Neutron monitors

The linear relation between the PSL signal and neutron fluence was established to exist over three decades up to 6. lO cm. The IP-ND can be used as fast and efficient neutron monitors at rather low neutron fluxes. However, for neutron dosimetry individual IP-ND must be calibrated individually since their sensitiviy can differ from one plate to another. In Gd/film based direct NR the film fog below the exposure dose of about 8.10 cm is the limiting factor. 

The measurement of neutron fluxes by foil activation is more complicated because the neutrons are not monoenergetic and the monitor cross sections are energy dependent. The simplest case is monitoring slow neutron fluxes. Radiative capture (ivy) reactions have their largest cross sections at thermal energies and are thus used in slow neutron monitors. Typical slow neutron activation detectors are Mn, Co, Cu, Ag, In, Dy, and Au. Each of these elements has one or more odd A isotopes with a large thermal (n,y) cross section, 1-2000 barns. The (n,y)... 

Time variations in the intensity of the flux during irradiation. This is an important consideration only when a single sample transfer system is used. Gas-filled BF3 neutron counter tubes are often used to monitor the neutron flux in order to normalize the data when the sample and the standard are not irradiated simultaneously. Gain shifts and dead-time effects associated with the use of neutron monitoring detectors also contribute to the errors associated with a single sample transfer system. 

Automatically determination of the SEP event starting by neutron monitor data. 

Additional extending of the model to the small energy range by using on-line one-minute data simultaneously from ground based neutron monitors and CR detectors on spacecrafts. 

The first identification of solar neutrons at Earth took place on June 3,1982 (Fig. 2a), by neutron monitor measurements at Jungfraujoch, Lomnicky Stit, and Rome [Debrunner et al., 1983 Chupp et al., 1987], This was two years after the discovery of solar neutrons in near-Earth space by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission (SMM) satellite [ Chupp et al., 1982], Thereafter, standardized neutron monitors were set up at favorable observational locations at Earth, such as Haleakala, Hawaii [Pyle and Simpson, 1991], Additionally, new ground-based detectors with enhanced sensitivity to solar neutrons were developed [e.g. Shibata et al., 1991 Muraki et al., 1993]. 

Figure 2. June 3, 1982, solar neutron event (a) Count rate enhancement of the Jungfraujoch 18-IGY neutron monitor, (b) Simulated omnidirectional spectra of secondary particles at 700 g cm-2 induced by 1068 MeV solar neutrons at onset time [Moser et al., 2003].

There are five safety systems in Lungmen DCIS. They are Reactor Protection System (RPS), Neutron Monitor System (NMS), Process Radiation Monitoring System (PRMS), Containment Monitoring System (CMS), and Engineered Safety Features (ESF). The software development for all these safety systems follows the BTP-14 requirements. Along with the development, the IV V activities are performed. Of the safety systems, RPS, NMS, PRMS and CMS are designed by GE NUMAC, and ESF is sub-contracted by GE to Eaton Corporation. 

The ex-vessel neutron detection equipment consists of neutron detectors mounted in six equally spaced vertical wells located just outside the reactor vessel, near the core midplane, as illustrated in Figure 4.3-4. This spatial distribution of detectors provides adequate neutron monitoring coverage and redundancy in measurement. 

Criticality. The process plant is designed on the principle of safe geometry under all conditions (e.g., the use of HARP tanks). Continuous monitoring is provided by an approved criticality detection and alarm system. Where additional operational control is required to maintain safe conditions, this is specified in the appropriate nuclear safety assessments and Criticality Clearance Certificate. The latter specifies limits and conditions that need to be complied with during operations for example, in respect of limited tap density, moisture content, isotopic inventory and mass. It identifies any systems or instrumentation that demonstrate that compliance is maintained during operation. In addition key points of the plant are monitored by neutron monitors to give early warning of the unanticipated build-up of solid plutonium which could lead to the development of unsafe conditions. 

These measurements have shown that It may be feasible to make a neutron monitoring system vhlch would be sensitive to the fission product delayed neutrons on an operating reactor s rear face yet Insensitive to the background photo-neutrons, thermal neutrons, and gamma radiation. 

An extensive review of the Superphenix commissioning tests has already been performed [1] and deals not only with neutron physics tests but also with thermal-hydraulics, neutron monitoring, dynamic behaviour, failed fuel detection and decay heat tests. 

Incident. While increasing power, erratic neutron monitoring readings eventually led to reactor Scram . There was a partial core meltdown due to intermittent blocking of reactor coolant flow by a loose baffle in the base of the vessel. Some radiation released. 

Laguna Verde Unit two started three fuel cycles after the unit one, during the construction process and start-up program of unit one some of the components of unit two were used as spare parts of unit one, for that reason during construction program of unit two such components were required but such components were out of the market, companies closed, or new advanced systems were developed for such purposes. That was the case of the Transverse In core Probe (TIP), Source (SRNM) and Intermediate range (IRNM) neutron monitoring systems. 

The original concept for neutron monitoring includes three systems. Source range. Intermediate range and Power range. During start-up the operator has to select and operate... 

As the neutron monitoring components in unit one approach to their end of life, substitution for spare parts are almost impossible, new concept design and computerized must be considered. 

Neutron monitoring should assure determination of neutron fluence to each test specimen for every container. 

The handheld neutron monitor (HHNM) is a portable ( 4 kg) neutron detection device with three He proportional neutron counters, a GM counter and integrated electronics, which provide a means of searching for and localizing neutron radiation sources. A measurement sequence consists of background and verification measurements. When a predetermined threshold is exceeded, the detector triggers an alarm and records the relevant information. 

The DUPIC safeguards neutron monitor (DSNM) monitors the rear access ports of the process glove boxes through total neutron monitoring using He detectors (Kim 2007). 

Enhanced man-machine interface design Automated plant operations Simplified neutron monitoring system Reduction in number of nuclear boiler instruments Fault-tolerent safety system logic and control Standardized distal control and measurement Multiplexing of plant control signals... 

The plant has now beoi recommissioned with neutron monitors installed on all vessels that are not safe by shape. The vessel drain lutes have also been modified to facilitate positive drainage and washout procedures. 

G. B. seaborn, "An Improved Fast Neutron Monitor, K-1642, Oak Ridge Gaseous Diffusion Plant (1965). 

A Passive Gamrm, Neutron Monitor for Fissile Material in Ser[Pg.386]

Fig. 1. Passive gamma, neutron monitor for fissile scrap and waste.

Recently, Schulze and Wuerz described the neutron monitor in the high-activity part of a reprocessing plant They reported a unique relationship between k and epithermal leakage flux multiplication. However, the basic importance has a knowledge of nuclear criticality index (e.g., keff). Physically, the relationship between Mepj and keff cannot be determined directly due to perturbations introduced by the presence of high flux modes. The problem... 

Interlocks are used on the intermediate range neutron monitors to ensure that all units are operating properly and on the proper range. Control rod withdrawal is blocked if the ratio of reactor power to recirculation flow exceeds a predefermined value. 

Neutron monitor trips—during startup-uprate, variable coolant flow to match power... 

Replacement of the existing boron meters with the new NAR-12 models which have increased measuring accuracy and the ability to monitor B-10 isotope. In addition, in order to have greater sensitivity immediately after replacement of 1/3 of the core, a new neutron monitoring system that uses new detectors (AKNP-7-02) with sensitivity and improved signal processing, displays and alarms are under development. 

Answer Fast acting neutron monitors (Beckman chambers) are presently the primary automatic control element. 

Ifeme two ways in which neutron monitors are used at operating power levels. 

Although cladding failure and break-up of the fuel can be detected very readily by delayed neutron monitors and fission product monitors, there is an inevitable transport delay of at least a few seconds, which may be long enough for danrage to propagate. Outlet flowmeters on individual subassemblies are very difficult and expensive to engineer. 

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