在日本福島核電廠事故陰影下談核能問題 Fukushima Nuclear Crisis (Cause, Consequence, Lessons, Challenges)

在日本福島核電廠 事故陰影下談核能問題Fukushima Nuclear Crisis(Cause, Consequence, Lessons, Challenges) 锺赐贤 (Philip T. Choong) 北京大学 May 5, 2011 Fuku Crisis

General Introduction 基本核能概念介紹 • What is nuclear energy? Where is it used today? 甚麼是核能?用於何處? • Different types of nuclear reactor around the world. 全球核電廠的類別 • Basic description of LWRnuclear power plant.沸水式以及壓水式核電廠簡 • FukushimaDaiichi Crisis 福島一号核電廠危機 • Troubled Fukushima Daiichi plants. 福島第1核電廠概況 • Sequence of major events at Fukushima Daiichi 福島核電廠危機始末 • What are the contributors to the crisis?事故發生的主因 • What is the latest status? Is the crisis over? 目前最新情況如何? 危機結束了嗎? • Potential impacts on LWR technologies 事故對輕水式反應爐技術的衝擊 • Aftermath of Radiation Leakage from Fukushima plants 福島核電廠幅射物洩漏後果 • Basic knowledge of radiation in biological world 核幅射基本常識以及生物界中的幅射 • Background radiation in daily life 日常生活環境中的幅射 • What people should know about radiation from Fuku crisis? 大眾對福島核電廠幅射物洩漏應有的認識 • Tips to reduce radiation exposure in your body 如何使身體減少接受幅射 • Beef-up Nuclear Power Plants Safety Standards Practice 各國對加強核電廠安全問題的做法 • Would PWR Be More Robust in SBO?在長時間停電下輕水式反應爐安全嗎? • Susceptibility of 台电 NPP to Meltdown台电核电厂堆熔化易感性 • Imposing “Walk-Away Safe” requirement 设立”不必介入”安全條款 • The Necessity of Nuclear Energy 核能的必要性I • Impacts on Energy Independence and Carbon Emissions 能源独立与地球暖化問題 • High-Temperature Pebble-bed Gas-cooled Rectors高溫球床氣冷反應堆 • New opportunities for China飞來橫祸-因祸得福 • Final Words - A Rational and Balanced View 平衡理性的結語 • Q&A (问题和解答) Fuku Crisis

基本核能概念介紹What is nuclear energy? • Radioactive decay energy (alpha, beta, gamma, neutron, etc.) • Nuclear fission • Nuclear fusion Fuku Crisis

Where is nuclear energy used? • Weapons • Electricity production • Submarine and ship propulsion • Medical diagnostics • Food processing • Agriculture • Detectors • Heating, desalination & Many others Fuku Crisis

10 MW PWR Launched in 1954 1950, ANL built and operated the first submarine reactor prototype, the Zero Power Reactor I (ZPR-1) for Westinghouse Electric to fit in 28 feet submarine beam. Fuku Crisis

Shippingport Pressure Vessel Fuku Crisis

Schematics of PWR Power Station Fuku Crisis

About 1/3 of commercial power reactors in USA are of BWR type; ¾ of nuclear power plants in Taiwan are of BWR type including the latest BWR-6 GEN-III type. Fuku Crisis

中国实验快堆- Critical in Spring of 2010 Fuku Crisis

Russian RBMK High Power Channel-type Reactor Fuku Crisis

CANDU Schematics Fuku Crisis

Pebble-Bed High-Temperature ReactorHTR-PM (China) Wu Zongxin, INET, Introduction of HTR-PM Demonstration Project, IAEA Technical Meeting on the Safety of HTGRs, Beijing, October 2007. Fuku Crisis

Fukushima I: Early Generation II Fuku Crisis

BWR Mark I Nuclear Island-3D Fuku Crisis

BWR Mark I Containment During Construction Fuku Crisis

BWR Internals Fuku Crisis

BWR Sub-Channels Fuku Crisis

Mark II BWR ECCS System Fuku Crisis

Distribution of 55 Nuclear Power Plants Fuku Crisis

Fukushima I & II Fuku Crisis

Fukushima Daiichi Nuclear Station • Six BWR units at the Fukushima Nuclear Station: • Unit 1: 439 MWe BWR, 1971 (unit was in operation prior to event) • Unit 2: 760 MWe BWR, 1974 (unit was in operation prior to event) • Unit 3: 760 MWe BWR, 1976 (unit was in operation prior to event) • Unit 4: 760 MWe BWR, 1978 (unit was in outage prior to event) • Unit 5: 760 MWe BWR, 1978 (unit was in outage prior to event) • Unit 6: 1067 MWe BWR, 1979 (unit was in outage prior to event) Unit 1 Fuku Crisis

Status of Fukushima Daiichi Plantas of March 2011 Fuku Crisis

Fukushima I Operating History Fuku Crisis

Fuel Assembly in Fukushima Reactors Fuku Crisis

BWR Mark I Nuclear Island Fuku Crisis

SFP during Refueling Fuku Crisis

Fukushima I Before Big Quake Fuku Crisis

福島一号核電廠危機 Event Initiation • The Fukushima nuclear facilities were damaged in a magnitude 8.9 earthquake on March 11 (Japan time), centered offshore of the Sendai region, which contains the capital Tokyo. • Plant designed for magnitude 8.2 earthquake. An 8.9 magnitude quake is 7 times in greater in magnitude. • Serious secondary effects followed including a significant tsunami, significant aftershocks and a major fire at a fossil fuel installation. Fuku Crisis

Location of Quake Center Fuku Crisis

Many Versions and Interpretations of Events • Tokyo Electric Company • 台湾电力公司 • TSC • Unofficial AREVA • Micro Simulation Technology Fuku Crisis

Summary March 11-15, 2011 Fuku Crisis

Initial Response • Nuclear reactors were shutdown automatically. Within seconds the control rods were inserted into core and nuclear chain reaction stopped. • Cooling systems were placed in operation to remove the residual heat. The residual heat load is decreasing from 6.6% of the heat load under normal operating conditions. • Earthquake resulted in the loss of offsite power which is the normal supply to plant. • Emergency Diesel Generators started and powered station emergency cooling systems. • One hour later, the station was struck by the tsunami. The tsunami was larger than what the plant was designed for. The tsunami took out all multiple sets of the backup Emergency Diesel generators. • Reactor operators were able to utilize emergency battery power to provide power for cooling the core for 8 hours. • Operators followed abnormal operating procedures and emergency operating procedures. Fuku Crisis

Loss of Makeup • Offsite power could not be restored and delays occurred obtaining and connecting portable generators. • After the batteries ran out, residual heat could not be carried away any more.??? • Reactor temperatures increased and water levels in the reactor decreased, eventually uncovering and overheating the core. • Hydrogen was produced from metal-water reactions in the reactor. • Operators vented the reactor to relieve steam pressure - energy (and hydrogen) was released into the primary containment (drywell) causing primary containment temperatures and pressures to increase. • Operators took actions to vent the primary containment to control containment pressure and hydrogen levels. Required to protect the primary containment from failure. • Primary Containment Venting is through a filtered path that travels through duct work in the secondary containment to an elevated release point on the refuel floor (on top of the reactor building). • A hydrogen detonation subsequently occurred while venting the secondary containment. Occurred shortly after and aftershock at the station. Spark likely ignited hydrogen. Fuku Crisis

Misleading Core Damage Sequence This is an incorrect depiction of multi-sub-channel BWR core. Core Uncovered Fuel Overheating Fuel melting - Core Damaged Containment pressurizes. Leakage possible at drywell head Releases of hydrogen into secondary containment Core Damaged but retained in vessel Some portions of core melt into lower RPV head Fuku Crisis

Sequence of major events at Fukushima Daiichi • 福島核電廠危機始末 • Containment Isolation • Closing of all non-safety related Penetrations of the containment • Cuts off Machine hall • If containment isolation succeeds, a large early release of fission products is highly unlikely • Diesel generators start • Emergency Core cooling systems are supplied • Plant is in a stable safe state Fuku Crisis

Fukushima Daiichi Sequence of Major Events-1 • 11.3. 15:41 Tsunami hits the plant • Plant Design for Tsunami height of up to 6.5m • Actual Tsunami height >7m • Flooding of • Diesel Generators and/or • Essential service water building cooling the generators • Station Blackout • Common cause failure of the power supply • Only Batteries are still available • Failure of all but one Emergency core cooling systems Fuku Crisis

Fukushima Daiichi Sequence of Major Events-2 • Reactor Core Isolation Pump still available • Steam from the Reactor drives a Turbine • Steam gets condensed in the Wet-Well • Turbine drives a Pump • Water from the Wet-Well gets pumped in Reactor • Necessary: • Battery power • Temperature in the wet-well must be below 100°C • As there is no heat removal from the building, the Core isolation pump cant work infinitely Fuku Crisis

Fukushima Daiichi Sequence of Major Events-3 • Reactor Isolation pump stops • 11.3. 16:36 in Unit 1 (Batteries empty) • 14.3. 13:25 in Unit 2(Pump failure) • 13.3. 2:44 in Unit 3 (Batteries empty) • Decay Heat produces still steam in Reactor pressure Vessel • Pressure rising • Opening the steam relieve valves • Discharge Steam into the Wet-Well • Descending of the Liquid Level in the Reactor pressure vessel Fuku Crisis

Fukushima Daiichi Sequence of Major Events-4 • Measured, and here referenced Liquid level is the collapsed level. The actual liquid level lies higher due to the steam bubbles in the liquid • ~50% of the core exposed • Cladding temperatures rise, but still no significant core damage • ~2/3 of the core exposed • Cladding temperature exceeds ~900°C • Balooning / Breaking of the cladding • Release of fission products form the fuel rod gaps Fuku Crisis

Fukushima Daiichi Sequence of Major Events-5 • ~3/4 of the core exposed • Cladding exceeds ~1200°C • Zirconium in the cladding starts to burn under Steam atmosphere • Zr + 2H20 ->ZrO2 + 2H2 • Exothermal reaction furtherheats the core • Generation of hydrogen • Unit 1: 300-600kg • Unit 2/3: 300-1000kg • Hydrogen gets pushed via the wet-well, the wet-well vacuum breakers into the dry-well Fuku Crisis

Fukushima Daiichi Sequence of Major Events-6 • at ~1800°C [Unit 1,2,3] • Melting of the Cladding • Melting of the steel structures • at ~2500°C [Block 1,2] • Breaking of the fuel rods • debris bed inside the core • at ~2700°C [Block 1] • Melting of Uranium-Zirconium eutectics • Restoration of the water supply stops accident in all 3 Units???No,No,No. • Unit 1: 12.3. 20:20 (27h w.o. water) • Unit 2: 14.3. 20:33 (7h w.o. water) • Unit 3: 13.3. 9:38 (7h w.o. water) Fuku Crisis

Fukushima Daiichi Sequence of Major Events-7 • Release of fission products during melt down • Xenon, Cesium, Iodine,… • Uranium/Plutonium remain in core • Fission products condensate to airborne Aerosols • Discharge through valves into water of the condensation chamber • Pool scrubbing binds a fraction of Aerosols in the water • Xenon and remaining aerosols enter the Dry-Well • Deposition of aerosols on surfaces further decontaminates air Fuku Crisis

Fukushima Daiichi Sequence of Major Events-8 • Containment • Last barrier between Fission Products and Environment • Wall thickness ~3cm • Design Pressure 4-5bar • Actual pressure up to 8 bars • Normal inert gas filling (Nitrogen) • Hydrogen from core oxidation • Boiling condensation chamber(like a pressure cooker) • Depressurization of the containment • Unit 1: 12.3. 4:00 • Unit 2: 13.3 00:00 • Unit 3: 13.3. 8.41 Fuku Crisis

t Fukushima Daiichi Sequence of Major Events-9 • Positive and negative Aspects of depressurizing the containment • Removes Energy from the Reactor building (only way left) • Reducing the pressure to ~4 bar • Release of small amounts of Aerosols (Iodine, Cesium ~0.1%) • Release of all noble gases • Release of Hydrogen • Gas is released into the reactor service floor • Hydrogen is flammable Fuku Crisis

Fukushima Daiichi Sequence of Major Events-10 • Unit 1 und 3 • Hydrogen burn inside the reactor service floor • Destruction of the steel-frame roof • Reinforced concrete reactor building seems undamaged • Spectacular but minor safety relevant Fuku Crisis

Fukushima Daiichi Sequence of Major Events-11 • Unit 2 • Hydrogen burn inside the reactor building • Probably damage to the condensation chamber(highly contaminated water) • Uncontrolled release of gas from the containment • Release of fission products • Temporal evacuation of the plant • High local dose rates on the plant site due to wreckage hinder further recovery work • No clear information's why Unit 2 behaved differently Fuku Crisis

Fukushima Daiichi Sequence of Major Events-12 • Current status of the Reactors • Core Damage in Unit 1,2, 3 • Building damage due to various burns Unit 1-4 • Reactor pressure vessels flooded in all Units with mobile pumps • At least containment in Unit 1 flooded • Further cooling of the Reactors by releasing steam to the atmosphere • Only small further releases of fission products can be expected ??? Fuku Crisis

The Fukushima Daiichi Incident Radiological releases Fuku Crisis

Fukushima Daiichi After 311 Fuku Crisis

在日本福島核電廠事故陰影下談核能問題 Fukushima Nuclear Crisis (Cause, Consequence, Lessons, Challenges)