An Industry Technical Position On LOCA Rulemaking 21 st Regulatory Information Conference Rockville, MD March 12, 2009 Ken Yueh Electric Power Research Institute

2 © 2008 Electric Power Research Institute, Inc. All rights reserved. Presentation Overview Safety significance Industry position on hydrogen pre-charging as a surrogate for irradiation Outstanding issues Industry position on issues and test plans Summary

3 © 2008 Electric Power Research Institute, Inc. All rights reserved. Safety Significance Evaluations indicate no significant safety concerns with respect to current design basis and therefore no need to rush rulemaking without resolution to important issues –IN with 15% hydrogen pickup is more conservative High burnup fuel can not reach high temperatures after 2 nd cycle –Most plants have PCT < 1100ºC using BE evaluations NUREG concluded “..beta layer does not appear to embrittle due to the low oxygen solubility (≈0.4 wt.%) in the beta phase at 1100ºC...”

4 © 2008 Electric Power Research Institute, Inc. All rights reserved. Industry Position on Hydrogen Pre-Charging Pre-hydriding Zircaloy-4, ZIRLO and M5 PQD ductile-to-brittle transition ECR Pre-hydriding appears to be a good surrogate for irradiation Pre-hydrided and Irradiated data from multiple vendors follow the same trend line

5 © 2008 Electric Power Research Institute, Inc. All rights reserved. Outstanding Issues Post-quench ductility scope –ANL testing focused on 1200°C, data needed at lower temperatures –Limited alloy testing, no Zircaloy-2 data with hydrogen –Critical PQD transition boundary recommendation at elevated hydrogen content in RIL-0801 not supported by data Requirement in RIL-0801 to use two-sided oxygen uptake away from the ballooned region is not supported by ANL data –Integral testing not complete Support for periodic testing on short breakaway oxidation time only observed from E110 material –Fundamental differences between Kroll (Western process) and Electrolytic process used for E110 –No incidence of short breakaway oxidation time observed in Western alloys over several decades of testing

6 © 2008 Electric Power Research Institute, Inc. All rights reserved. Lower Oxidation Temperatures Industry LOCA Oxidation & PQD Test Plans ANL data indicates ECR accumulated at lower temperatures is not as detrimental to ductility for Zircaloy-4 Test details –Entire range of relevant oxidation temperatures and hydrogen content –Full characterization of samples in addition to RCT Test goals –Generate sufficient test data to propose alternative PQD criteria not tied to 1200°C –Attempt to demonstrate ECR is not reduced to zero at elevated hydrogen contents –Determine feasibility of developing an embrittlement model

7 © 2008 Electric Power Research Institute, Inc. All rights reserved. ID Surface Oxygen Uptake Issue & Experimental Evidence Impact of ID surface oxygen uptake is not well understood –RIL-0801 referenced presence of a thin ID oxygen stabilized  layer in Halden test IFA as a justification for assuming equal oxygen uptake from the inner surface of the cladding as the outer surface –Limited oxygen source on the ID: ID surface oxide or fuel bonding layer –Impact of ID surface oxygen uptake is not quantified Data does not support the same magnitude PQD impact from ID surface oxygen uptake Test data do not support fuel bonding layer as an oxygen source –Where fuel bonding takes place there is always an oxide layer between the fuel clad and bonded fuel

8 © 2008 Electric Power Research Institute, Inc. All rights reserved. ID Surface Oxygen Uptake Experimental Evidence Limerick test showed no evidence of more oxygen stabilized alpha layer near bonded fuel Alpha layer (outer) Limerick fuel at GWd/MTu (B): Evidence of some local inner surface oxygen- stabilized alpha NUREG Interpretation (A): This inner-surface region does not have an alpha layer even though in close proximity to fuel material. More typical of what is observed for most of the inner surface at this axial location. ID surface oxide clearly consumed by the clad

9 © 2008 Electric Power Research Institute, Inc. All rights reserved. ID Surface Oxygen Uptake Industry Test Plans Test Goals –Determine if oxygen contained in a thin oxide can generate an oxygen stabilized alpha layer similar to the Halden IFA test –Quantify the effect of ID surface oxide on post quench ductility –Determine if pellet/clad reaction takes place at temperatures around 1100°C and if so to what extend can it be an oxygen source With or without pre-oxidation With or without contact pressure

10 © 2008 Electric Power Research Institute, Inc. All rights reserved. Breakaway Oxidation Issue NRC is considering including a requirement for periodic testing into revised LOCA rule –Time to onset of breakaway oxidation to be based on 200 ppm hydrogen pickup Issues –Requirement precipitate by short breakaway time observed in the Russian E110 alloy E110 is fabricated via an electrolytic process, fundamentally different from the Kroll process used by Western source material suppliers Western alloys are not susceptible to short breakaway oxidation –Realistic LOCA temperature profiles are not isothermal –Visual precursors prior to breakaway can be used to determine breakaway times, no need for 200 ppm hydrogen criteria Better suited for manufacturing environments –Realizes some form of breakaway testing will be required, but should not be addressed in the rule

11 © 2008 Electric Power Research Institute, Inc. All rights reserved. Breakaway Oxidation Industry Position and Test Plans Industry proposes existing QA and qualification procedures are adequate to preclude the effect –Offered an extensive qualification program to establish baseline parameters to preclude breakaway oxidation –Re-qualification for any process changes that could affect breakaway oxidation Isolate cause of breakaway oxidation in E110 –Planning tests to try and determine if the early breakaway phenomenon is due to impurities in the stock material –If successful institute procedures to control identified elements –Conduct breakaway oxidation tests early in the process to reduce risk and burden Collect data in support of a visual standard for breakaway oxidation test

12 © 2008 Electric Power Research Institute, Inc. All rights reserved. Summary Evaluations indicate no significant safety concerns with respect to current design basis, industry will need time to complete planned tests Industry is in the process or planning to conduct further testing to address some of the key issues –LOCA oxidation tests to complement ANL work –ID oxidation tests to evaluate the impact of ID oxygen uptake on PQD –Chemical analyses and oxidation tests to attempt to isolate the cause of short breakaway oxidation time observed in E110 Pre-hydriding appears to be a good surrogate for irradiation; allowing for implementation of new materials in a fast and cost effective manner New rule should be performance based and allow the industry flexibility in demonstrating compliance

13 © 2008 Electric Power Research Institute, Inc. All rights reserved. Together…Shaping the Future of Electricity