lec09

Operational Reactor Safety

22.091 /22.903

Professor Andrew C. Kadak Professor of the Practice

Safety Systems and Functions Lecture 9

Topics to be Covered

• Fundamentals of Safety

– Introduction to Safety Analysis

– Defense in Depth

– Design Basis Accidents

– Beyond Design Basis Accidents

– S afety Systems

– E mergency Safeguards Systems

– C ontainment

Key Safety Measures

• Prevention

– P roper Design and Training

• Protection

– Monitoring and Control Systems

– Active shutdown and cooling systems

• Mitigation – limit consequences

– Engineered Safety Systems

C alled Defense in Depth Approach

Energy Sources

• Stored Energy in Fuel, Steam and Structures

• Energy from nuclear transients

• Decay Heat

• Chemical Reactions

• External events – s eismic, tornadoes, hurricanes, etc.

Mission - Remove Heat

• Prevent fuel cladding failure or core melting – I nstall systems to do this under many

transient and accident conditions

• If unsuccessful, keep radioactive materials in the containment

– Assure containment function is maintained and not breached by overpressure or missiles

• If unsuccessful, limit releases

• If unsuccessful, implement emergency plan

Design Basis Accidents

• Overcooling

• Undercooling

• Overfilling

• Loss of Flow

• Loss of Coolant

• Reactivity

• Anticipated Transients without Scram

• Spent fuel or handling events

• External Events

Energetic Reactions in Reactors

Courtesy of MIT Press. Used with permission.

Pressurized Water Reactor Schematic

E l e c tr ic Ge n e r a to r

Co n c r e t e a n d S t e e l C o nta inme n t

P r i m a r y S i d e S e c o nd a r y S i de

Pr ima r y Co n c r e t e Sh ie ld

15 .5 M P a

Co n t r o l Rod s

P r e s s u r i z e r

32 4 Þ C

S t e a m to T u r b ine

6. 9 M P a

2 85 Þ C

St e a m Gen e r a t or

Tu r b i n e

Tu r b i n e B y p a s s

Co n d e n ser

- 40 Þ C

- 15 Þ C

Gr id

Re a c to r Co r e

Pr ima r y Ve s s e l

29 2 Þ C

Pr ima r y Co o l a n t P u m p

Hig h - P r e s s u r e H e a t e r s

Fe e d Pump

Co o l i n g To w e r

Lo w - P r es su r e Hea t e r s

Co n d e n s a t e Pu m p

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 8

Specific Design Basis Accidents

• Steam line break

• Loss of Flow

• Loss of heat sink

• Steam generator tube(s) rupture

• Control rod ejection or rapid withdrawal

• Anticipated Transients without Scram

• Pressurized thermal shock

• Loss of coolant

– D ouble ended guillotine break

– Small Break

Typical PWR

Severe Accidents

• Beyond Design Basis

– S uccessive failures of the engineering safety systems

– Looking for cliff edge effects that may need to be addressed if consequences are severe and scenario is plausible.

– Core Melt scenarios - v aporization

• Steam explosion

• Hydrogen explosion

• Fission product inventory for release

Fission Products for Release

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 12

Loss of Coolant Accident Sequence

Prof. Andrew C. Kadak, 2008

Department of Nuclear Science & Engineering

Page 13

Engineered Safety Systems

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 14

PWR Engineered Safety Systems

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 15

PWR Containment

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 16

Containment Pressure Response

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 17

BWR Early Engineered Safety Systems

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 18

Early BWR Containment Design

Prof. Andrew C. Kadak, 2008 Page 19

Department of Nuclear Science & Engineering

Later Version of BWR Containment

Prof. Andrew C. Kadak, 2008 Page 20

Department of Nuclear Science & Engineering

Containment Leakage

• Function of event and chemistry in building

• Driven by containment pressure

• Source terms

– Noble gases – n ot captured

– Elemental iodine – reactive and plated out

– Organic iodides – n ot chemically reactive

– P articulates and aerosols – heavy settle out

• What is not chemically reacted in containment, plated out or settled out is available for release.

Reading and Homework Assignment

1. Read Knief Chapter 13

2. Problems: 13.3, 13.5, 13.8, 13.12 Extra: 13.11

MIT OpenCourseWare http://ocw.mit.edu

22.091 Nuclear Reactor Safety

Spring 200 8

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