Appraisal for the operation safety of SPRR-300 in recent years

SPRR-300 reached first criticality in 1979. During its 27 years of safe operations, the reactor has never been renovated comprehensively. So the condition of the devices and the reactor must be analyzed to appraise the safety of the operation. A management networks for the safety and the quality of the reactor operation were built within the operation department. A general outline for quality of SPRR-300 during operation stage went into effect in 2004. A set of files have been written or rewritten to ensure that the outline is operated smoothly. The rules and regulations of the reactor are insisted on. The emergency scheme and its execution programs had been established around 2002. Emergency practices were held in 2003, 2004, and 2006. Through this series of practices, the abilities for emergency treatment of the staff have been boosted continually. The minimalist technical transformation of the reactor had only been done once around the year of 2002. The failure ratio of the reactor goes down year by year. Before 2002, 22 out of the 31 scrams occurred without even one warning signal showed at the same time. Since the minimalist technical transformation finished, that kind of scram has not occurred any more. The reactor resumed normal operation in 2003. In this year, there were 27 scrams, in which nine were caused by staff faults. 18 scrams in 2003 were cause by devices breakdowns, while most of them were originated from malfunctions of the old sets of power protection instruments. There were 14 scrams in 2004 and 2005. Five of them were caused by staff faults. More than half of the nine scrams caused by devices breakdowns were related to the electricity net lapse. It is reasonable that there are small quantities of manual failure. Every time before and after operation, the group of technical management would organize some kind of meeting to discuss the problem that may appear or have appeared. With the continued fostering of safety culture, the operation quality of the staff is enhanced constantly. To those old reactors like SPRR-300, devices are the key of the reactor safety although some suitable modifications have already been done. In this period, usually some new kinds of device failure would turn up. So it is a must that the quality of the staff should be enhanced steadily to solve every accident correctly and resolutely. There were 12 cases in 2003 that the power supplies for ionization chambers gave alarms of lower voltage because the voltage of local power grid was too low. The reactor was removed of automatic operation afterwards because of malfunction of the power regulate system. To solve this kind of hidden peril, the institute managing the reactor began to work together with local power supply bureau to stabilize the voltage during every period of operation. Also in 2003, the second regulate rod system worked abnormal two times. Its lifting speed was much lower than that of normal. In the first case, the reason was that the contact of its speed-adjust electric resistance was poor. In another case, the reason was short-circuit between the turns of the stator coil of the servo motor. Once in 2004 the drop-fuse of one transformer outside the reactor building struck arc. The reactor was forced to be shut down temporarily so the transformer could be disconnected to be repaired later. The bad installation of the second motor for the ventilation of the coolant tower was one of the inherent defects in SPRR-300. The retarder lapsed eventually. Thorough repair of the retarder had been accomplished in 2005. As a result, the most of threats to the normal operation of the reactor come from instability of power grids outside the reactor building. Because the inherent safety of the reactor and the developing of the ability for accident treatment within the reactor staff, instability of power grids can only influences the usages of the reactor to a certain extent. It will not produce an effect on the safety of the reactor. Through maintaining and repairing in accordance with certain cases apart from overhauling at regular intervals for the devices, all systems of the reactor are kept in good condition, which meets the demand to guarantee the safety of the reactor. So long as the regulations are abided by, the training of the staff is strengthened over and over, and the safety culture is fostered continually, the safety and the quality of the operation can be ensured. (author)