Chief of Nuclear Regulatory Commission investigating San Onofre Nuclear Station information provided by SCE
Saturday, February 9th, 2013
Issue 06, Volume 17.
SAN DIEGO - The chief of the Nuclear Regulatory Commission said today that it is investigating whether information provided by Southern California Edison on the San Onofre Nuclear Generating Station has been complete and accurate.
NRC Chairwoman Allison MacFarlane made the comment in a response to a letter from Sen. Barbara Boxer, D-Calif., and Rep. Edward Markey, D-Mass. sent Wednesday.
The elected officials alleged that a document provides "alarming" evidence that the utility and Mitsubishi Heavy Industries knew that steam generators installed at the plant in northern San Diego County in 2009 and 2010 were problematic.
They said the manufacturer, MHI, authored the cited document.
A steam pressure tube in one of the reactors sprang a small leak a little more than a year ago, forcing the unit to be shut down. The other reactor wasn't operating at the time due to scheduled maintenance.
Neither has been restarted.
"On September 28, 2012, the NRC's Office of Investigations initiated an expansive investigation of the completeness and accuracy of information that Southern California Edison provided to the NRC regarding the steam generators at SONGS," MacFarlane wrote. "This NRC investigation is ongoing, and includes examination of the MHI report along with Advertisement
[ Metalography ] other evidence."
She said the agency is using a variety of regulatory actions, including inspections and investigations, to address the plant's issues. A study of the MHI document is being evaluated as part of a review of SCE's replacement of the steam generators.
Opponents of a plan to restart the reactor that had been undergoing maintenance at the time of the leak contend the utility should have had to go through a rigorous license amendment process before the new steam generators were installed, because they were of a different design.
Boxer reacted to MacFarlane's response by saying the investigations were a "critical factor" in determining whether it was safe to restart the reactors. An NRC decision on a restart is scheduled for late April or early May.
SCE said Wednesday that it is taking the allegations in the Boxer-Markey letter seriously.
"SCE is fully cooperating with the NRC review process and is complying with all requests for information and documents related to the company's San Onofre Nuclear Generating Station," the utility said in a statement. "The plant has provided voluminous records, data, information and other accurate reports as requested in the months since the plant was safely shut down."
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Comment #1 | Saturday, Mar 2, 2013 at 5:28 pm
SCE presentation to NRC was very disappointing. Here is what the Los Angeles Times reported...
Southern California Edison may be at odds with federal regulators over what it means to run the San Onofre nuclear plant at full power. Edison officials met with U.S. Nuclear Regulatory Commission staffers Wednesday to discuss the agency's technical questions on a proposal by Edison to restart one reactor at the shuttered plant and run it at 70% power for five months before taking it back offline for more inspections. The company argued that running the reactor at reduced power will alleviate the conditions that led to unusual wear on steam generator tubes carrying radioactive water. The plant has been out of service for more than a year after one of the tubes in the plant's Unit 3 leaked a small amount of radioactive steam. The NRC has asked Edison to show that Unit 2 -- the unit proposed for restart and which showed less tube damage -- could be run at the full power level allowed under its license without danger of tube rupture. Activists have contended that if Edison fails to prove there is no risk then it should be required to apply for a license amendment to run at 70% power. In a response submitted Monday, Edison argued that 70% power is, in fact, "normal steady state full power." The company said that the "clear purpose" of the technical specification governing tube integrity is "to ensure that the … tubes will retain their integrity over the range of operating conditions to which they will be subjected. In this case, that range is limited to 70% power." Art Howell, who heads an NRC panel focused on San Onofre, told Edison officials Wednesday that "Your position on the technical specification is different than staff's position that was communicated to you on Jan. 29." Edison also promised to provide an analysis by March 15 showing that the unit can safely operate at 100% power. Edison Vice President of Engineering Tom Palmisano told the NRC staff, "We think it's appropriately conservative to operate at reduced power" and continue to collect data. Activists expressed outrage at Edison's response to the NRC request."With all due respect, it reads to me like a schoolboy's justification for why they couldn't complete a homework assignment," said Kendra Ulrich, a nuclear campaigner with the environmental group Friends of the Earth, which has been pushing the NRC to require a license amendment. Ulrich said Edison was "asserting they understand the regulations better than the regulators themselves." NRC staff have said they will make a decision on Edison's restart proposal no earlier than late April. In its quarterly earnings report Tuesday, Southern California Edison's parent company, Edison International, disclosed that the plant's outage has cost the company more than $400 million to date for repairs, inspections and replacement power.
NRC Steam Generator Regulations
The NRC places a high priority on ensuring that possible steam generator tube degradation is carefully addressed through inspections, strict repair criteria and the monitoring of water chemistry to detect radiation leaking from the primary to the secondary side of the plant. In addition, NRC regulations establish requirements for steam generator tube integrity. Tubes must have an extremely low probability of abnormal leakage and must be periodically inspected and tested.
To obtain an operating license, applicants must show that the consequences of a steam generator tube rupture would not exceed the NRC’s conservative limits for radiation doses offsite or outside the plant (described in the agency’s regulations in Title 10 of the Code of Federal Regulations, Part 100). Plant operators also are required to have emergency procedures for mitigating steam generator tube ruptures and leaks.
Once a plant is in service, its operator is required to inspect its steam generators and repair or remove from use any tubes found to contain flaws exceeding certain limits. Each plant’s technical specifications describe the frequency and scope of these inspections and tube repair limits. There are also operational leakage limits to ensure that if the tubes leak beyond these limits, the plant will be shut down quickly. Existing regulations in conjunction with industry guidance and NRC review have been effective in providing reasonable assurance for protecting public health and safety.
San Onofre/SCE Problems
The NRC has asked Edison to show that Unit 2 -- the unit proposed for restart and which showed less tube damage -- could be run at the full power level allowed under its license without danger of tube rupture. SONGS SG Program states, " The structural integrity performance criterion is described in SONGS Unit 2 TS 22.214.171.124.b.1 as follows: All in-service steam generator tubes shall retain structural integrity over the full range of normal operating conditions (including startup, operation in the power range, hot standby, cool down and all anticipated transients included in the design specification) and design basis accidents. Tubes found by in-service inspection to contain flaws with a depth equal to or exceeding 35% of the nominal tube wall thickness shall be plugged.” When Unit 3 was shutdown due to a leakage, 381 tubes in Unit 3 and 6 tubes in Unit 2 had a wear > 35%. The question is not that SONGS operates Unit 2 at 70% Power or 100% power. Really the question is, whether the plant can withstand FEI, let us say, at 70% power during accident conditions or anticipated operational transients.
Honorable Chairman Dr. McFarlane has publicly stated that SCE is responsible for the Work of MHI and other contractors. Let us look at a few problems below:
1. The first problem last time was that MHI did not benchmark the computer codes or used 100% mock up for SONGS High Steam Flows and SCE did not check their work.
2. The second problem was that SONGS Certified Design Specification did not specify the Value of FEI or SR and MHI did not design the RSGs for in-plane vibrations.
3. The third problem was that SONGS Certified Design Specification implicitly implied MHI to avoid the NRC License Amendment Process and make the tube bundle as tall as possible to achieve the maximum heat transfer area.
4. The fourth problem was that SCE or MHI did not review NUREG-1841 to see how Westinghouse and BWI were designing CE Replacement Generators AVBs to avoid excessive tube vibrations and areas with high dry steam.
5. The fifth problem is that SCE/MHI did not review the research papers by Dr.Pettigrew and Dr. Mureithi published in 2006, which states “In nuclear power plant steam generators, U-tubes are very susceptible to undergo fluid elastic instability because of the high velocity of the two-phase mixture flow in the U-tube region and also because of their low natural frequencies in their out of plane modes. In nuclear power plant steam generator design, flat bar supports have been introduced in order to restrain vibrations of the U-tubes in the out of plane direction. Since those supports are not as effective in restraining the in-plane vibrations of the tubes, there is a clear need to verify if fluid elastic instability can occur for a cluster of cylinders preferentially flexible in the flow direction. Almost all the available data about fluid elastic instability of heat exchanger tube bundles concerns tubes that are axisymmetrically flexible. In those cases, the instability is found to be mostly in the direction transverse to the flow. Thus, the direction parallel to the flow has raised less concern in terms of bundle stability.”
6. The sixth problem is Westinghouse OA ATHOS Analysis shows Unit 2 had 99.6% vapor fraction (FEI) and fluid velocities of 28 feet/sec, but based on results of ECT inspection, Westinghouse concludes that unit 2 did not experience FEI. Westinghouse also states, “Test data shows that the onset of in-plane (IP) vibration requires much higher velocities than the onset of out-of-plane (OP) fluid-elastic excitation. Hence, a tube that may vibrate in-plane (IP) would definitely be unstable OP. A small AVB gap (3 Mil) that would be considered active in the OP mode would also be active in the IP mode because the small gap will prevent significant in-plane motion due to lack of clearance (gap) for the combined OP and IP motions. Thus, a contact force is not required to prevent significant IP motion. Manufacturing Considerations: None were extensively treated in the SCE root cause evaluation.”
7. The seventh problem is AREVA states, “At 100% power, the thermal-hydraulic conditions in the U-bend region of the SONGS replacement steam generators exceeded the past successful operational envelope for U-bend nuclear steam generators based on presently available data. The primary source of tube-to-AVB contact forces is the restraint provided by the retaining bars and bridges, reacting against the component dimensional dispersion of the tubes and AVBs. Contact forces are available for both cold and hot conditions. Contact forces significantly increase at normal operating temperature and pressure due to diametric expansion of the tubes and thermal growth of the AVBs. After fluid elastic instability develops, the amplitude of in-plane motion continuously increases and the forces needed to prevent in-plane motion at any given AVB location become relatively large. Hence shortly after instability occurs, U-bends begin to swing in Mode 1 and overcome hindrance at any AVB location.”
8. The eight problem is that the average heated length of the tubes is too much (730 inches in RSGs versus 680 inches in OSGs. Unit 3 has historically produced more power than Unit 2 (1186 MWe vs. 1183 MWe, 1178 MWe vs. 1172). Westinghouse states, “In the U-bend region, the gap velocities are a strong function of power level. The steam flow in the bundle is cumulative and increases as a function of the power level and the bundle height which causes high fluid quality, void fraction, and secondary fluid velocities in the upper bundle.”
9. The ninth problem is that RSGs were operating at a circulation ratio of 3.3. Most of The CE RSGs are running at a circulation ratio of 5.0 or more.
10. The tenth problem AREVA Reports, “There are 36 U-bends in Unit 2 SG E-088 and 34 in SG E-089 with a separation less than or equal to 0.050 inches.” These tubes are the first ones to break/rupture in 5 months or during an accident.
11. The eleventh problem is that latest research paper in 2011 indicate that during FEI conditions, two-phase cross flow velocities are double on both sides of the U-bend compared to middle portion of the U-bend. According to Dr. Pettigrew, FEI is mostly in the in-plane direction with a small component in the out-of–plane direction. FEI out-of–plane direction velocities are high enough that it can move the AVBs out of their way irrespective of the contact force. When the AVBs are not designed for FEI, who will believe Pete Dietrich version of insufficient contact forces and manufacturing dispersions causing FEI in Unit 3 (loose supports) theory, which was reluctantly accepted by MHI. FEI did not occur in Unit 2, so there goes the double contact forces not causing FEI in Unit 2 (Better supports) out of the window.
12. The twelfth problem is that tube and support interaction leading to rapid wear in the U-bend region is a complex, highly nonlinear process involving impact dynamics, friction, boundary conditions and forcing functions that change with time during the process. Westinghouse is projecting wear of 2 Unit tubes with wear depth of 28% to 31.5% in 6 months based on benchmarking of Unit 3. There are a lot of assumptions and uncertainties in this analyses. SCE is taking credit of this OA as deterministic analysis. Lot of anonymous SG Experts from industry and my Asian Friends from the NRC and MIT are questioning the validity of Westinghouse, AREVA, Intertek, SCE and MHI Analyses. These analyses are contradicting, confusing, ambiguous, full of holes, smoking mirrors and fail to arrive at a clear and unanimous conclusions. Public Independent Experts (EX-NRC Branch Chiefs, MIT Staff need to perform a GAP Analysis to weed out the uncertainties and resolve the difference and Publish a Public Report before even thinking of giving a clear signal for SCE to Restart Unit 2.
Senator Boxer needs to start an inquiry with SCE/MHI Engineers testifying under oath as to what was wrong with the Original Combustion Engineering Steam Generators and what Industrial and Academic Research Benchmarking did they do to fix these problems in the SONGS MHI Replacement Steam Generators. Recommend a Joint Committee headed by US Justice Department and Independent Steam Generators Expert specializing in Thermal Hydraulics, Chemical, Nuclear, Reactor Engineering, Computer Modeling, Design Bases Accidents, 10 CFR 50.59 and FSAR. These Experts need to determine the exact Root Cause of damage to San Onofre Unit 3 Replacement Steam Generators and a damage assessment difference between Units 2 & 3.