Read Ebook: The Nuclear Ship Savannah First Atomic Merchant Ship One of the World's Safest Ships by United States Department Of Commerce United States Maritime Administration U S Atomic Energy Commission

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A study has been made concerning the penetration of the vessel wall by a piece of debris in an explosion. An analysis of the penetrating power of high-speed components indicated that the shell would contain the largest missile that could be expected.

The shell is cylindrical in shape, 35 feet in diameter by 50.5 feet long, and is centrally located on the ship's bottom.

The containment shell is sealed at all times during plant operation. Entry to the shell will be made only after the reactor has been shut down, the shell purged with air, and the radiation level has dropped below 200 mr per hour.

The bottom half of the shell rests in a cradle of steel surrounded by a 48-inch-thick wall of reinforced concrete.

The top half of the containment shell is covered by a 6-inch layer of lead plus a 6-inch layer of polyethylene. During normal power operation, this reduces the radiation level to less than 0.6 mr per hour at the nearest point of access by the crew.

CONTAINMENT SHELL AIR CONDITIONING

This system maintains a constant maximum ambient temperature of 140? F. and a maximum relative humidity of 72 percent inside the containment shell. The system operates in conjunction with the intermediate cooling water system, using 95? F. water.

During normal operation, the containment shell is sealed and no outside air will enter or leave the vessel. Ambient conditions will be maintained by regulating the cooling water flow as required according to instrument readings on the control panel.

In all areas where crew members have unlimited access, radiation levels will be less than 5 rem integrated dosage per year, the recommended maximum annual exposure of workers in the atomic energy field. Assuming that passengers would move about the ship, and on the basis of their calculated average distance from the reactor, the average exposure of a passenger remaining aboard for a year would be under 0.5 rem, i.e. ?/?? of the occupational value.

The 5 rem area is relatively small and not in general use. No crew member will be aboard ship or in the 5 rem area continuously for a full year, and it is doubtful that any crew member will actually receive an integrated dose of more than 0.5 rem in a year.

ELECTRICAL SYSTEM

This system supplies power to the reactor system and its auxiliaries and is designed to operate with a high degree of reliability to assure reactor safety during all phases of operation and shutdown.

It includes all load control and protective devices, containment wiring, metering, interlocking and alarms associated with electrical loads for the reactor system. Power for the system normally is supplied by two turbine-generators, each rated at 1,500 kw, 0.8 pf, 450-volts, 3 phase and 60 cycles. For increased reliability, a double bus type arrangement is used. In the event of a bus fault, an automatic transfer of all vital loads to the other bus will occur. During normal operation, a circuit breaker ties the two busses together.

RADIATION MONITORING

The radiation monitoring system of the SAVANNAH keeps a constant check on the intensity of radiation at various points within the reactor system as well as areas remote from the power plant. This system is divided into two areas for this description. They are power-plant monitoring and health physics monitoring. The latter is covered under its own heading.

POWER-PLANT MONITORING

Through keeping track of the radiation level at various points in the reactor system, any abnormalities in operation can be quickly detected and corrected.

A leak in the heat exchangers, for example, would show up on a radiation monitor located in the blowdown line from each of the heat exchangers.

The intermediate cooling system, which includes cooling water from the primary pumps, shield water cooler, containment air cooler, and other components not directly in the primary loop, is monitored at five locations. Leakage of primary loop water into the secondary water is possible only from the pumps and letdown coolers, because of differences in pressure. Consequently, radiation monitors are located downstream from the letdown coolers and in each of the return lines from the pump cooling coils.

The demineralizers are also monitored. When the resin bed is functioning, the flow downstream will have negligible radioactivity. Consequently, a monitor signal at this point will indicate when to switch to a new demineralizer. The monitor in the influent measures the activity level in the primary loop.

The fission product monitor keeps track of fission product activity in the primary system. The monitor consists of a cation and anion column, an amplifier, and an indicating system. This monitor is located in the primary coolant flow system.

TANKS HOLD LIQUID WASTE

Power plant liquid wastes are collected in tanks for storage prior to discharge into a specially designed servicing vessel in port. The liquid waste collection tanks are monitored. Gaseous wastes will normally be disposed of at sea through the radio mast, which contains two detectors for monitoring purposes. They are an air-particle monitor and a radio-gas monitor, and operate at all times so that gas is vented to the atmosphere. If gaseous radioactivity should rise above specified limits, the gas will be diluted to below the limit before being discharged to atmosphere.

The above monitor stations are the principal ones involved in reactor system operation. The monitors operate through a system of separate channels, with each channel responsible for a pre-selected range of activity. All detectors relay their readings to the main panel in the control room, where automatic recording and visual observation instruments are located.

STABILIZING BRACKET PORT AND STARBOARD POLYETHYLENE "C" DECK STEEL & REDWOOD COLLISION MAT WOOD PAD "D" DECK CONCRETE WATERTIGHT BULKHEAD REACTOR COMPARTMENT STIFFENING RINGS LEAD CONTAINMENT VESSEL COMPARTMENT BULKHEAD CONCRETE INNER BOTTOM FOUNDATIONS FORWARD

Portable monitoring equipment, samplers, and other health physics survey equipment are provided for access, survey, and maintenance monitoring.

REACTOR CONTROL AND SAFETY SYSTEMS

The entire reactor system is protected by the safety system. This system causes the reactor to terminate power production if a dangerous operating condition exists. The safety system also contains interlocks which prevent actions which would otherwise jeopardize the reactor system.

The control and safety systems are capable of protecting the reactor system from damage due to any credible accident except a major leak in the primary loop.

The reactor will "scram" automatically from any of seven causes: shorter than a safe reactor period, excessive power, excessive rise or fall in reactor pressure, excessive reactor outlet pressure, loss of flow, loss of power to safety circuits, and loss of power to control rod drives.

INSTRUMENTS DOUBLE CHECKED

The nuclear instrumentation system provides maximum reliability and safety, yet minimizes erroneous readings or signals from the monitoring channels. This is done by using two or more measuring channels in each operating range, and then interlocking the circuits so that at least two of them give the same signal of abnormal operating conditions before initiating a reactor "scram."

Increased reliability is obtained by using "solid state" instruments or magnetic amplifier units rather than electron tubes and relays.

REACTOR SAFETY SYSTEM

This system constantly monitors signals from the nuclear and non-nuclear instrumentation, and when necessary takes corrective action. Corrective action will be either in the form of "fast insertion" of the control rods, or in the form of reactor "scram." Fast insertion takes place at a rate of 15 inches per minute, while a scram is achieved in 1.6 seconds.

Fast insertion consists of moving all control rods to the full down position at the fastest rate possible through the electromechanical drives. For reactor "scram," all rods are driven to full down position under the force of a net hydraulic pressure of 1,250 psi.

SHORTER THAN A SAFE PERIOD

The reactor period is a measure of the rate of reactor power increase; the shorter the period the faster the rise. Ten neutron-measuring channels, covering the full range from source level to 150 percent of maximum power, measure neutron intensity and its rate of change. These data are continuously transmitted to the reactor operator and the automatic control and safety system. Too fast a rate of change, or shorter than a safe period, will automatically "scram" the reactor.

EXCESSIVE POWER

The amount of power produced is a function of the neutron flux and its resultant heat generation in the primary loop. The temperature selected to produce automatic "scram" is 540? F. This temperature "scram" circuit provides an independent backup to the neutron flux "scram."

EXCESSIVE RISE OR FALL IN PRESSURE

Too low a pressure could result in boiling of the primary coolant, while too high a pressure could result in poor heat transfer as well as placing unnecessary stresses on the reactor's fuel element core structure. There are a number of causes for either condition, all of which would relay a "scram" signal to the operator and to the automatic safety system.

EXCESSIVE OUTLET PRESSURE

In addition to protection against rapid rate of change in pressure, a scram circuit is provided to prevent any steady excessive outlet pressure that could result in damage to the core and related equipment.

LOSS OF FLOW

This condition would result from a mechanical failure in the primary loop pumps, piping, etc., or by accidentally stopping the pumps when the reactor is at power, or by loss of power to the pumps. When a single pump fails to operate for any reason, an alarm is sounded to warn the operator. If all four pumps fail to operate for any reason, a signal is sent to the reactor safety system to "scram" the reactor.

LOSS OF POWER TO SAFETY CIRCUITS

The hydraulic drives that operate the "scram" mechanism require reserve pressure to keep them in the "ready" position for "scram" condition and are an integral part of the safety circuitry. A power failure in the safety circuits would automatically put the hydraulic drives into operation to "scram" the reactor.

LOSS OF POWER TO CONTROL ROD DRIVES

Each of the 21 control rods has its own drive mounted vertically on the upper reactor head. Of these, 9 are servo controlled and 12 are of the nonservo type. The 9 servo rods have variable speed drives and operate in two groups in a synchronous manner, according to demand signals from the reactor system. The 12-rod group can be operated manually or in groups according to predetermined conditions. All of these operate at a speed determined by their gearing.

The safety considerations are as follows:

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