ML040500468
| ML040500468 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/30/2003 |
| From: | NRC/RGN-III |
| To: | |
| References | |
| Download: ML040500468 (6) | |
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September 2003 This is the thirteenth periodic update on the NRC response to the reactor vessel head damage at the Davis-Besse Nuclear Power Station. The updates will be available at public meetings of the NRC Davis-Besse Oversight Panel which is coordinating the agencys activities related to the damage. Each update will include background information to assist the reader in understanding issues associated with the corrosion damage.
NRC inspection underway NRC Inspections: Ongoing, Planned to monitor 7-day test and Reports Pending The NRC is conducting a special inspection to The NRC has a series of inspections planned before monitor a seven-day test of Davis-Besses reactor any decision on whether or not the Davis-Besse plant cooling system. may resume operations. These inspections include:
The reactor will not be started up for the test. Heat generated by the cooling system pumps will be Ongoing - Management and Human sufficient to raise the pressure in the reactor and Performance, Phase III (Safety Culture) -
associated piping to approximately 2155 pounds This inspection focuses on FENOCs per square inch -- the normal operating pressure - actions to improve management and approximately 530 degrees Fahrenheit, which effectiveness and human performance is near the normal operating temperature. and its processes to survey and assess the safety culture among the staff at The test is being conducted to assure that the Davis-Besse - how the management and reactor cooling systems, including the new reactor workers will identify and deal with safety vessel head, are leaktight. concerns.
The test will also assess FirstEnergys position that Report Pending - Corrective Action there is no leakage from the bottom of the reactor Team Inspection - This inspection looked vessel. There are 52 tubes which pass through at the effectiveness of the corrective the bottom wall of the reactor vessel to carry action program at Davis-Besse - how the reactor monitoring instrumentation. During an utility finds, evaluates, and fixes inspection of the reactor bottom last year, problems.
FirstEnergy identified chemical staining on the Report Pending - Safety System surface of the reactor vessel around the tubes. Design Reviews - The utilitys Systems Health verification program and earlier The utility determined that the source of the staining was leakage from the refueling area NRC inspections had found potential during refueling or runoff from cleaning activities design questions that needed to be for the reactor vessel head. An earlier test at a resolved. This inspection looked at the lower reactor pressure (250 psi) showed no effectiveness of the design reviews.
evidence of leakage from the bottom of the reactor Ongoing - Reactor Cooling System vessel. Test (Normal Operating Pressure) - This inspection will monitor the plants test of The NRC inspection team will focus on the test the reactor vessel and associated piping itself, examining the reactor vessel before and after the test, and also independently reviewing the
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 2 utilitys test data and evaluation. In addition, the NRC resident inspectors assigned to the plant, assisted by inspectors from the Region III office, will monitor the utilitys performance during the test.
On September 5 the NRC staff issued a license amendment to FirstEnergy to permit the plant NRC Inspections: Ongoing, Planned to perform the test without correcting a and Reports Pending potential problem with two high pressure emergency pumps. The utility previously found (continued) that the pumps might malfunction under certain conditions during a reactor accident. to assure there are no leaks in the system.
Since the reactor will not be started up for the test and since it has not operated for 18 Planned - Restart Assessment Team -
months, the NRC review found that the pumps As the utility nears the point where it will would not be exposed to the conditions that seek NRC authorization for restart, this might cause a malfunction. After the test is team inspection will thoroughly review the completed, FirstEnergy plans to modify the readiness of the plant and the plant staff to pumps to eliminate the potential problem. The resume plant operations safely and in pump problem must be resolved before the compliance with NRC requirements.
plant is permitted to resume operations.
The NRC inspection team will issue a report about 30 days after the completion of the inspection. The report will be available on the NRCs Davis-Besse web site under News and Correspondence. The NRCs license amendment and the safety evaluation supporting the amendment will also be available on the web site.
NRC Safety Culture Inspection Continues An NRC inspection team is continuing its review of FirstEnergys efforts to evaluate and improve the safety culture at the Davis-Besse plant. This review includes the utilitys program to foster a "safety conscious work environment" in which workers feel free to raise safety issues without fear of retaliation.
The remaining inspection activities are (1) review of the process for the plants internal assessment of safety culture; (2) observation of the activities of the plants Safety Conscious Work Environment Review Team; and (3) review of FirstEnergys plan for long-term improvement actions and assessment of plant staff safety culture.
FirstEnergy will meet with the NRC staff at the Region III Office in Lisle, Illinois, on October 1 to present its plans for long-term improvement actions and assessment of the plant staffs safety culture. The meeting will be open to public observation, and interested persons can also listen to the meeting by telephone. Details on how to participate will be on the NRCs Davis-Besse web site.
Third inspector added to NRC resident staff Monica Salter-Williams is a new NRC resident inspector at Davis-Besse, joining Senior Resident Inspector Scott Thomas and Resident Inspector Jack Rutkowski. The NRC normally assigns two resident inspectors at each nuclear plant, but has increased the Davis-Besse staff to better monitor activities there.
Ms. Salter-Williams has been a reactor engineer with the NRCs Region I office in Pennsylvania since May 2002. She was previously an engineer at a nuclear power plant in Pennsylvania. She has a masters degree in nuclear engineering from Pennsylvania State University and a bachelors degree in chemistry from Georgia State University.
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 3 NRC issues notice to industry on computer worm incident Mail Call The NRC has issued an Information Notice to all nuclear plant operators informing them of a computer security The NRC continues to receive incident in January 2003 at Davis-Besse in which a letters and e-mails expressing computer worm affected two plant computer systems. The interest and concern about Davis-worm infection increased data traffic in the plants computer Besse -- now totaling several network, resulting in the Safety Parameter Display System thousand.
and plant process computer being unavailable for several hours. These systems provide useful information to plant The agency will respond to all operators, but do not affect plant safety. NRC regulations individual letters and e-mails sent require safety-related systems to be isolated or have send- in by interested members of the only communication with other systems. public.
FirstEnergy investigated the incident and found a contractor established an unprotected computer connection to its corporate network, through which the worm reached the plant network. The investigation also found plant computer engineering personnel were unaware of a security patch that prevented the worm from working.
Corrective actions included requiring documentation of all external connections to the internal network, installing an additional layer of security software, and ensuring computer personnel review new security patches and install them promptly.
The utility notified the NRC resident inspectors and the NRC regional office when the computer security incident occurred. The NRC Regional Office and Office of Nuclear Security and Incident Response was also notified and evaluated the incident.
Davis-Besse Restart Checklist The Oversight Panel has created a restart checklist categorizing 31 actions in seven major areas which FirstEnergy needs to complete before the NRC can consider making a decision on whether Davis-Besse may restart. The NRC oversight panel has determined that the utility has adequately completed 18 of those actions.
NRC inspections are directed at evaluating the checklist items as well as reviewing the ongoing work at Davis-Besse.
The completed items are shown in italics and have a check mark in front of the item. For the completed items, the list also includes the inspection report which documents the NRCs review of the item. Two items were completed in the past month - 2.c.1 - the containment sump modifications and 6.g. - a license amendment.
- 1. Adequacy of Root Cause Determinations U 1.a Penetration Cracking and Reactor Pressure Vessel Corrosion (Report No. 50-346/03-04)
U 1.b Organizational, Programmatic and Human Performance Issues (Report No. 50-346/02-18)
- 2. Adequacy of Safety Significant Structures, Systems, and Components 2.a Reactor Pressure Vessel Head Replacement U 2.b Containment Vessel Restoration Following Reactor Pressure Vessel Head Replacement (Report No. 50-346/03-08) 2.c Structures, Systems, and Components Inside Containment U 2.c.1 Emergency Core Cooling System and Containment Spray System Sump (Report No. 50-346/03 to be issued) 2.d Extent-of-Condition of Boric Acid in Systems Outside Containment 2.e High Pressure Injection Pump Internal Clearance/Debris Resolution
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 4
- 3. Adequacy of Safety Significant Programs 3.a Corrective Action Program U 3.b Operating Experience Program (Report No. 50-346/03-09) 3.c Quality Audits and Self-Assessments of Programs U 3.d Boric Acid Corrosion Management Program (Report No. 50-346/03 to be issued)
U 3.e Reactor Coolant System Unidentified Leakage Monitoring Program (Report No. 50-346/03-09)
U 3.f In-Service Inspection Program (Report No. 50-346/03-09)
U 3.g Modification Control Program (Report No. 50-346/03-09)
U 3.h Radiation Protection Program (Report No. 50-346/03 to be issued) 3.i Process for Ensuring Completeness and Accuracy of Required Records and Submittals to the NRC
- 4. Adequacy of Organizational Effectiveness and Human Performance U 4.a Adequacy of Corrective Action Plan (Report No. 50-346/02-18) 4.b Effectiveness of Corrective Actions
- 5. Readiness for Restart 5.a Review of Licensees Restart Action Plan 5.b Systems Readiness for Restart 5.c Operations Readiness for Restart 5.d Test Program Development and Implementation
- 6. Licensing Issue Resolution (Not discussed in inspection reports)
U 6.a Verification that Relief Requests A8 and A12 regarding the Shell to Flange Weld (previously submitted by letter dated September 19, 2000) is not Impacted by the Midland RPV Head U 6.b American Society of Mechanical Engineers (ASME) Code Relief Request for Failure to Maintain Original Radiographic Tests of the Midland Head to Flange Weld (Planned Relief Request A26)
U 6.c ASME Code Relief Request for Inability to Radiographically Test 100% of the Midland Reactor Pressure Vessel Head to Flange Weld (Planned Relief Request A27)
U 6.d Resubmit Relief Request A2 (previously submitted by letter dated September 19, 2000) for ASME Code for Inability to Perform 100% volumetric and surface examination of Head to Flange Weld U 6.e Reconciliation Letter that Demonstrates How the New Reactor Pressure Vessel Head Correlates With the ASME Code and QA Index for Section III and Section XI - Commitments U 6.f Verification Letter of Technical Specification Pressure/Temperature Curves for New Vessel Head
- Commitment U 6.g Request to relocate High Pressure Injection and Low Pressure Injection Subsystems Flow Balance Testing from Technical Specifications 4.5.2.h to Updated Safety Analysis Report Technical Requirements Manual
- 7. Confirmatory Action Letter Resolution 7.a Verification that Confirmatory Action Letter Items are Resolved, Including a Public Meeting to Discuss Readiness for Restart Background Summary: What Happened at Davis-Besse Next Davis-Besse NRC Oversight Panel Meetings 2 p.m. and 7 p.m., Tuesday, October 7 Oak Harbor High School
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 5 In March 2002 plant workers discovered a cavity in the head or top of the reactor vessel while they were repairing control rod tubes which pass through the head. The tubes, which pass through the reactor vessel head, are called control rod drive mechanism nozzles. Cracks were detected in 5 of the 69 nozzles.
In three of those nozzles, the cracks were all the way through the nozzle, allowing leakage of reactor cooling water, which contains boric acid.
Corrosion, caused by the boric acid, damaged the vessel head next to Nozzle No. 3, creating an irregular cavity about 4 inches by 5 inches and approximately 6 inches deep. The cavity penetrated the carbon steel portion of the vessel head, leaving only the stainless steel lining. The liner thickness varies somewhat with a minimum design thickness of 1/8 inch. Subsequent examination by Framatome, FirstEnergys contractor, found evidence of a series of cracks in the liner, none of which was entirely through the liner wall.
After circumferential cracks - around the nozzle wall - were found in the control rod drive nozzles at Unit 3 of the Oconee Nuclear Power Station in 2001, the NRC required all pressurized water reactor (PWR) operators to report to the NRC on structural integrity of the nozzles and their plans to inspect the nozzles. Plants with similar operating history to Oconee Unit 3, including Davis-Besse, were to inspect their reactor vessel head penetrations by December 31, 2001, or to provide a basis for concluding that there were no cracked and leaking nozzles.
FirstEnergy Nuclear Operating Company requested an extension of the inspection deadline until its refueling outage beginning March 30, 2002, and provided the technical basis for its request. The NRC did not allow the plant to operate until March 30, but agreed to permit operation until February 16, provided that compensatory measures were taken to minimize possible crack growth during the time of operation. The NRC was unaware that nozzle leakage or corrosion had occurred at Davis-Besse when it agreed to the February 16 date.
Barriers Built into Nuclear Plants to Protect Public Health and Safety The design of every nuclear power plant includes a system of three barriers which separate the highly radioactive reactor fuel from the public and the environment. The Davis-Besse reactor head damage represented a significant reduction in the safety margin of one of these barriers, the reactor coolant system.
The reactor coolant system, however, remained intact, as well as the other two barriers, the fuel and the containment.
- 1. Fuel Pellets and Rods The first barrier is the fuel itself. The fuel consists of strong, temperature-resistant ceramic pellets made of uranium-oxide. The pellets are about the size of a fingertip. They retain almost all of the highly radioactive products of the fission process within their structure.
The pellets are stacked in a rod made of a zirconium alloy. At Davis-Besse, each fuel rod is about 13 feet long. The rods are assembled into bundles, with each assembly containing 208 rods. The reactor core contains 177 fuel assemblies. Any fission products which escape from the pellets are captured inside the cladding of the rod, which is designed to be leak-tight.
Small pin hole leaks do occasionally occur, however, and the operating license requires leakage monitoring and contains limits on the maximum allowable leakage of radioactive materials from the fuel rods.
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 6 The second barrier is the reactor coolant system pressure boundary. The reactor core is contained inside the reactor pressure vessel, which is a large steel container. Thick steel pipes supply cooling water to the reactor and carry away the heated water after it passes through the reactor core. The pressure vessel, the connected piping, and other connected components make up the reactor coolant system pressure boundary. At Davis-Besse, the reactor coolant system contains about 60,000 gallons of cooling water, circulated by four large pumps at a rate of about 360,000 gallons per minute.
This system is designed to be leak-tight at operating conditions which include a water temperature of 605E F and a water pressure of 2,150 pounds per square inch. The operating license contains limits on the maximum allowable amount of leakage from the system, and it specifies requirements for monitoring any leakage. If a leak is identified as being through any solid wall of the system (reactor vessel, cooling pipes or other components) continued operation of the plant is prohibited, no matter how small the leak rate.
- 3. Containment Building The third barrier is the containment building. This is a large cylindrical building which contains the entire reactor coolant system. None of the piping that contains the high-temperature and high-pressure reactor coolant water extends outside the containment building. The containment is a 1 1/2 inch thick steel cylinder, rounded at the top and bottom, which is designed to be leak-tight. This steel structure is surrounded by a reinforced concrete shield building, which is the round building visible from the outside of the plant. Its walls are 2 to 3 feet thick.
NRCs Response to Vessel Head Damage The NRC responded to the vessel head degradation with a series of actions, some specific to Davis-Besse and others aimed at other PWR plants. The agency directed all PWR licensees to report on the condition of their reactor heads and later specified more stringent examination for inspecting the reactor heads. The NRC also established a Lessons Learned Task Force to review the agencys activities associated with the Davis-Besse reactor head issue.
NRC Davis-Besse Oversight Panel An NRC Davis-Besse Oversight Panel was created in April 2002 to make sure that all corrective actions, required to ensure that Davis-Besse can operate safely, are taken before the plant is permitted to restart and that Davis-Besse maintains high safety and security standards if it resumes operations. Should the plant restart, the Oversight Panel will evaluate if Davis-Besses performance warrants reduction of the NRCs heightened oversight and, if so, recommend to NRC management that the plant return to a regular inspection schedule. The panel was established under the agencys Manual Chapter 0350.
The panel brings together NRC management personnel and staff from the Region III office in Lisle, Illinois, the NRC Headquarters office in Rockville, Maryland and the NRC Resident Inspector Office at the Davis-Besse site. The eight-member panels chair and co-chair are John Grobe, a senior manager from Region III, and William Ruland, a senior manager from NRC headquarters.
The agency will also supplement the resident inspection staff with an additional resident inspector who be at Davis Besse in September, bringing the total staff there to three.
NRC Update: Davis-Besse Reactor Vessel Head Damage DRAFT September 2003 - Page 7 Public Participation in the Process The NRCs experience is that members of the public, including public officials and citizens, often raise questions or provide insights that are important to consider. If you have questions or want to provide information or a point of view, please contact us. For feedback on this newsletter, contact Viktoria Mitlyng 630/829-9662 or Jan Strasma 630/829-9663 (toll free 800/522-3025 - ext -9662 or -9663). E-mail:
opa3@nrc.gov. Extensive information about the Davis-Besse reactor vessel head damage and the ensuing activities is available on the NRC web site: http://www.nrc.gov - select Davis-Besse under the list of key topics.