United States Nuclear Regulatory Commission - Protecting People and the Environment

NUREG-0744 Rev, 1; Pressure Vessel Material Fracture Toughness (Generic Letter No. 82-26)



                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                           WASHINGTON. D.C. 20555
                                     
                              November 12, 1982

TO ALL POWER REACTOR LICENSEES (EXCEPT FT. ST. VRAIN) 

Gentlemen: 

SUBJECT:  NUREG-0744 REV, 1; (GENERIC LETTER NO. 82-26 ) - 
          PRESSURE VESSEL MATERIAL FRACTURE TOUGHNESS 

Appendix G to 10 CFR 50 specifies fracture toughness requirements for 
pressure retaining components, fabricated from ferritic materials, in the 
reactor coolant pressure boundary of water cooled reactors. In the event a 
pressure retaining component fails to meet the material toughness 
requirements during its service life due to neutron radiation embrittlement,
continued operation of the component is permissible provided certain 
requirements, specified in Section V.C of Appendix G, are satisfied. 

One of the requirements of Section V.C is that a fracture analysis of the 
component is to be performed to demonstrate the existence of adequate margin
for continued operation. The proposed program for satisfying this 
requirement is to be submitted to the USNRC for review and approval at least 
3 years prior to the date fracture toughness levels are predicted to no 
longer satisfy requirements. 

Appendix H to 10 CFR 50 specifies the surveillance program which all power 
reactor licensees must maintain to monitor irradiation-induced fracture 
toughness changes. Impact data from this program are used to adjust the 
reference toughness curve for irradiation effects through the application of
the adjusted reference temperature. The Charpy V-notch 50 ft-lb level is 
used to determine the temperature shift; therefore, when the upper shelf 
energy falls below 50 ft-lb, the requirements of 10 CFR 50 Appendix G are no 
longer met. 

To provide guidance to licensees who may be required to submit a fracture 
analysis to justify continued operation of a pressure vessel, the USNRC has 
developed an elastic-plastic fracture mechanics analytical procedure. This 
analytical methodology is presented in NUREG-0744, Revision 1 (Office of 
Management and Budget Clearance Number 3150-0011), a copy of which is 
enclosed with this letter. 




8211160047 
.

ALL POWER REACTOR LICENSEES          -2-

This document presents one methodology which is acceptable to the USNRC 
staff for meeting the requirement for a fracture analysis with sufficient 
accuracy and reliability to demonstrate adequate margins for continued 
operation in accordance with Section V.C.3 of Appendix G to 10 CFR 50. 
Licensees, however, need not employ this specific fracture analysis 
methodology and may submit an analysis based on other techniques for NRC 
review and approval. 

Available evidence reveals that the upper shelf energy of a number of power 
reactor pressure vessels may fall below the 50 ft-lb level before the end of
their design life unless measures such as revised fuel management schemes 
are instituted. It is likely that several licensees may elect to submit 
fracture analysis to support continued operation. All licensees are 
encouraged to review NUREG-0744, Revision 1 and consider its application in 
those cases where it may be necessary to submit a fracture analysis to the 
NRC for review and approval. 

                                   Sincerely, 


                                   Darrell G. Eisenhut, Director 
                                   Division of Licensing 
                                   Office of Nuclear Reactor Regulation 

Enclosure:
NUREG-0744, Rev. 1
Page Last Reviewed/Updated Tuesday, June 18, 2013