| 1. |
- Demaziere, Christophe, 1973, et al.
(författare)
-
Investigation of the validity of the point-kinetic approximation for subcritical heterogeneous systems in 2-group diffusion theory for measurement of the reactivity in ADS
- 2005
-
Ingår i: Proc. Int. Conf. Nuclear Energy Systems for Future Generation and Global Sustainability (GLOBAL2005). - 4890471332
-
Konferensbidrag (refereegranskat)abstract
- In this paper, calculations are performed on a 2-D heterogeneous reflected subcricital system to determine the spatial distribution of the neutron noise induced by fluctuations of a neutron source located in the middle of the core. Likewise, the point-kinetic component of the neutron noise is determined and compared to the actual neutron noise. It is found that close to the source, the amplitude of the actual neutron noise is larger than its point-kinetic component, while smaller close to the core periphery. For increasing core subcriticalities and/or decreasing frequencies, the deviation of the reactor response from point-kinetics becomes smaller. Based on these observations, the source modulation method is considered for the evaluation of the core subcriticality, since this method is based on point-kinetics. Although the reactor response only deviates slightly from point-kinetics in practical cases such as for an ADS (i.e. a deeply subcritical medium), the reactivity estimated from the source modulation technique significantly deviates from its actual value. Small deviations of the reactor response from point-kinetics lead to large inaccuracies in the estimation of the reactivity, whereas perfect agreement with point-kinetics leads to a pathological case where the formula for estimating the reactivity is ill-posed. Therefore, the source modulation technique seems to be of limited applicability.
|
|
| 2. |
|
|
| 3. |
- Kitamura, Yasunori, et al.
(författare)
-
Derivation of pulsed Feynman- and Rossi-alpha formulae including delayed neutrons
- 2005
-
Ingår i: Annals of Nuclear Energy. ; 32:7, s. 671-692
-
Tidskriftsartikel (refereegranskat)abstract
- In previous works, the authors have developed an effective solution technique for calculating the pulsed Feynman- and Rossi-alpha formulae.Through derivation of these formulae, it was shown that the technique can easily handle various pulse shapes of the pulsed neutron source.Furthermore, it was also shown that both the deterministic (i.e.{} synchronizing with the pulsing of neutron source) and stochastic (non-synchronizing) Feynman-alpha formulae can be obtained with this solution technique.However, for mathematical simplicity and the sake of insight, the formal derivation was performed in a model without delayed neutrons.In this paper, to demonstrate the robustness of the technique, the pulsed Feynman- and Rossi-alpha formulae were re-derived by taking one group of delayed neutrons into account.The results show that the advantages of this technique are retained even by inclusion of the delayed neutrons.Compact explicit formulae are derived for the Feynman- and Rossi-alpha methods for various pulse shapes and pulsing methods.
|
|
| 4. |
|
|
| 5. |
- Pazsit, Imre, 1948, et al.
(författare)
-
Calculation of the pulsed Feynman-alpha formulae and their experimental verification
- 2005
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 32:9, s. 986-1007
-
Tidskriftsartikel (refereegranskat)abstract
- An effective method of calculating the pulsed Feynman-alpha formula for finite width pulses is introduced and applied in this paper. The method is suitable for calculating boththe deterministic and the stochastic Feynman-alpha formulae, while also being capable of treating various pulse shapes through very similar steps and partly identical formulae. In the paper both the deterministic and the stochastic cases are treated for square and Gaussianpulses. The solutions show a very good agreement with the results of currently performed experiments by some of the authors at the Kyoto University Critical Assembly (KUCA).The formulae obtained are also used for a quantitative evaluation of the prompt neutron decay constant from a large number of experiments made at the KUCA for a wide range of parameters such as subcritical reactivity, pulse repetition frequency and pulse width. The suitability of the formulae to determine the prompt neutron decay constant a by curve fitting to the measured data was investigated. It was found that, despite the larger deviation from thetraditional Feynman Y(T)-curves from the traditional ones with a constant source (i.e., larger ripples superimposed on a smooth curve), the stochastic pulsing method is superior to the deterministic one in that it yields the correct a value for all subcriticalities. The deterministicmethod also works fine for most cases, but its application is not so straightforward.
|
|
| 6. |
|
|
| 7. |
- Wright, Johanna, 1978
(författare)
-
Development and Investigation of Reactivity Measurement Methods in Subcritical Cores
- 2005
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Subcriticality measurements during core loading and in future accelerator driven systems have a clear safety relevance. In this thesis two subcriticality methods are treated: the Feynman-alpha and the source modulation method. The Feynman-alpha method is a technique to determine the reactivity from the relative variance of the detector counts during a measurement period. The period length is varied to get the full time dependence of the variance-to-mean. The corresponding theoretical formula was known only with stationary sources. In this thesis, due to its relevance for novel reactivity measurement methods, the Feynman-alpha formulae for pulsed sources for both the stochastic and the deterministic cases are treated. Formulaeneglecting as well as including the delayed neutrons are derived. The formulae neglecting delayed neutrons are experimentally verified with quite goodagreement.The second reactivity measurement technique investigated in this thesis is the so-called source modulation technique. The theory of the method was elaborated on the assumption of point kinetics, but in practice the method will be applied by using the signal from a single local neutron detector. Applicability of the method therefore assumes point kinetic behaviour of the core. Hence, first the conditions of the point kinetic behaviour of subcriticalcores was investigated. After that the performance of the source modulation technique in the general case as well as and in the limit of exact point kinetic behaviour was examined. We obtained the unexpected result that themethod has a finite, non-negligible error even in the limit of point kinetic behaviour, and a substantial error in the operation range of future accelarator driven subcritical reactors (ADS). In practice therefore the method needs tobe calibrated by some other method for on-line applications.
|
|
| 8. |
- Wright, Johanna, 1978, et al.
(författare)
-
Neutron kinetics in subcritical cores with application to the source modulation method
- 2006
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 33:2, s. 149-158
-
Tidskriftsartikel (refereegranskat)abstract
- The subject of this paper is an investigation of the performance of the so-called source modulation technique for the measurement of reactivity in subcritical, source-driven cores. Methods of measuring reactivity by a single detector, including the source modulation method, are based on the assumption of point kinetic behaviour of the core. Deviations from point kinetic behaviour will lead to an inaccurate estimation of the reactivity. Hence, first, the conditions of point kinetic behaviour in subcritical source-driven cores are revisited. In addition to the known conditions for such behaviour, which have an analogy to those in critical cores, some additional cases are found which only exist in subcritical cores. Then the performance of the source modulation technique is investigated. It is found that the error of the method, originally thought to be due exclusively to the deviation of the local detector signal from the amplitude factor of point kinetics, remains finite and non-zero even in the limit of exact point kinetic behaviour (e.g., with low frequencies or deep subcriticalities). This is demonstrated and explained by analytical formulae. Some remedies for this shortcoming of the method are also suggested and discussed.
|
|
