United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-38: Atmospheric Dump Valve Failures at Palo Verde Units 1, 2, and 3

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                  April 5, 1989

                               PALO VERDE UNITS 1, 2, AND 3


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
failures of main steamline atmospheric dump valves (ADVs).  It is expected 
that recipients will review the information for applicability to their facil-
ities and consider actions, as appropriate, to avoid similar problems.  
However, suggestions contained in this information notice do not constitute 
NRC require-ments; therefore, no specific action or written response is 

Description of Circumstances:

On March 3, 1989, Palo Verde Unit 3 experienced a large load rejection and a 
subsequent automatic reactor power decrease from 98 percent to 45 percent 
power.  The turbine bypass valves opened but the bypass valve controller 
malfunctioned, causing excessive steam relief and overcooling of the reactor 
coolant system (RCS).  A main steamline isolation and reactor trip were caused 
by low pressure in the number 2 steam generator.  Safety injection and 
containment isolation activated upon low RCS pressure.  Following steamline 
isolation, the ADVs remained closed after operators attempted to open them 
first from the control room and then from the remote shutdown panel.  The 
valves do not receive an automatic signal to open.  After the ADVs failed to 
open remotely, auxiliary operators experienced difficulty in opening the ADVs 
using the handwheels because of the lack of lighting (including emergency 
lighting), poor labeling of ADV equipment, poor procedures and training, a 
disengaged handwheel, and considerable noise caused by the opening of the main 
steamline safety relief valves.  The operators partially opened two ADVs. 

The pneumatic operators on the ADVs are actuated by using either plant instru-
ment air or a stored, pressurized nitrogen supply.  The valves were 
manufactured by Control Components, Inc. (CCI).  CCI indicated that previous 
problems had been experienced in the testing of ADVs at Palo Verde Unit 1 and 
other facil-ities.  Excessive bonnet pressure caused by abnormally high 
leakage past the main valve plug piston ring is suspected to have contributed 
to these problems.  Foreign particles from the steamlines in the clearance 
areas and under the piston ring sealing surfaces may produce the high piston 
ring leakage.  CCI has developed design modifications to address this problem.

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                                                            April 5, 1989
                                                            Page 2 of 2

Following the failures of the ADVs to open remotely at Palo Verde Unit 3, the 
licensee tested the ADVs at the other two Palo Verde units.  Four of the eight
valves failed the functional tests.  Preliminary results indicated that there 
were problems with valve positioners, possible valve stem binding problems, 
and calibration problems with nitrogen pressure regulators.  The licensee for 
Palo Verde is continuing to investigate the cause of valve failures but has 
not yet identified a root cause.

Contributing to the simultaneous ADV failures at Palo Verde is the lack of in-
service testing under hot steam conditions.  The valves are routinely tested 
during refueling outages with the steamlines cold and depressurized.  For 
testing, the pneumatic operators are actuated with plant air rather than 
with the pressurized nitrogen supply.  

Licensees may wish to reassess the frequency of ADV testing and to evaluate 
their ADV surveillance test procedures and consider performing the tests under
conditions that better simulate inservice conditions. 

No specific action or written response is required by this information notice.  
If you have any questions about this matter, please contact one of the 
technical contacts listed below or the Regional Administrator of the 
appropriate regional office. 

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical Contacts:  Horace Shaw, NRR
                     (301) 492-0906

                     Walton Jensen, NRR
                     (301) 492-1190

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment 
                                                            IN 89-38
                                                            April 5, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

89-37          Proposed Amendments to        4/4/89         All U.S. NRC 
               40 CFR Part 61, Air                          licensees. 
               Emission Standards 
               for Radionuclides

89-36          Excessive Temperatures        4/4/89         All holders of OLs
               in Emergency Core Cooling                    or CPs for nuclear
               System Piping Located                        power reactors.
               Outside Containment

88-86,         Operating with Multiple       3/31/89        All holders of OLs
Supp. 1        Grounds in Direct Current                    or CPs for nuclear
               Distribution Systems                         power reactors.

89-35          Loss and Theft of Un-         3/30/89        All U.S. NRC 
               secured Licensed Material                    byproduct, source 
                                                            and special 
                                                            nuclear material

89-34          Disposal of Americium         3/30/89        All holders of an
               Well-Logging Sources                         NRC specific 
                                                            authorizing well-
                                                            logging activities.

89-33          Potential Failure of          3/23/89        All holders of OLs
               Westinghouse Steam                           or CPs for PWRs.
               Generator Tube 
               Mechanical Plugs

89-32          Surveillance Testing          3/23/89        All holders of OLs
               of Low-Temperature                           or CPs for PWRs.

89-31          Swelling and Cracking         3/22/89        All holders of OLs
               of Hafnium Control Rods                      or CPs for PWRs 
                                                            with Hafnium 
                                                            control rods. 

89-30          High Temperature              3/15/89        All holders of OLs
               Environments at                              or CPs for nuclear
               Nuclear Power Plants                         power reactors.

OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Friday, May 22, 2015