United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-55: Degradation of Containment Isolation Capability by a High-Energy Line Break

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

                                  June 30, 1989

                                   CAPABILITY BY A HIGH-ENERGY LINE BREAK 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to the potential 
for a high-energy line break (HELB) inside containment causing the failure of 
piping in a closed system thereby negating one containment isolation barrier 
and leaving the plant with only a single containment isolation valve to miti-
gate potential radiological releases.  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: 

Millstone Unit 1 is a boiling-water reactor with a Mark I containment.  The 
original design basis for isolation of the reactor building closed cooling 
water (RBCCW) system required a single barrier outside containment.  That is, 
one check valve was provided in the inlet line to containment while a single 
remote, manually operated block valve was provided in the return line from 

Recently the licensee postulated a scenario in which a recirculation line 
failure (a HELB) inside containment could cause loss of the RBCCW system 
integrity.  To maintain containment integrity, both RBCCW system isolation 
valves would have to close; therefore, a single failure of either of these 
valves would result in the loss of containment integrity.  With failure of an 
RBCCW isolation valve to close, it would be possible for the containment 
atmosphere to displace water in the RBCCW piping and ultimately vent to the 
reactor building.  Thus, an unanalyzed condition existed which involved poten-
tial degraded containment integrity caused by HELBs. 

.                                                            IN 89-55
                                                            June 30, 1989
                                                            Page 2 of 2


The RBCCW system was originally considered to be a closed system inside con-
tainment and, therefore, part of the containment isolation provisions.  That 
is, the closed system was a supplement to the single isolation valve provided 
in both the inlet piping and the outlet piping.  (Note that the configuration 
of a single check valve outside containment in the inlet line of the RBCCW 
system was licensed prior to the formal issuance of the General Design 
Criteria for Nuclear Power Plants, Appendix A to 10 CFR Part 50 (GDC) and it 
does not meet the current implementation of General Design Criterion 57 
"Closed System Isolation Valves.")  The original safety evaluation did not 
consider that dynamic effects of HELBs could impact RBCCW system isolation 
integrity.  As a result, the RBCCW system is more properly viewed as a system 
open to the containment atmosphere under the postulated accident scenario.  As 
such, the applicable regulatory requirements are given by GDC 56 "Primary 
Containment Isolation" and TMI Action Plan Item II.E.4.2, "Containment Isola-
tion Dependability".  It is important that licensees recognize the need to 
assure adequate protection of systems within containment from pipe whip and 
jet impingement effects of HELBs when containment integrity must be maintained 
during and after a postulated accident consistent with the single failure 

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 regional 

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

Technical Contact:  J. Carter, NRR
                    (301) 492-1194

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment
                                                            IN 89-55
                                                            June 30, 1989
                                                            Page 1 of 1

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

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. 

89-50          Inadequate Emergency          5/30/89        All holders of OLs
               Diesel Generator Fuel                        or CPs for nuclear
               Supply                                       power reactors. 

89-49          Failure to Close Service      5/22/89        All holders of OLs
               Water Cross-Connect                          or CPs for nuclear
               Isolation Valves                             power reactors. 

89-48          Design Deficiency in the      5/22/89        All holders of OLs
               Turbine-Driven Auxiliary                     or CPs for nuclear
               Feedwater Pump Cooling                       power reactors. 
               Water System 

89-47          Potential Problems With       5/18/89        All holders of OLs
               Worn or Distorted Hose                       or CPs for nuclear
               Clamps on Self-Contained                     power reactors and
               Breathing Apparatus                          fuel facilities. 
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Friday, May 22, 2015