ML030140268

January 2003 Davis-Besse Reactor Head Damage, NRC Update

ML030140268
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Site:	Davis Besse
Issue date:	01/06/2003
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January 2003 This is the fifth 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 Activities: Ongoing NRC Inspections:

1. The NRC staff will conduct a public meeting 1. The Management and Human Performance January 30 with FirstEnergy officials in the Inspection completed its evaluation of FirstEnergys NRC Region III office in Lisle, Illinois, to root cause analysis associated with management, discuss the status of the companys evaluation organizational effectiveness and human performance of safety culture issues among the plant factors that are believed to have led to the degradation management and staff and its programs to of the reactor head. The inspection will now focus on address those issues. The meeting time and the adequacy of licensees proposed corrective actions additional details will be added to the public to create a more safety-focused environment and the meeting listing on the NRCs web site when efficacy of these actions.

arrangements are finalized. Teleconferencing will be available for persons unable to attend. 2. The Program Effectiveness Inspection is reviewing the plants progress in creating more

2. NRC staff will observe the licensees effective programs. The review of the corrective preparations and reloading of reactor fuel. actions and boric acid corrosion control programs has been completed. NRC inspectors are currently

3. NRC staff will inspect the first phase of the reviewing the plants in-service inspection and the modification to the sump screen planned by operating experience programs, including the the licensee to increase the area of the sump adequacy of improvements and their implementation.

strainers in the reactor containment to ensure that the strainers do not get clogged by debris 3. The Systems Health Inspection continues to which might collect at the bottom of the assess the licensees review of specific safety containment. The sump is a collection point significant plant systems, such as the emergency for water that would be recirculated for reactor reactor cooling systems and standby power systems.

cooling in the event of a loss-of-coolant The goal of this inspection is to verify that the plants accident. This sump modification, which was safety significant systems can perform their safety not required by the NRC, has been initiated by functions as designed.

FirstEnergy to create additional surface area of the sump strainers, which will substantially 4. The Two NRC resident inspectors continue their improve the plants design safety margin. inspections of day-to-day activities as well as supporting the specific inspections underway.

4. NRC staff will observe the Integrated Leak Rate Tests designed to verify that the reactor containment, which was cut open to move the new and old reactor vessel heads, meets NRC requirements for leak-tightness.

5. FirstEnergy will conduct a special seven-day pressure test of the reactor cooling system at normal operating temperature and pressure to determine if the system is leak tight. This test will be performed after

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 2 fuel has been loaded in the reactor, but before FirstEnergy seeks authorization from the NRC staff to restart the plant. (The reactor will not be started up for the test; heat added through the operation of the reactor cooling pumps will be sufficient to reach normal operating temperature and pressure.) The NRC staff will perform several specific inspections leading up to the test and during the test.

NRC Issues Reports on Two Special Inspections The Nuclear Regulatory Commission staff has issued reports for two special inspections related to work on steam generators at the Davis-Besse Nuclear Power Plant in February of last year that led to elevated worker radiation exposures and offsite radioactive contamination. The exposures and contamination were not related to the corrosion damage to the reactor vessel head.

On February 20 several contract workers were exposed to unexpected radiation levels while performing work on the steam generators and were contaminated both internally and externally with radioactive material. The workers underwent decontamination procedures before they were allowed to leave the plant site. Evaluation by the utility and the NRC found that none of the workers received radiation exposures beyond NRC limits.

Four of the contract workers were found to have minor radioactive contamination on their clothing when they reported for work at nuclear power plants in South Carolina and Texas. Utility radiation specialists surveyed the temporary housing used by the workers and other associated places and found tiny radioactive particles at several locations in Ohio, Virginia, and South Carolina.

The inspection of the worker radiation exposures resulted in two findings with a preliminary evaluation of white, indicating low to moderate safety significance:

 The utility failed to conduct adequate evaluations of the radiological work conditions prior to the steam generator work.

 The utility failed to make suitable measurements of radioactive material in the work area and to adequately monitor the intake of radioactive material by the workers.

The inspection which focused on the offsite radioactive contamination resulted in one green finding, meaning that it was of very low safety significance:

 Inadequate radiation surveys of the workers resulted in the uncontrolled release from the plant of low levels of radioactive material on their clothing. The low level of radioactivity involved was found to present little potential health risk to the workers or the general public.

The reports note that the utility has adopted corrective actions in its radiation protection program to preclude similar problems in the future. The utilitys radiation protection program, including its corrective actions, will be covered by NRC inspections prior to a decision by the agency on restart of the Davis-Besse facility.

NRC Inspector General Issues Report, Commission Responds The NRCs Inspector General issued a report December 30, 2002, on the findings of its inquiry into the agencys Regulation of Davis-Besse Regarding Damage to the Reactor Vessel Head. On January 6, 2003, NRC Chairman Richard Meserve responded to the report with a memorandum to the Inspector General. Both documents are available on the NRCs web site: http://www.nrc.gov. For the Inspector Generals report, select the Inspector General link at the bottom left of the page, and then click on the OIG Reports link. For the Chairmans reponse, select Davis-Besse from the key topics menu and the select News and Correspondence.

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 3

Background:

What Happened at Davis-Besse 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 NRCs Lessons Learned the vessel head, leaving only the stainless steel lining.

The liner thickness varies somewhat with a minimum The Nuclear Regulatory Commission is design thickness of 1/8 inch. Subsequent examination meeting January 14 with the agencys staff to by Framatome, FirstEnergys contractor, found evidence discuss the Lessons Learned Task Force of a series of cracks in the liner, none of which was Report, which focused on the agencys entirely through the liner wall. handling of issues related to the reactor vessel head damage, and with the Senior Earlier indications of the problem: Through-Wall Management Review Team, which has Cracking of Nozzles in France and at the Oconee developed plans for appropriate agency action Nuclear Power Station in South Carolina on the task force recommendations.

In the early 1990's control rod drive mechanism nozzle The review teams recommendations and any cracking was discovered at a nuclear plant in France. resulting commission actions will be available These cracks penetrated the nozzle wall along the length on the NRC web site. The meeting transcript of the nozzle (referred to as 'axial' cracking). In 1997 the and related documents will be on the web site NRC issued Generic Letter 97-01 to gather information at:

on the inspection activities for possible cracking in the control rod drive mechanism nozzles in plants in the http://www.nrc.gov/reading-rm/doc-collections/

United States. Subsequently, through-wall commission/

circumferential cracks -- around the nozzle wall -- were discovered in two control rod drive mechanism nozzles at the Oconee Nuclear Power Station, Unit 3, in 2001. While axial cracking had been found at several other plants and repaired, circumferential cracking had not been seen before. Circumferential cracking is more significant because it could lead to complete separation of the nozzle and a resulting loss-of-coolant accident.

After the Oconee discovery, the NRC issued Bulletin 2001-01, requiring all pressurized water reactor (PWR) operators to report to the NRC on structural integrity of the nozzles, including the extent of any nozzle cracking and leakage and their plans to ensure that future inspections would guarantee structural integrity of the reactor vessel boundary. The NRC's Bulletin instructed nuclear power plants with similar operating history to Oconee Unit 3, including Davis-Besse, 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.

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 4 Boric Acid Corrosion Control Procedure The water that circulates through a pressurized water reactor to cool the nuclear fuel contains a low concentration of boric acid. This borated water can potentially leak through flanges, pump and valve seals, and other parts of the reactor cooling system and cause corrosion.

The NRC has taken steps to make sure that PWR operators are aware of and pay attention to the corrosion boric acid can cause in certain environments:

• In 1986-89, the NRC issued a series of documents, called generic communications, informing PWR licensees that boric acid can corrode and damage steel reactor components.

• The NRCs Generic Letter 88-05 requested PWR operators to implement a program to ensure that boric accid corrosion does not lead to degradation of the reactor cooling system components. All nuclear power plants with PWRs, including Davis-Besse, reported to NRC that the Boric Acid Control Procedures had been established and would be implemented.

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 little finger-tip. 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.

2. Reactor Coolant System 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.

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 5 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 began a review of its regulatory activities as well.

Davis-Besse On March 12, 2002, the NRC initiated an Augmented Inspection Team to examine conditions that led to the head degradation and on March 13, 2002, the NRC issued a Confirmatory Action Letter to Davis-Besse documenting a number of actions the plant needed to implement for the unit to be allowed to restart. On April 29, 2002, the NRC established an Oversight Panel under the Agencys Manual Chapter 0350, to coordinate and oversee NRC activities necessary to address repairs and performance deficiencies at the plant in order to guarantee that it can operate safely. The plant will not restart until the NRC is satisfied that plant operators have met all necessary safety requirements.

Generic On March 18, 2002, the NRC issued Bulletin 2002-01, instructing PWR licensees to report on the condition of their head, past incidents of boric acid leakage and the basis for concluding that their boric acid inspection programs were effective. All plants sent their responses and indicated that no evidence of extensive corrosion of reactor vessel heads was found at these plants. On August 9, 2002, the NRC issued Bulletin 2002-02 advising PWR operators that more stringent inspection techniques may be necessary to detect head penetration nozzle cracks. Visual examination of reactor vessel heads and nozzles may need to be supplemented with other inspection techniques, such as the use of ultrasound, electric currents and liquid dyes. In October, the agency also requested PWR licensees to provide additional information on their boric acid inspection program with greater detail than initially covered in the responses to Bulletin 2002-01.

NRC Davis-Besse Oversight Panel An NRC Davis-Besse Oversight Panel was created 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

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 6 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 Dean, a senior manager from NRC headquarters.

As part of determining if plant corrective actions are adequate to support restart, the Oversight Panel will evaluate FirstEnergy's return to service plan, which is divided into seven areas of performance that the utility calls "building blocks." A series of NRC inspections are being performed to verify the company is taking proper actions in each of the seven areas. These reviews will include the work by the FirstEnergy staff and, in addition, the NRC staff will perform independent inspections in each of the "building block" areas.

Issues to be resolved in order for Davis-Besse to restart The NRC Oversight Panel will only consider recommending that Davis-Besse resume operations when the plant has demonstrated its readiness to operate safely. Key elements will include:

• Davis-Besse management and personnel properly understand the technical, organizational, programmatic and human performance problems that led to the extensive degradation of the plants reactor vessel head.

• Davis-Besse enhances programs for operating the plant safely, detecting and correcting problems, controlling boric acid corrosion, and is fostering a more safety-conscious environment among plant managers and workers.

• Davis-Besse improves the performance standards of its managers and workers, including their ownership of the quality of work products and the safety focus of decision-making.

• The replacement of the vessel head is technically sound and all reactor components are inspected, repaired as necessary, and demonstrated to be ready for safe operation.

• Plant safety systems inside and outside containment are inspected, repaired as necessary, and have been confirmed to be ready to resume safe operation of the plant.

• Plant operators demonstrate appropriate safety focus and readiness to restart the plant.

• Any organizational or human performance issues resulting from the ongoing investigation conducted by the NRCs Office of Investigations are addressed.

• All licensing issues that have arisen as a result of the reactor head replacement have been resolved.

• Resolution of radiation protection issues associated with the radiation exposure to workers during steam generator work and the particle contamination found in offsite locations.

• Modification of the strainer system for the containment sump, which would be the source of cooling water for recirculation in the event of a loss-of-coolant accident.

NRC Update: Davis-Besse Reactor Vessel Head Damage January 2003 - Page 7 What Happens If the Plant is Allowed to Restart If the facility is permitted to restart, the NRC Oversight Panel will continue to monitor plant activities and operations until panel members are confident that the root cause(s) of the problem have not recurred. Should FirstEnergy achieve that performance level, the NRC Oversight Panel would recommend to NRC management that responsibility for the plant oversight be transferred back to the Region III line organization for monitoring under the Reactor Oversight Process. The panel would then cease to exist. Should FirstEnergy not demonstrate sustained improved performance, the panel will recommend appropriate regulatory actions.

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.