic or worst-case assumptions and models. Most of the analyses presented to regulatory bodies follow this approach.

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ITER case

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Central Solenoid

Outer Intercoil Structure

Toroidal Field Coils

Poloidal Field Coils

Machine GravitySupports

Blanket Modules

Vacuum Vessel

Cryostat

Port Plug (Radiofrequency Heating)

Divertor

TorusCryopump


General Safety Objectives: ITER caseGeneral safety objectives

For personnel For the public and environment

Situations in design basis

Normalsituations

ALARA, and in any case less than:Maximum individual dose

≤ 10 mSv/yrAverage individual dose

≤ 2.5 mSv/yrCollective annual dose ≤ 500 mSv*p/yr

Releases less than the limits authorised for the installation,Impact as low as reasonably achievable and in any case less than:

≤ 0.1 mSv/yr

Incidental situations

As low as reasonably achievable and in any case less than:

10 mSv per incident

Release per incident less than the annual limits authorised for the installation.

[i.e. 0.1 mSv per incident]

Accidental situations

Take into account the constraints related to the management of the accident and post-accident situation

No immediate or deferred counter-measures (confinement, evacuation)

< 10 mSvNo restriction of consumption of animal or vegetable products

Situations beyond design basis

Hypothetical accidents

No cliff-edge effect; possible counter-measures limited in time and space

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Project Environmental Release Guidelines: ITER case

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DBAs: ITER case (1)

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DBAs: ITER case (2)

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Release fraction in incidents: ITER case

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Margins against Project Environmental Release Guidelines for Reference Events.

Sum of Tritium, Activated Dust and Activation Corrosion Product Releases


Release fraction in accidents: ITER case

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Margins against Project Environmental Release Guidelines for Reference Events.

Sum of Tritium, Activated Dust and Activation Corrosion Product Releases


Example: LOCA in Divertor cooling loop (1)

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- The accident postulated is a double ended pipe rupture in a large diameter pipe, at the pump inlet of the DV (divertor)/LIM (limiter) primary coolant loop.

- The coolant leak pressurises the vault. - The Fusion Power Shutdown System

(FPSS) will stop plasma burn in three seconds .

- This results in a plasma disruption that delivers 0.4 GJ of energy to the DV.

- The high stress conditions of the divertor plates are postulated to result in an in-vessel leak for a break on the DV/LIM HTS loop.

- The DV/LIM HTS coolant in-leakage pressurises the VV and, when VV pressure exceeds 110 kPa, the bleed lines to VVPSS and to drain tank open.

- In the mean time, the vault is pressurised and a high vault atmosphere pressure signal (the set point is at 105 kPa) triggers the isolation of the vault.

- When the VV pressure exceeds 150 kPa the rupture disks open towards the Vacuum Vessel Suppression System.



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0.E+0

1.E+5

2.E+5

1 100 10000

time [s]

Pres

sure

[Pa

]

VVTCWS

Post accident Hydrogen production

0.0

0.1

0.2

0.3

0 100 200 300

time [s]

Mas

s [k

g]

The chemical reactions between the steam and the PFC protective materials produce an amount of H2 far from the explosion risk (4kg).

Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 15/15

Mobilised Inventory Release path, transport of inventory

Releaseamount

Totalrelease

Tritium TCWS vault >> environment (before vault isolation)

4.1*10-7g-T Tritium:controlled release 4.1*10-7 g-Tuncontrolled 6.5*10-2 g-Ttotal release 6.5*10-2 g-T Dust:uncontrolled 1.7*10-2 gtotal release 1.7*10-2 g ACP:controlled release 1.7*10-7 guncontrolled 0.27 gtotal release 0.27 g

TCWS vault >> environment (after vault isolation)

6.5*10-2 g-T

Dust TCWS vault >> environment (before vault isolation)

No release


17 mg

ACP TCWS vault >> environment (before vault isolation)

1.7 *10-7 g


270 mg


Documents

Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Design Basis Accidents (DBA) M. T. Porfiri – ENEA UTFUS-TECN (Frascati)