Type: All VVER-440s; Units 1 and 2 are the V230 model; Units 3 and 4 are the V213 model.
Units: Four
Total megawatts (net): 1,632
Location: Jaslovske Bohunice, Slovak Republic
Dates of initial operation:
For an overview of the principal strengths and deficiencies of Soviet-designed plants, see Soviet Nuclear Power Plant Designs.
The Bohunice plant--especially units 1 and 2, older VVER-440 Model V230s--has caused some concern among the public, particularly in neighboring Austria. Although the plant was the subject of a series of programs--first begun in 1984--aimed at improving safety and performance, in 1991 the Czechoslovak government launched a major program to upgrade units 1 and 2.
The Slovak utility SEP--now SE--contracted with Western companies for a number of safety-related improvements.
In 1986, Germany's Siemens/KWU supplied loose-parts monitoring systems and component vibration-monitoring systems for Bohunice 3
In 1990, Siemens/KWU supplied component vibration-monitoring systems to Bohunice 1 and 2, and a year later, delivered leak-monitoring systems for the two units.
In 1990, the utility commissioned Siemens/KWU to analyze the reactor safety systems at Bohunice 1 and 2. Areas covered included safety-system design, reactor performance under accident conditions, and instrumentation and control technology.
In June 1991, SEP awarded a contract to a French consortium of Cegelec and Thermatome to supply security systems at Bohunice, including an electronic entry-control system and Thermatome, a site-surveillance system.
The CSFR government said in April 1992 that a study of instrumentation and control system replacement in VVER-440 Model V213 reactors would be carried out under the European Communities' PHARE program. The study found that extensive I&C refurbishing or replacement was needed at Bohunice units 3 and 4, and a contract was signed with the U.K.'s NNC Ltd. in 1993 to provide full technical specification of the I&C system.
During the plant's 1996 outage, the United Kingdom's Rolls-Royce and Associates will take material samples from the units' reactor pressure vessels to enable the plant to identify the exact properties of welds for safety assessments.
Units 1 and 2. The government's phased safety-related backfit program for units 1 and 2--launched in 1991--consisted of 81 improvements. Under the program, which resulted from an extensive safety assessment by the Czechoslovak Atomic Energy Commission's Nuclear Safety Inspectorate, the reactor pressure vessel at Unit 2 was annealed in February 1993 and the vessel at Unit 1, in April.
In April 1992, the Slovak government reviewed a technical and economic analysis of the units' operation, and requested studies on three options: safety upgrading, conversion of the units to combined cycle, and closure of the units and their replacement with a new combined cycle plant. Studies of the three options concluded that safety upgrading of the units would entail lower capital and operating costs than the other two options. In addition to allowing units 1 and 2 to operate beyond 1995, a major backfitting program would significantly decrease the core melt frequency.
The Slovak regulatory authority asked that the proposed upgrading be reviewed by international experts. In July 1993, the IAEA convened such a meeting. After hearing presentations by Slovak safety authorities and Bohunice management on safety improvements already made and the options for future major upgrades, the experts agreed that a major safety upgrade was technically feasible and would significantly raise the plant's level of safety. The experts made a number of recommendations on various options to help Slovak authorities make a final decision.
SEP proposed that upgrading be carried out gradually in two phases, during extended refueling outages. In January 1994, the republic's Nuclear Regulatory Authority laid out the conditions that would have to be met so that the two units could be licensed after each refueling. Different sets of tasks must be completed by December 1995, December 1996 and December 1997.
SEP approached both Westinghouse and Siemens about the units' reconstruction and both companies made proposals. SEP divided the project into two phases: basic engineering and implementation. In May 1994, Siemens was awarded the contract for basic engineering; this phase was completed by May 1995. Siemens also reportedly won the 5-billion Slovak crown ($172.4 million) contract for the implementation phase, which will begin in 1998.
Under a European Union-funded contract, the United Kingdom's Electrowatt carried out a comprehensive Level 1 probabilistic safety assessment (PSA) of Unit 1, estimating core damage frequency and identifying major contributors to it. The company evaluated the influence on core damage frequency of various plant and procedural modifications incorporated during the reconstruction of units 1 and 2, and also transferred the PSA methodology to plant staff.
According to Bohunice's manager, units 1 and 2 will have to operate beyond their original planned shutdown dates of 2003 and 2005, respectively, to cover the costs of the upgrading. But only the country's regulatory authority can renew the units' licenses.
WANO Exchange Visits. The World Association of Nuclear Operators has sponsored several exchange visits involving the Bohunice plant. The plant has hosted personnel from the following plants:
In addition, personnel from Bohunice have visited the following plants:
Plant Twinning. The Bohunice plant has been twinned with France's Nogent plant and Germany's Grohnde plant.
Simulator Trial. In December 1993, a severe accident simulator developed jointly by the International Atomic Energy Agency (IAEA) and the U.S. company Risk Management Associates entered trial operation at the Bohunice plant's Model V213 reactors. The desktop, personal computer-based simulator is used to train plant operators, but it can also evaluate accident management strategies.
In 1990, the Czech and Slovak Federal Republic asked the IAEA to document the special measures that had been taken at Bohunice 1 and 2 to improve plant safety.
Technical Exchange Visit. An IAEA team visited the plant Sept. 3-7, 1990, to review equipment upgrades and modifications, personnel qualification and surveillance, and to note the effectiveness of each safety measure.
ASSET Mission (Units 1 and 2). A month later, Oct. 1-12, an IAEA Assessment of Safety Significant Events Team (ASSET) mission visited Bohunice in connection with the IAEA's project to assess the adequacy of the VVER-440 Model V230 plants.
The team examined Bohunice's operating history and incident-prevention program and said that plant management deserved credit for the small number of safety-significant events. It noted, however, that the future safe operation of units 1 and 2 would require further efforts.
The IAEA team recommended development of a comprehensive program for the prevention of incidents, including increased surveillance and preventive maintenance. The team also questioned the advisability of continued operation over the long term, given the design and operational deficiencies of the Model V230 units.
Safety Review Mission (Units 1 and 2). As part of the IAEA's VVER-440 Model V230 project, an IAEA Safety Review Mission visited Bohunice-1 and -2. During its April 7-26, 1991, the review team assessed not only basic design deficiencies but plant modifications. The review pinpointed shortcomings in management's identification and correction of nuclear safety issues, deficiencies in fire protection, and incomplete vital operating procedures.
In addition, a seismic safety review mission visited Bohunice to review the plant's ongoing program of seismic upgrading. The team recommended the review of several measures, including the seismic ruggedness of on-site emergency power.
Follow-Up Safety Review Mission (Units 1 and 2). The IAEA carried out a follow-up to its 1991 Safety Review Mission April 27-30, 1992. The team was satisfied with the progress that plant management had made in responding to many of the original mission recommendations. While the team said good progress had generally been made in addressing safety significant issues in the design area, some issues needed more urgent attention, including: the development and implementation of quality assurance programs; the development of operating procedures; the improvement of operating shift staffing; and plant reorganization efforts.
Follow-Up ASSET Mission (Units 1 and 2). An ASSET follow-up mission visited Bohunice units 1 and 2 July 5-9, 1993, to assess the progress made in implementing the recommendations made by the ASSET mission that reviewed the units in 1990.
The team noted that the plant had responded vigorously to the recommendations, reviewing and acting on them with thoroughness.
The team reviewed 223 events that had occurred at the two units between July 1990 and March 1993. Of these, 102 were considered to be safety relevant; 10 were classified as Level 1 on the International Nuclear Event Scale and the rest as Level 0. Most of the Level 1 events were related to equipment failures, and the team suggested it may be necessary to review the frequency of routine maintenance.
As a result of its analysis of events, the team identified only one safety problem for which it felt corrective actions--both taken and planned--were insufficient: the quality of work preparation and procedural guidance for plant personnel and contractors, which could lead to degradation of safety functions.
To correct this pending safety problem, the team suggested that plant management:
Carefully revise the procedures related to transferring ownership of equipment from one plant department to another to highlight the operational implications and avoid inappropriate transfer of responsibilities.
Revise the training of contractor personnel, especially in the plant's safety aspects; end-of-training testing and periodic retesting should be considered.
Should consider a means to verify compliance of contractor personnel with existing safety procedures.
Planned OSART Mission. An IAEA Operational Safety Review Team (OSART) mission to Bohunice is scheduled for Sept. 10-27, 1996.
December 1995
