Explosion at a Pipe in a Nuclear Power Plant
A hydrogen explosion had ruptured a pipe in the core spray system at the Brunsbttel BWR in Germany. Although the control room instrumentation had at the time indicated a leak of radioactive steam, the nature of the event had not been fully recognized: operators had isolated the leak and continued operation. Investigations suggested that the hydrogen (formed by radiolysis of the water) accumulated in a part of the pipe between catalytic recombiners. In the Brunsbttel design, the core spray system provides extra cooling when shutting down the reactor but does not serve a safety function during operation. The explosion was close to a valve connected to the reactor pressure vessel, but the valve was closed at the time and was not affected. A subsequent investigation of all German BWRs indicated that the Brunsbttel design had a unique vulnerability to this type of event.
Event Date
December 14, 2001
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
Although there is no clear explanation of the explosion, it is suspected that a hydrogen explosion occurred. Neutron radiation from the reactor core can split water into hydrogen and oxygen gas. These can then recombine explosively.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Pipe, core spray system, radiolythic hydrogen
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The explosion took place in the so-called reactor core spray system. That system sprays cold water into the reactor vessel to cool the reactor down and remove residual heat in case of shutdown. It is not an emergency cooling system but a tool to reduce by about two hours the time needed to cool the vessel in normal maintenance shut downs. The spray system situated inside the containment vessel, a steel vessel of 27 meters in diameter in which the reactor vessel itself is located. The system is connected by an isolation valve to the reactor vessel. The valve is opened to allow injection of fresh coolant into the vessel during shutdowns.
Currency
Lessons Learned
Lessons Learned
"The ministry will only allow the reopening of the reactor if the cause of the explosion is clear and a repeat is excluded, all damage is repaired and the competence of the operator is proven. That competence is in doubt as the operator decided to continue operation after the explosion instead of starting inspections after the observed leakage"A subsequent investigation of all German BWRs indicated that the Brunsbttel design had a unique vulnerability to this type of event.
Event Nature
Emergency Action
The reactor operators recognized a leakage but considered it of no importance to essential safety parts of the reactor. The system's water supply was cut off and the leakage stopped. The operators suspected that a flange leakage in the system had caused the problem and they continued operating the reactor(2). Immediate inspection of the system itself was not considered necessary and neither was it possible, as the containment vessel can not be opened during operation of the reactor at 100% capacity.Three days later operator Kernkraftwerk Brunsbttel GmbH (KKB) informed the supervising authority of the ministry of Finance and Energy of the State of Schleswig-Holstein. The authority however was not satisfied with the conclusions of the operator. The observed indications in the control room could not fully declare what could have happened inside the containment vessel. The supervising authority urged the shut down of the reactor but the operator refused to do so. Only after weeks of discussions, and after threatening with a formal order to shut it down, the reactor operator settled the issue on 18 February by reducing power output to 10% so that inspections were possible.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
A Publication of World Information Service on Energy (WISE) and the Nuclear Information& Resource Service (NIRS), incorporating the former WISE News Communique
March 8, 2002
Same as above, but online version