Issues associated with the closure of San Onofre NPP

1. Issues associated with the closure of San Onofre NPP Vojin Joksimovich, PhD Anthony J. Spurgin, PhD IEEE Meeting 26th February, 2014

2. AgendaThis seems to be like a Shakespearean play with an assorted group of heroes, fools and villains • VJ: Introductory Remarks/ Background • AJS: Issues associated with Hydro-Elastic effects on Steam Generators: Lifetime limits and Safety issues (tube ruptures) • VJ: Licensing Issues • Comments from Audience • AJS/VJ Summary of Findings

3. Introductory Remarks/Background • Presenters have over century of experience in nuclear industry but no San Onofre insider knowledge; hence provide limited outside view • 437 nuclear plants operate worldwide; 68 under construction, 160 on order/planned • >83% LWRs, ~2/3 PWRs, which use SGs • SGs typically do not last 40 yr design life plus RSG replacement needed for life extension to 60 yrs • The Life of a Steam Generator are affected by chemical effects and so-call hydro-elastic effects. This latter effect is extensively addressed here, since this is what led to the shut-down of San Onofre. • San Onofre, SONGS 1080 MWe Units 2&3, (SCE, SDG&E, Riverside); Palo Verde PVNGS 1333 MWe Units 1-3 (15.8% by SCE), similar CE/Bechtel plants both had to replace SGs • PVNGS contracted with Westinghouse for the design of RSGs and Ansaldo for manufacturing, whilst SCE contracted for both with Mitsubishi Heavy Industries (MHI)

4. Steam Generators:Westinghouse 51 series and Combustion Engineering (system 80)

5. Steam Generators and Tube Rupture Effects • Steam Generators seem to be very simple as a bundle of tubes to exchange heat between the reactor fluid inside the tubes and the water-steam space, are actually very complex • The interaction between the tubes and the steam/water flow involve complex hydraulic forces, structural implications and three dimensional effects. These interactions lead to tube-tube-support structure motions and wear causing tube wall thinning • This wall thinning leads to potential tube ruptures • Another cause of problems is the presence of small amounts corrosive materials in the water concentrated in the evaporation process • Years of experience have dealt with both of the things. With second problem, water treatment has reduced the impact of corrosion • Small improvements in the support structures have increased the life of Steam Generators, this process has been accomplished by the use of computer models of SGs and in the experience of designers

6. Vortex generation: Reynold’s number Flow is from left to right, the SG tube provides the source of the disturbance, leading to a series of vortices. In a SG, the flow is more complex and interactive. The vortices impact other tubes and this is called turbulence One can imagine that the forces generated by the fluid flow on the elastic structure (tubes) leads to impingement of the tubes and wear. The designer of the Steam Generator has to find methods to constrain this movement, while at the same time allow for thermal expansion

7. Replacement of Steam Generators:Views of CE SG supports

8. Steam Generators Support structures requirements: • Supports are required for stability of tubes during operation, avoid tube to tube impact • Supports must allow for thermal expansion from cold to full power conditions, avoid inducing stresses in tubes • Supports must avoid impingement effects on tubes, induced cracking of tubes • The supports are there to help control the movements of the tubes, so that the forces induced by the hydro-elastic effects do not cause tube wear

9. EPRI SG Research Studies • The Electric Power Research Institute (EPRI) has been involved into the research of Steam Generators problems (wear & corrosion) for some number of years, 1980 to present. • Here we are interested in the field of wear, i.e. tube wall thinning, due to the hydro-elastic forces that occur in SGs. These are like the forces that exist in aircraft (aero-elastic forces) • EPRI has taken the study very seriously and it is estimated that ERPI has spent approx $50MM, on the studies • The approaches have led to building a number of computer codes, carrying out experiments and relating predictions to actual results • Some utilities have engaged with EPRI in providing information on wear, locations, which can be correlated to the models • EPRI data, codes and results are restricted to EPRI utilities. SCE is a member of EPRI and should have had full access to all info. • A paper given in 1997 gives information on ‘The Prediction of Tube Wear due to Flow-induced vibration in PWR Steam Generators.’ This discusses various computer codes used in the study and compares results • EPRI has suggested that if utilities made alterations to SG designs they should be tested for incipient wear

10. Steam Generators:NRC Requirements related to tube wear • The NRC laid down criteria for plugging tubes based upon tube wall thickness, in order to avoid possible tube failures leading to radioactive releases: • Measured wear of more than 40% of wall thickness will require plugging • Projected wear extending to 75% of the wall thickness before the next scheduled outage requires repair or plugging • A stabilizer cable or motion limiter is to be installed before the next outage, if the projected wear is expected to exceed 40% of the tube diameter

11. Steam Generators:Safety Considerations • Tube failures can be classified into single tube leaks, single tube ruptures, multiple tube leaks and multiple tube ruptures. • Quite obviously the results of these from a safety point are quite different, a small leak maybe tolerable, whereas a multiple tube ruptures is not • The concern from a safety point of view is that one could lead to another worse state • Given this situation the NRC has set up a set of criteria to prevent just that • On the surface, the small leak at San Onofre was detected (1/31/2012) and the plant shutdown, did not present a hazard • However, in the process of examination of the Steam Generators revealed a large number of tubes did not satisfy the NRC criteria • Subsequently, the tubes, for both plants, were plugged. On the fact that the Steam Generators were now within the criteria limits, they should have been safe to operate at the 70% full Load level and inspections after 5 months of operation

12. Licensing -I • NRC regulations: 10CFR50.59 rule without NRC approval on like for like basis, 10CFR50.90 licensing amendment (LA) • 2001: PVNGS Unit 2 files LA; 2003 LA issued • 2006: SCE informed NRC RSGs implemented under 10CFR50.59 despite 6 design changes • 2011: NRC approved PVNGS life extension for all three units to 2044/2045/2047 respectively • 3/2012 SCE informed NRC about Unit #3 leak (1/31/2012), NRC issued restart roadmap • 6/2012: NRC initiates series of public hearings, reported MHI computer code flawed

13. Licensing -II • 10/2012: After 170,000 inspections and expert consultations SCE proposed Unit 2 restart at 70% power for 5 months: Friends of Earth (FoE) demand legal restart hearings citing PVNGS precedent • 3/2013: NRC posts redacted MHI report admitting high T/H conditions and inadequate supports caused excessive tube wear phenomena • 4/2013: SCE files request for LA at 70% power for 5 months; FoE with support from Senator Boxer filed request for stay of restart • 9/2013: NRC issues notice of non-conformance to MHI/SCE for flawed computer modeling

14. Licensing-III • 5/2013: NRC’s Atomic Safety and Licensing Board (ASLB) ruled SCE needed to obtain LA before restart with associated public hearings • 6/7/2013: SCE after performing economic analyses announced decision to retire both SONGS units citing licensing uncertainties (LA couldn’t be expected before mid/late 2014) and blaming MHI for failure to meet contractual repair or replace requirements • SONGS Opponents triumphant; “We did it”

15. What is the cost of all of this? • There are a number of costs involved : • 2.2 GW replacement power for the grid, Nuclear Power from Palo Verde, cost of alternative energy sources, gas, wind, solar etc • Costs associated with staff, operational (released) and decommissioning , grid related redesign to effect control and stability • Costs associated after decommissioning the plant, storage of parts, and spent fuel storage • Legal costs between SCE, MHI and other concerned parties

16. Who pays the bill? • SCE should have reservoir of money set aside to cover the decommissioning of the units, however plants did not last to full licensed term 2022, unlikely enough in the account to cover the costs • 10/13: CPUC initiated public hearings on SONGS costs; CPUC issued first in series of proposed decisions to protect consumers; $94 MM refunds ($74MM SCE, $19.3 MM SDG&E) citing “unsound decision-making after 5/2012” • Mitsubishi has to cover some costs, less than $4bn requested by SCE in arbitration • Legal costs for SCE arbitration, SDG&E law suit • We expect large amount of the money needed will be obtained from the public, via various mechanisms • Unlikely that anyone will be held directly responsible and face fines or jail