IE Circular No. 79-24, Proper Installation and Calibration of Core Spray Pipe Break Detection Equipment on BWRs
CR79024
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
K. V. Seyfrit, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Norman C. Moseley, Director, Division of Reactor
Operations Inspections, IE
SUBJECT: IE CIRCULAR NO. 79-24, PROPER INSTALLATION AND
CALIBRATION OF CORE SPRAY PIPE BREAK DETECTION EQUIPMENT
ON BWRs
The subject IE Circular is transmitted for issuance on November 26,
1979. The Circular should be issued to all holders of a power reactor
operating license or construction permit.
The text of the Circular and draft letter to the licensees and permit
holders are enclosed for this purpose.
Norman C. Moseley, Director
Division of Reactor Operations
Inspection
Office of Inspection and Enforcement
Enclosures:
1. Draft Transmittal Letter
2. IE Circular No. 79-24
CONTACT: C. J. DeBevec, IE
49-28180
.
(Draft transmittal letter for Circular No. 79-24 to each holder of a power
reactor operating license or construction permit.)
IE Circular No. 79-24
Addressee:
The enclosed Circular No. 79-24 is forwarded to you for information. No
written response is required. Should you have any questions related to your
understanding of the recommendations on this matter, please contact this
office.
Sincerely,
Signature
(Regional Director)
Enclosure:
1. IE Circular No. 79-24
2. Recently Issued
IE Circulars
.
Accession No: 7910250492
SSINS No. 6830
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
November 26, 1979
IE Circular No. 79-24
PROPER INSTALLATION AND CALIBRATION OF CORE SPRAY PIPE BREAK DETECTION
EQUIPMENT ON BWRs
Description of Circumstances:
During 1976 the Iowa Electric Light and Power Company identified and
corrected a potential problem involving the core spray (CS) pipe break
detection system at the Duane Arnold Energy Center (DAEC). The problem
relates to the setpoint, function, and installation of the differential
pressure (dp) instrument which monitors for a CS pipe break that is located
in the annulus area of the reactor vessel (i.e., located outside the core
shroud but inside the reactor vessel). The installed instrument, range of 0
-24 psid, was found deflecting downscale (i.e., reading negative psid)
during operation.
The licensee's investigation of the downscale deflection revealed that the
original piping arrangement and calibration did not adequately take into
account the effect of density changes of the water in the pressure leg
connections. The original installation had the high pressure side of the dp
instrument (see attached Figure 1) connected to the reference leg in the
vessel (Figure 1 Connection X) and the low pressure side to the core spray
piping outside the vessel but inside the drywell (Figure 1 Connection Y).
With the piping intact, this arrangement senses the pressure difference
between bottom and top of core. With a break in CS piping in the annulus
area the instrument then senses the additional pressure drop across the
separators (dp ~ 7 psi additional) and dryers (dp ~ 7-inches water). This
installation was in accordance with GE design requirements.
Also in accordance with GE instructions the calibration of the dp instrument
was performed with the reactor in the cold condition and the alarm was set
to trip at 5 psid increasing. Because of this cold calibration the dp
instrument then indicated full downscale negative during operation. This
negative dp was due to the heat up of the reference leg (Figure 1 Connection
X) which caused the fluid density to decrease as the plant reached hot
conditions. The magnitude of this dp was determined to be about 3.5 psid
following completion of the modification discussed below.
.
IE Circular No. 79-24 November 26, 1979
Page 2 of 3
Adding the 3.5 psi downscale deflection to the 5 psi alarm setpoint results
in a total required deflection of 8.5 psi to initiate the alarm at the
setpoint. Since the total dp available across the separators and dryer is
only 7 psi (1.5 psi less than the total required deflection), the alarm
would not be actuated by a CS pipe break in the annulus. Therefore, the
original installation, including calibration procedure, was deficient.
To correct the problem, Iowa Electric modified the installation by
interchanging the pressure leg connections and resetting the alarm to trip
at 2 psid decreasing. In this orientation it was found that going from cold
to hot produced a 3.5 psid positive deflection. The technical specifications
were changed to reflect the revised alarm setpoint.
Further review by the NRC has revealed that the above described lack of trip
which precipitated the piping modification and technical specification
change at DAEC, exists on other operating BWRs and that BWRs under
construction have or will have piping arrangements on the core spray system
(i.e., high pressure core spray system on BWR 5's and 6's) that will
potentially generate the same problem.
The specific concern is that failure of the injection piping would not be
detected on the plants in question, because the alarm is the only control
room indication involved. The actual differential pressure can only be read
at local gauges located on instrument racks in the reactor building.
General Electric has recently sent correspondence to utilities which
recommends that:
"1. BWR operators, who have differential pressure ( P) instrumentation
which reads only positive values, interchange their core spray line
break instrument connections so that the high side connection is to the
core spray sparger sensing line and the low side connection is to the
above the core plate sensing line. This instrumentation should be
calibrated for a zero P reading during cold shutdown; it will then
give a positive P reading during normal rated power operation and a
pegged zero reading for a line break indication during normal rated
power operation.
Also, when this change is made, the recommended alarm setpoint (on
decreasing ( P) setting is 0.5 +/- 0.25 PSID; and for those plants that
have a value in their technical specifications, > 0 PSID is recommended
as a limit.
This change will produce an alarm during normal shutdown. When the
plant is returned to service, clearing of the alarm by a positive P
reading near rated power will indicate that the instrumentation is
working.
"2. BWR operators, who have installed or who prefer to install P
instrumentation (e.g., -10 to +10 PSID) that covers their range of
negative and positive P values and who continue with the instrument
high side connected to the above the core plate sensing line, use the
same alarm set point of 0.5 +/- 0.25 PSID (and a technical
specification limit, if applicable, of < 1 PSID). The instrument should
again be calibrated to read zero P during cold shutdown."
.
IE Circular No. 79-24 November 26, 1979
Page 3 of 3
Recommended action for BWR licensee's and permit holders considerations:
All holders of operating licenses for BWR power reactor facilities (other
than Duane Arnold) should be aware of the potential problems described
above. It is recommended that the matter be reviewed at your facility in the
following respects:
1. If your facility utilizes a core spray leak detection system similar to
that described above, determine if the described problems exist. If so,
initiate appropriate corrective action at the next planned refueling
outage.
2. Propose changes, as appropriate, to those technical specifications
which must be revised as a result of your modifying the item above.
3. For interim operations until full corrective measures have been taken
it is recommended that direct readings from dp gauges be periodically
taken or setpoints changed along with providing necessary instructions
to the operators regarding indications from this system.
All holders of construction permits for BWR power reactor facilities should
be aware of this potential problem and initiate appropriate modification
prior to the initial fuel loading.
This Circular is being forwarded for information to all other power reactor
facilities with an operating license or construction permit. No written
response to this Circular is required. If you need additional information
regarding this matter, contact the Director of the appropriate NRC Regional
Office.
Enclosure:
Figure 1
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021