Frequently Asked Questions about the Safety of the Research Reactor BER II
(last updated Nov. 2011)
1. Why do we need a research reactor in Berlin?
The research reactor BER II delivers neutrons for scientific studies. Neutrons are uncharged particles – parts of an atom's nucleus – that are excellently suited to studying materials. Neutrons can be bundled together into a ray, much like the way light can, and then shined onto many different kinds of sample. A neutron source is like a large microscope that researchers can use to study the inner properties of materials. Scientists from many disciplines, such as biologists, chemists, physicists, medical physicists, materials scientists, and even art historians, use our research reactor BER II to find answers to their questions. The research reactor is not used for developing or sampling nuclear power technology.Research using neutrons delivers insights that scientists cannot obtain using other research methods. That means there is often no alternative to researching with neutrons. Many of the technologies we use today were researched using neutrons, much of which over the decades has been performed at the Berlin research reactor because of its unique experimental conditions.
2. How is the research reactor BER II of Helmholtz Zentrum Berlin different from a nuclear power plant?
Our research reactor BER II in Berlin-Wannsee cannot be compared with a nuclear power plant. It is not used to produce heat or electricity. We produce neutrons by nuclear fission for use in research. Neutrons are tiny, electrically neutral particles. At Helmholtz Zentrum Berlin, they are needed to understand the deep, inner structure of matter to improve solar cells, for example, or to answer long-standing questions in archaeology, biology and many other fields of research.
Given their different purposes, they are built very differently as well. Our research reactor works at low temperature and at normal pressure. A power plant, on the other hand, produces steam at high temperature and pressure for generating electricity. Because this is not the case, our research reactor does not have a reactor pressure vessel as nuclear power plants do. Since we do not use the excess heat, it is released through heat exchangers and cooling towers. To compare, the power of our research reactor is 10 megawatts. The thermal power of an average nuclear power plant is 3,000 to 4,000 megawatts.
3. What fuel elements are used in the research reactor BER II?
BER II works with so-called LEU, or low-enriched uranium. The concentration of the isotope 235 is lower than 20%.
4. What safety measures exist to monitor operation of the research reactor, or to stop the nuclear fission if necessary?
The research reactor has automatic shutdown systems that will be triggered by any deviation from normal operating conditions. This includes failure of instruments and controls, for example. Other systems will immediately cut in, otherwise the reactor will be shut down. Control rods will drop down into the reactor core if necessary to stop the nuclear fission chain reaction directly (see also Question 5).
5. How is the cooling system at BER II built?
The research reactor is a so-called "pool-type reactor" or "swimming pool reactor": The core of the reactor is immersed in an open pool of water. The core contains around 7 kilograms of fissile uranium 235, which is needed for nuclear fission. The research reactor consumes 2.5 kilograms of this uranium per year. By comparison, nuclear power plants consume around 1.5 metric tons of fissile uranium per year. The water around the reactor core serves as three things: a neutron moderator, meaning it slows down the fast neutrons released during fission, which then sustain the chain reaction; a cooling agent; and a radiation shield.
This design has a crucial advantage: since no pressure vessel is present, the entire pool is under normal pressure. The high temperatures and pressures typical of nuclear power plants do not occur. The water in the pool heats to around 40° Celsius during operation. The heat is dissipated through heat exchangers and pumped in a circuit. No water is released to the outside.
6. What happens if the cooling fails?
There are control rods held suspended above the reactor core by electromagnets so that, if the electricity cuts out, they will fall down under their own weight into the reactor core and thereby shut the reactor down. Once nuclear fission has stopped, the core requires only one minute of active cooling. This would be ensured by the continuation of the pumps, which are also backed up by batteries. After this one minute of active cooling, the natural convection of the water (dissipation of heat through the movement of water molecules) is enough to dissipate the residual heat on its own. That means no pumps are required to dissipate the residual heat. Nevertheless, there are two backup diesel generators should there ever be an electrical power outage.
7. Are the claims made on a TV news magazine true, that there is a crack in the cooling system?
The claims made in the show are based on malicious statements made by a former employee. This employee had been dismissed because he had threatened subordinate employees.
The show summarized his statements and claimed there was a crack in the cooling system. This suggested that either water was escaping or that the cooling would not function under certain circumstances, which is not true. The reality is that a divider that can be used to divide the main pool of the reactor into two parts does not form a completely tight seal. This divider is used only for certain maintenance work on the reactor while it is shut down, if there is a need to maintain different water levels in the two parts of the pool. In such a situation, water would only drip from one part of the pool into the other part of the pool as a result of this leak. This divider is not part of the cooling system, rather a component reserved for maintenance. TÜV Rheinland confirmed in an independent report that the leak in question has no relevance to safety. Safe cooling is assured at all times, both during operation and when shut down. Read also the statement by the State Atomic Energy Agency (Landesatomaufsicht) from 9 June 2011.
8. What about the claims made on the TV show about the material of an exchanged part?
Again, the ex-employee who was dismissed for coercion was attempting to discredit his former employer. The material used when changing the conical beam tube satisfies all values defined in the specifications. Safety always comes first when operating BER II. It is for this very reason that we use only safety-tested materials that are approved for use in the operation of nuclear facilities. These must prove to maintain their material properties even under neutron flux. The Landesatomaufsicht refers to this in its statement as well.
9. Does radioactivity escape into the environment from operating BER II?
The research reactor BER II is technically designed so that the release of radioactivity is only a tiny percent of the permissible limits. Corresponding proof had to be furnished to receive approval for operation in 1991. The radiation protection department of HZB and the supervisory authority continuously and independently monitor the release of radioactive material.
The instruments that monitor the release of radioactive material are located in the exhaust air stack of the reactor and on the HZB premises. In addition to this are 18 continuously measuring sensors within a radius of approximately five kilometres. Within a radius of 30 kilometres are further measuring stations of a Germany-wide monitoring network. All relevant data are continuously transmitted to the supervisory authority for remote reactor monitoring.
10. How is the research reactor BER II tested for safety?
The supervisory authority, the Senate Department for Health, Environment and Consumer Protection, regularly tests the safety of the research reactor with the assistance of independent experts. Furthermore, members of the European Atomic Energy Community (EURATOM) and the International Atomic Energy Agency (IAEA) verify the stocks of nuclear fuels every year. Operation of the facility is subject to the strictest safety requirements.
11. Where are the spent fuel elements of BER II stored, and how are they disposed of?
Far fewer fuel elements are spent than in a nuclear power plant. Until transporting, they are kept in a spent fuel pool, where their power drops to below 40 watts. Only then is the uranium obtained from the USA returned to there. Spent fuel elements are transported off every two or three years in special thick-walled containers.
12. What measures do the operators take against terrorist attacks?
A security service seamlessly guards the entire HZB premises. Unauthorized entering of the campus cannot go unnoticed. The reactor itself and its surroundings are additionally guarded by armed security personnel who are trained and examined according to the relevant regulations. The facility is under tightest monitoring and access control.
13. What protection does the reactor building offer?
The research reactor is built according to the prevailing safety regulations. These do not call for additional building containment. The roof of the building is a brick-lined steel skeleton construction that is lined gas-tight inside with steel plates. The hall guarantees enclosure of all materials used and arising in operation. The hall is under slightly negative pressure, so that if a crack should ever form, air would not flow outwards, but would be drawn inwards instead.
14. What danger exists if the research reactor lies beneath the flight route of Berlin Brandenburg International airport?
The Noise Commission gave its recommendation on 9 May 2011 that the flight routes should not pass across Wannsee. We welcome this decision. Yet, even if the Deutsche Flugsicherung does not agree with these suggestions, aircraft taking off from BBI airport that would fly over Wannsee close to BER II would have already reached an altitude of around 1.5 to 2 kilometres. As above any nuclear facility in Germany, there is a flight restriction above BER II to approximately 700 metres altitude. This flight restriction would therefore be respected.
15. Is the research reactor currently in operation (May 2011)?
The research reactor has been out of operation since October 2010 for planned renovation. All measures taken at BER II are performed in close cooperation with and after approval by the responsible authorities, who call for reports from independent experts.
16. Why is BER II being renovated?
These renovation measures were planned years ahead, and have nothing to do with the safety testing discussed in the media. Some parts and components are changed routinely after a certain amount of neutrons have flown through them. The present work concerns the tube that directs the neutrons from the reactor core into the neutron guides. As the facility was planned, the maximum amount of neutrons would have been reached in 2011, so the renovations were planned for and commenced in October 2010 to allow for a time buffer.
The scientists at HZB prepared and planned this renovation time to great detail. They are using the operating break namely to improve the scientific instruments and thereby upgrade the neutron guides so that up to five times more neutrons will arrive at the instruments. This is an enormous improvement for science and keeps BER II internationally competitive. The new experimental stations will increase the global attractiveness of the Berlin research location.
17. Why is meant by the “stress test” for BER II? (last updated 2012)
Even BER II had to undergo a so-called stress test. This is an analysis of how a reactor will behave in specific scenarios – such as a power failure, flood or earthquake. Such scenarios were analysed for the research reactor BER II. The responsible authorities then delivered their evaluation. The experts appraised the facility as having a high degree of robustness. BER II successfully passed this stress test ordered by the Senate.
18. Why does a disaster control plan exist for BER II?
Operation of the research reactor results unavoidably in radioactive materials. We have taken many measures to ensure these remain contained during every operating phase of the research reactor. Nevertheless, the Berlin and Brandenburg authorities have drafted a detailed disaster control plan to allow quick, efficient and effective action to be taken even in an extreme, hypothetical situation that can only be caused by extreme impact from outside. This disaster control plan defines the tasks for all authorities and bodies involved in the event of any fear that radioactive materials may be released into the environment. HZB distributes a pamphlet every five years informing the population around the research reactor about this disaster control plan. This is regulation, as stipulated in § 53 of the Radiation Protection Ordinance (Strahlenschutzverordnung). The last information pamphlet distributed was in summer 2009.
19. Why is the state collection centre for radioactive waste on the premises of HZB in Wannsee?
Every German federal state is under obligation by the German Atomic Energy Act to set up a state collection centre for processing and storing the radioactive waste originating in its area. The Land of Berlin has entrusted Helmholtz Zentrum Berlin to operate the state collection centre for radioactive waste, ZRA (Zentralstelle für radioaktive Abfälle).
The ZRA houses low-level to intermediate-level radioactive materials that arise primarily from medicine, industry, research and teaching. No fuel elements from the research reactor are stored at the ZRA. The spent fuel elements are returned to the USA.
20. Is it possible to visit the research reactor?
To guarantee safe operation, the operating personnel must be allowed to work in concentration and undisturbed. The research reactor BER II can therefore only be visited by appointment. Those wishing to take a visit must go through security clearances by the responsible offices.
However, on Open House Day, we allow interested visitors to take guided tours through the experimental halls around the research reactor. Our scientists and reactor experts will be there on these days to answer questions about the facility and the safety measures.
