United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-58: Disablement of Turbine-Driven Auxiliary Feedwater Pump due to closure of one of the Parallel Steam Supply Valves

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 August 3, 1989


Information Notice No. 89-58:  DISABLEMENT OF TURBINE-DRIVEN AUXILIARY 
                                   FEEDWATER PUMP DUE TO CLOSURE OF ONE OF 
                                   THE PARALLEL STEAM SUPPLY VALVES


Addressees:

All holders of operating licenses or construction permits for pressurized 
water reactors.

Purpose:

This information notice is being provided to alert addressees to the potential 
for causing the turbine-driven auxiliary feedwater pump to be incapable of 
completely performing its intended safety function by closing one of the 
turbine's two parallel steam supply valves.  It is expected that recipients 
will review the information for applicability to their facilities and consider 
actions, as appropriate, to avoid similar problems.  However, suggestions 
contained in this information notice do not constitute NRC requirements; 
therefore, no specific action or written response is required.

Description of Circumstances:

On January 17, 1989, Diablo Canyon plant personnel closed one of the two 
parallel steam supply valves to the turbine-driven auxiliary feedwater pump 
without realizing that this would make the auxiliary feedwater system 
incapable of meeting the condition assumed in the plant's accident analysis; 
that is, that the auxiliary feedwater system would supply water to at least 
two steam generators.  

Steam to the turbine-driven auxiliary feedwater pump is normally provided from 
two of the unit's four steam generators, as illustrated in the enclosed figure 
of the auxiliary feedwater system.  The operators considered operation with 
one steam supply available to the auxiliary feedwater pump turbine acceptable 
because the technical specification covering the turbine-driven auxiliary 
feedwater pump does not specify two sources of steam.  It refers only to "an 
operable steam supply system" for the auxiliary feedwater pump turbine.  The 
operators believed that the flow path through one steam supply system 
satisfied this requirement. 






8907080169
.                                                            IN 89-58
                                                            August 3, 1989
                                                            Page 2 of 3


Discussion:

The assumption that the auxiliary feedwater system supplies water to at least 
two steam generators in the event of a main feedwater line break was not made 
in the original Diablo Canyon main feedwater line break analysis.  However, 
the results of this analysis indicated that the pressurizer would fill and 
vent liquid coolant for a significant period of time.  After the TMI accident 
in which liquid coolant venting from the pressurizer was believed to have 
contributed to the accident, the Diablo Canyon main feedwater line break 
analysis was redone.  Among the major assumptions made in the new analysis was 
the assumption that auxiliary feedwater would be supplied to two steam 
generators.  As a consequence, the new analysis predicted that the reactor 
coolant system would sustain the transient without filling the pressurizer.

As shown in the figure, the auxiliary feedwater system has one turbine-driven 
pump, which supplies water to all four steam generators, and two motor-driven 
pumps, each of which supplies water to a pair of steam generators.  In keeping 
with the single-failure criterion, the main feedwater line break analysis 
assumes that, in addition to the line break, one of the motor-driven pumps 
fails.  The unacceptability of operation with one of the auxiliary feedwater 
pump turbine steam supplies isolated becomes apparent when the broken line is 
assumed to be the line feeding the steam generator that provides the remaining 
steam supply to the turbine, and the failed pump is assumed to be the one 
feeding the remaining pair of unaffected steam generators.  Since the steam 
generator with the broken feed line rapidly vents all of its coolant, it 
cannot supply steam to the pump turbine; with the other steam supply isolated, 
the turbine-driven auxiliary feedwater pump is lost also.  The one remaining 
auxiliary feedwater pump feeds the pair of steam generators that includes the 
one with the broken feed line.  This pump's output will be vented through the 
broken line until this line is isolated.  After this, the pump can supply 
water to only one steam generator.  Thus, the assumption in the analysis that 
two steam generators will be supplied by auxiliary feedwater cannot be 
satisfied.

Pacific Gas and Electric Company has revised the procedures at Diablo Canyon 
to make it clear to the operators that isolation of one of the auxiliary feed-
water pump turbine steam supplies does cause the turbine-driven pump to be 
inoperable with respect to the emergency requirements.  It should be noted, 
however, that auxiliary feedwater systems having turbine-driven pumps vary 
significantly from plant to plant, even among Westinghouse-supplied plants.  
Therefore, isolation of one of the auxiliary feedwater pump turbine steam 
supplies at a particular plant might not be contrary to the assumptions in the 
safety analyses for that particular plant.  Nevertheless, the second steam 
supply is an important enhancement in regard to the reliability of the 
turbine-driven pump.  Regardless of the effect on the safety analysis, it is 
not likely that one of the steam supplies can be isolated without 
significantly reducing the margin of safety for any plant. 

.                                                            IN 89-58
                                                            August 3, 1989
                                                            Page 3 of 3


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




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

Technical Contact:  J. Wermiel, NRR
                    (301) 492-0870

Attachments:
1.  Figure 1, Diablo Canyon Auxiliary Feedwater System
2.  List of Recently Issued NRC Information Notices
.                                                            Attachment 2 
                                                            IN 89-58
                                                            August 3, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES

______________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to_________

89-57          Unqualified Electrical        7/26/89        All holders of OLs
               Splices in Vendor-Supplied                   or CPs for nuclear
               Environmentally Qualified                    power reactors. 
               Equipment 

89-56          Questionable Certification    7/20/89        All holders of OLs
               of Material Supplied to the                  or CPs for nuclear
               Defense Department by Nuclear                power reactors. 
               Suppliers 

89-45,         Metalclad, Low-Voltage        7/6/89         All holders of OLs
Supp. 1        Power Circuit Breakers                       or CPs for nuclear 
               Refurbished With Substandard                 power reactors. 
               Parts 

89-55          Degradation of Containment    6/30/89        All holders of OLs
               Isolation Capability by a                    or CPs for nuclear
               High-Energy Line Break                       power reactors. 

89-54          Potential Overpressurization  6/23/89        All holders of OLs
               of the Component Cooling                     or CPs for nuclear
               Water System                                 power reactors. 

89-53          Rupture of Extraction         6/13/89        All holders of OLs 
               Steam Line on High                           or CPs for nuclear 
               Pressure Turbine                             power reactors. 

88-46,         Licensee Report of            6/8/89         All holders of OLs
Supp. 3        Defective Refurbished                        or CPs for nuclear
               Circuit Breakers                             power reactors. 

89-52          Potential Fire Damper         6/8/89         All holders of OLs
               Operational Problems                         or CPs for nuclear
                                                            power reactors. 

89-51          Potential Loss of Required    5/31/89        All holders of OLs
               Shutdown Margin During                       or CPs for nuclear
               Refueling Operations                         power reactors. 

88-88,         Degradation of Westinghouse   5/31/89        All holders of OLs
Supp. 1        ARD Relays                                   or CPs for nuclear
                                                            power reactors. 
______________________________________________________________________________
OL = Operating License
CP = Construction Permit 
..
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