Information Notice 1993-67, Bursting of High Pressure Coolant Injection Steam Line Rupture Discs Injures Plant Personnel
U
-AU
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
August 16, 1993
BURSTING OF HIGH PRESSURE COOLANT INJECTION
STEAM LINE RUPTURE DISCS INJURES PLANT
PERSONNEL
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 remind addressees of the hazards associated with steam driven
coolant injection systems such as the high pressure coolant injection (HPCI)
system and the reactor core isolation cooling (RCIC) system at BWRs and the
auxiliary feedwater system at PWRs. 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
X
contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Background
The purpose of HPCI steam exhaust rupture discs is to protect the HPCI turbine
casing and associated exhaust piping from an overpressure event if the normal
exhaust path to the suppression pool becomes blocked.
At Quad Cities Station, two 40.6-cm [16-inch] stainless steel discs are installed in series with a
6.4-cm [2.5-inch] spacer between them to allow for a pressure sensor
instrumentation line. The pressure sensor, while serving no control function, actuates an alarm in the control room at 68.9 kPa [10 psig] to alert the
operators that the inner disc is leaking.
The normal range of the HPCI
exhaust steam pressure is 172 to 207 kPa [25 to 30 psig].- The HPCI high
exhaust pressure turbine trip setpoint is 689 kPa [100 psig] and is sensed by
pressure sensors located downstream from where the section of piping
containing the rupture discs branches off from the exhaust piping. The
section of piping containing the rupture discs is mounted vertically over the
turbine exhaust and vents directly to the HPCI room.
Pressure greater than
1034 kPa [150 psig] in the exhaust line will cause the inner disc to rupture
and impact the outer disc, releasing steam into the HPCI room.
Description of Circumstances
During a quarterly inservice test of the HPCI pump at the Commonwealth Edison
Quad Cities Station, Unit 1, on June 9, 1993, the exhaust steam line rupture
9308100248 F
QrRi
IN 93-67 August 16, 1993 discs burst, releasing steam into the HPCI room, burning, and slightly
contaminating, five workers.
The rupture discs burst within one second after
the turbine was started.
Fire doors between the Unit 1 and Unit 2 HPCI rooms
were blown off their hinges into the Unit 2 HPCI room.
Both sets of double
doors that are part of the secondary containment boundary were also blown
open.
The floor latch on the inner containment door was bent; the outer doors
were also slightly damaged, but were repaired, closed and sealed approximately
35 minutes after the event. The steam release was terminated by automatic
isolation of the steam supply line on high HPCI turbine area temperature about
20 seconds into the event.
Discussion
Upon investigating the event, the licensee determined that water had
accumulated in the turbine casing because the drain system level switches for
the Unit 1 HPCI system had failed. In April 1992, the licensee performed a
reliability-centered maintenance study which recommended the level switches be
included in the preventive maintenance program but the recommendation had not
been acted on at the time of the event. The Unit 2 HPCI drain system level
switches were also found to be inoperable.
The slug of water created during the HPCI turbine roll passed from the turbine
casing to the vertical exhaust line and compressed the air in the 40.6 cm
[16 inch] line containing the rupture discs.
The resulting pressure pulse
caused the inner rupture disc to burst, which impacted the outer disc as
designed and caused it to burst as well.
The exhaust line pressure sensors, located in the horizontal 61 cm [24 inch] exhaust line that tees off from the
vertical 40.6 cm [16 inch] rupture disc line, did not detect a high pressure
(see Figure 1).
The pressure switches were within tolerance and should have
immediately isolated the steam supply upon sensing a high exhaust pressure
before the rupture discs burst.
The fact that a high exhaust line pressure
was not detected indicates two possible causes for the disc rupture.
Either
the inner rupture disc was degraded and burst at lower-than-design pressure, or the pressure pulse actually exceeded the design pressure and caused the
disc to burst, relieving the exhaust line pressure before the downstream
pressure sensors detected a high pressure condition.
While inspection of the rupture discs did not reveal any degradation from
corrosion or aging, the vendor, Black Sivalls & Bryson, Inc, stated that the
discs are warranted for one year of service under normal conditions.
The HPCI
and RCIC rupture discs at Quad Cities Station had been in service for 20 years
and were not part of any scheduled inspection or preventive maintenance
program.
When consulted about the event, the vendor advised against using the
spare discs in the plant storeroom because they were purchased at the same
time as the failed discs. The licensee later replaced the failed discs with
new units.
Before this event, the licensee recently replaced a HPCI rupture
disc during a refueling outage at the Dresden Station, a plant similar to Quad
Cities, after finding a crack in the disc during an inspection.
The rupture
discs were inspected at the Dresden station as part of an enhancement to the
preventive maintenance program that was recommended by a reliability-centered
analysis.
I
I
IN 93-67 August 16, 1993 The steam injured five workers, four of whom were participating in the HPCI
pump surveillance test. The fifth, and m6st severely. injured worker was a
health physics technician in the room on routine rounds, who was not aware of
the danger posed by the surveillance test.
The test procedure contained no
specific guidance on room occupancy.
Interviews with the workers revealed
that they had performed the surveillance in the past and were familiar with
the process.
This familiarity may have led to a relaxed attitude toward
personal safety.
The workers stated that during previous surveillances they
sometimes evacuated the room before rolling the turbine, or stood near the
doors to be ready to escape. The licensee made no routine announcement over
the plant paging system to alert plant personnel before the HPCI-turbine
start, and the workers were not prepared for the turbine to start.
A lack of constant communication between the workersand the control room may
have contributed to the personnel injuries. If a control room operator had
been in contact with the workers in the HPCI room during the turbine roll, the
workers would have been aware of the impending turbine start and, after start, the steam supply might have been manually-isolated or the turbine manually
tripped before the automatic isolation caused by the high area temperatureoin
the HPCI room.
When the Unit 1 HPCI rupture disc failure caused the fire doors to be blown
off their hinges and into the Unit 2 HPCI room, one of the doors impacted a
pipe hanger in the room and moved it 5.1 centimeters [2 inches].
If the steam
release had resulted from a high energy line break from the inlet side of the
HPCI steam line instead of the exhaust line, the damage to the Unit 2 HPCI
system could have been more severe.
While high energy line breaks have been
analyzed for safety systems at all plants, the doors to rooms containing high
energy steam lines may not have been included in the analysis.
For example, at Duane Arnold Energy Center, the licensee discovered that while the HPCI and
RCIC rooms were qualified for pressures of 26.2 kPa [3.8 psig], the doors
between these rooms and the reactor building would yield at 6.9 kPa [1 psig].
The licensee for the Quad Cities Station will implement a preventive
maintenance schedule for both the HPCI and RCIC rupture discs and the level
switches. The licensee will review the surveillance test procedure and
evaluate the missile hazard created by the fire doors. The licensee replaced
the rupture discs for the Unit 2 HPCI and RCIC systems with new ones after the
event at Unit 1 and is considering burst testing the removed discs to
determine if they are degraded.
IN 93-67 August 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
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Brian K. Grim s, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
Clark Vanderniet, RIII
(708) 790-5594
David Skeen, NRR
(301) 504-1174 Attachments:
1. Figure 1, "Simplified Layout of Quad Cities
Station HPCI Turbine Exhaust Steam Line"
2. List of Recently Issued NRC Information Notices
Cq~
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SUPPRESSION
POOL
1 OUTER RUPTURE DISC
_____
CLOSABLE
CHECK
VALVE
I
INNER RUPTURE DISC
[1 In]
2
40.6 cm
[16 in]
VENT TO
HPCI ROOM
STEAM INLET LINE
FROM "B" MAIN
STEAM LINE
LOCKED
OPEN
I
I
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I
RX BLDG
I
I
I
I
50.8 cm
[20 In]
61 cm
[24 In]
HPCI ROOM
25 cm
[10 In]
D
NOTES:
1. PRESSURE SWITCH ACTUATES ALARM IN CONTROL ROOM WHEN PRESSURE BETWEEN THE INNER RUPTURE DISC AND OUTER
RUPTURE DISC IS GREATER THAN 68.9 kPa [10 psig]. ALARM IS FOR INNER RUPTURE DISC LEAK DETECTION.
2. REDUNDANT PRESSURE SWITCHES IN EXHAUST STEAM LINE TRIP THE HPCI TURBINE IF PRESSURE IS GREATER THAN 689 kPa [100 psig].
3. RUPTURE DISC MAXIMUM DESIGN BURST PRESSURE IS 1034 kPa [150 psig].
Figure 1 - Simplified Layout of Quad Cities Station HPCI Turbine Exhaust Steam Line
Attachment 2
August 16, 1993 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
93-66
93-65
93-64
93-63
93-62
93-61
93-60
93-59
93-58 Switchover to Hot-Leg
Injection Following
A Loss-of-Coolant
Accident in Pres- surized Water Reactors
Reactor Trips Caused
by Breaker Testing
with Fault Protection
Bypassed
Periodic Testing and
Preventive Maintenance
of Molded Case Circuit
Breakers
Improper Use of Soluble
Weld Purge Dam Material
Thermal Stratification
of Water in BWR Reactor
Vessels
Excessive Reactor Coolant
Leakage Following A Seal
Failure in A Reactor
Coolant Pump or Reactor
Recirculation Pump
Reporting Fuel Cycle and
Materials Events to the
NRC Operations Center
Unexpected Opening of
Both Doors in An
Airlock
Nonconservatism in Low-
Temperature Overpressure
Protection for Pressurized-
Water Reactors
08/16/93
08/13/93-
08/12/93
08/11/93
08/10/93
08/09/93
08/04/93
07/26/93
07/26/93
All holders of OLs or CPs
for pressurized water
reactors.
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.
All holders of OLs or CPs
for boiling water reactors.
All holders of OLs or CPs
for nuclear power reactors.
All fuel cycle and materials
licensees.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for pressurized-water
reactors.
OL = Operating License
CP = Construction Permit
l
IN 93-67 August 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
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
orig /s/'d by CIGrimes/for
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
Clark Vanderniet, RIII
(708) 790-5594
David Skeen, NRR
(301) 504-1174 Attachments:
1. Figure 1, "Simplified Layout of Quad Cities
Station HPCI Turbine Exhaust Steam Line"
2. List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE.
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[OFFICIAL RECORD COPY]
DOCUMENT NAME: 93-67.IN
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IN 93-XX
July 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
the technical contact 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: Clark Vanderniet, RIII
(708) 790-5594 David
(301)
Skeen, NRR
504-1174 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE.
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[OFFICIAL RECORD COPY]
DOCUMENT NAME: IN93 XX.QC1
IN 93-XX
July 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:
Clark Vanderniet, R-III
(708) 790-5594 David Skeen, NRR
(301) 504-1174 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFFICE *OEAB:DORS
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July 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:
Clark
(708)
Vanderniet, R-III
790-5594
David Skeen, NRR
(301) 504-1174 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFFICE
- OEAB:DORS
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Brian K. Grimes, Director
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you have any questions about the information in this notice, please contact
the technical contact 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:
Clark
(708)
Vanderniet, R-III
790-5594
David Skeen, NRR
(301) 504-1174 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
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