ML11216A245

0523 - R504P - Westinghouse Advanced Technology - 07.4 - Core Damaging Events

ML11216A245
Person / Time
Site:	Three Mile Island
Issue date:	12/02/2008
From:	NRC/HR/ADHRTD/RTTB-PWR
To:
References
Download: ML11216A245 (20)

Text

Core Damaging Events Objectives

1. State how the following parameters respond to a stuck-open pilot-operated relief valve (PORV) following a reactor trip from 100% power:

• PORV tail-pipe temperature

• Reactor coolant system pressure

• Pressurizer level

• Reactor vessel level 2

Objectives

2. State the significance of superheated conditions in the reactor coolant system.

3. State the key operator errors that contributed to core damage during the Three Mile Island

((TMI)) accident.

4. Describe the event that initiated the core damage sequence at TMI.

5. Discuss industry and regulatory changes that resulted from the accident at TMI.

6. Describe the differences in technology that make U.S. commercial reactors not susceptible to an event similar to the Chernobyl accident.

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Core Damaging Events

• Three Mile Island Accident

• Chernobyl Accident 4

RCDT TO PZR MAIN SG "B" SG "A" STEAM FROM FEEDWATER OUTSIDE RCPs RCPs REACTOR BWST CFT CFT LETDOWN CCW HEAT EXCHANGER REACTOR SCW BUILDING AUXILIARY BUILDING ION DHR EXCHANGERS SCW FILTER HPI AND MAKEUP MAKEUP TANK PUMPS

Accident Contributors

• Equipment failure

• Poor design

• Personnnel error 6

Equipment Failure

• PORV failed to close as required 7

Poor Design

• PORV position indication

• Poor human factors

• No reactor vessel level indication 8

Personnel Error

• Failed to isolate the open PORV

• Reduced R d d makeup k flflow iin response to PZR level 9

Common Sense vs. Uncommon Sense

• Pressurizer level

• PORV tail pipe temperature 10

Plant Response to Open PORV 11

12 Industry and Regulatory Response to TMI accident

• INPO

• Operator training and examination

• EOPs

• E-Plan

• NUREG-0737, Clarification of TMI Action Plan Requirements 13

Chernobyl Accident 14

15 RBMK-1000

• Graphite moderated

• Boiling water reactor

• Positive void coefficient (water is a poison)

• Total power coefficient usually negative 16

Transient

• Partial loss of flow (test) with positive power coefficient

• Voiding causes prompt criticality

• Two T power peaks k - 11,000%

11 000% and d 47,000% of RTP

• Core becomes a large burning crater

• 30 individual fires where graphite was spewed 17

Why this accident is not possible at U.S. reactors.

• Graphite moderation (moderation continues when coolant leaves)

• Positive void coefficient

• No N containment t i tb building ildi 18

Objectives

1. State how the following parameters respond to a stuck-open pilot-operated relief valve (PORV) following a reactor trip from 100% power:

• PORV tail-pipe temperature

• Reactor coolant system pressure

• Pressurizer level

• Reactor vessel level 19

Objectives

2. State the significance of superheated conditions in the reactor coolant system.

3. State the key operator errors that contributed to core damage during the Three Mile Island

((TMI)) accident.

4. Describe the event that initiated the core damage sequence at TMI.

5. Discuss industry and regulatory changes that resulted from the accident at TMI.

6. Describe the differences in technology that make U.S. commercial reactors not susceptible to an event similar to the Chernobyl accident.

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