- THE MAGAZINE
Renaissance: a rebirth or revival, e.g., of culture, skills, or learning forgotten or previously ignored. This definition is truly applicable to the nuclear industry in this decade. Considered the energy source of the future in the late 1960s and early 1970s, nuclear power lost its luster and momentum in the U.S. after the Three Mile Island incident. Other countries followed suit on a lesser scale, and the nuclear age moved into a period of stagnation.
Times have changed and more nuclear reactors are under review, construction, and startup today than ever before. The resurgence in construction is a major shift due to both the observed need for less dependence on fossil fuels and the global focus on long-term greenhouse gas emission reduction. The revitalization of the industry has also spurred the rebirth of advancing technologies. While the existing reactor fleet serves as a technology basis for near-term reactor construction, advancement in power plant designs to improve efficiency and fuel usage is gaining momentum.
Advancing TechnologyAs the reactor designs advance, operating temperatures and conditions are placing an increased burden on the materials used for construction and criticality control. Materials compatible with the lower temperature boiling water reactors cannot provide mechanical stability, operate at high temperatures or resist the extremely corrosive atmosphere for the desired operating parameters of new designs. Increased fuel enrichments and high flux designs require greater neutron control and emergency shutdown capabilities without excessive burden to primary and secondary cooling loops.
Boron Products, LLC, a Ceradyne Company, is supporting the ongoing technical advancement of pressure water reactors while investigating material alternatives for advanced high-temperature reactors (AHTR). The company's position in the advancement of nuclear power is based on technical ceramic expertise, materials replacement, and the ability to supply a critical material: the boron 10 isotope for criticality and neutron control. Boron Products is currently supplying 10B enriched boric acid and 7Li enriched lithium hydroxide monohydrate for the first European Pressurized Reactor(tm) (EPR) designed to optimize the use of nuclear fuel and minimize the production of long-lived, high-level radioactive waste.
Isotopes are different types of atoms of the same chemical element. For instance, oxygen has five isotopes, carbon four, silicon three and boron two. The natural percentage contributions are used to determine the molecular weight found in the periodic table. The natural isotope percentage for each element, combined with the atomic mass for each isotope, correlates to the atomic mass or molecular weight. With boron, the molecular weight of 10.81 is derived from the 19.8% 10B isotope and the 80.1% 11B isotope. The challenge is separating materials that have a mass difference of one atomic unit and extremely similar chemical and physical characteristics. Boron Products has optimized a proprietary process based on a unique characteristic difference found between the two isotopes. This proprietary process allows boron isotope separation to be conducted on an industrial scale and at reasonable costs.
Enriched boric acid is a design feature of the EPRs currently under construction in Finland, France and China. The use of boric acid enriched in the 10B isotope produces safety benefits as a result of the reduction in exposure of plant personnel to ionizing radiation. As reported by EPRI (report TR-109992, dated March 1998), the use of enriched boric acid allows for operation at optimum reactor coolant system pH control for extended periods of time throughout the fuel cycle. The use of enriched boric acid also enables a reduced concentration of lithium in the primary coolant that is required to maintain pH in a regime, which results in minimal corrosion rates of the internal reactor components and maintains a positive temperature coefficient of solubility for the corrosion product oxides. Additional benefits realized with enriched boric acid are related to fluid systems and safety aspects associated with extended fuel cycles, reduced boron and lithium costs, reduction in the size of equipment for boric acid systems, and the elimination of heat tracing.
The EPR is a pressurized water reactor (PWR) requiring that fast fission neutrons be slowed down in order to interact with the nuclear fuel and sustain the chain reaction. The coolant water is used as a moderator by letting the neutrons undergo multiple collisions with light hydrogen atoms in the water, losing speed in the process. The use of water as a moderator is an important safety feature of PWRs, as any increase in temperature causes the water to expand and become less dense, thereby reducing the extent to which neutrons are slowed down and thus reducing the reactivity in the reactor. If reactivity increases beyond normal, the reduced moderation of neutrons will cause the chain reaction to slow down, producing less heat. This property, known as the negative temperature coefficient of reactivity, makes PWR reactors very stable.
The reactivity adjustment required to maintain 100% power as fuel is burned up in most commercial PWRs is normally achieved by varying the concentration of boric acid dissolved in the primary reactor coolant. Boron 10 readily absorbs neutrons; increasing or decreasing its concentration in the reactor coolant will thus affect the corresponding neutron activity. An entire control system involving high-pressure pumps is required to remove water from the high-pressure primary loop and re-inject the water with differing concentrations of boric acid.
Lithium 7 hydroxide monohydrate is added as a pH buffer to neutralize acidity created by the addition of boric acid to primary coolant solutions of PWRs. However, naturally occurring lithium contains both 6Li and 7Li isotopes. 6Li adsorbs thermal neutrons and subsequently decays, producing unwanted tritium. Lithium hydroxide monohydrate enriched in 7Li mitigates this decay reaction and subsequent tritium formation in the cooling water. The extremely low levels of tritium produced when using 7Li-enriched material offers distinct operational advantages under existing environmental guidelines.
Long-Term ObjectivesWorking proactively with government agencies, national laboratories and academia, Boron Products is focused on ensuring that adequate isotopic materials are available on an industrial scale and evaluating ceramic alternatives in material limiting areas. Longer term objectives established by the U.S. Department of Energy (DOE) will drive continued advancement in reactor designs to promote low-cost, safe and reliable nuclear energy in the U.S. The DOE has established five long-term imperatives:
- Extend life, improve the performance, and sustain the health and safety of the current U.S. reactor fleet
- Enable new plant builds and improve the affordability of nuclear energy
- Enable the transition away from fossil fuels in the transportation and industrial sectors
- Enable sustainable fuel cycles
- Understand and minimize proliferation risks
Understanding the role of nuclear power in providing safe and reliable energy to a growing world, working closely with industry, government and academia to advance nuclear technology, providing direct support to the existing fleet, and relying on 35 years of knowledge has placed Boron Products in a unique position to support the renaissance in the nuclear industry.
For more information regarding the use of enriched boron materials in nuclear energy applications, contact Ceradyne Boron Products at P.O. Box 798, Quapaw, OK 74363; (918) 673-2201; fax (918) 673-1052; e-mail firstname.lastname@example.org; or visit www.ceradyneboron.com.