United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 79-06, Stress Analysis of Safety-Related Piping

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 

Page Last Reviewed/Updated Thursday, November 13, 2014