Hallam Nuclear Power Facility
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The Hallam Nuclear Power Facility (HNPF) in
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...
was a 75 MWe
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
-cooled
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
-moderated
nuclear power plant A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a electric generator, generato ...
built by
Atomics International Atomics International was a division of the North American Aviation company (later acquired by the Rockwell International company) which engaged principally in the early development of nuclear technology and nuclear reactors for both commercia ...
and operated by Consumers Public Power District of Nebraska. It was built in tandem with and co-located with a conventional
coal-fired power station A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts Nameplate capacity, capacity. They ...
, the Sheldon Power Station. The facility featured a shared
turbo generator A turbo generator is an electric generator connected to the shaft of a steam turbine or gas turbine for the generation of electric power. Large steam-powered turbo generators provide the majority of the world's electricity and are also used b ...
that could accept steam from either heat source, and a shared
control room A control room or operations room is a central space where a large physical facility or physically dispersed service can be monitored and controlled. It is often part of a larger command center. Overview A control room's purpose is produc ...
. Full power was achieved in July 1963. The facility shut down on September 27, 1964 to resolve reactor problems. In May 1966, Consumers Public Power District rejected their option to purchase the facility from the Atomic Energy Commission (AEC). In response, the AEC announced its plan to decommission the facility in June, 1966. The facility operated for 6,271 hours and generated 192,458,000 kW-hrs of electric power. It was located near Hallam, about 25 miles southwest of
Lincoln Lincoln most commonly refers to: * Abraham Lincoln (1809–1865), the sixteenth president of the United States * Lincoln, England, cathedral city and county town of Lincolnshire, England * Lincoln, Nebraska, the capital of Nebraska, U.S. * Lincol ...
.


Description

The sodium-cooled graphite-moderated reactor (SGR) design (of which HNFP was a demonstration) targeted economical commercial nuclear electricity. The
liquid metal A liquid metal is a metal or a metal alloy which is liquid at or near room temperature. The only stable liquid elemental metal at room temperature is Mercury (element), mercury (Hg), which is molten above −38.8 °C (234.3 K, −37.9&nbs ...
coolant enabled operation at temperatures sufficiently high to produce steam conditions identical to those used in fossil-fueled power plants, enhancing power conversion efficiency and making use of commodity
steam turbines A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
. It also enables low-pressure operation. The
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
moderator enabled operation with low-enriched nuclear fuel as well the potential use of the
thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
. These benefits were expected to overcome the added complication of a using chemically reactive coolant. The reactor was initially fueled with 3.6% enriched uranium-10 molybdenum alloy with
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
cladding. The graphite moderator was clad in stainless steel hexagons with each corner scalloped to make room for the process tubes, which contained the fuel clusters and control rods. Three sodium heat-transfer loops (each with a radioactive primary loop and a non-radioactive secondary) moved heat to three steam generators. Steam fed into a common header to a single turbine generator. The primary hot leg temperature was 945 °F, and the secondary hot leg temperature was 895 °F. Uranium carbide was selected for the second core at 4.9% enrichment.


Proposal, Development, and Construction

Hallam was proposed in March 1955 in response to the first round of invitations by the Atomic Energy Commission's Power Demonstration Reactor Program. It used technology being developed in the smaller
Sodium Reactor Experiment The Sodium Reactor Experiment was a pioneering nuclear power plant built by Atomics International at the Santa Susana Field Laboratory near Simi Valley, California. The reactor operated from 1957 to 1964. On December 20, 1951, the first Experimen ...
(SRE), also built by Atomics International. Lessons from SRE applied to HNPF include: * Fuel rod blowing * Poor control of sodium convection flow * Stratification of sodium in intermediate heat exchanger * Difficulties due to freeze-seal sodium pumps * Difficulties in preheating of sodium systems Because HNPF was more than ten times larger than SRE, a components development and test program were performed to provide final design data. All major components were tested, including fuel, control rods, instrumentation, pumps, and valves. The fuel handling machine was assembled and tested. Scale model of a steam generator was tested in a sodium loop along with related equipment and instrumentation. A formal three-session training program for operators was conducted in 1960. 30 personnel attended the first session for six months. Each person received approximately 900 hours of training. Construction began on April 1, 1959. Employment during construction peaked at 270 in March 1961, and 107,600 person-days total were required to complete the construction. Various construction assembly interferences were anticipated, and detailed scale models were procured. Labor problems resulted in the loss of 1750 person-days. The entire facility was completed on November 30, 1961, 4 months past the originally planned date of completion.


Operation and shutdown

Initial criticality was achieved in January 1962, followed by wet criticality six months later. Difficulties that arose during operation and required plant shutdown and correction included leaking control rod thimbles, seizure of secondary sodium pumps, leaking steam generator instrumentation and pipe flanges, difficulty of adjusting fuel channel flow orifices, and failure of primary and secondary sodium throttle valves. The most severe issue was the ruptures of moderator elements. Seven elements ruptured in February 1964. The ruptures and subsequent absorption of sodium into the graphite reduced the thermal neutron flux in the core and caused a reduction in local power. The moderator elements swelled as well, reducing coolant and process space. Examination disclosed that failure was caused by low ductility stress-rupture leading to a one-inch-long crack about three inches below the top of each element. Chauncey Starr, the president of Atomics International, testified that they had identified and claimed to have fixed the issue with the moderator can. He proposed a repair operation involving attaching snorkels to each moderator can into the cover gas space, which would cost $1.8M and require 6-9 months. Nonetheless, the AEC under Milton Shaw decided to terminate their contract with the utility. Consumers chose not to purchase the plant, and it was instead decommissioned with the nuclear components sealed in concrete. The plant's single 75 MWe reactor operated from 1963 to September 27, 1964. Decommissioning was completed in 1969. ;Present day Currently, the site holds a fossil-fuel plant, Sheldon Power Station. The site is monitored from 17 monitoring wells, and no radioactivity above background levels in any samples has been detected.


References


External links


Hallam Nuclear Station on 1960's TV!
– Additional historical images and discussion of the Hallam site and plant {{U.S. Nuclear Plants Nuclear power plants in Nebraska Decommissioned nuclear power stations in the United States Energy in Nebraska Buildings and structures in Lancaster County, Nebraska Atomics International Energy infrastructure completed in 1963 1963 in Nebraska 1964 in Nebraska