Temelin – the challenge of safety improvements

The decision to build a nuclear power plant at Temelin was first taken in 1980, for four VVER-1000 reactors. The contract for supply of technical design from Atomenergoproject Moscow was signed in 1982. This design included the reactor, auxiliary buildings and diesel generating stations. The balance of plant was designed by EGP Prague and Skoda.

The basic design of Temelin 1 and 2 was completed in 1985, the site licence was issued in 1985, and the construction licence in November 1986. Actual erection of the buildings began in February 1986. The original design was modified up until 1989.

After 1989, under the new political and economic conditions in the Czech Republic, the need for a 4000MWe plant was re-evaluated, and new safety design analyses carried out. In March 1993, the government decided to complete construction of Temelin with just two units.

Fuel has since been loaded into Temelin 1 (July 2000), and commercial operation is due in mid 2001. Unit 2 will have fuel loaded at the end of 2001, with commercial operation due in August 2002. Loading fuel into Temelin 1 triggered protests from Austria, with claims that Temelin was unsafe.

Expert appraisals

There have been numerous international missions to examine and evaluate the safety of the Temelin plant (see box).

These missions concluded that the design, siting and organisation of Temelin was not significantly different from international practice. In particular, three missions were organised by the IAEA in 1990, which offered some recommendations to enhance the plant’s safety level, and a 1992 visit was carried out to confirm that the recommendations had been implemented.

In addition, in 1991, CEZ contacted the consultants Halliburton to carry out an independent audit focused on the plant’s technical concept and to verify whether or not the plant would be licensable with respect to standards that would apply in western Europe or the USA in the mid 1990s. Halliburton concluded that the overall technical concept of Temelin was consistent with modern reactor design used in the West. Temelin included, or could easily be modified to include, all the features reflecting Western nuclear power plant design of the mid 1990s. Some of the initial design concepts fell short of modern practice, but these shortcomings could be removed by changes in the design. These included the installation of a new I&C system, improved fuel and core design, improvements resulting from VVER operating experience, and improvements resulting from the audit team recommendations.

Some analyses were performed by Colenco of Switzerland and TUV Bayern of Germany, which specifically assessed the I&C design.

A special mission of the IAEA in 1996 examined how Temelin has overcome safety issues identified by the IAEA as generic for VVER-1000 reactors. The mission evaluated the revised design, the implementation of previously suggested alterations, and preparations for operation. This included compatability issues, reviewing the compatability of modern western technology with the original Russian design.

In general, this mission concluded that the future plant operator had made a significant effort to improve the plant design, and highly commended this effort. The mission emphasised that the combination of western and Russian technology in the Temelin design had been considered very carefully. In the mission’s opinion, the combination of western and Russian technology resulted in some cases in a pronounced improvement of the safety assurance level, compared with international practice.

Another IAEA mission focused on commissioning Temelin took place in February 2000, and an OSART (Operational Safety Assessment Review Team) mission is planned for February 2001.

Main design changes

The results of the independent reviews were used as a basis for technical improvements which, following implementation, ensured that both Temelin units reached western standards.

Among a number of improvements related to the replacement of components and systems, the following items have been replaced:

•The I&C system.

•The core and nuclear fuel.

•The radiation monitoring system.

•The diagnostic system, which has also been supplemented.

•Cables replaced with fire-retardant and fire-resistant ones.

In addition, significant changes were made to the electrical design (electrical protection, addition of two non-safety grade diesel generators, increased discharge time of batteries, etc). The significant design modifications are shown in the panel (p38).

Safety analyses

Westinghouse provided the fuel, I&C system, safety analyses and emergency response guidelines for Temelin. The scope of Westinghouse’s involvement permits the application of the same systematic and integrated approach to nuclear safety (control, monitoring, protection) that is applied to a Westinghouse-designed plant.

This approach integrates core design, plant and core monitoring, plant and core control, protection system design, safety analyses, core and plant operating limits, and emergency response guidelines. It also enhances safety defence-in-depth, which is composed of the following elements:

•Control systems (maintain plant parameters during normal operation).

•Alarms and manual controls (allows the operators to observe and correct deviations from normal operation).

•Limitation systems and back-up controls (the Temelin design provides for extensive supervisory control that can automatically take rapid action in the event of a malfunction, thus avoiding the need for protective action that would trip the plant).

•Primary Reactor Protection System (PRPS) – a safety system of Class 1E providing automatic protection to shut down the reactor, and automatic actuation and control of emergency safeguards feature.

•Diverse Protection System (DPS) – a safety system of Class 1E providing backup protection for a postulated failure in the PRPS (provides reactor trip, some ESF actuation and control).

Safety improvement

In accordance with CEZ policy, it is planned to carry out continual safety assessments on the plant and to incorporate additional improvements beyond the framework of the legal requirements.

The Safety Improvement Programme has been defined for the period after the start of the trial operation of Unit 1. However, fulfilment of some items of the programme has been or will be initiated in advance. The programme is an open document that will be systematically updated on the basis of:

•Periodic safety assessments of the units.

•WANO performance indicators.

•The results of operational experience.

•Assessments of supervisory bodies (the nuclear and civil safety authorities).

•Recommendations of independent assessments (by WANO, IAEA, external audits).

The aim of the programme is not only to improve safety, but also the analytical assessment of safety and the impact on the environment, as well as improvements in the organisation and human factors. The programme will be updated every December.

The IAEA Mission

The IAEA had recognised that CEZ has made a large effort to improve the design of Temelin independently of the identification of safety issues by the IAEA. The organisation of its actions in terms of the IAEA issues was only a convenient way to demonstrate that all the issues were considered.

The scope of participation in the Temelin design, manufacturing and construction has had a positive impact on solving several safety issues identified in VVER-1000 reactors. The adoption of Western technology and practices for the part of the scope of supply (eg fuel, I&C, radiological protection, accident analysis) has helped to solve a large number of safety issues identified for the VVER-1000.

The combination of Eastern and Western technology and practices and the potential compatability problems seem to have been carefully considered at Temelin. In several cases, the combination of technologies has led to safety improvements in comparison with international practise.