IE Circular No. 79-24, Proper Installation and Calibration of Core Spray Pipe Break Detection Equipment on BWRs


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 

                    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 
                                        Office of Inspection and Enforcement

1.   Draft Transmittal Letter
2.   IE Circular No. 79-24

CONTACT:  C. J. DeBevec, IE 

(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 


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 


                                        (Regional Director) 

1.   IE Circular No. 79-24
2.   Recently Issued
       IE Circulars

                                                 Accession No: 7910250492 
                                                  SSINS No.  6830 

                               UNITED STATES 
                          WASHINGTON, D.C. 20555 
                             November 26, 1979 

                                                      IE Circular No. 79-24 


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 
"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 

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 

Figure 1


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