ML17320A645
| ML17320A645 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah, Cook, 05000000 |
| Issue date: | 07/11/1983 |
| From: | Zukor D NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML17320A643 | List: |
| References | |
| TASK-AE, TASK-E316 AEOD-E316, NUDOCS 8307290377 | |
| Download: ML17320A645 (8) | |
Text
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AEOD ENGINEERING EVALUATION REPORT EE REPORT NO.
AEOD E
DATE: July 11, EVALUATOR/CONTACT:
D. Zukor EVENT DATES:
Many UNIT:
Sequoyah 1/2 and D.
C.
Cook 1/2 DOCKET NO.:
327/328.and 315/316 LICENSEE:
TVA and Indiana and Michigan Electric NSSS/AE:
Westinghou'se/TVA and Westinghouse/AEPSC
SUBJECT:
FROZEN ICE CONDENSER INTERMEDIATE DECK DOORS
SUMMARY
The ice condenser system is a passive system designed to limit the peak pressure spike in containment following a LOCA.
To function properly all inlet and,outlet doors must open, when required to allow steam to pass through the ice condenser.
There have been a number of failures at Cook and Sequoyah involving:the intermedi ate deck doors freezing shut.
This does not appear to be a safety concern unless large numbers of doors fail; Improved surveillance and maintenance procedures have effectively prevented
~ large numbers of failures.
Isolated individual door failures'o not appear to jeopardize the ability of the ice condenser to perform its safety function.
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DISCUSSION The Ice Condenser System is designed to be a totally passive system.
It
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provides a means of absorbing the. energy released to the containment following a Reactor Coolant System or steam pipe break.
The ice condenses the steam thereby reducing the maximum containment pressure.
An isometric. of the ice
'ondenser system is shown in Figure 1.
When the pressure across the lower inlet doors exceeds 1 psfd, these doors open, directing steam up through the ice baskets and out through the intermediate deck doors, the top deck
- doors, and ultimately into'he upper containment.
The'intermediate deck doors are immediately above the intermediate deck'.
The top deck doors are not shown on the figure.
During,normal operation, the air handling units (AHU) and air distribution ducts direct cool air around the ice baskets to keep the ice from melting.
The. intermedi ate deck doors form.the ceiling of the ice-bed region and the floor of the upper plenum.
They also act as a walking surface which is used for maintenance of the AHU's, and inspection of the ice bed.
There are 192 intermediate deck doors.
Only three plants are currently equipped with ice condenser containments:
Sequoyhh 1 and 2, Cook 1
and 2 and McGuire 1
and 2.
FINDINGS
,The following events 'have. been reported. involving freezing of the intermediate
. deck doors at Sequoyah and Cook;: McGuire has reported no events where the intermediate deck doors froze shut.
Sequoyah:
Unit Date 10/16/80 LER 80-170 EVENT
.Two intermediate deck doors were found frozen closed due to failure of heat tape on AHU drain.
12/16/80 80-203 Leaking AHU drain line flange cause door under AHU 3A to freeze closed.
12/29/80 80-205 Ice in the defrost drain line caused two intermediate deck doors to freeze shut below AHU '3A on two occasions.
1/9/81.
1/16/81 81-002 81-008 Loose flange bolts caused AHU 3A defrost drain line to leak into two intermediate deck doors freezing them shut.
Due to a fuse failure in one section of the heat tape con-troller, water froze in the drain lines of'three AHUs-6A, 8A, and 8B causing the lines to rupture.
Three intermediate deck doors were found frozen closed.
4 AIR.HANDLING UNIT CRANE INTERKED I ATE OECX ICE BASXET I
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LOWER INLET DOORS LOWER SUPPORT STRUCTURE figure X..
psomegyjc Of tc Conciensel Unit 1
Date 6/29/81 LER 81-073 EVENT Ice condenser intermediate deck doors were frosted.
Damaged tape seals on the upper deck doors allowed moisture to dri p from the upper deck doors onto the intermediate deck doors.
8/22/81 81-105 AHU condensate drain pan heater mat failed permitting the drain pan to ice over and allow water to spill into the Bay 14 intermediate deck doors.
The door was iced over.
1/3/82 4/26/82 82-001 82-052 Condensate on I-Beams under top deck doors dripped into
.intermediate deck door 9B freezing it shut..
AHU 9B drain,pan apparently installed out of level allowed ice to build up and ultimately caused intermediate deck doors below it to freeze closed.
5/28/82 82-065 A leaking drain line from AHU 3A caused one ice condenser intermediate deck door to freeze shut.
6/9/82.
82-.07) 7 A broken solder joint in an AHU drain line allowed water to spill onto one intermediate deck door and freeze it shut.
7/6/82 82-093 Failure of heat tape allowed water to freeze in AHU 12A causing the line to rupture.
Three intermediate deck doors were found frozen closed.
3/24/83 83-049 Leaks in condensate drain lines. of AHU 13 and 14.allowed water to drip down onto an intermediate deck door in bay ll and freeze it shut.
D. C.
Cook:
Unit Date LER EVENT 7/.5/79 79-034 Two ice condenser intermediate doors could not be opened because of ice buildup around the doors caused by water leak-age from an AHU.
7/9/79 79-036 Two intermediate deck doors were found to be frozen shut.
The cause of the ice buildup could not be determined.
8/31/79 9/17/79 045 One intermediate deck door frozen shut.
Six intermediate doors frozen'hut.
Prior to each event (8/31/79 and 9/17/79) the ice bed temperature was decreasing and this in combination with the high summer humidity, caused condensation.
11/16/79
'/22/,80 060 80-010 A plugged AHU drain line caused drainage to overflow and spill into 'the door.
The door below the AHU then froze shut.
Eight intermediate deck doors were found frozen shut.
Top deck door divider beam con-densation was the source of the water.
8/17/80 80-021 Two intermediate deck doors were found frozen.
The source of the moisture was condensate off of the Top deck door divider beams.
9/17/80 7/29/81 80-024 81-038.
Twenty-one intermediate deck doors were found frozen due to moisture condensing on the top deck door divider beam.
A design change was begun which would insulate the beams to prevent condensation.
Surveillance was increased from three times weekly to daily.
One intermediate deck door. was found frozen shut.
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Unit Date 8/10/81 LER EVENT Another interme'diate deck door was found frozen shut; Both events (7/29/81 and 8/10/81) were attributed to a broken AHU drain line.
12/23/82 82-109 also 83-002 A plugged drain line in an AHU caused one intermediate deck door to freeze shut..
12/30/82 82-110 also 83-001 One intermediate deck door found frozen shut.
No cause could be found.
The only instances where a large number of doors failed occurred at Cook l.
Following the 9/17/80 event the top deck door divider beams were insulated which effectively eliminated further problems with-'many doors, failing simultaneously.
In all other cases only one or two doors froze shut, usually due to some problem wi th the AHU above it.
Analysis and full-scale testing have shown that the doors could take 1405 of the maximum pressure load -predicted to occur during a LOCA.
This indicates
. that about 50 doors need to freeze shut before the operating doors may be damaged by the pressure load.
One must also consider the effect of steam channeling of the ice when large numbers of doors fail.
This occurs when there are insufficient inlets or outlets for'the steam flow through the, ice baskets.
In this case, the steam carves a direct path through the ice and adequate condensation does not occur and adequate pressure suppression does not take
'lace.
Although the technical specifi cations require that all doors be operational, it seems unlikely that steam channeling would occur following a LOCA unless many adjacent doors failed simultaneously.
No analysis could be found giving the number of doors which would have to fail before the ice.
condenser could not adequately condense the steam from a.LOCA.
CONCLUSIONS Since there have been no significant multiple failures': at either Cook or Sequoyah recently, it appears that improved maintenance and surveillance have solved most of the freezing problems.
It should also be noted that most of the problems occurred when the plants were fairly new and that all incidents of this type decreased after the plant had been in operation a few years.
The problem of a few-isolated cases of frozen intermediate deck doors will persist because of the atmospheric conditions in containment which promote condensation onto any surface; however, this does not appear to jeopardize
'he ability of the ice condenser unit to perform its safety function.
AEOD plans no further action on this issue.