Heat and heat sinks; safety and cost competitiveness - Remarks Before OECD/CSNI Workshop on Advanced Thermal- Hydraulic and Neutronic Codes

There was a time when it was thought that safety could be achieved fully independent of cost. Then the U.S. nuclear industry entered into an era where cost became important... and safety improved. I submit that two independent yet related variables - safety and cost competitiveness - determine the viability, indeed the survivability, of nuclear power and nuclear technologies. They are both integral quantities and embody most of the determinant issues. Safety and cost competitiveness are both dynamic variables and easily tailored for use in decision-making. They have been, and could be, at odds with each other but should not be. In fact, it is imperative that they work together and not against each other. Safety is the priority that enables cost competitiveness while safety-conscious cost considerations strengthen safety. This coupling is obvious when looking at averaged safety and cost performance indicators, and it is dramatic for 'top performers'. There is no doubt that the safest nuclear power plants in this country are generating electricity at very competitive production costs, often lower than coal. The U.S. NRC has matured into a more safety-focused regulator; the industry is now able to focus more sharply on real safety, and regulatory requirements. In fact, it was the industry that first enabled the NRC's shift to real safety from prescriptive regulation by lowering the number and significance of events and improving overall performance. It is the industry that must keep it so. There is a very strong correlation between heat generation and heat sinks. There is a strong correlation between thermal-hydraulics development and nuclear safety. Thermal-hydraulics is the science and technology that plays the key role in determining safety and performance. At the beginning of the commercial nuclear age, plants were designed and built before much of our current knowledge was developed. During the 1960's, safety analyses and licensing reviews of the earlier plants were done on almost an ad-hoc, or case-by-case basis. As new issues arose, the means to address them and the formulation of rules and regulations developed concurrently. At that time, the technical basis was generally lacking for performing best-estimate analysis or to determine the magnitude of uncertainties. Therefore, conservative assumptions were often imposed in an attempt to provide bounding analyses. Through 40 years of operating experience and safety research, we now have enough information to establish a regulatory framework based on risk perspectives and to allow more realistic analyses. In fact, the current initiatives on risk-informed regulatory framework presents an opportunity to launch a major effort to utilize state-of-the-art technology for consolidating and upgrading the existing thermal hydraulic and neutronic codes used in reactor safety analyses. This is because in risk-informed regulation, we should strive to reduce unnecessary conservatism, and develop the best- estimate analytical tools while maintaining the defense-in-depth philosophy. In the meantime, it also presents a challenge to code developers because of the sheer size and complexity of these codes. A better thermal-hydraulics and neutronics understanding will allow the operators and regulators to improve nuclear safety and its efficient use; to help the regulator quantify safety requirements and support the nuclear industry's efforts to achieve a positive feedback between safety and cost competitiveness. The recent progress in thermal hydraulic codes has enabled us to enhance significantly our ability to better simulate the transient physical phenomena in the nuclear steam supply system. The familiar RELAP 5 nodding diagram is now replaced by a GUI (Graphical User Interface) input. The 3-D Model Viewer now allows us to verify the intended piping configuration. Because of the more realistic computer simulation, we should be able to reduce some unnecessary conservatism that was necessary for the first generation codes and to develop a set of best-estimate computer codes that ca n be used consistent with the concept of risk-informed regulation. At this point in the maturity of both the nuclear industry and the regulators, we have learned much in how to enhance the value of nuclear technology to society by improving its safe and efficient use. The issue is how best to systematically use state-of-the-art thermal-hydraulics and neutronics to improve safety and cost competitiveness, and to lay the foundation for a new generation of nuclear power plants. In other words, the nuclear industry and the regulator must face the realities of a world of finite resources, to ensure that the benefits of nuclear technology can be realized without compromising safety. There are many ways to accomplish this goal, but the goal should be the same