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)

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Core Damaging Events Objectives1.State how the following parameters respond to a stuck-open pilot-operated relief valve (PORV) following a reactor tripfrom100%power:

2 trip from 100% power:*PORV tail-pipe temperature*Reactor coolant system pressure

• Pressurizer level

• Reactor vessel level Objectives2.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.

3 ()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.

Core Damaging Events*Three Mile Island Accident 4*Chernobyl Accident BWSTOUTSIDESG"B"SG"A"CFTCFTRCPsPZRRCDT TOMAINSTEAMFROMFEEDWATERLETDOWNHEATEXCHANGERCCWRCPsREACTORHPIANDMAKEUPPUMPSMAKEUPTANKFILTERIONEXCHANGERSSCWDHRSCWREACTORBUILDINGAUXILIARYBUILDING Accident Contributors*Equipment failure *Poor design 6*Personnnel error Equipment Failure*PORV failed to close as required 7 Poor Design*PORV position indication *Poor human factors 8*No reactor vessel level indication Personnel Error*Failed to isolate the open PORVRddkfli 9*R e d uce d ma k eup fl ow i n response to PZR level 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 13*E-Plan

• NUREG-0737, "Clarification of TMI Action Plan Requirements" Chernobyl Accident 14 15 RBMK-1000*Graphite moderated*Boiling water reactor

• Positivevoidcoefficient(water 16*Positive void coefficient (water is a poison)*Total power coefficient usually negative Transient*Partial loss of flow (test) with positive power coefficient*Voiding causes prompt criticality Tk11000%d 17*Two power pea k s -11 , 000% an d 47,000% of RTP*Core becomes a large burning crater

• 30 individual fires where graphite was spewed Why this accident is not possible at U.S. reactors.*Graphite moderation (moderation continues when coolant leaves)*Positive void coefficientNtitbildi 18*N o con t a i nmen t b u ildi ng Objectives1.State how the following parameters respond to a stuck-open pilot-operated relief valve (PORV) following a reactor tripfrom100%power:

19 trip from 100% power:*PORV tail-pipe temperature*Reactor coolant system pressure

• Pressurizer level

• Reactor vessel level Objectives2.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.

20 ()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.