Top Banner
Operational Reactor Safety 22.091/22.903 Professor Andrew C. Kadak Professor of the Practice Lecture 19 Three Mile Island Accident
33

Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

Apr 03, 2018

Download

Documents

phamngoc
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

Operational Reactor Safety22.091/22.903

Professor Andrew C. KadakProfessor of the Practice

Lecture 19 Three Mile Island Accident

Page 2: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

3

Pilot operated relief valve

Feedwater line

Primary system

Secondary System

Emergency Cooling Pump

PressurizerFigures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 3: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

4Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 4: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

5

Davis Besse Event: September 24, 1977 - 9:24 PM

Power Level 9%Transient initiated - Loss of “feedwater” to steam generatorTemperature increased in reactorWater level in pressurizer increasedPilot Operated Relief Valve (PORV) openedPORV did not close but stuck openReactor Automatically ShutdownEmergency Feedwater pumps automatically startedPrimary coolant system cooled and shrunk

Page 5: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

6

Pilot operated relief valve

Feedwater line

Primary system

Secondary System

Emergency Cooling Pump

Pressurizer

.Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license.For more information, see http://ocw.mit.edu/fairuse.

Page 6: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

7

Event Sequence Continued

Primary circuit pressure dropped rapidlyCoolant leakage out of PORVCoolant shrinkage (cooldown)

Emergency Core Cooling System (ECCS) automatically starts to provide more waterOperators monitoring water level in pressurizer which was changing until with ECCS water level became normal.Operators shutdown ECCS cooling water systemHowever PORV still open - “small break loss of coolant accident”

Page 7: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

8

Event Sequence Continued

Since PORV was open - pressure kept dropping reaching “saturation pressure” of coolant which allowed the water to boil - forming steam voids which caused the pressurizer water level to rise.22 Minutes later, operators determined that there was a continuing primary coolant leak and closed the block valve downstream of the pressurizer.Operators then restored cooling water by ECCS and water make up system of reactor and returned reactor to normal shutdown condition.

Page 8: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

9

Consequences

Core damage accident avoided by timely operator action.NRC, Babcock and Wilcox and the utility investigated the incidentNeither NRC nor the nuclear steam supplier - B&W shared this information with other B&W plants or the rest of the industry.1975 Rasmussen (MIT Prof) Report analyzed probabilistic risks (PRA) of nuclear plants

Conclusion - small break LOCAs are dominant accident contributorsNRC and critics did not want to use PRA is safety determinations

Page 9: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

10

18 MONTHS LATER

March 28, 1979

Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 10: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

11

Three Mile IslandWhat Happened and Why ?

Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 11: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

12

What Is Three Mile Island ?

TMI is a two unit nuclear plant site in Middletown, PennsylvaniaUnit 1- 792 Mwe: Unit 2 - 880 MweBabcock & Wilcox Designed PWR2 Steam Generators - once through4 Main Coolant PumpsCondensers cooled by Cooling Towers

Page 12: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

13

Pilot operated relief valve

Feedwater line

Primary system

Secondary System

Emergency Cooling Pump

PressurizerFigures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license.For more information, see http://ocw.mit.edu/fairuse.

Page 13: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

14

Steam Generators

B&W Once Through Steam Generator Recirculating U Tube Steam GeneratorCourtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 14: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

15

Reactor Shutdown Signals

OverpowerHigh Temperature OutletHigh PressureReactor Building PressureLow PressurePower imbalance/flowReactor Coolant PumpsARTS - anticipatory reactor trip system (not at TMI) - for feedwater and turbine trip for Integrated Control

System)

Page 15: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

16

Precursors

TMI Unit 2 - Newest Unit on SiteSmall coolant leak in the pressurizer relief valve raises temperature downstream of valve which drains into the drain tankOperators unaware that two valves on emergency feedwater valves were closed following maintenance (were supposed to be open).Small blockage in a transfer line for demineralizerresins which could not be cleared.

Page 16: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

17

Initiation

Plant operating normally at 97% power4:00:37 (AM) loss of condensate flow due to a condensate pump trip (shutdown).

Page 17: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

18

Key Sequence of Events

Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 18: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

19Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 19: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

20Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 20: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

21Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 21: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

22Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 22: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

23Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 23: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

24

Bubble Trouble

Hydrogen Production Due to zirconium water reaction

Oxygen generation due toRadiolysisBoiling

Possible explosive mixture ?Why or why not ?Why missed in analysis ?

Was reactor vessel in danger of exploding ?What was missing in the approach ?NRC - Industry

Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 24: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

25Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license.For more information, see http://ocw.mit.edu/fairuse.

Page 25: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

26

Inside TMI Reactor Vessel Post AccidentCourtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 26: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

27

1979

TodayCourtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 27: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

28

Public Health and Environmental Consequences

Studies by EPA, Health and Human Services, DOE, NRC and the State of PennsylvaniaThousands of environmental samplesConclusions

Average dose to 2 million people in area < 1 mremMax dose at site boundary full time - 100 mremNatural background in area - 100-125 mrem/yr1 Chest x-ray - 6 millirem

No adverse Health Effects

Page 28: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

29

Lessons Learned (Good)

Water helps even if core is severely damagedVessel did not fail even with molten core in the bottomNo energetic steam explosionMost fission products contained insideContainments work

Page 29: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

30

Lessons Learned (not so good)

Inadequate operator training - formed INPOInstrumentation needs upgrading - did itAdded Safety Parameter Display SystemAdded new instrumentation

Reactor Water Level Post Accident Sampling System

Added Shift Technical Advisor to all shiftsEmergency planning needed upgrading - doneFocused attention on severe accident researchNeed new operator emergency response procedures - critical safety functions - doneRisk focus should not be on Large Break LOCA but more likely eventsUse of Probabilistic Risk Analysis to understand safety of plants not just depend on regulations

Page 30: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

31

Courtesy of Three Mile Island Nuclear Power Station. Used with permission.

Page 31: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

32

Bottom Lines

Precursors are important indicators of problems -need to be addressed not ignoredIndustry Complacency is a risk.Attention to detail and understanding how plants work is vitalOn-line risk monitors very helpful in gauging plant statusKnowledgeable and well trained staff and engineers very importantManagement and Safety Culture hugely important to safe operations.

Page 32: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

33

Homework

Read Rogovin Report Executive SummaryAnalyze event from the perspective of why the accident happened and why it became a such serious problem. (Beyond the obvious of failing to recognize the open PORV). Given your experience in the simulators (recall that the simulator you were in did not represent control rooms of the 1970’s).

Consider operator trainingRegulationsTechnical responseKnowledge Control room Design and instrumentationFundamental design of reactorManagement culture

Read Steam Generator Report for background on designs

3 pages of analysis (11 font - 1.5 line spacing).

Page 33: Operational Reactor Safety - MIT OpenCourseWare · Operational Reactor Safety ... Babcock & Wilcox Designed PWR 2 Steam Generators - once through ... Oxygen generation due to

MIT OpenCourseWarehttp://ocw.mit.edu

22.091 Nuclear Reactor SafetySpring 2008

For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.