ML13155A430
| ML13155A430 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/23/2013 |
| From: | Arora V - No Known Affiliation |
| To: | Dan Dorman, Macfarlane A, Borchardt R Rules, Announcements, and Directives Branch, NRC/EDO, Office of Nuclear Reactor Regulation |
| References | |
| NRC-2013-0070, 78FR22576 00432 | |
| Download: ML13155A430 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001
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SUNSI Review Complete Template = ADM - 013 E-RIDS= ADM-03 Add= B. Benney (bjb)
Joosten, Sandy From:
Vinod Arora [vinnie48in@gmail.com]
Sent:
Tuesday, April 23, 2013 12:38 AM To:
CHAIRMAN Resource; Dorman, Dan; Borchardt, Bill; Lantz, Ryan; Leeds, Eric; R4ALLEGATION Resource; Benney, Brian; Hall, Randy
Subject:
Updated - San Onofre Dark Past and Dangerous Future The Dark Past of San Onofre A review of nuclear'plant operating history and.A.cademi cR esearch Paper shows thatvoid fractions have to be. 98.5% to prevent forTiation of areas of high dry steam (fluid elastic instability) in nuclear steam generators. According to Dr. Pettigrew, the steam-mixture veiocities in, U-tube bundle have to be 5 20 feet/sec to prevent flow-induced Vibrations. The above parameters. are generally achieved by operating steam generators with circulations~ratios.> 4 and steamn pressures > 900 psi.
The ratio of flow rate of the steam water mixture, which flows through the SG tube bundle, to the flow rate of steam out of the steam nozzle, is called the circulation ratio. It is desirable to maintain a high circulation ratio above > 4 (preferably over 5) to reduce the concentration of chemicals, debris, steam blanketing and steam dry-outs in the SG. San Onofre Unit 3 RSGs had a circulation ratio of around 3.3, which along with high steam flows, lack-of in-plane restraints, narrow tube clearances, excessive number of extremely tall and tightly packed tubes and low pressure of secondary side (838 psi) caused fluid elastic instability (Void fractions > 99.6%, high dry steam) in 4% area of the RSGs.
Everything between San Onofre Units 2 and 3 was the same, except Unit 2 was operating with a steam pressure between 892-942 psi (consistent with NRC AIT Report). At low steam pressure and low circulation ratios, a RSG can produce more heat and more thermal megawatts (more profits in the pocket of SCE). But, low steam pressures and low circulation ratio are severe for vibrations, steam blanketing and steam dry-outs. These are basic elementary facts established about the design and operation of nuclear steam generators prior to San Onofre RSG design, which SCE and Mitsubishi should have known.
Because of the high secondary pressure operation, fluid elastic instability did not occur in Unit 2, which is consistent with Westinghouse Operational Assessment. Contact forces play a role in the out-of plane FEI, but SCE/MHI inadvertently designed better supports and double the contact forces in Unit 2 are not the reason that FEI did not occur In Unit 2. That is just an attempt to mislead the public and NRC and is contested based on an in-depth review of conflicting AREVA, Westinghouse, John Large, SCE and MHI Reports.
Now MHI says, "Thus, not using ATHOS, which predicts higher void fractions than FIT-Ill at the time of design represented, at most, a missed opportunity to take further design steps, not directed at in-plane FEI, that might have resulted in a different design that might have avoided in-plane FEI. However, the AVB Design Team recognized that the design for the SONGS RSGs resulted in higher steam quality (void fraction) than previous designs and had considered making changes to the design to reduce the void fraction (e.g., using a larger downcomer, using larger flow slot design for the tube support plates, and even removing a TSP). But each of the considered changes had unacceptable consequences and the AVB Design Team agreed not to implement them. Among the difficulties associated with the potential changes was the possibility that making them could impede the ability to justify the RSG design under the provisions of 10 C.F.R.§50.59. Thus, one cannot say that use of a different code than FIT-Ill would have prevented the occurrence of the in-plane FEI observed in the SONGs RSGs or that any feasible design changes arising from the use of a different code would have reduced the void fraction sufficiently to avoid tube-to-tube wear.
For the same reason, an analysis of the cumulative effects of the design changes including the departures from the OSG's design and MHI's previously successful designs would not have resulted in a design change that directly addressed in-plane FE."
To reduce void fractions, would have meant (1))ihcrease in circulation ratios, which wouldhave entailed using a larger down-comer, using larger flow slot design for the tube support plates, and.even removing a TSP, (2) increasing the~steam pressure,. Making change (1) would have increased cost, delayed construction and installation schedules, increased shutdown and plugging costs for OSGs.and triggered.the Lengthy.10 CFR 50.90 Licensed Amendment and Public Hearings,..(2) would have reduced the thermal megawatts for RSGs and decreased the profit margins. Now MHI States, "But each of the considered changes had unacceptable consequences and.the AVB Design.Team agreed not.toimplementthem." The question is why were the consequences unacceptable. The consequences were unacceptable for MHI, because MHI, most likely had a fixed contract, and would have lost money in money in the short-term making these changes. But, SCE would have lost money in the short-term and long term, if they would have gone along the changes, that is why the changes were more unacceptable to SCE than MHI. SCE wrote the specifications, were the customer and controlled Money & SCE/MHI AVBDesign Team, that iswhy the change was not mostly beneficial to SCE and may be to. some degree to MHI. That is why. AVB Design Team agreed not to implement them Let us examine the table below. By making these changes, voidfractions and fluidvelocities would have been reduced and the darrage:to both Units 2 and 3 could have been minimized although not fully averted, because fluid velocities due to flow-induced random vibrations caused by high steam flows would have been still higher than 20 feet/second rec mmended by.Dr..Pettigrew. If SCE would hot have made the design changes to increases the heat transfer area by 11%, San Onofre would have been like Plant A, the problems could have been fully avoided; Therefore, the above. statement In MHi reflects beyond the shadow of doubt, negligence, ignorance, excuses and cover-up both byMHI/SCE.
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lc Description Power Steam Circulation Void Fluid Steam Fluid Flow-Level Pressure Ratio Fraction Velocity
- Quality, Elastic induced
feet/sec Instability Random Vibrations
.S53wfi 76f r 4Ait US 1'00°,
8,38ýý'
- ý 3f..34 591;V%*,
252' 9010/ 1
- ES tYES San Onofre Unit.2 99%
892-942 3.3*
98.5%
23
- 75%**
NO YES psi
- San OhbfrUnit:2 70%
946ý si 4.9 92.5%/*
d12 36%
NO NO SaWOrOfr&Unit:'2 80%
939:psi 4.2 97.2%
T14 6:1%,
NO NO PI'i't:A 88%
NIA N/A 98.5%
18 73%
NO NO San Onofre OSG 99%
900 psi 3.2*
96.1%
23
- N/A NO YES 2/3 ANOUnit::t2 N/,A 900:.psi
?r4 98.5%
N/A f75%
NO NO
- Optimum Values:Void Fraction 598.5%, Void Fraction :20 feet/sec, Circulation Ratio. 2 4,.Steam Dome:Pressure.a.900 psi Note: With Unit 2 at reduced 70% power, the circulation ratio and steam generator pressures are 4.87 and 946 psi respectively. This will change void fraction to 92.5% fluid velocity to 12.5 feet/sec and fluid quality to 36%. With Unit 2 at reduced 80% power, the circulation ratio and steam generator pressures are 4.20 and 939 psi respectively. This means void fraction to 97.2%. fluid velocity to 14 feet/sec and fluid quality to 61%. With Unit 3 at 100% power, the circulation ratio and steam generator pressures were 3.26 and 838 psi respectively. Because of lower circulation ratios and lower steam pressures, the void fraction was 99.6%, out-of -plane fluid velocity to 25 feet/sec, in-plane velocity of 50 feet/sec and steam quality to 90%. What this data shows, that RSG would have been safe even with the flawed design, if the steam pressures were at 950 psi and circulation ratios were at < 4, the void fraction would have been 5 98.5% even with high steam flows at 95%
reactor thermal power.
The Dangerous Future of San Onofre San Onofre Unit 2 Retainer Bar and AVB Performance Analysis during Anticipated Operational Transients and MSLB San Onofre replacement steam generators (RSGs) consist of about 9,727 extremely tall and very tightly packed inverted U-tubes. The tubes in each RSG, are arranged in a triangular pitch in 142 rows and 177 columns. The tubes form the boundary separating the steam-water mixture in the secondary circuit from the highly pressurized hot radioactive coolant contained in the primary circuit (tubes). After San Onofre Unit 3 Accident, the integrity and the life expectancy of the Unit 2 tubes are therefore of prime concern 8.4 Million Southern Californians.
The tube bundle top region, known as the U-bend region is supported by a floating Anti-Vibration Bar (AVB) structure consisting of three sets of two V-shaped AVBs between each tube column. The AVBs are made of Type 405 ferritic stainless steel and are equipped with two Alloy 690 end caps. Each AVB end cap is welded to an Alloy 690 retaining bar. The continuous retaining bar wraps around the tube bundle to which is fixed the outboard ends of the AV bars. The retaining bar is pulled in, wrapped around the tube bundle by the hairclip-like retainer bar, this being captured in situ by being threaded through the first two rows of tubes, and held in this position by friction between the retainer bar and the inboard top surfaces of the AV bars. Thirteen Alloy 690 bridges run perpendicular to the retaining bars and hold the entire structure together. A total of 24 Alloy 690 chrome-plated retainer bars welded to the retaining bars is provided to prevent AVB structure displacement during SG fabrication and during anticipated operational transients and main steam line breaks.
In San Onofre replacement steam generators, to accommodate the increased number of tubes, the retainer bars are relatively long and thin as compared to the retainer bars in other SGs designed by MHI, resulting in their having low natural frequencies (56 Hz). The retainer bars anchor the AVB structure to the tubes, but are designed such as to not contact the tubes under operating conditions. The AVB structure is not attached to any other SG component and under operating conditions is held in place by friction between the AVBs and the tubes.
In San Onfre replacement steam generators, the relative motion between the tubes and the anti-vibration bars (AVBs), tube support plates, and the retainer bars have resulted in tube wear and fatigue damage in tubes due to fluid elastic instability (FEI), flow-induced random vibrations and hydrodynamic pressures. SCE, Westinghouse, AREVA, MHI and Intertek have not addressed the synergic effects of tube wear and fatigue damage. These adverse phenomena can produce instant (> 10 minutes) multiple tube failures when the stresses generated during vibrations are sufficiently large due to the collapse of unique MHI anti-vibration bar structure and retainer bars during anticipated operational transients and main steam line breaks as discussed below.
MHI reports, "The Steam Generator tube wear adjacent to the retainer bars was identified as creating a potential safety hazard. The maximum wear depth is 90% of the tube thickness. The cause of the tube wear has been determined to be the retainer bars' random flow-induced vibration caused by the secondary fluid exiting the tube bundle. Since the retainer bar has a low natural frequency, the bar vibrates with a large amplitude. This type tube wear could have an adverse effect on the structural integrity of the tubes, which are part of the pressure boundary.
The plugging of the tubes that are adjacent to the retainer bars was performed. MHI has recommended to the purchaser to remove the retainer bars that would have the possibility of vibration with large amplitude or to perform the plugging and stabilizing for the associated tubes."
Plugging of the at-risk tubes is not a satisfactory solution because it is the retainer bar that vibrates via random fluid flow processes at sub FEI critical velocity levels - these are likely to continue in play or, indeed, exacerbate at the proposed U2 restart at 70% power, leading to through-tube abrasion, the detachment of tube fragments, lodging at other unplugged and in-service tube localities, resulting in the so-called 'foreign object' tube wear. MHI's recommendation that those retainer bars at risk of large-amplitude fluid flow excited vibration should be removed or plugging and stabilizing for the associated tubes is, of course, dependent upon reliable analysis to identify the at-risk assemblies. SCE and MHI have a repeated history of catastrophic design failures and cover-ups with San Onofre RSGs.
During anticipated operational transients and main steam line breaks, the whole u-tube bundle will be subject to fluid elastic instability (due to formation of 100% void fractions) and would be connected to the outside environment as described below. According to the latest research papers, the in-plane velocity caused by fluid elastic instability is more than double the out-of-plane velocity caused by flow-induced random vibrations. Retainer bar vibrations caused by flow-induced random vibrations was the reason identified by MHI to remove the retainer bars that would have the possibility of vibration with large amplitude or to perform the plugging and stabilizing for the associated tubes. Retainer bars 2
Iave not been removed, but more than 180 tubes in SONGS Unit 2 RSGs have been plugged and/or stabilized. The problem stems from that none of the SCE consultants and MHI have analyzed what will happen to the structural integrity of the retainer bars and floating Anti-Vibration Bar (AVB) structure, and thousands of worn, cracked, plugged and stabilized tubes during adverse effects of anticipated operational transients and main steam line breaks. Let us examine the scenarios:
Based on SONGS Unit 3 tube leakage, failure of 8 tubes at main break steam line testing conditions and more than three hundred damaged tubes, the following two potentially risk-significant events have not been considered as beyond-design basis accidents in SONGS NRC Approved FSAR or SCE proposed License Amendment for Unit 2 restart at 70% power with significant adverse consequences:
(1) Operating experience from SONG Unit 3 and design information of RSGs suggests that the potential exists for a line breach to significantly increase RSG leakage, because of resonant, out-of-plane and in-plane vibrations of RSG tubes from a main steam line break. These events could potentially cause increased tube leakage due to multiple tube ruptures resulting from thousands of worn, cracked, plugged and stabilized tubes.
(2) Significant RSG tube leakage could lead to secondary system breaches (lifting of main steam line relief valves) from anticipated operational transients (e.g., a loss of offsite power). The resulting SG secondary side blowdown could further increase tube leakage due to resonant, out-of-plane and in-plane vibrations within the affected SG tube bundle.
From any such leakages, concurrent with containment bypass, these events might cause offsite radiation doses in excess of 10 CFR Part 100 as evaluated in the SONGS FSAR. Any of these two events would cause a simultaneous reactor, turbine, feedwater and reactor coolant trips.
Due to feedwater pump trip, the RSG U-bundle secondary water level will shrink and tubes will be uncovered for a period of at least 10 minutes and experience a sharp drop in secondary side pressure. The entire sub-cooled feedwater inventory contained in the faulted RSG will instantaneously flash to high dry steam. The combination of resonant, out-of-plane, in-plane vibrations, jet impingement forces, broken tube fragments and RSG debris will cause large axial, bending, dynamic and cyclic loads on all the tubes, tube support plates, retainer bars and anti-vibration structure. The strength of the welded and mechanical connections of these low frequency retainer bars, retaining bars and bridges have not been analyzed for the effects of these cumulative loads to prevent AVB structure displacement, deformation or collapse during anticipated operational transients and main steam line breaks. The displacement, deformation or collapse of AVB structure along with the large axial, bending, dynamic and cyclic loads can potentially cause thousands of worn, cracked, plugged and stabilized tubes to exceed several times the allowed tube ASME Endurance Limit of 13.6 ksi. If this happens, multiple tube ruptures will occur at tube-support plates, mid-spans, free spans and tube-to-anti-vibration bar notched interfaces. Since all the water from the RSG would escape to the environment, the iodine-131 from un-partitioned reactor coolant leaking out the rupture tubes will also escape to the environment in less than 10 minutes with 60 tons of radioactive coolant. Consistent with Fukushima Task Force Lessons Learnt and NRC Commissioner Meeting Transcripts, this event will be considered as a beyond design basis event, and SONGS Operators will be unable to take any timely mitigation actions to stop a severe nuclear accident in progress. If the prevailing winds are towards San Clemente, consistent with NRC Inspector General Reports, NRC Studies and observations of SONGS Emergency Plan Drills for the last six years, SCE and Offsite agencies would not have time to respond, notify, evacuate, shelter or give Potassium Iodide to the affected residents within the 10-mile affected emergency planning zone. The casualties, and short, long-term cancer affects to the affected population will depend upon the iodine spiking factor and the duration of blowdown, but will significantly exceed the NRC approved SONGS Control Room limit of 5 Rem Total Effective Dose Equivalent (TEDE), and the Exclusion Area Boundary and Low Population Zone limit of 2.5 Rem TEDE 3