United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular No. 80-07, Problems with HPCI Turbine Oil System


                                                            SSINS No.: 6830 
                                                            Accession No.: 
                                                            8002280657

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

                                April 3, 1980

                                                     IE Circular No. 80-07 

PROBLEMS WITH HPCI TURBINE OIL SYSTEM 

Description of Circumstances: 

During 1979 a number of events were experienced at BWRs in which the High 
Pressure Coolant Injection (HPCI) system failed to perform its function due 
to HPCI turbine problems.  Most of the failures were found during normally 
required surveillance testing, although others occurred during demand 
conditions.  Events which are examples of these occurrences are described 
below.  The turbines in these events were Terry Steam Turbines. 

Failure Due to Water in the HPCI Turbine Oil System: 

Georgia Power Company reported on June 4, 1979, that the Hatch Unit 2 HPCI 
system failed to function upon receiving an initiation signal.  The turbine-
driven HPCI pump failed to start because the turbine steam stop valve failed
to open.  Investigation revealed water in the turbine oil system, which is a
combined lubrication and hydraulic control system.  Hydraulic oil pressure 
is supplied to the turbine control and the stop valves and also to system 
bearings by an auxiliary DC powered oil pump during startup and then by the 
Shaft-driven hydraulic oil pump when the turbine reaches operating speed. 

The water contamination changed the oil characteristics; as a result, 
sufficient hydraulic oil pressure was not developed to open the turbine stop
valve. 

Two sources of water in leakage into the turbine oil system were identified. 
One source of leakage was determined to be from a defective mechanical seal 
on the HPCI pump seal injection line.  A second source of in leakage was 
determined to be the oil cooler.  Repairs to the  cooler tube sheet and 
mechanical seal were made.  Additional corrective action included locking 
open the bracket cavity drain valve which had not been included on system 
drawings or procedures, and the initiation of routine sampling of the 
turbine oil system. 

Failure of Hydraulic Cylinder Seal in HPCI Turbine Stop Valve: 

Nebraska Public Power District reported at the cooper Station that on August
9, 1979, upon receipt of an auto start signal, the HPCI system did not 
properly start.  However, a short time (14 minutes) after the initiation 
signal, the HPCI did start and maintained reactor vessel water level. 
Investigation showed that the initial failure of the HPCI system to start 
was 
.

IE Circular No. 80-07                                       April 3, 1980 
                                                            Page 2 of 3 

due to the failure of the HPCI turbine stop valve to open.  Further 
investigation revealed a failure of the seal rings in the hydraulic cylinder
actuator of the turbine stop valve.  The seal rings were allowing oil 
leakage to bypass the piston of the operator and insufficient force was 
available to open the stop valve at full system steam pressure. 

The HPCI turbine stop valve is a vertically mounted, hydraulically operated,
piston type globe valve with the actuating cylinder on the bottom and an 
internal balance chamber of top of the globe valve piston.  The balance 
chamber functions to provide smooth operation of the valve during its 
actuation.  This function is provided by an internal orificed steam 
passagewhich permits a portion of the incident steam pressure to accumulate 
in the balance chamber.  During this event the valve actuation did not have 
sufficient force, due to the leaking seal rings, to overcome the initial 
steam pressure in the balance chamber.  As the main steam pressure decreased 
to about 600 psig after the reactor scram, the force on the valve actuator 
piston became sufficient to open the stop valve thereby permitting the HPCI 
turbine to start and aid in restoring the water level in the reactor. 

The failed piston ring seals were fabricated from resin impregnated leather. 
The design and failure cases were reviewed by General Electric together with
Terry turbine and component suppliers and the review resulted in 
recommending that the hydraulic cylinder be examined for bypass leakage and 
replacement of the seals upon determination of excess leakage.  It was also 
recommended that subsequent seal replacement by placed on a five year 
schedule. 

Recommended action for BWR licensee's and permit holder's considerations: 

All holders of operating licenses for BWR power reactor facilities having 
Terry turbines should be aware of the potential problems described above (it
is noted that the seal problem is related to the HPCI turbine and not to the
RCIC turbine which does not use a hydraulic actuated stop valve).  It is 
recommended that the matters identified above be reviewed at your facility 
in the following respects: 

1.   Each BWR licensee should assure that the as built system is consistent 
     with operating procedures and drawings and that their preventive 
     maintenance program includes the means of routinely detecting water or 
     other deterioration of the turbine oil systems.  Periodically, the 
     turbine oil should be sampled for moisture immediately following 
     turbine operation.  Procedures specifying appropriate corrective 
     actions should be provided as necessary. 

2.   Each BWR licensee should initiate an examination of the stop valve 
     hydraulic cylinder seals for excess bypass leakage and proceed with 
     seal replacement on determination of excess leakage followed by the 
     recommended 5 year schedule.  Thereafter, periodic re-examinations of 
     the seals are to be made to provide assurance that seal replacements 
     are functioning as required. 
.

IE Circular No. 80-07                                       April 3, 1980 
                                                            Page 3 of 3 

All holders of construction permits for BWR power reactor facilities 
shouldbe aware of the potential problems identified above and initiate 
appropriate procedures prior to 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 these matters, contact the Director of the appropriate NRC 
Regional Office. 

Page Last Reviewed/Updated Wednesday, July 09, 2014