Nuclear power plants are categorized according to the type of nuclear reactor that is the primary heat source. In this book, reactor types are identified by the coolant used to extract heat from the nuclear fuel *

Bressunzed-water rent tors reactors cooled by water in the liquid state

Boiling water realtors reactors cooled by water in the liquid and gaseous states

Sodium-i ooled realtors reactors cooled by liquid sodium Gas-cooled reaetois reactors cooled by gas (helium in the United States)

‘Reactors can also be classified m other ways according to the energy spectrum of the neutron population (thermal, intermediate, and fast), according to use (research, development, test, plutonium production, and power), according to fuel arrangement (homo­geneous or heterogeneous), or according to whether the fuel fissioned is less than or greater than the fuel generated (breeder, nonbreeder, and converter).

Fvery nuclear power plant presently m operation in the United States derives its heat from a reactor in one of these four categories

Classification of nuclear power plants according to the primary reactor <oolant is particular^ appropriate to a consideration of power-reactor instrumentation systems since the coolant properties determine many aspects of instrumentation design. This is not surprising since the basic function of the nuclear reactor in a power plant is to generate the heat and to transfer it to a coolant that ean then transfer heat to the steam that drives a turbogenerator The coolant that extracts the heat from the nuclear fuel is the key link in the sequence of operations that converts nuclear energy to electrical energy. Moreover, because material constraints are critically important in any heat engine, the properties of the coolant have a strong influence on the plant design.

Figures 1.12 through 1.1 5 illustrate the basic configura­tions of the four categories of nuclear power plants It must be emphasized that the figures do not purport to show any actual plant configuration (see Chaps. 15 through 18) but rather show those features of each reactor type which are relevant to the design of the principal instrumentation systems

1-4.2 Sensed Variables

The nuclear chain reaction produces heat (primarily from the dissipation of the kinetic energy of the fission fragments) and nuclear radiations. Consequently, nuclear — power-reactor instrumentation depends primarily on ther­mal sensors and nuclear-radiation sensors The former

big. 1.14 —Sodium-cooled reactor. (From A. Pearson and C. G. Lennox, The Technology of Nuclear Reactor Safety, Vol 1, p. 289, The M I. T. Press, Cambridge, Mass., 1964.)

(thermocouples and resistance thermometers) are discussed m Chap 4 and the latter in Chaps. 2 and 3. Although a number of nuclear radiations are associated with the fission process, only neutrons can be unambiguously related to the occurrence of fissions, because of this, neutron sensors are the most important of the nuclear-radiation sensors. The neutron sensors are used to determine the rate of fissions, the time derivative of the fission rate, and the fission rate as
a function of position in the reactor. (The circuits required to convert the signals from neutron sensors into outputs that are directly related to nuclear reactor performance are described in Chap. 5 )

The primary coolant that transfers heat from the nuclear fuel to the turbogenerator (or to a heat exchanger coupled to the turbogenerator) must be examined by suitable sensors to determine such important parameters as

(1) the temperature of the coolant entering the reactor (T, in Figs. 1.12 through 1 15), (2) the temperature of the coolant leaving the reactor (To in the figures), (3) the temperature of the coolant at other positions in the reactor, (4) the rate of flow of coolant into and out of the reactor (Fc in the figures), (5) the rate of flow of coolant in various coolant channels in the reactor, (6) the radioactivity of the coolant after leaving reactor, (7) the purity of the coolant, and (8) the presence of water vapor in the coolant when the coolant is a gas To sense these parameters, there must be temperature sensors, flowmeters, humidity detectors, nu­clear-radiation (gamma in this case) sensors, etc

Reactor operation itself involves a number of parame­ters, including (l)the position of the control rods (La in Fig. 1.15), (2) the water level of the moderator (Lm in Fig. 1.12), (3) the water level in the reactor (Lc in Fig. 113), (4) the pressure in the primary system (Pp in Fig. 1.13), (5) the pressure at the coolant outlet (Pc in Figs. 1.12 and 1.15). and (6) the temperature ot the moderator (Tm in Fig. 1.15) Temperature sensors, position indicators, pressure transducers, etc., are required to take data on these parameters.

The steam system is characterized by such parameters as steam flow rate (Fs in the figures), steam pressures (Ps in the figures), steam quality, and feedwater flow (Ff in Fig. 1.13). Thermal sensors, pressure and differential-
pressure transducers, flowmeters, water-level indicators, and other sensors (Chap. 4, Sec. 4-6), must be used

In addition, there will be sensors associated with the important components of the plant. Thus, for example, tachometers to sense turbine rotation, meters to sense electrical generator output, thermal and mechanical devices to sense the performance of primary-coolant-pump drive motors, etc., must be installed

REFERENCES

1 American National Standards Institute, American National Stan dard Glossary of Terms tn Nuclear Science and Technology, N1 1 1967, American National Standards Institute, New York, New York

2. A. M. Weinberg and I P. Wigner, The Physical Theory oj Neutron Chain Reactors, University of Chicago Press, Chicago, 1958

3. S. Glasstone and M C Edlund, The / lements of Nuclear Reactor Theory, D. Van Nostrand Company, Inc., Princeton, N. J, 1952.

4. R V. Meghrebhan and D К Holmes, Reactor Analysis, McGraw Hill Book Company, Inc, New York, 1960

5. J. M Harrer, Nuclear Reactor Control engineering, D Van Nostrand Company, Inc., Princeton, N. J., 1963.

6. S Glasstone and A Sesonske, Nuclear Reactor engineering, D. Van Nostrand Company, Inc., Princeton, N. J, 1963

7. Reactor Physics Constants, USAEC Report ANI -5800(2nd I d ), Argonne National Laboratory, Superintendent of Documents, U. S. Government Printing Office, 1963