What is being done for safety?
The potential radiation risks of nuclear technology were known before it was used in Germany. At a very early date legislation issued a safety network consisting of laws, regulations, and guidelines. This network has culminated in a safety standard for nuclear facilities that is exceptionally high compared with that for conventional facilities. Today safe operation is supported with the following:
- active safety devices for analysing, monitoring, controlling, and regulating,
- passive safety devices in the facility’s basic concept, e.g. the multiple barrier principle,
- organisational measures for operators of nuclear facilities,
- measures for supervisory authorities based on an established network of guidelines and regulations.
Active safety devices
The active “reactor protection system” springs into action in the event of an incident. This must fulfil a series of fundamental requirements.
- Protective action must be clearly aligned to safety. In other words, when it is activated by accident it may not impede other protective action.
- If the necessity of protective action is signalled this may not be impeded under any circumstances, e.g. by unfinished testing or maintenance work on the safety system or by a simultaneous failure of safety components. In general this is assured by the existence of three identical device groups operating independently of each other.
- Faults must signal themselves.
- Only devices approved by the authorising body after a corresponding suitability test may be installed. This test takes into consideration the worst operating conditions, e.g. with respect to operating temperature, too high or too low a voltage, moisture, mechanical influences, etc.
The active safety systems are automated to a great extent. Any necessary interventions by hand must not be necessary until thirty minutes at the earliest after the incident. This leaves enough time to make calm decisions and to determine the cause of the malfunction.
Passive safety devices
One example of passive safety devices in nuclear technology is the multiple barrier system for retaining radioactive fission products. In the case of the HZB research reactor the first barrier is formed by the core fuel itself, the second the envelope encasing the core fuel, the third the water, and the last the reactor hall.
One other example is the removal of heat that is still generated even after the HZB research reactor has been shut down: heat is drawn off by natural convection, the independent circulation of water in the reactor well – a pump is not necessary.
Also the shutdown system for BER II provides passive safety: in the event of a malfunction the control rods drop into the reactor core alone under the action of gravity and so put the reactor out of operation. Passive safety devices assure safe operation without the need to activate any additional installations or apparatus.
The active and passive safety devices take into account the greatest measure of all technical possibilities serving to prevent malfunctions and to protect against damage.
Measures for operators
The operator of the facility – in this case the Helmholtz-Zentrum Berlin – must verify how safety is assured. For instance, when the facility is being built only those parts may be used that have been examined by a designated expert. Also during subsequent operations the facility must be inspected at regular intervals. This inspection is conducted with the collaboration of the Technical Control Board TÜV. Finally the operating personnel must have the corresponding qualifications and expertise. This too must be verified before the supervisory authority.
Measures for supervisory authorities
Before a nuclear facility is set up or modified a safety report must first be submitted to the competent authorising body. This report must explain precisely all operating sequences and the measures implemented against all malfunctions. The authorising body retrieves an expert opinion on the safety report from independent professional bodies, e.g. the Technical Control Board TÜV. Assessment criteria are state of the art and the rules and regulations applying to nuclear facilities. The supervisory authority bases its decision on this expertise and generally issues injunctions together with its approval.
Several times a year officials from the European Community and the International Atomic Energy Authority examine the stocks of nuclear fuels. These examinations are to assure that no core fuels are misappropriated for use in contradiction to the exclusively peaceful operation of the reactor. And with no less rigour the Radiation Protection Department at the HZB checks constantly for radioactive leaks to the environment and the radiation levels employees may be exposed to. All of these factors assure the safe operation of the reactor. The radiation impact of reactor operations in the direct vicinity is less than one millirem a year: a fraction of the natural background radiation of 90–220 millirems a year in Berlin.
All conceivable technical malfunctions were analysed in the planning stages and taken into account in the design of the facility. Even in the unlikely event of a so called design basis accident the radiation impact on the environment will remain clearly below the thresholds fixed under the Radiation Protection Ordinance.
In spite of all of these exhaustive efforts however, absolute safety cannot be obtained. This is the same for all technical installations. The smaller size of the HZB research reactor when compared with a nuclear power station leads to a correspondingly smaller radioactive inventory. This too keeps the residual risk extremely low and certainly less than other risks that our society is generally prepared to accept.
Measures for controlling bodies and operators of nuclear facilities are:
- quality assurance for the components
- specialised training for personnel
- regular inspections e.g. by the Technical Control Board TÜV
- independent radiation protection experts monitoring persons, buildings, and the environment for radioactivity
The authorities of the Federal States of Berlin and Brandenburg have also drawn up an emergency protection plan for the research reactor as a supplementary precautionary measure. A summary for the people living in the environment of the research reactor presents the essential measures of these plans for emergency protection.