Information Notice 1995-10, Potential for Loss of Automatic Engineered Safety Features Actuation
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 3, 1995 NRC INFORMATION NOTICE 95-10:
POTENTIAL FOR LOSS OF AUTOMATIC ENGINEERED
SAFETY FEATURES ACTUATION
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
PurDose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential for loss of the automatic
actuation function of engineered safety features (ESF) as a result of
electrical faults in some non-class 1E input signals. 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 February 2, 1995, the licensee for the Diablo Canyon facility reported to
the NRC a condition that could result in the failure of one train of their
solid state protection system (SSPS) during a main steamline break in the
turbine building (10 CFR 50.72 report number 28318). The licensee postulated
a break of a main steamline at the turbine stop valve in the turbine building.
If the steamline breaks completely, it is free to rotate approximately 10
degrees. The 10-degree rotation of the steamline could result in the steam
jet from the faulted steamline striking an electrical Junction box. The
Junction box contains terminations for non-safety input signals to the SSPS,
turbine stop valve position indication (four circuits, two circuits for each
train).
The force of the steam jet impinging on the Junction box is postulated to
destroy the box and result in electrical faults in the affected non-safety
inputs to the SSPS. The high current resulting from the electrical faults
would cause 15-ampere fuses to open, interrupting 120-V ac power supply to the
faulted circuits. Since dc power supplies for SSPS logic and ESF train
actuation relays are supplied by the same 15-ampere fuses, opening of the
fuses would also interrupt power to the SSPS logic channels and possibly one
ESF train actuation relay bank. This would render one SSPS train inoperable.
If a single failure of the other SSPS train is considered, as is required in
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February 3, 1995 the high energy line break analysis methodology, both trains of the SSPS would
be rendered inoperable and no ESF actuations would be automatically available
to mitigate the consequences of the steamline break. The reactor trip
circuitry would be de-energized resulting in a reactor trip. Manual action
could be initiated to operate individual pieces of equipment.
NRC inspectors determined that other non-class IE circuits that provide input
to the SSPS were not properly isolated. These circuits include turbine auto
stop oil (three circuits), seismic trip (constructed to class lE standard),
12-kV undervoltage, 12-kV underfrequency, and reactor coolant pump breaker
position indication.
An electrical fault in any of these circuits could cause
loss of power to SSPS logic circuit in the same way described above.
Although a single main steamline break would likely render only one SSPS train
inoperable, either train could be rendered inoperable depending upon the
location of the steamline break. The licensee declared the ESF portion of the
solid state protection system inoperable and entered Technical Specification 3.3.2 for inoperable ESF instrumentation and then Technical Specification 3.0.3 limiting condition for operation to start shutdown of both units within
1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
On February 1, 1995, the licensee for the Salem facility notified the NRC that
it had been determined that the design of the SSPS at its facility was similar
to that at the Diablo Canyon facility (10 CFR 50.72 report number 28321). The
Salem licensee concluded that a main steamline break could have the same
effect on non-class 1E circuits as that postulated at the Diablo Canyon
facility. In addition, the licensee concluded that a seismic event could
challenge both trains of SSPS since both junction boxes associated with both
trains of SSPS are located in the turbine building (the Diablo Canyon licensee
is continuing to evaluate seismic and other vulnerabilities of these non-class
IE circuits). The circuits that are potentially affected at Salem include
turbine stop valve position indication, auto-stop oil pressure switches, and
reactor coolant pump breaker position indication. The circuit faults
initiated by the steamline break or seismic event could result in loss of
power to SSPS logic circuitry similar to that postulated by the Diablo Canyon
licensee. The resulting impact would be either a partial or total loss of the
automatic actuation function of the SSPS. The reactor trip circuitry would be
de-energized, resulting in a reactor trip. Manual action would be required to
mitigate the consequences of a main steamline break event. The licensee
declared the SSPS inoperable and began a shutdown of Unit I as required by
Technical Specifications.
(Unit 2 was already shut down.)
Discussion
The licensees are undertaking similar corrective actions. The electrical
supply to the SSPS dc power supplies will be taken from a point electrically
upstream of the 15-ampere fuse referred to above.
This modification will
ensure that opening of the fuse, because of faults in the non-class IE
circuits, does not cause a loss of power to the class IE dc power supplies.
Figure 1 is a one-line diagram illustrating the as-found condition of a single
channel of the SSPS at Diablo Canyon. Two out of four channels are
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February 3, 1995 potentially affected in SSPS Train A and two out of four channels are
potentially affected in SSPS Train B.
The Diablo Canyon licensee plan for repairs includes drafting a formal
modification procedure, curtailing work near the vulnerable junction boxes, deferring train-related maintenance and surveillance during the modificatidn
period, maintaining constant power level, testing the procedure on a mock-up, de-energizing one channel at a time while modifying that channel (the reactor
trip bypass breaker will be closed during the modification), training
operators on safety considerations during the repairs, and postmodification
testing. The licensee estimated that the increase in core damage frequency
during the repair period would be less than 2E-7.
(The Salem licensee repair
plan was not available when this information notice was prepared.)
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 Project Support
Office of Nuclear Reactor Regulation
Technical contacts: E. Nick Fields, NRR
(301) 415-1173
Cliff Doutt, NRR
(301) 415-2847 Attachments:
1. Figure 1
2. List of Recently Issued NRC Information Notices
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KPtachment 2
February 3, 1995 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
95-09
95-08
95-07
95-06
Use of Inappropriate
Guidelines and Criteria
for Nuclear Piping and
Pipe Support Evaluation
and Design
Inaccurate Data Obtained
with Clamp-On Ultrasonic
Flow Measurement Instruments
Radiopharmaceutical Vial
Breakage during Preparation
Potential Blockage of
Safety-Related Strainers
by Material Brought Inside
Containment
01/31/95
01/30/95
01/27/95
01/25/95
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All USNRC medical licensees
authorized to use byproduct
material for diagnostic
procedures.
All holders of OLs or CPs
for nuclear power reactors.
95-05
95-04
Undervoltage Protection
Relay Settings Out of
Tolerance Due to Test
Equipment Harmonics
Excessive Cooldown and
Depressurization of the
Reactor Coolant System
Following a Loss of
Offsite Power
01/20/95
01/19/95 All holders
Permits for
reactors.
All holders
for nuclear
of Construction
nuclear power
power reactors.
95-03
Loss of Reactor Coolant
Inventory and Potential
Loss of Emergency Mitiga- tion Functions While in
a Shutdown Condition
01/18/95
All holders of Ols or CPs
for nuclear power reactors.
OL = Operating License
CP - Construction Permit
February 3, 1995 potentially affected in SSPS Train A and two out of four channels are
potentially affected in SSPS Train B.
The Diablo Canyon licensee plan for repairs includes drafting a formal
modification procedure, curtailing work near the vulnerable Junction boxes, deferring train-related maintenance and surveillance during the modification
period, maintaining constant power level, testing the procedure on a mock-up, de-energizing one channel at a time while modifying that channel (the reactor
trip bypass breaker will be closed during the modification), training
operators on safety considerations during the repairs, and postmodification
testing. The licensee estimated that the increase in core damage frequency
during the repair period would be less than 2E-7.
(The Salem licensee repair
plan was not available when this information notice was prepared.)
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 Project Support
Office of Nuclear Reactor Regulation
Technical contacts:
E. Nick Fields, NRR
(301) 415-1173
Cliff Doutt, NRR
(301) 415-2847 Attachments:
1. Figure 1
2. List of Recently Issued NRC Information Notices
DOCUMENT NAME: 95-10.IN
- See
revious concurrence
OFC
OECB:DOPS
SC/OECB:DOPS
PUB:ADM
C/OECB:DOPS
NAME
NFields*
EGoodwin*
Tech Ed*
AChaffee*
DATE
02/03/95
02/03/95
02/03/95
02/03/95 OFC
HICB:DRCH
C/HICB:DRCH
D/DRCH
NAME
CDoutt4'
JWermiel
o
BBoger+
___________
DATE
02/03/95
02/03/95
02/03/95
02/ 3!/95
OFFICIAL RECORD COPY
IN 95-XX
February xx, 1995 potentially affected in SSPS Train A and two out of four channels are
potentially affected in SSPS Train B.
The Diablo Canyon licensee plan for repairs includes drafting a formal
modification procedure, curtailing work near the vulnerable junction boxes, deferring train-related maintenance and surveillance during the modification
period, maintaining constant power level, testing the procedure on a mock-up, de-energizing one channel at a time while modifying that channel (the reactor
trip bypass breaker will be closed during the modification), training
operators on safety considerations during the repairs, and postmodification
testing.
The licensee estimated that the increase in core damage frequency
during the repair period would be less than 2E-7.
(The Salem licensee repair
plan was not available when this information notice was prepared.)
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 Project Support
Office of Nuclear Reactor Regulation
Technical contacts: Nick Fields, NRR
(301) 415-1173
Cliff Doutt, NRR
(301) 415-2847 Attachment:
1. Figure 1
2. Figure 2
3. List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\OECB\\DIABLO1.IN
See previous concurrence
OFC
OECB:DOPS
SC/OECB:DOPS
PUB:ADM
C/OECB:DOPS
NAME
NFields*
EGoodwin*
Tech Ed*
AChaffee*
DATE
/
/95
/
/95
02/03/95
/ /95 OFC
HICB:DRCH
D DDRQH
D/DRCH
D/DOPS
NAME
CDoutt
BBoger
BGrimes
DATE
93
5
/ 3 /95
/ /95
IN 95-XX
February xx, 1995 potentially
cted in SSPS Train A and two out of four channels are
potentially af
ed in SSPS Train B. Figure 2 illustrates the proposed
design change, i
ing replacing the 15-ampere fuse with an 8-ampere fuse to
ensure proper coor
ion of circuit protective devices. (The Salem design
change employs a diff
t 'ujse size)
The Diablo Canyon license
lans for repairs include drafting a formal
modification procedure, cur
ing work near the vulnerable panels, deferring
train-related maintenance and s -veillance during the modification period, maintaining constant power level, esting the procedure on a mock-up, de- energizing one channel at a time wh e modifying that channel (the reactor
trip bypass breaker will be closed du ng the modification), training of
operators on safety considerations durn
the repairs, and post-modification
testing. The licensee estimated that the ncrease in core damage frequency
during the period of repair would be less t n 2E-7.
(The Salem licensee's
repair plans were not available when this inf mation notice was prepared).
This information notice requires no specific act
or written response. If
you have any questions about the information in thi notice, please contact
one of the technical contacts listed below or the app
iate Office of
Nuclear Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Project Support
Office of Nuclear Reactor Regulation
Technical contacts:
Nick Fields, NRR
(301) 415-1173
Cliff Doutt, NRR
(301) 415-2847 Attachments:
1. Figure 1
2. Figure 2
3. List of Recently Issued NRC Information Notices
DOCUMENT NAME:
G:\\OECB\\DIABL01.IN
- See previous concurrence
OFC
lOECB:DOPS
lSC/OECB:DO$
l PUB:ADM
l C/OECB:DOPS
l
NAME
NFields
EGoodwin D
Tech Ed*
AC& &e
DATE
2 /f
1
9
/95 i3 902/03/95
/3 /95 OFC
HICB:DRCH
C/HICB:DRCH
D/DRCH
D/DOPS
NAME
CDoutt
JWermiel
BBoger
BGrimes
DATEl //95
/
/95
/
95
/_ /95 OFFICIAL RECORD COPY