Neutron detector instrument

The worst operating condition in a common design practice consists of overly conservative assumptions on the hot-channel input. These assumptions must be realistically evaluated in a subchannel analysis by the help of in-core instrumentation measurements. In the early subchannel analysis codes, the core inlet flow conditions and the axial power distribution were preselected off-line, and the most conservative values were used as inputs to the code calculations. In more recent, improved codes, the operating margin is calculated on-line, and the hot-channel power distributions are calculated by using ex-core neutron detector signals for core control. Thus the state parameters (e.g., core power, core inlet temper-... 

There are two distinct advantages of the self-powered neutron detector (a) very little instrumentation is required—only a millivoltmeter or an electrometer, and (b) the emitter material has a much greater lifetime than boron or U235 lining (used in wide range fission chambers). 

A simplified illustration of neutron gauging is shown in Fig 2. The essential components are an isotopic neutron source, the sample to be measured, a thermal neutron detector and appropriate nuclear counting instrumentation to record changes in thermal neutron count rates. Neutron gauging can be performed in two distinct modes. If a bare or unmoderated isotopic... 

The improved neutron detector spatial resolution has been a recent advance, with user instruments first available at the end of 2006 and 2007 at NIST and PSI, respectively. The work can be classified as proof-of-principle,9,10 in situ measurement of the steady-state through-plane water content during fuel cell operation," 13 and dynamic through-plane mass transport measurements.14,15... 

In practice, the instruments are properly calibrated to read directly Sv (or rem), or Gy (or rad). For some neutron detection instruments, the neutron flux is recorded. Then the dose equivalent is obtained after multiplying the flux by the conversion factor given in Table 16.4. Since different detectors do not have the same efficiency or sensitivity for all types of radiation and for all energies, there is no single instrument that can be used for all particles (a, y, n) and all energies. 

High purity germanium (detector) Instrumental neutron activation analysis... 

Because the five senses are useless for detecting radiation, each facility must have readily available portable radiation detection instruments. These instruments should be selected to detect and quantify the three basic types of radiation alpha particles, beta particles, and gamma rays, as discussed in Chapter 2. In some cases, neutron detectors may be required. The RSO/RCM generally is responsible for calibrating the instruments at selected intervals, typically six months. The individual user is responsible for daily operational and source checks prior to each use. 

ZAT a.s., Pribram, Czech Republic. ZAT is responsible for the design, documentation, manufacturing, and installation of the module M2 systems, which are the IN-CORE, SGPS, and PCS systems. The in-core upgrade is the data processing portion only. The in-core instruments (thermocouples and neutron detectors) will not be replaced. 

Signals to the Plant Protection and Instrumentation System (PPIS) and the NSSS Control Subsystem (NCS) are supplied by neutron detectors. During power operation, the neutron flux levels are monitored by detectors located in wells between the reactor vessel and the concrete cavity wall. These detectors are distributed symmetrically around the reactor vessel at about the core midplane. During low power operation, starting up, shutting down, and while shut down, the neutron flux levels are monitored by source-range detectors, located in selected side reflector elements near the bottom of the active core. 

Provide instrumentation and controls to process the signals from two ex-core vessel neutron detectors in each well. 

The ex-vessel neutron detection equipment consists of fission chamber neutron detectors mounted in six equally spaced vertical wells located just outside the reactor vessel as illustrated in Figure 4.3-4. The signals from these detectors are supplied to the nuclear instrumentation cabinet and Safety Protection Subsystem equipment located primarily in the reactor building. These data are used by the automatic control systems to operate the control rod drives or the reserve shutdown equipment, thereby changing the neutron flux levels within the reactor core. 

This instrumentation and control equipment consists of the neutron detectors that provide inputs to the PPIS, NCS, and the rod control assemblies. It is described in Section 4.3.4.1.3. 

The apparatus consists of encapsulated and sealed nuclear (radioactive source), thermal neutron detectors and a read-out instrument. The detectors are sensitive to outside influences therefore, any other source of neutron radiation is kept at least 10 m from the apparatus during use. The area around the apparatus should also be kept free of large amounts of hydrogenous material, such as water, plastics or asphalt during use. 

A mono-energetic, collimated beam of neutrons (wavelength. A, typically 0.5-1.5nm), is directed at the specimen, and the angular scattering is recorded using a position-sensitive neutron detector. A schematic of the 35m long SANS instrument. Dll, installed on the ILL high flux reactor at... 

Nuclear instrumentation system neutron detectors and ranges of operation. 

The primary function of the in-core instrumentation system is to provide a three-dimensional flux map of the reactor core. This map is used to calibrate neutron detectors used by the protection and safety monitoring system, as well as to optimise core performance. A secondary function of the in-core instrumentation system is to provide the protection and safety monitoring system with the thermocouple signals necessary for the post-accident inadequate core cooling monitor. The in-core instrument assembhes house both fixed in core flux detectors and core exit thermocouples. 

I said No, no. I ll have a go, 1 just haven t thought about that before . Pause. I don t think you would detect any significant difference in reactor coolant outlet temperature. The instrument response time will be too slow . Pause. However, 1 know the sodium coolant absorbs some neutrons, because that is how radioactive sodium-24 forms in the primary coolant. So, if bubbles of argon were passing up through the reactor core, the absence of sodium would mean that the neutron flux would increase a bit and we would see some noise on the signals from the neutron detectors . 

Li, is a common reaction employed in neutron detectors, and these detectors are especially sensitive to slow neutrons because of large thermal neutron cross section of B -°. Another neutron detecting scheme using secondary charged particles to ionize the gas is the fission counter. Here, fission fragments do the ionizing and this detector type is also primarily sensitive to slow neutrons. Most detectors used in reactors and health physics instruments detect slow neutrons by one of the above (or similar) reactions. 

Perform operations related to a test scale reactor such as (1) repeat procedure reach criticality, (2) calibrate nuclear instrumentation, eg, neutron detectors, and (3) install and calibrate instrumentation for radiation detection. 

In the area of planetary studies, NASA s Mars Odyssey mission is also scheduled for launch in 2001. Among its suite of instruments are a gamma-ray spectrometer and two neutron detectors. These will be used to fully map the Martian surface and determine its elemental composition. The neutron and gamma-ray measurements in combination will also be used to obtain an estimate of the water content of the Martian near-surface. 

The main reason to monitor neutron flux in a reactor is that it is proportional to the power density, and this is the variable which we are concerned about. There are mainly five types of neutron detectors, BF3 proportional counters. Boron ( B) lined detectors, fission chambers, He proportional counters, and self powered neutron detectors Two other instruments are widely used to monitor the reactor power, calorimeters, used to monitor power density, and N-16 detectors, used to monitor integral reactor power... 

NAA is a quantitative method. Quantification can be performed by comparison to standards or by computation from basic principles (parametric analysis). A certified reference material specifically for trace impurities in silicon is not currently available. Since neutron and y rays are penetrating radiations (free from absorption problems, such as those found in X-ray fluorescence), matrix matching between the sample and the comparator standard is not critical. Biological trace impurities standards (e.g., the National Institute of Standards and Technology Standard Rference Material, SRM 1572 Citrus Leaves) can be used as reference materials. For the parametric analysis many instrumental fiictors, such as the neutron flux density and the efficiency of the detector, must be well known. The activation equation can be used to determine concentrations ... 

The NAA measurements on the paper samples were made at the Breazeale Nuclear Reactor Facility at the Pennsylvania State University with a TRIGA Mark III reactor at a flux of about 1013 n/cm2-sec. Samples were irradiated from 2 to 20 min and counted for 2000 sec, after a 90 min decay time for Ba and a 60 hr decay for Sb, Analyses were performed instrumentally, without radiochemical separation, using a 35cm3 coaxial Ge-Li detector and a 4096-channel pulse height analyzer. With these procedures, detection limits for Ba and Sb were 0.02ug and 0.001 ug, respectively. These sensitivities are comparable to those obtained by GA s radiochemical separation procedure, and are made possible by the use of the higher neutron output from the more powerful reactor and in combination with the higher resolution solid state detector... 

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