Information Notice 1993-45, Degradation of Shutdown Cooling System Performance
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
June 16, 1993
NRC INFORMATION NOTICE 93-45: DEGRADATION OF SHUTDOWN COOLING
SYSTEM PERFORMANCE
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to degradation of shutdown cooling system
performance at the Oyster Creek Nuclear Generating Station resulting from
inadequate operating procedures. It is expected that recipients will review
the information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in
this information notice are not NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances
On January 23, 1993, the Oyster Creek Nuclear Generating Station was in day 57 of the 14R refueling outage. The plant was in a normal cold-shutdown
condition with the primary containment open and the reactor coolant system at
about 43' C [110* F]. One reactor recirculation loop was in service, one
recirculation loop was open, and the remaining three recirculation loops were
either idled or isolated. Two shutdown cooling loops were operating with a
combined flow rate of 11,735 liters per minute 13,100 gpm].
In order to support the planned activities, the licensee elected to secure
operation of all recirculation pumps and lower reactor water level.
This
configuration would allow completion, in parallel, of recirculation pump
maintenance activities and main steam isolation valve local leak rate testing.
When the operators lowered the reactor water level to approximately 419 cm
(165 inches] above the top of active fuel and secured the running.
recirculation pump, the shutdown cooling water took the least resistance path
through the open recirculation loop, and the majority of flow bypassed the
core (see Attachment 1).
During the time that the planned activities were in
progress, plant personnel did not realize that shutdown cooling system
performance was degraded, allowing unmonitored heatup of the reactor core.
On January 25, 1993, after completing the main steam isolation valve local
leak rate testing, an operations engineer discovered that the reactor vessel
metal temperature was about 109C 1228F] at the mid-vessel point.
Several
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IN 93-45 June 16, 1993 Technical Specifications prerequisites for exceeding 100. C [212 F] were not
met, including the requirement to establish primary containment integrity.
After discovery, operators took immediate measures to reduce reactor coolant
system water temperature by first maximizing flow in the two operating
shutdown cooling loops and then placing a third shutdown cooling loop in
service. Additionally, the reactor water level was raised to approximately
508 cm [200 inches] above the top of active fuel and a recirculation pump was
started.
The immediate cause of the event was determined to be plant conditions
established by a temporary procedure change to the shutdown cooling operating
procedure that failed to provide sufficient forced flow through the reactor
core to prevent thermal stratification. The temporary procedure change had
been implemented to allow shutdown operations with all recirculation pumps
secured and the nominal reactor water level less than the level at which
spillover from the core region to the annulus is assured (approximately 470 cm
[185 inches] above the top of active fuel). The change had been developed
from a draft engineering evaluation, but did not include a requirement (stated
in the body of the evaluation) to maintain a specified shutdown cooling flow
of 22,712 liters per minute [6,000 gpm].
Instead, the usual shutdown cooling
flow of about 11,735 liters per minute [3,100 gpm] was maintained which, due
to the specified configuration, allowed the inadvertent reactor heatup.
Further details can be found in Licensee Event Report 50-219/93-002 and NRC
Augmented Inspection Team Inspection Report No. 50-219/93-80.
Discussion
This event at Oyster Creek indicated that the temporary procedure change
represented a significant procedure revision and that the review process did
not identify deficiencies in the procedure before it was implemented. The
temporary procedure change had been developed from a draft engineering
evaluation which concluded that two shutdown cooling loops in operation would
adequately cool the core. An additional assumption in the body of the
evaluation was that each loop of shutdown cooling would be operating at its
design flow rate of 11,356 liters per minute [3,000 gpm], for a total flow
rate of 22,712 liters per minute [6,000 gpm]. This flow rate would be
adequate to induce spillover from the core region to the annulus at the
reduced nominal water level. The temporary procedure change that implemented
the engineering evaluation did not require a minimum flow rate of 22,712 liters per minute [6,000 gpm]. As a result, the operators following the
deficient temporary procedure change placed two shutdown cooling loops in
operation, but did not provide sufficient shutdown cooling water to the
reactor core to maintain reactor vessel temperatures. In addition, the
temporary procedure change contained no provision or guidance for monitoring
available instruments to ensure that decay heat was being adequately removed
from the reactor core.
As part of the licensee corrective actions, the licensee reviewed the
effectiveness of its safety review process concerning temporary changes and
provided training on the subject of this event to all site personnel who
perform technical and safety reviews.
IN 93-45 June 16, 1993 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Offic of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor
Support
Office of Nuclear Reactor Regulation
Technical contacts: James S. Stewart, RI
(215) 337-5240
Peter C. Wen, NRR
(301) 504-2832 Attachments:
1. Figure 1, *Oyster Creek Shutdown Cooling System
Flow With Open Recirculation Loop"
2. List of Recently Issued NRC Information Notices
K. /
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Steam Flow *-
4-
TO Recirculation
~Loop
Shutdown Cooling
System
(3 Cooling Loops)
Figure 1
Attachment 1
1iK 93-45
June 16, 1993 Open Recirculation
Loop
Oyster Creek Shutdown Cooling System Flow With Open Recirculation Loop
I
Attachment 2
June 16, 1993 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
93-44
93-43
93-42
Operational Challenges
During A Dual-Unit
Use of Inappropriate
Lubrication Oils in
Safety-Related Applications
Failure of Anti-Rotation
Keys in Motor-Operated
Valves Manufactured by
Velan
06/15/93
06/10/93
06/09/93
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
93-41
One Hour Fire Endurance
Test Results for Thermal
Ceramics Kaowool, 3M
Company FS-195 and
3M Company Interam E-50
Barrier Systems
05/28/93 All holders
for nuclear
power reactors.
93-40
,93-39
93-38
Fire Endurance Test
Results for Thermal
Ceramics FP-60 Fire
Barrier Material
Radiation Beams from
Power Reactor Biolog- ical Shields
Inadequate Testing of
Engineered Safety
Features Actuation
System
05/26/93
05/25/93
05/24/93
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All holders
for nuclear
power reactors.
93-37 Eyebolts with Indeter- minate Properties In- stalled in Limitorque
Valve Operator Housing
Covers
05/19/93
All holders of OLs or CPs
for nuclear power reactors.
0L - Operating License
CP - Construction Permit
IN 93-45 June 16, 1993 This information notice requires no specific action or written response.
If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Original !1gnd by
Brian K. Gdmeg
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
James S. Stewart, RI
(215) 337-5240
Peter C. Wen, NRR
(301) 504-283],
Attachments: 6
1. Figure 1, "Oyster Creek Shutdown Cooling System
Flow With Open Recirculation Loop'
2. List of Recently Issued NRC Information Notices
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OFFICE
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NAME
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JSStewart
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DATE
04/29/93
05/03/93
03/19/93
03/19/A3
.03/19/93
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DOCUMENT NAME:
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- SEE MEMO FROM M..
HODGES TO B.K. GRIMES
DATED 3/19/93 PM (A. Dromerick), EAB (J. Carter) and AIT
Team Leader (J. Beall) were consulted during
the development of this IN.
IN 93-XX
May xx, 1993 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
James S. Stewart, Region I
(215) 337-5240
Peter C. Wen, NRR
(301) 504-2832 Attachments:
1. Oyster Creek Shutdown Cooling System Flow With Open Recirculation Loop
2. List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFFICE
- OGCB:DORS
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NAME
PCWen/vsb
JSStewart
PKEapen
JPDurr
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DATE
l04/29/93 l05/03/93 I
03/19/93 l 03/19/93 l03/19/93
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DATED 3/19/93 PM (A. Dromerick), EAB (J. Carter) and AIT
Team Leader (J. Beall) were consulted during
the development of this IN.
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IN 93-XX
May xx, 1993 This information notice requires no specific action or written response.
If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
James S. Stewart, Region I
(215) 337-5240
Peter C. Wen, NRR
(301) 504-2832 Attachments:
1.
2.
Oyster Creek Shutdown Cooling System Flow With Open Recirculation Loop
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE .
OFFICE
- OGCB:DORS
DRS:RI
SC:DRS:RI
BC:DRS:RI
D:DRS:RI
NAME
PCWen/vsb 4SStewart
PKEapen
JPDurr
MWHodges
DATE
04/29/93
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IN 93-XX
May xx, 1993
Page 2 of
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
James S. Stewart, Region I
(215) 337-5240
Peter
(301)
C. Wen, NRR
504-2832 Attachments:
1.
2.
Oyster Creek Shutdown Cooling System Flow With Open Recirculation Loop
List of Recently Issued NRC Information Notices
OFFICE OBORS
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