| 1. |
- Jammes, C., et al.
(författare)
-
Progress in the development of the neutron flux monitoring system of the French GF:N-IV SFR : simulations and experimental validations.
- 2015
-
Ingår i: 2015 4Th International Conference On Advancements In Nuclear Instrumentation Measurement Methods And Their Applications (Animma). - : IEEE. - 9781479999187
-
Konferensbidrag (refereegranskat)abstract
- France has a long experience of about 50 years in designing, building and operating sodium-cooled fast reactors (SFR) such as RAPSODIE, PHENIX and SUPER PHENIX. Fast reactors feature the double capability of reducing nuclear waste and saving nuclear energy resources by burning actinides. Since this reactor type is one of those selected by the Generation IV International Forum, the French government asked, in the year 2006, CEA, namely the French Alternative Energies and Atomic Energy Commission, to lead the development of an innovative GEN-IV nuclear- fission power demonstrator. The major objective is to improve the safety and availability of an SFR. The neutron flux monitoring (NFM) system of any reactor must, in any situation, permit both reactivity control and power level monitoring from startup to full power. It also has to monitor possible changes in neutron flux distribution within the core region in order to prevent any local melting accident. The neutron detectors will have to be installed inside the reactor vessel because locations outside the vessel will suffer from severe disadvantages; radially the neutron shield that is also contained in the reactor vessel will cause unacceptable losses in neutron flux; below the core the presence of a core-catcher prevents from inserting neutron guides; and above the core the distance is too large to obtain decent neutron signals outside the vessel. Another important point is to limit the number of detectors placed in the vessel in order to alleviate their installation into the vessel. In this paper, we show that the architecture of the NFM system will rely on high-temperature fission chambers (HTFC) featuring wide-range flux monitoring capability. The definition of such a system is presented and the justifications of technological options are brought with the use of simulation and experimental results. Firstly, neutron-transport calculations allow us to propose two in-vessel regions, namely the above-core and under-core structures. We verify that they comply with the main objective, that is the neutron power and flux distribution monitoring. HTFC placed in these two regions can detect an inadvertent control rod withdrawal that is a postulated initiating event for safety demonstration. Secondly, we show that the HTFC reliability is enhanced thanks to a more robust physical design and the fact that it has been justified that the mineral insulation is insensitive to any increase in temperature. Indeed, the HTFC insulation is subject to partial discharges at high temperature when the electric field between their electrodes is greater than about 200 V/mm or so. These discharges give rise to signals similar to the neutron pulses generated by a fission chamber itself, which may bias the HTFC count rate at start-up only. However, as displayed in Figure 1, we have experimentally verified that one can discriminate neutron pulses from partial discharges using online estimation of pulse width. Thirdly, we propose to estimate the count rate of a HTFC using the third order cumulant of its signal that is described by a filtered Poisson process. For such a statistic process, it is known that any cumulant, also called cumulative moment, is proportional to the process intensity that is here the count rate of a fission chamber. One recalls that the so-called Campbelling mode of such a detector is actually based on the signal variance, which is the second-order cumulant as well. The use of this extended Campbelling mode based on the third-order cumulant will permit to ensure the HTFC response linearity over the entire neutron flux range using a signal processing technique that is simple enough to satisfy design constraints on electric devices important for nuclear safety. We also show that this technique, named high order Campbelling method (HOC), is significantly more robust than another technique based on the change in the HTFC filling gas, which consists in adding a few percent of nitrogen. Finally, we also present an experimental campaign devoted to the required calibration process of the so-called HOC method. The Campbelling results show a good agreement with the simple pulse counting estimation at low count rates. It is also shown that the HOC technique provides a linear estimation of the count rates at higher power levels as well.
|
|
| 2. |
- Verma, Vasudha, 1988-, et al.
(författare)
-
CALCULATION METHODOLOGY ASSESSMENT TO DETECT LOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTOR WITH EX-CORE INSTRUMENTATION
- 2016
-
Ingår i: CALCULATION METHODOLOGY ASSESSMENT TO DETECTLOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTORWITH EX-CORE INSTRUMENTATION.
-
Konferensbidrag (refereegranskat)abstract
- Safety and reliability are essential requirements for development and operation of SodiumcooledFast Reactors. Development of a neutron flux monitoring system (NFMS) for the FrenchSFR is one of the key R&D areas identified. Diverse possibilities of detector system installationshould be studied for different locations in the reactor vessel in order to detect any perturbations inthe core. In this paper, we aim to explore two calculation routes available for neutron flux monitoring,assess them for their efficiency to detect fission rate variation at Above-core structure (ACS)location and discuss the associated pros and cons. The two calculational approaches we refer hereare criticality mode and external source mode. We discuss the feasibility of choosing this locationfor detecting in-core perturbations and evaluate the methodology needed to achieve it. The paperfocuses on the difficulties associated with neutron detection when the detectors are located at far-offdistances from the source. We found that for a difficult case such as ours where the detectors arelocated far-away from the source, criticality mode doesn’t work. Variance reduction techniques,employed in the external source mode are indispensable to drive neutrons to areas of interest.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Verma, Vasudha, 1988-
(författare)
-
Development of a Neutron Flux Monitoring System for Sodium-cooled Fast Reactors
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Safety and reliability are one of the key objectives for future Generation IV nuclear energy systems. The neutron flux monitoring system forms an integral part of the safety design of a nuclear reactor and must be able to detect any irregularities during all states of reactor operation. The work in this thesis mainly concerns the detection of in-core perturbations arising from unwanted movements of control rods with in-vessel neutron detectors in a sodium-cooled fast reactor. Feasibility study of self-powered neutron detectors (SPNDs) with platinum emitters as in-core power profile monitors for SFRs at full power is performed. The study shows that an SPND with a platinum emitter generates a prompt current signal induced by neutrons and gammas of the order of 600 nA/m, which is large enough to be measurable. Therefore, it is possible for the SPND to follow local power fluctuations at full power operation. Ex-core and in-core detector locations are investigated with two types of detectors, fission chambers and self-powered neutron detectors (SPNDs) respectively, to study the possibility of detection of the spatial changes in the power profile during two different transient conditions, i.e. inadvertent withdrawal of control rods (IRW) and one stuck rod during reactor shutdown (OSR). It is shown that it is possible to detect the two simulated transients with this set of ex-core and in-core detectors before any melting of the fuel takes place. The detector signal can tolerate a noise level up to 5% during an IRW and up to 1% during an OSR.
|
|
| 6. |
- Verma, Vasudha, 1988-, et al.
(författare)
-
Feasibility Study of Self Powered Neutron Detectors in Fast Reactors for Detecting Local Change in Neutron Flux Distribution
- 2015
-
Ingår i: Feasibility Study of Self Powered Neutron Detectors in Fast Reactors for Detecting Local Change in Neutron Flux Distribution.
-
Konferensbidrag (refereegranskat)abstract
- Neutron flux monitoring systems form an integral part of the design of a Generation IV sodium cooled fast reactor. Diverse possibilities of detector systems have to be investigated with respect to practicality and feasibility according to the detection parameters. In this paper, we demonstrate the feasibility of using self powered neutron detectors as in-core detectors in fast reactors for detecting local changes in the neutron flux distribution. We show that the gamma contribution from fission products decay and activation of structural materials and sodium is very small compared to the fission gammas. Thus, it is possible for the in-core SPND signal to follow changes in local neutron flux as they are proportional to each other. This implies that the signal from an in-core SPND can provide dynamic information on the neutron flux perturbations occuring inside the reactor core.
|
|
| 7. |
|
|
| 8. |
- Verma, Vasudha, 1988-, et al.
(författare)
-
Neutron flux monitoring with in-vessel fission chambers to detect an inadvertent control rod withdrawal in a sodium-cooled fast reactor
- 2016
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 94, s. 487-493
-
Tidskriftsartikel (refereegranskat)abstract
- The neutron flux monitoring system forms an integral part of the safety design of a Generation IV sodium-cooled fast reactor. During the initial design phase of the neutron flux monitoring system, one needs to explore various detector locations and configurations. Diverse possibilities of the detector system installation should be studied for different locations in the reactor vessel in order to detect any perturbations in the core. In this paper, we investigate the possibility of placing fission chambers beyond the lateral neutron shield, ex-core but in-vessel and study the detectability of an inadvertent control rod withdrawal with these fission chambers. A generic core design of a Generation IV 1500 MWth French sodium-cooled fast reactor is used for the study, and calculations are performed with the Monte Carlo code SERPENT2. We propose certain design changes that are needed to be incorporated, w.r.t. the facilitation of neutron transport to this ex-core location.We are able to show that there is a detectable signature in the fission chambers following an inadvertent control rod withdrawal in the core. The equally-spaced azimuthal detectors are able to follow changes in the neutron flux distribution in the core. This study helps us to analyze multiple detector locations and give the general trends for monitoring indications to detect any perturbations in the core.
|
|
| 9. |
- Verma, Vasudha, 1988-, et al.
(författare)
-
Self Powered Neutron Detectors as in-core detectors for Sodium-cooled Fast Reactors
- 2017
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 860, s. 6-12
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron flux monitoring system forms an integral part of the design of a Generation IV sodium cooled fast reactor. Diverse possibilities of detector system installation must be studied for various locations in the reactor vessel in order to detect any perturbations in the core. Results from a previous paper indicated that it is possible to detect changes in neutron source distribution initiated by an inadvertent withdrawal of outer control rod with in-vessel fission chambers located azimuthally around the core. It is, however, not possible to follow inner control rod withdrawal and precisely know the location of the perturbation in the core. Hence the use of complimentary in-core detectors coupled with the peripheral fission chambers is proposed to enable robust core monitoring across the radial direction.In this paper, we assess the feasibility of using self-powered neutron detectors (SPNDs) as in-core detectors in fast reactors for detecting local changes in the power distribution when the reactor is operated at nominal power. We study the neutron and gamma contributions to the total output current of the detector modelled with Platinum as the emitter material. It is shown that this SPND placed in an SFR-like environment would give a sufficiently measurable prompt neutron induced current of the order of 600 nA/m. The corresponding induced current in the connecting cable is two orders of magnitude lower and can be neglected. This means that the SPND can follow in-core power fluctuations. This validates the operability of an SPND in an SFR-like environment.
|
|
