The Effect of Neutron Source Distribution on Subcriticality Measurement of Pressurized Water Reactors Using the Modified Neutron Source Multiplication Method

Shimazu

2005

Self Cite

A mockup experiment of subcriticality measurement with a digital reactivity meter during criticality approach in a PWR was carried out using plant data. There are some difficulties in the direct application of a digital reactivity meter to the subcriticality measurement. Some treatments were needed in using the count rate of Source Range (SR) detector as input signal to the digital reactivity meter. To overcome these difficulties, we proposed a digital reactivity meter combined with a methodology of the modified Neutron Source Multiplication (NSM) method with the fundamental mode extraction. In this study, the neutron source strength was defined as a constant in terms of a known initial stable subcriticality and the neutron signal from a steady state condition. Even though initial stable subcriticality might be contained some errors, the errors of estimated subcriticalities do not depend on the error contribution of initial stable subcriticality when we normalize the estimated subcriticalities with exactly known reference subcriticality. It was proved that the digital reactivity meter could be used not only for the subcriticality measurement or control rod worth measurement but also for the continuous monitoring of the subcriticality during criticality approach.

Section: Correction Factors Of the Modified Nsm Methodsmentioning

confidence: 99%

Section: Correction Factors Of the Modified Nsm Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Subcriticality Measurement of Pressurized Water Reactors during Criticality Approach using a Digital Reactivity Meter

Naing

Shimazu

2005

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“…The count rates corresponding to various control rod configurations were calculated using neutron flux distributions obtained with fixed source problems and the detector response as explained in Ref. 5). The simulated result is shown in Fig.…”

Section: Prediction Of the Expected Response Of Neutronmentioning

confidence: 99%

Examination of Actual Neutron Count Rate Data during a Control Rod Drop Testing for Estimation of Control Rod Worth in PWRs

Shimazu

Narabayashi

2011

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The Modified Neutron Source Multiplication (MNSM) method, which is based on the extraction of the fundamental mode of neutron flux distribution, has been proposed to estimate subcriticality. It has been proven applicable to a small critical assembly and domestic PWRs during criticality approach. In the following study, it is also shown by numerical simulation that it is applicable to estimate the subcriticality using neutron count rate data during the control rod drop testing in PWRs. As the next step, we looked further into the actual data of neutron count rate in order to examine whether the expected signal response was observed for the estimation. It was found that the actual data have shown the expected response, and the control rod worth could have been estimated in the same manner as during criticality approach. A new procedure is also proposed to measure a reference reactivity that is essentially required to evaluate the reactivity of each control rod worth.

“…6). The subcriticality for each control rod pattern was calculated by solving the eigenvalue problem.…”

Section: Numerical Simulationmentioning

confidence: 99%

Feasibility Study for Evaluation of Control Rod Worth in Pressurized Water Reactors using Neutron Count Rate during a Control Rod Drop Testing

Shimazu¹,

Okazaki

2006

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Applicability of the modified Neutron Source Multiplication (NSM) method with extraction of the fundamental mode to subcriticality measurement has been proposed. Following the feasibility verification in the previous study based on numerical analyses, its applicability has been proven in a more realistic situation; in a withdrawal sequence of control rod banks during the PWR startup. Subcriticalities with various control rod insertion configurations were estimated based on the modified NSM method. The subcriticality could be evaluated with a good accuracy even with the mockup experiment where any special treatments for accurate measurement were not taken into account and furthermore the insensitivity of measured signals by reactivity changes and their large fluctuations were seen.Based on this fact, we further investigated a feasibility to use neutron count rate data obtained during the control rod drop testing, which is carried out before the reactor physics tests at hot zero power condition. When it is proven that these data could be used for the estimation of each control rod worth, the following reactor physics tests could be performed with the advanced knowledge of each control rod worth and procedures for detailed control rod worth measurement could be simplified or eliminated from the reactor physics tests.