10. In most commercial thermal reactors the fuel is either uranium (0.7% uranium-235 ),w ith heavy water or graphite as the moderator, or uranium containing 2-4 percent of the fis with ordinary water as the moderator.>> l1. Based on the purpose, the reactor can fall into experimental (or research)reactor, pro uction reactor, power reactor, dual purpose (power and production) reactor or nuclear heati 12. According to the type of coolant and moderator, reactor can be called pressurized wat r reactor, boiling water reactor, heavy water reactor (e.g. CANDU), graphite reactor, or li quid metal cooled reactor. UNIT 7 INSTRUMENTATION<OV 1. In addition to conventional instrumentation, such as that required fir measuring temperat ures, pressures,coolant flow rates, etc, devices(sensors)for determining the neutron flux play an important role in reactor control and safety. > 2. Many instruments for the detection of nuclear radiation are dependent upon the behavio r in an electrical field of the ion-pairs formed by the ionizing particles in their passage th rou 3. Neutrons are unchanged particles and therefore cannot cause ionization directly, so they must interact with matter by means of a nuclear reactor which, in turn, will generate cha 4. The changed particles will cause ionization within a gas-filled detector and these ion pa irs will produce a voltage pulse or some mean level current when collected at the electro des of the detector.>> 5. Since the neutron flux covers a wide range(12 decades), no single instrument can prov ide a satisfactory indication of the neutron flux and hence three ranges, i.e., source range intermediate range and power range, of instrumentation are used to obtain accurate flux I evel measures. >> 6. BF3 gas generated filled detectors (proportional counter) are used in source range, com pensated ion chamber are in the intermediate range, and uncompensated ion chamber in th e power range in some nuclear power plant.>> 7. Since gamma radiation from fission and fission products in a reactor can be very inten se, the compensated ionization chambers are required in the intermediate range 8. The fission chamber is coated with a uranium compound and pulse produced by the fis sion fragments resulting from the interaction of neutrons with the uranium-235 are so larg10. In most commercial thermal reactors the fuel is either uranium (0.7% uranium-235), w ith heavy water or graphite as the moderator, or uranium containing 2-4 percent of the fis sile isotope, with ordinary water as the moderator.>> 11. Based on the purpose, the reactor can fall into experimental (or research) reactor, prod uction reactor, power reactor, dual purpose (power and production) reactor or nuclear heati ng reactor.>> 12. According to the type of coolant and moderator, reactor can be called pressurized wat er reactor, boiling water reactor, heavy water reactor (e.g. CANDU), graphite reactor, or li quid metal cooled reactor. UNIT 7 INSTRUMENTATION<O 1. In addition to conventional instrumentation, such as that required fir measuring temperat ures, pressures, coolant flow rates, etc., devices (sensors) for determining the neutron flux play an important role in reactor control and safety.>> 2. Many instruments for the detection of nuclear radiation are dependent upon the behavio r in an electrical field of the ion-pairs formed by the ionizing particles in their passage th rough a gas.>> 3. Neutrons are unchanged particles and therefore cannot cause ionization directly, so they must interact with matter by means of a nuclear reactor which, in turn, will generate cha rged particles.>> 4. The changed particles will cause ionization within a gas-filled detector and these ion pa irs will produce a voltage pulse or some mean level current when collected at the electro des of the detector.>> 5. Since the neutron flux covers a wide range (12 decades), no single instrument can prov ide a satisfactory indication of the neutron flux and hence three ranges, i.e., source range, intermediate range and power range, of instrumentation are used to obtain accurate flux l evel measures.>> 6. BF3 gas generated filled detectors (proportional counter) are used in source range, com pensated ion chamber are in the intermediate range, and uncompensated ion chamber in th e power range in some nuclear power plant.>> 7. Since gamma radiation from fission and fission products in a reactor can be very inten se, the compensated ionization chambers are required in the intermediate range. 8. The fission chamber is coated with a uranium compound and pulse produced by the fis sion fragments resulting from the interaction of neutrons with the uranium-235 are so larg