FIRE HAZARDS OF ATOMIC REACTORS
THE INCREASED application of nuclear energy to all phases of modern living will soon create new problems for the fire service. At present several commercial installations of reactors are being constructed or planned and it is important that firemen learn some of the hazards which may present themselves in the very near future. Nearly all of the experience to date has been accumulated by the United States Atomic Energy Commission and this article will deal with one government installation.
The National Reactor Testing Station occupies a 431,000-acre tract of sage-
brush land in Southeastern Idaho. It is a place where the A.E.C. builds, tests and operates various types of nuclear reactors. Since its establishment in 1949, 12 reactors have been built and operated at the station and 10 more are in the design or construction phase. Its size and remote location permits scientists and engineers engaged in nuclear research to carry on experiments vital to the Commission’s program, with minimum public hazard.
One of the hazards which must be considered is the possibility of a fire in a reactor plant. While there are many unique theoretical possibilities, most of the fire experience has been due to the materials and conditions which have long been known in industry. However, the possibility of a fire which may result in a nuclear incident or be the cause of release of radioactive material cannot be lightly brushed aside.
—A. E. C. photo
A. E. C. photo
A. E. C. photo
In studying the fire hazards of atomic reactors, it is necessary to know some of the fundamentals. A reactor consists of a shielded assembly of fissionable materials, equipped with devices to control the rate of nuclear fission. The fission process produces neutrons, radioactive particles and heat. Except for some low power critical facilities, reactors are provided with a medium to remove the heat. It is in this heat transfer medium that fire hazards may arise.
There are many possible arrangements and types of reactors, but to simplify hazard estimates, two basic subdivisions have been made to cover reactors at the National Reactor Testing Station:
1. Research and Testing—This grouping of reactors applies primarily to those which produce neutrons or other radiations to be used for research and testing of components, coolants, and materials of many kinds. The Materials Testing Reactor and the Engineering Test Reactors are of this type.
2. Prototype and Experimental Reactors—In this type the performance of the reactor itself is tested.
The Research and Testing Reactors are not necessarily in themselves a fire hazard. However, we feel this type of operation presents a high hazard. Operations of these plants are somewhat similar to chemical pilot plants; experiments and samples of all types are run into the reactor.
Flammable liquids and gases, sodium, NaK and other pyrophoric metals are used and large quantities of paraffin and wood are employed for neutron shielding. Small spills of radioactive materials call for extensive cleaning (not just wiping with a mop) requiring the use of rags and absorbent paper. Blotting paper is purchased by the ton and used on
floor and work benches, to absorb stray radioactive particles. When working in contaminated areas, employees are required to wear special clothing to protect themselves and their street clothes from becoming contaminated. As a result, large quantities of coveralls, aprons, shoe covers and gloves are stored in reactor buildings.
Reactors in the second grouping do not have the fire hazards associated with the research and development type. This includes the so-called power reactors which are run on a routine basis and it is possible to design safety into the plant more readily. There are usually no experiments inserted in these reactors. Runs are made with varying conditions to determine the behavior characteristics and capabilities of the machine. Changes may be made in fuel elements, control rods, moderators, reflectors, etc.
In these plants the testing of the reactor is the central object and everything revolves about this. It would be similar to the testing of any large heat-producing device. The fire hazard is then based on the hazard associated with tire reactor. This is due primarily to the material used as a coolant, and we have made a further breakdown of hazards under this general type:
1. Water or nonflammable-gas-cooled reactors are a low fire hazard.
2. Air-cooled reactors are considered to be a moderate fire hazard. Until recently it had been thought that these were a low hazard, but incidents with pyrophoric metals have shown that this position is not valid.
3. Organic-liquid-cooled (or moderated) reactors and liquid-pyrophoric-metalcooled reactors must be considered as high fire hazards. While the materials used are not normally considered to be highly hazardous, the operating temperatures are usually well above the flash point, or even the ignition point, and a leak results in an immediate fire.
A fire in a reactor facility presents all the problems which may have to be faced in any fire plus a potential radiation hazard. Radioactive gases or air-borne par-
ticles will present an ingestion hazard and a contamination problem, while exposed sources create a direct radiation hazard. The hazard may be different from time to time, depending on the power level of the reactor and the length of time it has been in operation.
It must be emphasized that radioactivity cannot be seen, smelled or felt. It is not possible for a fireman to start attacking a fire where this hazard exists, and to depend on his senses to keep him out of trouble. It is extremely important to plan fire fighting procedures for reactor installations and to have trained personnel available with instruments to advise the officer-in-charge of the hazard. It is also desirable that each man be equipped with a film badge to record individual exposures.
Methods of extinguishing reactor fires or fires involving reactor components, of course, depend upon the type of material involved. Pyrophoric metals due to their violent reaction with water require special fire control materials. Class A materials, which in most cases consist of wooden blocks, blotting paper, clothing, etc., are controlled with water fog.
Contrary’ to the general belief of the past several years, water can usually be used on reactor fires or fires involving radioactive materials, if the material is the type that does not react violently with water. The important point to remember on using water for fire fighting around contaminated materials is to keep the water damage to an absolute minimum, to prevent excessive water run-off which in all probability will be contaminated.
Personnel must be monitored
All personnel must be thoroughly monitored to determine the amount of contamination, if any, they may have on their clothing. In addition, fire fighting equipment must be monitored before being placed back on the apparatus. Materials found to be contaminated must be thoroughly cleaned before they can be returned to use.
Similarly, contaminated personnel must clean themselves before returning to quarters. Firemen who operate in a building where radiation is a problem are not allowed to return to the outside and remove equipment from the apparatus. The pump operator stays outside the contaminated area and passes necessary materials and equipment to the working force.
Fire fighting procedures in reactors and in reactor experiments must, of a necessity, be different than those used in normal industrial type fires, because of radiation problems. Normal fire fighting tactics which include saving of life, protection from exposure, confinement, extinguishment, overhaul and salvage must be changed to (1) saving of life and protection of personnel from radiation; (2) protection of exposures not only from fire but also from contamination; (3) confinement of both fire and contamination; and (4) extinguishment, with utmost regard to the prevention of excess water run-off.