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Safety Implications of the Fukushima Nuclear Accident Sheldon L. Trubatch, Ph.D., J.D. Vice-Chairman Arizona Section American Nuclear Society.

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Presentation on theme: "Safety Implications of the Fukushima Nuclear Accident Sheldon L. Trubatch, Ph.D., J.D. Vice-Chairman Arizona Section American Nuclear Society."— Presentation transcript:

1 Safety Implications of the Fukushima Nuclear Accident Sheldon L. Trubatch, Ph.D., J.D. Vice-Chairman Arizona Section American Nuclear Society

2 Overview What happened at Fukushima Why Fukushima can’t happen here – Differences between Fukushima and U.S. plants – Differences between Japanese and U.S. regulation Why Fukushima can’t happen at Palo Verde – Differences between Fukushima and Palo Verde – What we learned from Three Mile Island-Unit 2 – What we learned from Chernobyl

3 Fukushima Before Earthquake Units 1-4 on left Units 5-6 on right

4 Fukushima Accident Causes Earthquake magnitude 9.0 Richter scale – Plant designed to withstand magnitude 8.6 based on historical earthquake record back to 1600 most powerful recorded earthquake (since 1800) Tsunami wave height more than 14 meters – Plant on meter high cliff protected by 6 meter high wall for maximum probable tsunami 5.7 meters high based on 1960 Chilean tsunami historical maximum 8 meters

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6 Earthquake Damage

7 Tsunami Wall of Water

8 Tsunami Breaching Sea Wall

9 Tsunami Coming Onshore

10 Tsunami Hits the Plant

11 Inundation Level

12 Fukushima Station Blackout D/G = Diesel Generator ECCS = Emergency Core Cooling System

13 Fukushima Accident Details Earthquake disabled offsite power Tsunami disabled onsite emergency diesels, batteries, and switchgear for external power Station blackout led to loss of reactor cooling and generation of steam and hydrogen Unit 1:100% of molten core fell out bottom of steel vessel and sank 2 feet into concrete floor Hydrogen exploded in Units 1-4

14 Mark I Boiling Water Reactor (BWR)

15 Meltdown Phase 1

16 Meltdown Phase 2

17 Hydrogen Generation Frame 1 shows Hydrogen starting to bubble into the torus and containment Frame 2 shows Hydrogen starting to collect in the reactor vessel Frame 3 shows Hydrogen escaping from the vessel and collecting in the secondary containment building Frame 4 shows Hydrogen in the secondary containment building reaching the density needed for exploding

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19 Hydrogen Explosion

20 Secondary Containment Damage

21 Destruction Overview

22 No Fukushima Danger to U.S. Mark I BWRs None sited in comparable high risk area All designed for maximum likely natural events All subject to intense U.S. NRC oversight – U.S. Nuclear Regulatory Commission (NRC) only regulates, unlike in Japan, where regulator also promotes nuclear power – Resident inspectors on site all the time Operators subject to oversight by Institute for Nuclear Power Operation (INPO) Safety culture deeply ingrained

23 Mark I Site Properties No Mark I is in a high earthquake zone – All plants designed for maximum likely earthquake 6 Mark I’s subject to only river flooding – Cooper, Duane Arnold, Ft. Calhoun, H.B. Robinson, Quad Cities, Wolf Creek – All plants designed for maximum flood and have emergency power protected from flood

24 Fukushima Differs from Palo Verde Palo Verde a Pressurized Water Reactor (PWR) – Large dry, robust containment unlike Mark I BWR No secondary containment where Hydrogen can accumulate Three Mile Island-2 accident shows hydrogen explosion completely contained inside robust containment building – Spent fuel in either separate robust pool building or in dry casks away from reactor – Emergency power diesels in robust buildings Palo Verde not subject to extreme natural events – Site in low magnitude earthquake area – Tsunami clearly not an issue in the desert Water in ultimate heat sink can’t submerge any part of plant

25 Palo Verde Large Dry Containment

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32 Palo Verde in the Desert

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34 Palo Verde Water Use

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37 Tight Security at Palo Verde

38 Why Palo Verde NOT Fukushima

39 Why TMI-2 Accident not Fukushima Hydrogen explosion completely contained – No damage breached large dry containment – No radiation escaped due to accident Core melt only partial – No breach of pressure vessel by molten core – No radioactive materials escaped into containment NRC and state government quickly responded – NRC effectively involved in accident management

40 Three Mile Island

41 TMI is a Large Dry Containment

42 Melted TMI Core Post-Accident

43 TMI After Accident

44 Why Chernobyl Accident not Fukushima Caused by bad design and operator errors – Not result of inadequate design for natural event Operator experiment after low power operation – Also little time to prepare for experiment Experiment conducted at midnight – Operators’ mistakes caused massive power spike Procedures violated to complete test on time – Soviets lacked effective safety culture

45 Chernobyl RBMK4 Destroyed

46 Chernobyl Design Issues No containment as with Western reactors RBMK uses graphite which burns Each fuel rod in a separate tube – Accident assumed not to rupture more than one – Several ruptured initially at accident start Backup diesels took too long to reach full power Low power operation causes power instability

47 Chernobyl Post-Accident Schematic

48 Conclusion Fukushima event can’t happen in Arizona No comparable earthquake/tsunami risk Much more robust, different plant design Ingrained safety culture at U.S. plants Extensive training in accident management Effective regulation by NRC and operational oversight by INPO


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