IE Circular No. 80-16, Operational Deficiencies in Rosemount Model 510du Trip Units and Model 1152 Pressure Transmitters

                                                 SSINS No.: 6830           
                                                 Accession No.:            
                                                 8005050067

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, D.C. 20555

                                 June 27, 1980

                                             IE Circular No. 80-16

OPERATIONAL DEFICIENCIES IN ROSEMOUNT MODEL 510DU TRIP UNITS AND MODEL 1152 
PRESSURE TRANSMITTERS

Description of Circumstances:

The NRC has recently been advised through a 10 CFR 21 report that operational 
deficiencies exist in Rosemount Inc. Model 510DU trip units and Model 1152 
pressure transmitters as follows:

MODEL 510DU TRIP UNITS

The 510DU trip units have common mode failures of two switches; S1 in the
trip  status output, LED logic circuit and S2 in the trip output logic
circuit. The  trip units involved are those with serial Numbers 3001 to 4203.
The 510DU  units having serial numbers within this range that are not trip
units are not  affected (i.e., Card Files, Readout Assemblies, Calibration
Units, etc.).  Malfunction of these switches appears as an open circuit in
the output logic  upon receipt of an actual trip signal. Switch (S2) failure
could result in  failure to automatically activate a safety function.

MODEL 1152 PRESSURE TRANSMITTERS

The model 1152 pressure transmitters have a common mode failure of a
capacitor  when the transmitter operating environmental temperature is
greater than 175F,  and when the damping potentiometer is rotated clockwise.
The failure results  in a decrease in transmitter output current of up to 10
percent of the correct  current. For example, when the transmitter is used
in an indication circuit,  the parameter indication would be correspondingly
lower than the correct value  if the capacitor failure occurred. The failure
potentially involves all  pressure transmitters with the following model
designations:

Rosemount Pressure Transmitter Models:

1152 _ _ _ E _ _ T0280
1152 _ _ _ E _ _ T0445
1152 _ _ _ E _ _ T0400

Available information indicates that the problems outlined above have been 
reported to each customer who was furnished the Model 510DU trip units and
Model 1152 pressure transmitters.



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IE Circular No. 80-16                            June 27, 1980             
                                                 Page 2 of 2

RECOMMENDED ACTION FOR LICENSEES AND HOLDERS OF CONSTRUCTION PERMITS

All licensees of nuclear power reactors and holders of construction permits 
should be aware of the potential problems discussed above. It is recommended 
that the following actions be taken: 

1. Determine if your facility has installed or plans to install the Rosemount 
Model 510DU trip units and/or the pressure transmitters described herein in 
any safety-related equipment.

2. If it is determined that your facility has installed or plans to install 
any of the affected units described herein, contact the supplier for 
performance of the required modifications to the units to resolve the 
problems.

3. Modifications should be performed on all affected units prior to plant 
operation. If the affected units are installed in plants that are operating, 
the following actions are recommended for continued operation until the units 
are modified.

a. 510DU Trip Units

A functional test verifying proper operation of the trip units should be 
performed.

b. Model 1152 Pressure Transmitters

On pressure transmitters that are affected and that may be subjected to 
operating environmental temperatures greater than 175xF, the transmitters 
should be operated with the damping potentiometer (R12) in the fully 
counterclockwise position.

CAUTION

The circuit output should be monitored to assure that no action detrimental
to  operation results from placing R12 in the counter clockwise position,
such as  spurious tripping caused by unstable operation.

No written response to this circular is required. If you require additional 
information regarding this matter, contact the Director of the appropriate
NRC  Regional Office.