Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 30, 1989
Information Notice No. 89-55: DEGRADATION OF CONTAINMENT ISOLATION
CAPABILITY BY A HIGH-ENERGY LINE BREAK
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
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
containment.
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.
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June 30, 1989
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Discussion:
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
criterion.
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
office.
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
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