United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 81-11: Alternate Rod Insertion for BWR Scram Represents a Potential Path for Loss of Primary Coolant

                                                            SSINS No.: 6835 
                                                            Accession No.: 
                                                            8011040266     
                                                            IN 81-11       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                               March 30, 1981

Information Notice No. 81-11:   ALTERNATE ROD INSERTION FOR BWR SCRAM 
                                   REPRESENTS A POTENTIAL PATH FOR LOSS OF 
                                   PRIMARY COOLANT 

Description of Circumstances: 

During an engineering evaluation of the scram discharge air system in 
response to recently issued NRC requirements, the Boston Edison Company 
identified a potential path for loss of primary coolant at its Pilgrim 
Nuclear Power Station. The licensee found that the installed location of an 
anticipated transient without scram (ATWS) alternate rod insertion (ARI) 
solenoid valve could cause insertion of control rods without an associated 
closure of the scram discharge volume vent and drain valves. The loss of 
coolant could then follow an ARI actuation through the open vent and drain 
valves to the reactor building equipment drain tank and then to the reactor 
building sump. The rate of coolant loss through the inserted drives could be
approximately 500 gpm (based on 3 to 4 gpm per drive for 145 control rod 
drives) that would be released by the open vent and drain valves. This loss 
rate is well within the 4250 gpm capability of the high pressure coolant 
injection (HPCI) system. However, the 400 gpm capability of the reactor core
isolation cooling (RCIC) system would need the 100 gpm of the CRD pumps to 
maintain level. 

The alternate rod insertion installation was completed at the Pilgrim BWR 
during the refueling outage ending in May 1980. The installation was 
intended to permit dumping the air header supplying the scram valves. This 
function is similar to that provided by the backup scram valves, and it 
provides a means for inserting the control rods in the event of an ATWS that 
includes failure of the reactor protection system. The testing of the ARI 
installation at Pilgrim apparently failed to confirm vent and drain valve 
function. 

Following identification of the potential path for loss of primary coolant, 
the licensee reviewed plant procedures to assure that until system 
modifications could be completed, immediate operator actions during an ATWS 
event would include closing the scram discharge vent and drain valves. It is
noted that instrumentation installed in the scram discharge header in 
response to Bulletin 80-17 and the instrumented volume level switches should
alert the reactor operator to the presence of reactor coolant following ARI 
actuation. 

The licensee modified the system during a scheduled outage in February, 1981
to cause the scram discharge volume vent and drain valves to close in the 
event of ARI actuation. 
.

                                                             IN 81-11      
                                                             March 30, 1981 
                                                             Page 2 of 2   

Discussion with General Electric indicates that they plan to provide 
pertinent information to operating BWR licensees regarding the described 
potential path for loss of primary coolant. 

This information is provided as a notification of a possibly significant 
matter which is still under review by the NRC staff. In case the continuing 
NRC review finds that specific licensee actions would be appropriate, an IE 
bulletin or circular may be issued. In the interim, we expect that BWR 
licensees will review this information for applicability to their 
facilities. Licensee testing of the ARI installation should also be 
reexamined to confirm that vent and drain valves close as a direct result of 
ARI actuation. 

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

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