ML11216A245
| ML11216A245 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| 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:
2 trip from 100% power:
PORV tail-pipe temperature Reactor coolant system pressure Pressurizer level Reactor vessel level
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.
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
BWST OUTSIDE SG "B" SG "A" CFT CFT RCPs PZR RCDT TO MAIN STEAM FROM FEEDWATER LETDOWN HEAT EXCHANGER CCW RCPs REACTOR HPI AND MAKEUP PUMPS MAKEUP TANK FILTER ION EXCHANGERS SCW DHR SCW REACTOR BUILDING AUXILIARY BUILDING
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 PORV R d d
k fl i
9
- Reduced makeup flow in 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
- Operator training and examination
- EOPs 13
- NUREG-0737, Clarification of TMI Action Plan Requirements
Chernobyl Accident 14
15
RBMK-1000
- Graphite moderated
- Boiling water reactor
- Positive void coefficient (water 16
- Positive void coefficient (water is a poison)
- Total power coefficient usually negative
- Partial loss of flow (test) with positive power coefficient
- Voiding causes prompt criticality T
k 11 000%
d 17
- Two power peaks - 11,000% and 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 coefficient N
t i t b ildi 18
- No containment building
Objectives
- 1. State how the following parameters respond to a stuck-open pilot-operated relief valve (PORV) following a reactor trip from 100% power:
19 trip from 100% power:
PORV tail-pipe temperature Reactor coolant system pressure Pressurizer level Reactor vessel level
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.
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.