ML19308C181
| ML19308C181 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/28/1979 |
| From: | NRC - NRC THREE MILE ISLAND TASK FORCE |
| To: | NRC - NRC THREE MILE ISLAND TASK FORCE |
| References | |
| TASK-TF, TASK-TMR NUDOCS 8001210518 | |
| Download: ML19308C181 (5) | |
Text
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. p.
7.
a.
Times when instruments were oisbelieved by operators 1.
One pressurizer code safety valve tail pipe high temperature alarm with RCOT pressure at 12 psig and increasing should have alerted operator to continuous flow of primary coolant to RCDT.
6 / - f j~
2.
The pressurizer level was generally increasing during the 1-4 minute time frane and this is the indication that controlled operator response. The decreasing primary system pressure was not believed as an indicator of water inventory.
Gi lo, 73 3.
Same as 1 above.
9 f-4.
RCS hot leg tenperature reached saturation with pressure.
//f Should have indicated to operators that voids existed in system.
/20 5.
Reactor building level alarm (10 min. 48 sec.) should have told operator a leak existed in system.
jgg 6.
Increase in RB pressure of about one psi at 14 minutes should have indicated leak.
/Jp 7.
Loop flow indication -- slow reduction in flow from about 2 min.
to 15 min. should have indicated presence of voids, 8.
Intermediate cooling water radiation monitor alarms were believed g c7 to be due to high background radiation levels-61 minutes.
800y810 [/h
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/72 9.
Operators were unable to account for increased reactor building tenperature, should have indicated leak.
/'E$
10.
When loop B RCPs were turned off at 74 minutes, OTSG pressure dropped from 960 psig to 140 psig in 18 minutes.
This should have indicated presence of voids in loop and lack of backflow.
/Ff
- 11. At 81 minutes, operater requests conputer printout of pressurizer relief and safety valve outlet temperatures.
Takes no action based on high temperature readings.
/c/t)
- 12. RCS sanple shows a factor of 10 increase in activity at 90 minutes.
Apparently not attributed to fuel failure even through a crud burst or iodine spike in a "new" plant is very unlikely.
202.
- 13. All radiation monitors exhibiting substantial ranp increase at 100 minutes should have indicated fuel damage.
pgg
- 14. RCS hot and cold leg temperatures diverged widely with the hot leg reaching superheated conditions.
Should have indicated core uncovery to operators (~103 minutes).
Db
- 15. Station manager did not believe direct readings of incore thermo-couples which were reading as high as 2620*F (4-5 hrs.).
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Indication believed to be " noise" or electrical problem and not indicative of real pressure.
Recognition of H2 burning did not occur.
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3 b.
Times when Instrumentation was Inadeauate 3
1.
Instruments in the condensate polisher resin transfer system may have been inadequate in that water was able to enter the compressed air system.
'g 2.
Alarm Printer output for nakeup punp 1A,1B, and 1C status (norm /
trip) found to be reversed due to sof tware error, potentially misleading operators who read printout.
N[1 3.
No emergency feedwater flow indication, operators assumed flow because pumps were running.
Relied upon water hammer noise for flow indication.
b/
4.
Accuracy of pressurizer level instrumentation Because of the nature of the TMI-2 accident, the pressurizer level did not accurately represent the water levels in the RCS. The indications of high pressurzer level apparently misled the operators into believing tnat the RCS was full of water throughout the accident; thus, actions to refill and cool the core were not believed to have been needed.
/70 5.
Conputer storage and printout capabilities The alarm conputer printout located in the control room began experiencing significant backups early in the accident, and was actually out of service for some time period. No permanent storage in the coguter occurs, so that when the printer is out of service, information is lost conpletely. As a result of these problems, the computer apparently was of little value to the operators.
l v
4 6.
Operators misinterpreted SRM count rate increases (more than 2 decades) as a concern for criticality and borated system.
kate increase was apparently due to uncovering of core.
7.
Instrunentation Ranges Various important instruments in the control room had ranges of indication which were quickly exceeded, so that inadequate or misleading information was presented to the operator. RCS hot leg temperature sensors, core exit thernocouples, and nany radiation monitors experienced this problem.
8.
Instrumentation environmental qualification Sone instrumentation which was significant in controlling and understanding this accident experienced environmental conditions beyond their design basis. Pressurizer level sensors were sporadically failing throughout the accident; apparently some Reactor Building radiation monitors also failed.
9.
PORV status instrumentation In the TMI-2 control room, the position of the PORV is indicated by a light.
Since this light actually indicates that the electric power to the valve has been removed, it does not indicate the physical position of the valve. Thus the operators were led to believe by the PORV indicator that the valve had,reclosed when in fact it remained open, causing the loss of RCS coolant.
l I
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'T 5
- 10. No reactor vessel water level indication In all PWRs, water level in the RCS is measured in the pressurizer.
Thus in an accident such as that at TMI-2, wher,. phenomena such 2
as that discussed in 2.3.3 occur, an accurate measure of water level in the vessel and core is not available.
- 11. No remote visual observation equipment No remote visual equipment such as television cameras are installed in the Reactor Building of any PWR; so no visual indication of the status of euipment, etc. was available to the operators in the TMI-2 control room.
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