Information Notice 1993-27, Level Instrumentation Inaccuracies Observed During Normal Plant Depressurization: Difference between revisions
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
||
| Line 3: | Line 3: | ||
| issue date = 04/08/1993 | | issue date = 04/08/1993 | ||
| title = Level Instrumentation Inaccuracies Observed During Normal Plant Depressurization | | title = Level Instrumentation Inaccuracies Observed During Normal Plant Depressurization | ||
| author name = Grimes B | | author name = Grimes B | ||
| author affiliation = NRC/NRR | | author affiliation = NRC/NRR | ||
| addressee name = | | addressee name = | ||
Revision as of 05:24, 14 July 2019
UNITED STATES NUCLEAR REGULATORY
COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 April 8, 1993 NRC INFORMATION
NOTICE 93-27: LEVEL INSTRUMENTATION
INACCURACIES
OBSERVED DURING NORMAL PLANT DEPRESSURIZATION
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 inaccuracies
in reactor vessel level indication
that occurred during a normal depressurization
of the reactor coolant system at the Washington
Nuclear Plant Unit 2 (WNP-2) and to the fact that errors in level indication
may result in a failure to automatically
isolate the residual heat removal (RHR) system under certain conditions.
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.Background
As discussed
in NRC Information
Notice 92-54, "Level Instrumentation
Inaccuracies
Caused by Rapid Depressurization," and Generic Letter 92-04,"Resolution
of the Issues Related to Reactor Vessel Water Level Instrumentation
in BWRs Pursuant to 10 CFR 50.54(f)," noncondensible
gas may become dissolved
in the reference
leg of water level instrumentation
and lead to false indications
of high level after a rapid depressurization
event.Reactor vessel level indication
signals are important
because these signals are used for actuating
automatic
safety systems and for guidance to operators during and after an event. While Information
Notice 92-54 dealt with potential
consequences
of rapid system depressurization, this information
notice discusses
level indication
errors that may occur during normal plant cooldown and depressurization.
Description
of Circumstances
On January 21, i993, during a plant cooldown following
a reactor scram at WNP-2, "notching" of the level indication
was observed on at least two of four channels of the reactor vessel narrow range level instrumentation. "Notching is a momentary
increase in indicated
water level. This increase occurs when a gas bubble moves through a vertical portion of the reference
leg and causes a temporary
decrease in the static head in the reference
leg. The notching at 9304020319 PD9Z X 3 MoC J 3pzu 13 oqat P- o'itv k
IN 93-27 April 8, 1993 WNP-2 was first observed on channel NC" at a pressure of approximately
827 kPa (120 psig]. Channel IBS experienced
notching starting at approximately
350 kPa [50 psig]. At these pressures, the level error was on the order of 10 to 18 centimeters
(4 to 7 inches] and persisted
for approximately
one minute.Beginning
at a pressure of approximately
240 kPa [35 psig], the level indication
from channel IC' became erratic and, as the plant continued
to depressurize, an 81-centimeter
(32-inch]
level indication
error occurred.This depressurization
was coincident
with the initiation
of the shutdown cooling system. The 81-centimeter
[32-inch]
level error was sustained
and was gradually
recovered
over a period of two hours. The licensee postulated
that this large error in level indication
was caused by gas released in the reference
leg displacing
approximately
40 percent of the water volume. The licensee also postulated
that the slow recovery of correct level indication
was a result of the time needed for steam to condense in the condensate
chamber and refill the reference
leg. The licensee inspected
the IC" reference
leg and discovered
leakage through reference
leg fittings.
This leakage may have been a contributing
factor for an increased
accumulation
of dissolved
noncondensible
gas in that reference
leg.The licensee determined
that the type of errors observed in level indication
during this event could result in a failure to automatically
isolate a leak in the RHR system during shutdown cooling. The design basis for WNP-2 includes a postulated
leak in the RHR system piping outside containment
while the plant Is in the shutdown cooling mode. For this event, the shutdown cooling suctlon valves are assumed to automatically
isolate on a low reactor vessel water level signal to mitigate the consequences
of the event. For the January 21, 1993 plant cooldown, the licensee concluded
that, with the observed errors in level indication, the shutdown cooling suction valves may not have automatically
isolated the RHR system on low reactor vessel water level as;designed.
The licensee has implemented
compensatory
measures for future plant cooldowns
to ensure that a leak that occurs in the RHR system during shutdown cooling operation
would be isolated promptly.
These measures include touring the associated
RHR pump room hourly during shutdown cooling and backfilling
the water level instrument
reference
legs after entry into mode 3 (hot shutdown).
The licensee is also evaluating
measures to minimize leakage from the IC' reference
leg.Discussion
The event described
above is different
than events previously
reported because of the large magnitude
and sustained
duration (as opposed to momentary notching)
of the level error that occurred during normal plant cooldown.
A large sustained
level error is of concern because of the potential
for complicating
long-term
operator actions. In addition, the scenario of a postulated
leak in the RHR system evaluated
by WNP-2 suggests that some safety systems may not automatically
actuate should an event occur while the reactor is in a reduced pressure condition.
Generic Letter 92-04 requested, in part, that licensees
determine
the impact of potential
level indication
errors on
IN 93-27 April 8, 1993 automatic
safety system response during licensing
basis transients
and accidents.
The information
in this notice indicates
that sustained
level instrument
inaccuracies
can occur during a normal reactor depressurization.
Therefore, events occurring
during low pressure conditions
may also be complicated
by level indication
errors.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 Operational
Events Assessment
Office of Nuclear Reactor Regulation
Technical
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
Notices
Attachnent
IN 93-27 April 8, 1993 Pge I of I ME0 a-dc LIST OF RECENTLY ISSUED HRC INFORMATION
NOTICES inroruauon
Inforuti0n
Notice No.93-26)93-25 93-24 93-23 93-22 93-21 Subject Grease Solidification
Causes Molded Case Circuit Breaker Failure to Close Electrical
fenetration
Assembly Degradation
Distribution
of Revision 7 of NUREG-1021,*Operator
Licensing Examiner Standards'
Veschler Instruments
Model 252 Switchboard
Meters Tripping of Ilockner-toeller Molded-Case
Circuit Breakers due to Support Level Failure Sumary of NRC Staff Observations
Compiled'during Engineering
Audits or Inspections
of Licen-see Erosion/Corrosion
Programs Thermal Fatigue Cracking of Feedwater
Piping to Stem Generators
Slab Hopper Bulging Portable Moisture-Density
Gauge User Responsibilities
during Field Operations
u te OT Issuance Issued to 04/07/93 All holders of OLs or CPs for nuclear power reactors.04/01/93 All holders of OLs or Cps for nuclear power reactors.03/31/93 All holders of operator and senior operator licenses at nuclear power reactors.03/31/93 All holders of OLs or CPs for nuclear power reactors.03/26/93 All holders of Ots or CPs for nuclear power reactors.03/25/93 All holders of Ots or CPs for light water nuclear power reactors.93-20)93-19 93-18 03/24/93 All holdefs of Os or CPs for PFRs supplied by Westinghouse
or Combustion
Engineering.
03/17/92 All nuclear fuel cycle licensees.
03/10/93 All U.S. Nuclear Regulatory
Couuission
licensees
that possess moisture-density
gauges.2° _clo co o 001 c 2 o II 2 u z J qq:3 0 0 a.LwU):)4 aL.OL -Operating
License CP
- Construction
Permit
IN 93-27 April 8, 1993 automatic
safety system response during licensing
basis transients
and accidents.
The information
in this notice indicates
that sustained
level instrument
inaccuracies
can occur during a normal reactor depressurization.
Therefore, events occurring
during low pressure conditions
may also be complicated
by level indication
errors.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.Original signed by Brian K. Grime: Brian K. Grimes, Director Division of Operational
Events Assessment
Office of Nuclear Reactor Regulation
Technical
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
Notices*See previous concurrence
- OGCB:DORS:NRR
JLBirmingham
04/01/93*SRXB:DSSA:NRR
ACubbage 03/19/93*C/OGCB:DORS:NRR
GHMarcus 04/01/93*C/SRXB:DSSA:NRR
RJones 03/26/93*TECH:ED RSanders 03/18/93*D/DSSA:NRR
AThadani 03/26/93 Document name: 93-27.IN
IN 93-XX March XX, 1993 errors on automatic
safety system response during licensing
basis transients
and accidents.
The information
in this notice indicates
that sustained
level instrument
inaccuracies
can occur during a normal reactor depressurization.
Therefore, events occurring
during low pressure conditions
may also be complicated
by level indication
errors.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
contact(s)
listed below or the appropriate
Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operational
Events Assessment
Office of Nuclear Reactor Regulation
Technical
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
Notices*See previous c OGCB:DORS:NRR
JLBirmingham
03"' 3 gY.Z-*SRXB:DSSA:NRR
ACubbage 03/19/93 concurrence
C/OGCB:DORS:NRR
GHMarcusas
°f 1 /93C tW*C/SRXB:DSSA:NRR
RJones 03/26/93 D/DORS:NRR
BKGrimesrMk
03/ /931'*D/DSSA:NRR
AThadani 03/26/93*TECH:ED RSanders 03/18/93 Document name: RVLEVEL.IN
\ I This information
notice requires no specific action or written response.
If you have any questions
regarding
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
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
Notices Document name: RVLEVEL.IN
- SEE PREVIOUS CONCURRENCE
OGCB:DORS:NRR
C/OGCB:DORS:NRR
D/DORS:NRR
JLBirmingham
GHMarcus BKGrimes 03//903/ 93 03 /93*SRXB:DSSA:NRR
B:DSSA:NR
& D/DSSA:NR ACubbage RJ nes Thadani 03/ /93 0 t;/ /93 03 X/931*TECHED:ADM
RSanders 03/ /93 IN 93-XX March XX, 1993 This information
notice requires no specific action or written response.
If you have any questions
regarding
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
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
Notices Document name: INFONOT2.RVL
OGCB:DORS:NRR
JLBirmingham
03/ /93 C/OGCB: DORS:NRR GHMarcus 03/ /93 0/DORS:NRR
BKGrimes 03/ /93 TECHED LADM JMain 03/8 /93 SRXB:DSSA~:NlRR
ACubbagqAtf-~
03/lcj/93 C/SRXB:DSSA:NRR
RJones 03/ /93 D/DSSA:NRR
AThadani 03/ /93