Submission Title
Characteristics of Pt-Clad Inconel SPNDs for use in IPHWRs
Presentation Type
Contributed
Start Date
19-12-2018 9:00 AM
Abstract
The relatively high neutron flux (thermal) in large PHWRs requires the widespread use of Self Powered Neutron detectors (SPNDs) in power reactors. SPNDs are only feasible or practically possible devices which are used for control and protection system in large reactor cores. This is due to their small or compact size, rugged design, radiation resistance, adequate life for use inside the reactor core etc.
SPNDs are mainly used to determine the neutron flux at specific location or at the point of measurement. These flux readings can be used to produce a 3D flux map. However, the measurement of neutron flux is not an end in itself but serves to provide a measure of the local fuel power and hence the heat flux through the fuel sheath. A knowledge of the power being transferred to the coolant is required to optimize the fuel power to avoid the conditions of central line melting and/or critical heat flux. The signals from the safety or protection system detectors are normalized to the power in the fuel, integrated over the fuel channel. Thus the detector signal represent the channel (fuel) power. Similarly the detectors used in control system represents the zone power. There are three types of SPNDs, in general, one which are sensitive to neutrons e.g. Rh, Co, Inconel, and V etc. SPNDs, the other which are sensitive to gamma flux e.g. Zr, Bi and Pb etc. SPNDs and the final type of SPNDs which are sensitive to both neutron as well as gamma such as Mo and Pt emitter based SPNDs. The first two types are called as single response detectors as they are predominantly sensitive to either of the fluxes viz. neutron or gamma. The third type is known as mixed response detector as it is sensitive to both kind of fluxes.
There are two different characteristics of a SPND which should be understood in detail, viz. the variation of sensitivity with time due to continuous exposure to neutron or gamma field and second the response of SPND signal in varying flux known as the dynamic response of SPND. Thus not only the overall signal of SPND is important but also the dynamic response of the detector signal is important as it should match the heat production rate in the fuel rather than the local neutron or gamma flux. It is due to the fact that about 93% fuel power is prompt and 7% is delayed (mainly coming from fission product decay).
Therefore if the maximum benefit is to be obtained from using flux detectors in power reactors, a thorough understanding of the factors that affect the detector’s response such as, sensitivity, burnout, prompt and delayed fraction of detector’s signal etc. is required. In the present note the advantage of Pt-clad Inconel in comparison to other detectors (SPNDs) is discussed.
Recommended Citation
Raj, Manish; Ray, Sherly; and Pradhan, A. S. (2018). "Characteristics of Pt-Clad Inconel SPNDs for use in IPHWRs," Symposium on Advanced Sensors and Modeling Techniques for Nuclear Reactor Safety.
Characteristics of Pt-Clad Inconel SPNDs for use in IPHWRs
The relatively high neutron flux (thermal) in large PHWRs requires the widespread use of Self Powered Neutron detectors (SPNDs) in power reactors. SPNDs are only feasible or practically possible devices which are used for control and protection system in large reactor cores. This is due to their small or compact size, rugged design, radiation resistance, adequate life for use inside the reactor core etc.
SPNDs are mainly used to determine the neutron flux at specific location or at the point of measurement. These flux readings can be used to produce a 3D flux map. However, the measurement of neutron flux is not an end in itself but serves to provide a measure of the local fuel power and hence the heat flux through the fuel sheath. A knowledge of the power being transferred to the coolant is required to optimize the fuel power to avoid the conditions of central line melting and/or critical heat flux. The signals from the safety or protection system detectors are normalized to the power in the fuel, integrated over the fuel channel. Thus the detector signal represent the channel (fuel) power. Similarly the detectors used in control system represents the zone power. There are three types of SPNDs, in general, one which are sensitive to neutrons e.g. Rh, Co, Inconel, and V etc. SPNDs, the other which are sensitive to gamma flux e.g. Zr, Bi and Pb etc. SPNDs and the final type of SPNDs which are sensitive to both neutron as well as gamma such as Mo and Pt emitter based SPNDs. The first two types are called as single response detectors as they are predominantly sensitive to either of the fluxes viz. neutron or gamma. The third type is known as mixed response detector as it is sensitive to both kind of fluxes.
There are two different characteristics of a SPND which should be understood in detail, viz. the variation of sensitivity with time due to continuous exposure to neutron or gamma field and second the response of SPND signal in varying flux known as the dynamic response of SPND. Thus not only the overall signal of SPND is important but also the dynamic response of the detector signal is important as it should match the heat production rate in the fuel rather than the local neutron or gamma flux. It is due to the fact that about 93% fuel power is prompt and 7% is delayed (mainly coming from fission product decay).
Therefore if the maximum benefit is to be obtained from using flux detectors in power reactors, a thorough understanding of the factors that affect the detector’s response such as, sensitivity, burnout, prompt and delayed fraction of detector’s signal etc. is required. In the present note the advantage of Pt-clad Inconel in comparison to other detectors (SPNDs) is discussed.
