Information Notice 1989-67, Loss of Residual Heat Removal Caused by Accumulator Nitrogen Injection
-
.
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 13, 1989
NRC INFORMATION NOTICE NO. 89-67: LOSS OF RESIDUAL HEAT REMOVAL CAUSED
.:BY
ACCUMULATOR NITROGEN INJECTION
Addressees
'.:
-
All holders of operating licenses or construction permits forLpre~surized water
reactors (PWRs).
Purpose
.
'. .
.
This information notice is intended to alert addressees to potential problems
resulting from the loss of residual heat removal (RHR) cauied'by the injection
of nitrogen from an accumulator.into the reactor coolantisystemi (RCS). It is
expected that recipients will review the information f6r applicability to'their
facilities and consider actions, as appropriate,'to'avoid'tsimilai problems.
However, suggestions contained in thislinformation notice do' not constitute
NRC requirements; therefore:,-no specific'action or written response is required.
Description of Circumstances
Salem Unit 1 lost both RHR pumps for about 50 minutes'6n:May 20, 1989, as a
result of an injection of nitrogen from an accumulator into the RCS'and, sub- sequently, into the:RHR system. This injection'occurred while the licensee
was conducting full-flow testing of the accumulator check yalves' The reactor
was in Mode 5 (cold shutdown) after-a recent refueling with the reactor.head
installed. .The RCS was filled to a cold calibrated pressurizer level of
10 percent withiair contained;in.the reactor vessel 'head and in'the steam
generator U-tubes. All accumulators were filled to normal operating level
and were pressurized to approximately 600 psig.
At.9:25 a.m., while performing a post-maintenance full-flow test of the check
valves for accumulator 13, the accumulator isolttion valve remained open'for
about 70 seconds as a result of an operator error. During this time, approxi- mately 1800 cubic feet of nitrogen at about 62 psig entered the RCS. As the
nitrogen expanded into the RCS, the pressurizer level went off-scale high, and
the reactor pressure rose from 14 psig to about 51 psig. The operator, not
realizing that nitrogen had been injected-into the RCS, initiated pressurizer
level ,restoration by draining the RCS to the refueling water storage tank
(RWST). At 9:35 a.m., the operator observed zero RHR flow and a reduction
of the pump motor current from 44 amps to about 21 amps.
K
890907004)
A
r
IN 89-67 September 13, 1989 The operator, assuming that the pump was'mechanfically damaged, secured the pump
and started the second RHR pump, When this pump exhibited the same character- istics as the other pump, the operator real'zed that the pumps were gas bound
and started venting the RHR system.
Venting was slow because of the size of
the vent lines and .an RHR. system qonfiguration that allowed air entrapment.
Operators also had dIfficulty-in locating one vent and drain valve; when it
was located,-an-installed cap had to be removed.
Slow venting continued until
10:18 a.m. when the operators initiated filling of the RHR system, using gravity
feed from the RWST. At this time, the core exit temperature had increased to.
1221F from a pre-event value of 920F. At 10:23 a.m., the RHR system was filled, and RHR pump 11 was successfully started.
At 10:37 a.m.,.RHR pump 12 was placed
in'service, and RHR pump 11 was secured to'return the system to normal operation.
Because of an inadequate abnormal operating procedure and emergency classifi- cation guide, a 10 CFR 50.72 report for this loss of RHR pumps was not made.
until May 22, 1989.
Discussion:
<
i
An assessment of this loss-of-RHR-pump event at S'alem'Unit I identified the
folloWing'concernis' '
.'
Uni 1 i
the
1. 'IThe operators appeaied to believe that nitrogen i~njection lntQ the RCS
'-
was not possible'dui-ng the full-flow test of'the accumulator check valves.
This mindset caused the operators to drain the RCS when the pressurizer
level kept increasing due to the expansion of tnj'ected.nitrogen.'
2.
The abnormal operat'in" procedures and the memrge'ncy classification guide
did not adequately address the potentiay' for loss of RHR cooling.
The
symptom-oriented procedures did not address the reactor parameters during
a loss of shutdown cooling while in Modes 5 and 6..'Consequently, the
event was nbot r'eporteddfmmediitely under 10 CFR 50.72.
3.
The operators were not adequqte ly trained, to differenitiate gas binding of
- theRHR pumps from methanical damage'.
Thi s caused the operators to.start
RHR pump 11 when they erroneously' concluded that RHR pump 1Z was mechani- cally damaged.
.
4. Elevation differences
-f'
the RHR suction pipe, the difficulty in locating
one vent and drain' vialve;aid the $ize'of the vent lines caused'the venting
I:opdration to be extrenely-slow. Iaddition, complete system yenting was
not possible because
"as was trapped in the high pointsfof the RHR system.
5. .:The appropriateness oif performing-a full-flow test of the accumulator
check valves with fuel in the reactor vessel had not been fully assessed.
An event similar to the one described in this information notice would.
not occur to this extent if this test'had been conducted while the core
was off-loaded.
Furthermore, if this test had been performed with either
reduced accumulator nitrogen pressure or with the reactor vessel head
removed, the effects of nitrogen injection into the RCS would have been
minimized.
IN 89-67 September 13, 1989 Ituis important to note that if the accumulator check valve full-flow tests had
been conductedlwhen'they.are more commonly performed, during the shutdown prior
to refueling, and an event similar to the one described in this information
notice had occurred, the consequences could have been much'more significant.
It is also important to'note that operator training provided in response to
NRC Generic Letter 88-17, "Loss of Decay Heat Removal," did assist the operators
in restoring the RHR system once gas binding of the system was recognized.
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 NRR project manager.
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Daniel Prochnow, NRR
(301.) 492-1166 Warren Lyon, NRR'
-
-
.. (301) 492-0891
.
Attachment: List of Recently Issued NRC Information'Notices
-
.
.'_... .. _.
..
ih aunt
Septesber 13, 1989
Page 1 of I
LIST Of RECENTLY ISSUED
XRC INFORMATION NOTICES
Itotice No
89-66
88-41*
Supp. 4
89-65
89-64
89-63
89-62
89-61 s8-48, Supp. 2 SubJect
Qualification Life of
Licensee Report of
Defective Refurbished
Circuit Breakers
Potential for Stress
Corrosion Cracking in
Steen Generator Tube
Plugs Supplied by
Babcock and Wilcox
Electrical Bus Bar Failures
u.Lw or"
issuance
9/11/89
9/11/83
9/8/89
9/7/89 Issued to
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLE
or CPs for PURs.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLE
or CPs for nuclear
pcwer reactors.
Possible Subaurgence of
9/1/89
Electrical Circuits Located
Above the Flood Level Because
of Water Intrusion and Lack
of Drainage
Malfunction of Borg-Warner
8/31/89
Pressure Seal Bonnet Check
Valves Caused By Vertical.
Misalignment of Disk
Failure of Borg-Warner Gate
8/30/89 valves to Close Against
Differential Pressure
Licensee Report of Defective 8/22/89
Refurbished Valves
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLE
or CPs for nuclear
power reactor.
All NRC Medical
T ii1verag-ticense
89-60
Maintenance of Teletherapy
__
_
-
Unit
8/18/89
_t
eas
- Operating License
- Construction Permit
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE. $300
FRT CLASS MAI
POSTAGE
- FEES PAID
USNRAC
PERMIT No. 0- w
IN 89-67 September 13, 1989 It is important to note that if the accumulator check valve full-flow tests had
been conducted when they are more commonly performed, during the shutdown prior
to refueling, and an event similar to the one described in this information
notice had occurred, the consequences could have been much more significant.
It is also important to note that operator training provided in response to
NRC Generic Letter 88-17, "Loss of Decay Heat Removal," did assist the operators
in restoring the RHR system once gas binding of the system was recognized.
This information notice requires
you have any questions about the
of the technical contacts listed
no specific action or written response. If
information in this notice, please contact one
below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Daniel Prochnow, NRR
(301) 492-1166
Warren Lyon, NRR
(301) 492-0891 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
- OGCB:DOEA:NRR*SRXB:DEST:NRR
DProchnow
WLyon
8/16/89
8/16/89
9/f/89
- C/SRXB:DEST:NRR
MHodges
8/18/89
- C/OGCB:DOEA:NRI
CHBerlinger
9/6/89
- SAD/DEST:NRR
AThadani
8/20/89 I *RPB:ARM
TechEd
9/01/89
- D/DEST:NRR
JRichardson
8/20/89
.:
I.
'a
IN 89-xx
September xx, 1989 It is important to note that if the accumulator check valve full-flow tests had
been conducted when they are more commonly performed, during the shutdown prior
to fuel refueling, and an event similar to the one described in this informa- tion notice had occurred, the consequences could have been much more signifi- cant. It is also important to note that operator training provided in response
to NRC Generic Letter 88-17, "Loss of Decay Heat Removal," did assist the
operators in restoring the RHR system once gas binding of the system was
recognized.
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 contacts listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Daniel Prochnow, NRR
(301) 492-1166
Warren Lyon, NRR
(301) 492-0891 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
- OGCB:DOEA:NRR*SRXB:DEST:NRR
DProchnow
WLyon
8/16/89
8/16/89 D/DOEA:NRR
CERosSi
9/
/89
- C/SRXB:DEST:NRR
MHodges
8/18/89 C/OGC
- RPB:ARM
CHBerlin etI
TechEd
9/ /89
9/01/89
- SAt/DEST:NRR
- D/DEST:NRR
AThadani
JRichardson
8/20/89
8/20/89
IN 89-xx
August xx, 1989 It is also important to note that this event indicated that operator training
provided in response to NRC Generic Letter 88-17 (Loss of Decay Heat Removal)
did assist the operators in restoring the RHR system once gas binding of the
system was recognized.
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 NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Daniel Prochnow, NRR
(301) 492-1166
Warren Lyon, NRR
(301) 492-0891 Attachment:
List of Recently Issued NRC Information Notices
OGCB:DOEA:NRR
DProchnow
8/i1 /89 VSRPM:ARM
Tech Ed
X1 1/89 RXB:DEST:NRR
W8/o/8
8/Y6/89 C:S DEST: NRR
MHod es
8/l1F/89 -
SAD:DEST:NRR
AThadani
8/ V4/89 f
DEST:NRR
'Richardson
8/2A /89 C:OGCB:DOEA:NRR
CHBerlinger
8/
/89 D:DOEA:NRR
CERossi
8/
/89