A letter in Power Engineering, December 1994, concerning low-level nuclear waste gives the wrong information about the availability of waste disposal sites. At this time the sites are Richland, Wash., and Barnwell, S.C., and they only accept wastes from the states which are members of their compacts.
Thirty states currently have no access to low-level radioactive waste disposal. This problem is having a very serious effect on research and medical uses of radionuclides.
Robert D. Gallagher
NSSI/Sources & Services Inc.
Linear regression leak rate
I?m always excited about saving time and expense through the use of statistical methods. The Power Engineering December 1994 article (OLinear regression leak rate calculation helps avoid premature shutdown,O page 47) left me with many questions. Here are a few of them.
1. The opening paragraphs state that there is a relationship between the reactor?s pressurizer level, volume control tank, primary drains control tank and average coolant temperature. What is the relationship and how is it used to calculate a leakage rate in gpm?
2. Figure 1 shows the PZR level versus time and the average temperature versus time. The graph is labeled Tave vs. pressurizer level. Did the authors intend to show the relationship between pressurizer level and temperature or is the graph mislabeled? What are the units of the PZR level? Are they in head pressure on a linear scale such as OfeetO or in a force per unit area such as psi?
3. Figure 2 shows a linear regression of the temperature with time. In a linear regression analysis, the x-axis is usually the independent variable while the y-axis is the dependent variable. How does time cause the temperature to change? Is the tank level changing so that a change in coolant flow causes the temperature to rise or fall? If that?s true, shouldn?t the regression be done with temperature versus tank level?
4. Figure 3 shows that the leakage rate remains constant with time when a linear regression is used. Time and leakage rate are not actually related in any way. How can you correlate time and leakage when the passage of time is not affecting the rate of leakage by any physical connection? I hope the authors can set me straight on these. Their method is accepted as valid, so there must be some miscommunication.
Edward J. Kaminski, P.gif.
Professional Loss Control
Surry?s article on linear regression was targeted for readers in the nuclear power generation industry and describes our application of statistical methods to reactor coolant system (RCS) leakrate calculation. RCS leakrate is an esoteric parameter known mainly by operators and engineers who monitor and analyze it by professions.
An in-depth understanding on nuclear power plant theory and operation is essential to understanding the relationship between the constituents of the calculation and an appreciation for the superior results obtained by the application of linear regression.
I hope the paragraphs that follow will provide the clarification requested, and encourage other pressurized water reactor (PWR) power plants to explore its benefits. If a PWR power plant were able to operate under ideal steady state conditions, RCS leakage rate calculation would be as simple as measuring the loss of mass in the volume control tank (VCT) over time. But because of variations in load of the main generator?s electrical distribution network (the grid), primary and secondary plant parameters change constantly to keep generator power output constant.
Even in the base load energy generation market where a power station?s output is maintained at full power, load changes on the grid are seen as slight power demand changes on the generator. Their changes, coupled with inherent tolerances in Tave controls, create variations in the heat transfer rate through the plant?s steam generators resulting in fluctuations in RCS Tave and pressurizer level. The relationship between Tave and pressurizer level forms the basis for leakrate measurement.
The level control system of the pressurizer is designed to adjust level based on Tave to maintain a constant mass in the RCS. Slight changes in RCS Tave because of load variations on the grid are accompanied with level changes in pressurizer level, although not necessarily simultaneously as indicated in Figure 1 of the referenced article.
Figure 1 reflects actual data taken from the plant?s computer and shows that Tave (in degrees Fahrenheit) and pressurizer level (in percent) vary significantly over just a few minutes.
The RCS leakrate calculation considers the total loss of reactor coolant mass to be equal to the level drop in the VCT over time, and corrects for RCS mass loss or gain due to changes in Tave and pressurizer level. Ideally any mass increase (or decrease) because of Tave would be accompanied by a mass decrease (or increase) in the pressurizer. These changes in level and temperature generate regression equations for the Tave and pressurizer level variable which typically cancel each other out because of their inverse slope.
Surry is bound by its operating license to locate the origin of RCS leakage, with a limit of 1 gallon per minute being the maximum permissible OunidentifiedO leakage (origin unknown). OIdentifiedO leakage is considered to be that portion of the total mass leakage which shows as an increase in the primary drains transfer tank (PDTT), sometimes called the reactor coolant drain tank, over the same time frame of the RCS leakage rate calculation.
The PDTT collects reactor coolant that leaks through RCS valve stem packing glands, which typically experience leakage, and coolant pump seals that are designed to leak a small amount. The change in PDTT level is not calculated using the linear regression equation because its level trend is observed to be straightline.
The difference between the total coolant leakage and the OidentifiedO coolant leakage seen in the PDTT is termed OunidentifiedO leakage.
Analysis of RCS parameters shows that leakage is extremely constant from day to day because RCS pressure is maintained constant. Surry calculated RCS leakage each day for a one-hour time period, normally between midnight and 5 a.m. when
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the grid is stable. Figure 3 shows a comparison between daily leakage results over the same one-hour period as calculated by the snapshot approach and the new method, using linear regression. The linear regression results accurately reflect leakage rate each day while the snapshot method is plagued with data scatter. Virginia Power welcomes further inquiries into its leakrate calculation method at P.O. Box 26666, Richmond, Va. 23261, or at (804) 365-2155.
Craig T. Olsen
I read with interest your Power Engineering January issue?I especially appreciated the pricing details on re-lining the pipe at Smith Mountain on page 42. I too agree that Insitu-Form is way over-priced for gravity drain lines!
I found an error on page 48. The speed of the hurricane winds was listed at 1,240 miles per hour. I always through Mt. Washington, in New Hampshire?s? Presidential range of mountains, held the record for highest recorded surface wind?that of 231 mph on April 12, 1934. Has a new record been set or does a hurricane?s surface wind actually exceed this surface station situation/record?
Thanks for your helpful magazine and factual articles.
(Editor?s note: Mack, thanks for what we hope is the last gust of hot air on our January OField NotesO error. According to Storm Data and Unusual Phenomena from the U.S. Department of Commerce, Hurricane Andrew had a maximum sustained surface wind of 145 mph.)
ANS is gloomy, CEED?s not
Steven Kuehn?s January article in Power Engineering, ONuclear Power EngineeringO column, page 11, described the recent American Nuclear Society?s winter meeting in one word?gloomy. On the other hand, the mood at the Center for Energy and Economic Development (CEED) can best be described in two words?optimistic and energized.
Why? Because CEED, as the historic union of coal companies, railroads and utilities formed to promote the use of coal at the state and local levels, has been in the arenas where key decisions about America?s energy future are being made. We have seen a profound change in attitudes held by decision makers when the scientific facts about our energy choices have been presented effectively. Based on our experiences across the nation, we were surprised by the underlying premise of Kuehn?s article?that the imposition on monetized environmental externalities by states will result in nuclear power being competitive, in terms of price, with coal and other major fuel sources for the production of electricity. The premise is fundamentally flawed in two ways.
Flaw No. 1: The assumption that the imposition of environmental externalities is coming to be an accepted part of America?s energy policy. On the contrary, the trend is clearly to reject the use of environmental externalities. After the initial burst of acceptance by California, Nevada, New York and Massachusetts, other states which have more seriously examined environmental externalities have rejected their use. Of particular note, the Florida Public Service Commission unanimously rejected environmental externalities last year in one of its most extensive dockets ever. Also, after months of contemplation, the Illinois Commerce Commission soundly rejected the Tellus Institute?s desire to impose environmental externalities last fall. This is the same Tellus Institute that Kuehn cited as the source of Ocurrently accepted valuesO for environmental externalities. Recently, a Massachusetts appellate court struck down the state Department of Public Utilities? establishment of environmental externalities. As the Massachusetts state legislature considers the decisions made in Florida and Illinois, it is not certain that the legislators will act to reimpose externalities in light of the appellate court decision. Additionally, the states of Virginia, Michigan and Maine have taken a look at environmental externalities and said, ONo thanks.O
Flaw No. 2: The assumption that the nuclear industry will gain a competitive advantage as a result of environmental externalities. The nuclear power industry should not count on being exempt from the financial burden of environmental externalities. As Kuehn pointed out, the nuclear industry carries the heavy baggage of waste and spent fuel disposal, radon emissions and accidents. Advocates of environmental externalities, no doubt, will attempt to impose on the nuclear industry the kind of monetized adders they have attempted to place on coal and other fuels. The environmental externality theory is a brush that will eventually tar the nuclear industry just as badly as any other domestic energy source. We at CEED have worked diligently to provide accurate scientific evidence and sound legal arguments to decision makers in those states which have and are considering environmental externalities. That?s why this marked trend against the use of externalities has caused us to be both optimistic and energized about coal?s continued dominance as the number one source (56 percent) of America?s energy production.
CEED urges the nuclear industry to join a growing number of states that have rejected environmental externalities as a flawed, unwarranted and unwise theory which will needlessly raise the cost of electricity.
Environmental externalities are bad policy for American businesses, workers and consumers at a time when new technologies are making abundant, domestic fuel sources, such as coal, even more environmentally compatible.
Stephen L. Miller
(Editor Steve Kuehn replies: In my January column, I reported on an argument proposed in a presentation by GE?s John Redding and Chris Veitch at the American Nuclear Society?s winter meeting, held in November 1994. Stephen Miller?s letter does bring up some excellent points and highlights some of the most popular arguments against externality-based ratemaking, but to attribute the facts and analysis presented in my column to me may mislead some readers into thinking my piece contained my opinion on the subject. For those readers wishing to know my opinion of externalities, please call me at (918) 831-9852.)