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Norway’s Halden reactor takes first step toward decommissioning
The government of Norway has granted the transfer of the Halden research reactor from the Institute for Energy Technology (IFE) to the state agency Norwegian Nuclear Decommissioning (NND). The 25-MWt Halden boiling water reactor operated from 1958 to 2018 and was used in the research of nuclear fuel, reactor internals, plant procedures and monitoring, and human factors.
Wolfgang Kröger, Johannes P. Wolters
Nuclear Technology | Volume 74 | Number 1 | July 1986 | Pages 53-64
Technical Paper | Neuclear Safety | doi.org/10.13182/NT86-A33818
Articles are hosted by Taylor and Francis Online.
Advanced nuclear reactors in the Federal Republic of Germany (FRG) must analogously fulfill the deterministic safety criteria developed for the light water reactor (LWR). In earlier high-temperature reactor (HTR) concepts, the interpretation of this requirement led to exaggerated safety precautions. Efforts are being made in recent HTR concepts to develop a more specific safety concept making use of probabilistic risk assessment and probabilistic safety analysis. The basis for development and evaluation is formed by a requirement concept of frequencyoriented limits. Design-relevant accidents are divided into three categories and the appertaining maximum permissible doses are allocated based on the FRG Radiation Protection Ordinance. For even more infrequent events it must be demonstrated that the collective damage and risks remain clearly below those of a comparably large LWR. This probabilistic requirement concept has been applied to two HTR concepts under development and the result has been judged positively by a group of experts established by the Federal Ministry of the Interior. The most extensive experience for HTR-500 is discussed in detail. At the planning stage, the accident spectrum was studied and results were compared with predefined limit values. If necessary, design modifications were undertaken by the manufacturer. The safety concept thus developed is essentially different from that of other reactor facilities. Accidents initiated by the failure of active core cooling result in a slow rise in core temperatures; a period of ≈5 h remains for repair and for operator actions. Core heatup alone does not lead to unacceptable doses. It could therefore be accepted as an accident relevant for design. The envisaged two-train design of the afterheat removal system and the comparatively low degree of automation of the reactor protection system have proved to be sufficient. Core heatup accidents associated with failure of the liner cooling lead to the highest consequences and dominate risk. A simple modification—provision of an emergency feed for the liner cooling system — turned out to be necessary for risk reduction. The analyses were further used to replace the usual gastight containment by a more economical vented confinement with filtered release in case of small helium leaks. All together the safety concept of the HTR-500 ensures that accidents (>10≈5/yr) remain below the frequency-related dose limits and that the risk is extraordinarily slight. In no case does the necessity of evacuation and rapid resettlement arise.
