Thermal Shield Temperature Monitor

Referring to Fig. 5.6, the 3He refrigerator [25] contains a pump P and an evaporator E. They are connected by a stainless steel tube T internal to the copper support C. The latter is in good thermal contact with the working plane B of a pumped 4He cryostat (for example that of Fig. 5.3) not shown in figure. The tube is connected to a charcoal cryopump P linked to the 4lie bath by a thermal connection L. A thermometer Th monitors the temperature of the pump. A thermal shield (not shown), at the temperature of the 4He bath, surrounds the refrigerator. 

Capsule holders are typically located circumferentially around the core to provide assurance that test specimens and monitors duplicate, as closely as possible, the irradiation history of the reactor vessel, including neutron spectrum, temperature history and maximum neutron fluence. Holders must be designed to avoid interference with in-service inspections required by Section XI of the ASME Code (ASME, 2010a). Most surveillance programs have the capsules located between the thermal shield and the reactor vessel wall with the vertical center at the core mid-plane. C-E, General Electric and B W designs have the holders attached directly to... 

In 900MWe units, the capsules are irradiated along the outer surface of the thermal shield assembly. In 1300 and 1450 MWe units, the capsules are directly attached to the core barrel. In the case of Chooz-A, the thermal shield assembly was removed in 1970 and the surveillance capsules were then located under the core. The capsules are equipped with neutron dosimeters and thermal monitors, with some variations according to the reactor series. In all cases, activation dosimeters of nickel, copper and cobalt, as well as fissile dosimeters of uranium-238 and neptunium-237 are used. This instrumentation is complemented by iron and cadmium-shielded cobalt dosimeters in most cases and, in the most recent plants, also by niobium dosimeters. Each capsule contains temperature detectors based on eutectic alloys with melting points generally of 304 and 310 °C. 

In addition, SCTA offers a unique possibility for preparative scale thermal analysis whilst maintaining high levels of sensitivity and resolution. Such an SCTA system has recently been developed.The focus of the system is a microbalance and a high-temperature water-cooled furnace, located above the balance and allowing operation to 1000°C. The sample is contained in a silica or platinum crucible and sits on top of a rise rod connected directly to the balance pan. Samples in excess of 1 g can be investigated, but routinely, samples of 500 mg are usually involved. Grinding of powdered samples to mesh size 150-250 pm is advantageous. The sample temperature is monitored by a thermocouple located centrally within the furnace tube. Radiation shields attached to the thermocouple... 

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