Power level uprates are based on an anachronism

Following is excerpted from a 2007 ACRS letter, ML071490090. It refers to Baker-Just as an anachronism although it does not say Baker-Just. This is so very interesting because ACRS approved several power level uprates that were justified based on compliance with Baker-Just.

UNITED STATES NUCLEAR REGULATORY COMMISSION

ADVISORY COMMITTEE ON REACTOR SAFEGUARDS

WASHINGTON, DC 20555 - 0001

May 23, 2007

The Honorable Dale E. Klein
Chairman
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

SUBJECT: PROPOSED TECHNICAL BASIS FOR THE REVISION TO 10 CFR 50.46 LOCA EMBRITTLEMENT CRITERIA FOR FUEL CLADDING MATERIALS

DISCUSSION
Zirconium alloy cladding used in current power reactors is embrittled by hydrogen absorption during normal operation and by oxidation and absorption of oxygen during the temperature transient associated with a LOCA. The requirements of 10 CFR 50.46 (a) and (b) limit the amount of embrittlement that may occur as result of a design basis accident. They specify limits for the peak clad temperature, the global oxidation of cladding, and the local oxidation of cladding. There are several deficiencies with the current regulations. The correlation specified for the rates of steam reaction with the cladding is viewed by the technical community as an anachronism. Cladding oxidation resulting from normal operation also contributes to embrittlement during a LOCA and can be significant in high-burnup fuel. Currently, not all licensees account for oxidation during normal operation in LOCA analyses. Also, since current requirements refer only to Zircaloy and ZIRLO cladding, the use of modern cladding alloys with superior performance requires regulatory exemptions.

Furthermore, in addition to its convenience in licensing power level increases, Baker-Just is referenced by power reactor licensees in their justification for pilot testing of "modern" cladding alloys. For example San Onofre's application to run some pilot M-5 assemblies is justified by Baker-Just. The approval by NRC is dated December 2009, over 2.5 years following the ACRS description of Baker-Just as an anachronism. Thus, San Onofre Units 2 and 3 will run some pilot M-5 bundles. They cite data reported by Framatome Cogema Fuels (FCF) to establish that M-5 metal-water reaction characteristics are bounded by Baker-Just. Click on the slide below to enlarge and then use your return arrow to get back here.