Reactor-Building Fire

Path From Cable-Spreading Room to Reactor-Building Fire Area... 

The tire analysis was assisted by SNL using methods described in NUREG/CR-4840 and the extensive operating history and fire experience. For 94 reactor-years from 1958 and 1987, 20 significant fire events were recorded. Hence, frequencies for the reactor building and the diesel generator buildings of 0.12 and 0.03 /y, respectively. A control room fire has never occurred at a SRS reactor. 

The plant fire brigade and the local volunteer fire department were notified by the supervisor of the catalyst preparation area by 11 12 A.M. On their arrival to the scene of the fire at 11 15 A.M., the plant fire brigade saw the lead outside operator down about 40 feet from the fire, in between the catalyst preparation area and reactor building No. 1. They also found a seriously burned unknown person about 120 feet from the fire, near the finishing building. (This person was eventually determined to be a service contractor who entered the premises at 10 30 A.M. to calibrate equipment in the instrument house for Reactor No. 1.)... 

Stairways Stairways in the northeast and southeast corners are for traffic between the first floor and basement stairways in the northwest and southwest corners are for traffic between all floor levels. This number of stairways is necessary not only for convenience but also for safety considerations. The stairways are encased to provide fire wall protection. A one-way escape door is located on the first floor level of each stairwell. The southwest stairwell contains the main entrance door into the Reactor Building. A similar setup, is provided in the northwest stairwell however, this door should be normally locked so that only one screening point is necessary for personnel entering the Reactor Building-... 

As shown in Table 1, 351 compartments had to be analyzed within the reactor building of the investigated German BWR. The fire load density of 287 compartments is less than 90 MJ/tx . For all of the remaining compartments the frequencies of fire induced plant hazard states are pessimistically estimated. 

Finally, the frequency of fire induced plant hazard states of the reactor building is estimated to be 3.8 E-06/a. This is the result of summarizing the plant hazard state by fire for all the 28 compartments. Considering accident management measures, the frequency of fire induced plant hazard states in the reactor building of the reference plant decreases to 7.8 E-07/a. 

The Fire PSA for the reference plant results in a fire induced core damage frequency of 1.9 E-06/a being higher than the CDF value of 1.4 E-06/a for internal events in case of fuU power operational states. Approx. 69 % of the CDF result from fires inside the reactor building, while fires in the auxiliary building provide a contribution of 17 %. 

Similar improvements can be performed in specific compartments inside the reactor building. The installation of fire detector chains with 2-4 fire detectors in compartments for the pre-heaters, an installation stairwell, a room with a control board for the safety valves, and other process rooms will significantly reduce the compartment specific CDF. 

The fire load density of the compartment for the additional water supply vessel inside the reactor building has been treated quite pessimistically. Although the plant documentation provided a fire load of 560 Ml resulting in a fire load density of less than 90 Ml/m for the compartment floor size of approx. 50 m, the compartment has been included in the analysis due to the permanently as well as temporarily available fire loads. Here, again the CDF may be reduced by installation of adequate fire detectors or by a reduction of fire loads. 

The transport of the fuel aerosols and fission products from the cover gas to the various cells of the reactor building and to the environment is calculated with the CONTAIN-LMR. Papers on this code were presented during the IWGFR TCM [ref 4] on "Evaluation of Radioactive Materials Release and Sodium Fires in Fast Reactors". 

There is concern that sodium fire may be caused by sodium leaking out from the piping and vessels. As for a sodium leak, all pipes and vessels in the containment vessel are generally covered with guard pipes and vessels or filled with inert gas. However, sodium leaks from outside the containment vessel could cause sodium combustion and damage the reactor building. Fortunately, sodium outside the containment vessel is only secondary sodium without radioactive contamination. 

Non-combustible or fire retardant and heat resistant materials shall be used wherever practicable throughout the research reactor facility, in particular in locations such as the reactor building and the control room. Flammable gases and liquids and combustible materials that could produce or contribute to explosive mixtures shall be kept to minimum necessary amounts and shall be stored in adequate facilities to keep reacting substances segregated. 

ILLUSTRATIVE EXAMPLE 21.12 A reactor explosion precipitates a fire in the building housing the reactor. If a building fire occurs, a smoke alarm sounds with probability 0.9. The sprinkler system functions with probability 0.7 whether or not the smoke alarm sounds. The consequences are minor fire damage (alarm sounds, sprinkler works), moderate fire damage with few injuries (alarm sounds, sprinkler fails), moderate fire damage with many injuries (alarm fails, sprinkler works), and major fire damage with many injuries (alarm fails, sprinkler fails). Construct an event tree and indicate the probabilities for each of the four consequences. 

The assistant shift engineer left the area and called the Athens Fire Dept, at 1 09 p.m. The fire truck arrived at 1 30 p.m., and, by 1 45 p.m., seven firemen had been admitted to the plant and were prepared to assist in fighting the fire but in support of, and under the direction of, Browns Ferry personnel. It has been stated that there appears to have been no central organized direction of the fire-fighting efforts i.i the reactor building between approximately 1 00 p.m. and 4 20 p.m. However, it should be noted that the ventilation system was lost at 12 45p.m. 

Due to the historical emphasis on fire prevention versus fire protection, few automatic fire suppression and detection systems are present in the reactor building. There are several Halon suppression systems for the diesel buildings and select computer rooms. Manual fire suppression for the reactor building is provided by way of portable fire extinguishers and limited capacity water hoses. The manual suppression capability and other measures are utilized by a combined response of area fire support teams and the Savannah River Site Fire Department. 

DB-4.9 -- Review by Certified Fire Protection Engineer to Determine Adequate Fire Detection in Reactor Buildings... 

The provision of guidelines and criteria to be utilized in performance of a WSRC review to document the assurance that sufficient fire detection to support SRS program objectives is in the reactor building remains an open item. 

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