L’incidente di Three Miles Island Università di Pisa Facoltà di Ingegneria Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione L’incidente di Three Miles Island Marino Mazzini Professore Ordinario nel s.s.d. “Impianti Nucleari”

DOCUMENTAZIONE PER LA LEZIONE SULL’INCIDENTE DI THREE MILES ISLAND Slides (M. Mazzini) G. Petrangeli: “Nuclear Safety” Elsevier Pub. 2006, reperibile anche su CD “NUCLEAR ENERGY” E-Book Collection

CONTENT Introduction The TMI 2 Nuclear Power Plant Phases of the TMI 2 Accident The Consequences of the TMI 2 Accident: - Reactor Disruption - Radioactivity Releases Immediate and Underlining Causes of the TMI 2 Accident Conclusions

Schematic of TMI 2 NPP

TMI 2 Pressurizer

Top View of TMI 2 Reactor

Trend of the Main Quantities and Events during the first minutes of TMI 2 Accident

Pressure Trend and Main Events during the 1.st phase of TMI 2 Accident min

Level Trend and Main Events during the 1 Level Trend and Main Events during the 1.st Core Degradation of TMI 2 Accident

Water Levels in Primary and Secondary Circuits of TMI 2 NPP at t = 0 s

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 8 Minutes (Liquid Expansion at Increasing T)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 20 Minutes (Cooling-down through SG)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 1Hour (Increase of Voids in Primary Circuit)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 1 Water in Primary and Secondary Circuits of TMI 2 NPP at t = 1.5 Hours (Loop A Operating, Loop B Stagnant)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 2 Hours (All Pumps off. Core Drying and Heating)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 2 Water in Primary and Secondary Circuits of TMI 2 NPP at t = 2.8 Hours (Core Heating Continues)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 3 Water in Primary and Secondary Circuits of TMI 2 NPP at t = 3.2 Hours (Partial Core Quench due to Loop B Restart)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 3 Water in Primary and Secondary Circuits of TMI 2 NPP at t = 3.5 Hours (Vessel Refill by HPI Manual Operation)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 6 Hours (System Pressurization by HPI Operation)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 8 Hours (PC Depressurization and H2 Release in Containment)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 10,3 Hours (PC Pressure Achieves Minimum Value)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 13 Hours (Natural Circulation through SG Blocked by H2)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 15 Hours (PC Repressurization by HPI Intervention)

Water in Primary and Secondary Circuits of TMI 2 NPP at t = 16 Hours (Heat Removal by Forced Circulation in Loop A)

Primary Pressure Trend during TMI 2 Accident h

Core Level during the 1.st Phase of TMI 2 Accident

TMI 2 Accident Core Damage Progression: Time 174 Minutes

TMI 2 Accident Core Damage Progression: Time about 200 Minutes

TMI 2 Accident Core Damage Progression: Time about 225 Minutes

TMI 2 Accident Core Damage Final Configuration

TMI 2 Accident: Estimated Distribution of Core Materials

Inventory of Fission Products in TMI 2 Reactor

Fission Products in PC Water

Fission Products in TMI 2 Containment Atmosphere

Radioactivity Release Paths

Conclusioni L’incidente di TMI 2 è il più grave incidente verificatosi in impianti nucleari LWR. Le cause immediate dell’incidente sono da ascrivere ad un guasto della PORV non rilevato dagli operatori. Le vere cause dell’incidente vanno ricercate nella mancanza di un’adeguata cultura della sicurezza nell’esercente dell’impianto ed anche della NRC: esercizio dell’impianto in condizioni non ammesse, sostanziale assenza di controlli da parte dell’Autorità di sicurezza, inadeguato addestramento del personale, ecc.

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