Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
IN79006
March 22, 1979
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
K. V. Seyfrit, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Norman C. Moseley, Director, ROI:IE
SUBJECT: Information Notice No. 79-06, STRESS ANALYSIS OF
SAFETY-RELATED PIPING
The subject document is transmitted for issuance on March 23, 1979.
The Information Notice should be issued to all holders of Reactor Operating
Licenses and Construction Permits.
Also enclosed is a draft copy of the transmittal letter.
ELJordan /for
Norman C. Moseley, Director
Division of Reactor Operations
Inspection
Office of Inspection and Enforcement
Enclosures:
1. IE Information Notice
No. 79-06
2. Draft Transmittal Letter
CONTACT: R. W. Woodruff, IE
49-28180
.
(Transmittal letter for Information Notice No. 79-06 to each holder of an
NRC Operating License and Construction Permit.)
Information Notice No. 79-06
Addressee:
This Information Notice is provided as an early notification of a possibly
significant matter. It is expected that recipients will review the
information for possible applicability to their facilities. No specific
action or response is requested at this time. If further NRC evaluations so
indicate, an IE Circular, Bulletin or NRR Generic Letter will be issued to
recommend or request specific licensee actions. If you have questions
regarding the matter, please contact the Director of the appropriate NRC
Regional Office.
Signature
(Regional Director)
Enclosure:
Information Notice No.
No. 79-06
.
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 23, 1979
Information Notice No. 79-06
STRESS ANALYSIS OF SAFETY-RELATED PIPING
Summary:
On March 13, 1979, the Nuclear Regulatory Commission issued Orders to
licensees for five power reactors to shut down within 48 hours and to show
cause why they should not remain shutdown pending reanalysis of certain
safety-related piping systems and pending completion of any modifications
indicated by the reanalysis. This action was based on the discovery of a
potentially unconservative calculational technique within a computer program
that has been used by an architect-engineer for analysis of certain piping.
Description of Circumstances
During construction of Unit 1 at the Beaver Valley Power Station and the
four other reactor units involved in the above orders, a version of a
computer program, PIPESTRESS, was used by Stone & Webster in performing "as
built" stress analyses of piping requiring a seismic analysis for which the
architect-engineer was responsible. Later, modification of the safety
injection system at BVPS-1 to improve net positive suction head and
correction of an error in the weight of some components in that system led
to re-evaluation of the stresses in this piping and associated pipe
attachments. These components whose weights had been incorrectly entered
were six-inch check valves manufactured by Velan Valve company. The error in
weight was caused by an incorrect weight shown on Velan drawings. As a
result of this reanalysis, the licensee reported the existence of stress
levels above those stated in the FSAR to the NRC on October 26, 1978. NRC
review of the Licensee Event Report and inspection followup identified the
existence of significant discrepancies between stresses calculated by the
PIPESTRESS code and by NUPIPE, a code currently used by Stone & Webster.
.
Information Notice No. 79-06 March 23, 1979
Page 2 of 3
In some instances, NUPIPE yielded stress results which were significantly
higher than those obtained with PIPESTRESS. The differences in the results
are attributable to the force summation method utilized by SHOCK 2, a
subroutine of the PIPESTRESS computer code. Based on an examination of a
sample run, the NRC staff learned on March 8, 1979 that this computer
program subroutine algebraically summed horizontal response components from
the seismic input components. It also algebraically summed vertical response
components from the seismic input components. Such response loads should not
be algebraically added (with predicted loads in the negative direction
offsetting predicted loads in the positive direction) unless far more
complex time-history analyses are performed. Rather, to properly account for
the effects of earthquakes, as required by General Design Criterion 2 for
systems important to safety, such response loads should be combined
absolutely or, as is the case in the newer codes, using techniques such as
the square root of the sum of the squares (SRSS). This conforms to current
industry practice and Reg Guide 1.92.
Stone & Webster also used the SHOCK 2 subroutine of PIPESTRESS in the
analysis of piping in safety systems for FitzPatrick, Maine Yankee, and
Surry 1 and 2. NRC review on March 10-13, 1979, of preliminary results from
the reanalysis of portions of the Beaver Valley piping at Stone & Webster's
offices in Boston, Massachusetts, indicated several instances of pipe stress
beyond allowable limits. In the face of this deficiency information, the NRC
concluded that until full reanalysis of all potentially affected piping
systems important to safety has been completed with a piping analysis
computer code which does not contain the algebraic summation method, it
would be prudent to assume that the potential for reducing intended design
margins at each of the facilities in question exists in the event of an
earthquake and could be sufficiently widespread such that the basic
defense-in-depth provided by redundant safety systems may be compromised.
On March 13, 1979, NRC issued to licensees for these facilities, Orders to
Show Cause why: (1) potentially affected safety system piping should not be
reanalyzed using an appropriate computer program; (2) modifications
indicated by reanalysis should not be done; and
.
Information Notice No. 79-06 March 23, 1979
Page 3 of 3
(3) facility operation should not be suspended pending completion of this
work. Because of the safety significance of this problem, these Orders were
made effective immediately to require that these facilities be in the cold
shutdown condition within 48 hours of receipt of the Order and remain in
that condition until further Orders are issued.
This Information Notice provides details of a significant occurrence that is
still under review by the NRC staff. After completion of the staff review,
this Information Notice will be followed with specific actions to be taken
by licensees.
No written response is required. If you desire additional information
regarding this matter, please contact the Director of the appropriate NRC
Regional Office.
Enclosure:
List of IE Information
Notices Issued in 1979
