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Atomic Insights

Atomic energy technology, politics, and perceptions from a nuclear energy insider who served as a US nuclear submarine engineer officer

Atomic Insights July 1996

In the News: July 1996

July 1, 1996 By Rod Adams

Russian Floating Power Stations

(June 11, 1996: Source-NucNet, an Internet service of the European Nuclear Agency) – Officials at the Kurchatov Atomic Energy Institute in Moscow have announced that the technical design stage for a series of floating nuclear power stations is now complete.

Each power plant will consist of two 70 Mwe pressurized water reactor plants based on the proven KLT-40 ice breaker engine design. The plants will produce electricity and possibly heat for water distillation.

The proposed market for the plants is the remote areas of Russia where there is no electrical power grid and where fuel deliveries are prohibitively expensive because of distance and obstructions like ice. Spokesmen claim that the projected life of the plants will be forty years with a 13 year refueling cycle. Projected break-even time for the $250 million plants is 10 years.

Areas where the plants might be best employed include areas near the Arctic Ocean and the Bering Strait. Negotiations are also underway in China and the Philippines, both of which have remote areas close to large bodies of water that could make use of the plants. With a desalination capability, the potential market expands to include areas of the Middle East and Latin America.

Japan to Provide Pressure Vessels to China

(June 19, 1996: Source-NucNet, an Internet service of the European Nuclear Agency) – China has cancelled a previously signed contract with a Korean consortium led by Hanjung to provide pressure vessels and other key reactor components to Qinshan units 2 and 3.

The decision was tied to the failure of the Korean government to provide the promised export credits to back up the sale.

The Chinese have now signed an agreement with Mitsubishi, a Japanese heavy industrial firm. Under the agreement, Mitsubishi will provide the reactor vessel for Qishan unit 2 and will transfer technology to the Shanghai Boiler Works that will enable the company to construct the pressure vessel for unit 3. This arrangement is similar to the one agreed to by the Koreans and marks another step in the Chinese goal of being able to construct the major components of large nuclear power stations on their own.

Mitsubishi will also supply coolant pumps and charging pumps for both units. Framatome will supply the reactor controls and instrumentation systems, and other components will be supplied by a variety of manufacturers from China and other countries.

Filed Under: Atomic Insights July 1996

Accident Consequences: Design Added to Magnitude

July 1, 1996 By Rod Adams

The reactor was more reactive than planned due to problems with the aluminum-boron alloy burnable poison strips. Apparently, these strips had begun to rapidly deteriorate, causing some of the poison material to be lost from the core area.

The SL-1 accident was initiated by the rapid withdrawal of the central control rod. Starting from a fully shutdown condition, the action produced a condition in the core technically known as a prompt criticality.

When the SL-1 reactor achieved prompt criticality, a number of events happened in rapid succession. The core power level pulsed to nearly 20,000 MW, more than 6000 times as high as its rated power level. This power pulse lasted about 4 msec, ending due to a combination of void formation and fuel element heating. The total nuclear energy release was calculated to be approximately 140 Mw-seconds with an additional 24 Mw-seconds released in a chemical reaction between fuel and water.

The nuclear power transient caused some of the fuel material to reach its vaporization temperature of 2060 C (3740 F). This fuel boiling caused the fuel plates to swell and the cladding to fail, allowing approximately 20 percent of the fuel to be released.

A large steam bubble formed in the core, which lifted the mass of water above it at a rate of approximately 49 m/sec (160 ft/sec). This water hammered into the core head approximately 34 msec later, ejecting the head shielding and causing the pressure vessel to lift out of its support structure. It jumped nearly 3 meters to collide with the overhead crane before settling back into its original position. Essentially all water left the pressure vessel.

The vessel ejection sheared off all piping connections. The steam bubble also caused the pressure vessel to bulge, increasing its circumference in one place from 4.31 m (14.14 ft) to 4.627 m (15.18 ft).

While the pressure vessel was up in the air, the reactor was not shielded. Calculations indicate that the operators were exposed to an integrated neutron flux on the order of 1013 n/cm3. This explains why the victims became radioactive and could not be decontaminated.

Design Contributions

Though the initiating event was a prompt criticality – an event which is at least theoretically possible in some other reactor designs – the consequences of the SL-1 accident were made worse because of several unique design features that proved to be mistakes.

The reactor was more reactive than planned due to problems with the aluminum-boron alloy burnable poison strips. Apparently, these strips had begun to rapidly deteriorate, causing some of the poison material to be lost from the core area. The physical deterioration of the poison strips also seems to have contributed to a growing problem with sticking control rods.

Highly enriched uranium helps to improve the compactness and responsiveness of a nuclear reactor. Often, this is a benefit, in that it allows reactors that can respond to rapid changes in power demand, but it can lead to more radical consequences in the event of a rapid insertion of reactivity.

Uranium-aluminum alloy has a much lower melting and vaporization point than the uranium dioxide that is commonly used as the fuel form in modern reactor plants. Uranium-aluminum will vaporize at 2060 C, uranium dioxide will not even melt until its temperature exceeds 2800 C.

Aluminum is not the optimal cladding or structural material in a reactor that must operate at elevated temperatures. It will corrode, deform and melt in accidents more readily than several other available materials.

The low design pressure for the vessel allowed it to catastrophically fail at a pressure that would cause little or no damage to most other reactor pressure vessels. Essentially, the SL-1 accident was a boiler explosion, a type of accident that has caused death and destruction since the beginning of the Industrial Age.

Any time there is water and a heat source in a confined space, there is the possibility of forming a steam bubble rapidly enough to cause a significant pressure surge. A 400 psi design pressure leaves little safety margin for a steam boiler containing a nuclear reactor.

The small number of rods made each rod far more important than it should be. One of the results of the SL-1 accident analysis was to ensure that all reactors adhered to the “one stuck rod” criteria that was already in use in several other reactor design programs.

One partial success story is that of the reactor building. Though not designed as a containment, it still retained essentially all of the non-volatile fission products. The total release was on the order of 100 curies of Iodine-131 and other gases. More than 99.99 percent of all fission products remained in the reactor building.

Operational Contributors

It is clear from reading the historical records that the SL-1 project was run by weak managers. The plant procedures had well documented weaknesses and inadequacies, but corrective action was not taken.

For a developmental program deemed important to national security, the project appears to have suffered from serious budget constraints and from being understaffed in comparison to the responsibilities assigned.

The plant managers claimed during post-accident hearings that they had no knowledge of sticky control rods, even though the problems were clearly documented in the engineering logs in a series of entries that began several months before the accident.

Despite knowing of problems with the burnable poisons and other growing difficulties with the reactor core performance, the decision was made to continue operating the plant until the new core was ready. The managers and others in positions of responsibility apparently did not want to take any action that would slow down the project or the deployment of the production reactors.

Lessons Learned

Many good lessons were learned following the SL-1 accident. Organizational lines of responsibility were more clearly defined, reactor design codes became more useful, operational oversight was increased and several sensible new criteria (like the “one stuck rod”) were implemented.

Unfortunately, poor understanding of the specific causes of the accident has slowed the development of small, distributed nuclear power stations. The idea of small, lightweight nuclear power plants that can perform a variety of functions with a small operating crew is a good one. It should not be lost because the first people who tried it failed to understand the need for durability and robust system design.

Filed Under: Army Nuclear Program, Atomic Insights July 1996, Technical History Stories

SL-1: Designed for Remote Power and Heat

July 1, 1996 By Rod Adams

The Army’s designation , SL-1, tells us that the plant was a stationary, low power reactor, and that it was the first of its kind. The design work was done by Argonne National Laboratory in 1955-1956 under the name Argonne Low Power Reactor (ALPR). SL-1’s mission was to provide power to radar stations along the […]

Filed Under: Army Nuclear Program, Atomic Insights July 1996, Small Nuclear Power Plants, Technical History Stories

Letter from the Editor: Solving the SL-1 Mystery

July 1, 1996 By Rod Adams

One common link in the training of most nukes is the viewing of a grainy, black and white documentary on the aftermath of an accident at a reactor known as SL-1. The accident occured on January 3, 1961 at the Atomic Energy Commission’s National Reactor Testing Station near Idaho Falls Idaho. Three people died in […]

Filed Under: Accidents, Army Nuclear Program, Atomic Insights July 1996, Technical History Stories

What Caused the SL-1 Accident?: Plenty of Blame to Share

July 1, 1996 By Rod Adams

(Note from the editor: The following story is conjecture supported by interviews of first hand sources and a careful review of the written history. It is tempered with an understanding of reactor operations and human nature gained during more than six years in supervisory positions in military nuclear power plants. The mystery, however, is more […]

Filed Under: Army Nuclear Program, Atomic Insights July 1996, Technical History Stories

January 1961: SL-1 Explosion Aftermath

July 1, 1996 By Rod Adams

At 9:01 pm on January 3, 1961, the first indication of trouble at SL-1 was received at Atomic Energy Commission Fire Stations. The alarm, which was triggered by one of several measured parameters at the plant, was immediately broadcast over all National Reactor Testing Station radio networks. By 9:10 pm, fire trucks and security personnel […]

Filed Under: Accidents, Army Nuclear Program, Atomic Insights July 1996, Technical History Stories

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