Improvement and testing of radiation source models in DecDose for public dose assessments during decommissioning of nuclear facilities

Shimada, Taro; Sukegawa, Takenori

Journal of Nuclear Science and Technology, 52(3), p.396 - 415, 2015/03

https://doi.org/10.1080/00223131.2014.953615

Radiation source models in DecDose code for assessing public and worker exposure doses during the decommissioning of nuclear facilities were improved in this study. A segmentation model evaluating the length, volume, and surface area of kerfs in the object to be dismantled was improved to deal with seven shapes of objects simulating most of the components and the structures in nuclear facilities. Models for the evaluation of the external dose by direct and skyshine radiation were also improved to deal with the distribution of waste containers temporarily placed in the building and the quantity of radionuclides stored in the individual container. Good agreement was observed between actual and calculated kerf volumes in cutting some components such as the reactor pressure vessel of the Japan Power Demonstration Reactor. It is an indication of the validity of the model improved in this study. On the other hand, some discrepancies were observed between actual and calculated quantities of radionuclides discharged into the ocean, indicating the necessity of further validation of the model.

Evaluation of uncertainties in model parameters for evaluating decommissioning project management data based on JPDR decommissioning experience data

Ishigami, Tsutomu; Sukegawa, Takenori*; Mukai, Masayuki

JAEA-Technology 2013-027, 124 Pages, 2013/10

JAEA-Technology-2013-027.pdf:5.9MB

In order to safely and efficiently implement decommissioning of nuclear installations, it is important to beforehand predict decommissioning project management data (PMD) and to develop a decommissioning plan based on the predicted results. The PMD prediction is made with PMD evaluation equations including model parameters such as unit work activity coefficients. Although model parameter values developed so far include uncertainties, little evaluation of the uncertainties and resulted uncertainties in predicted PMD has been made. However information on the uncertainties is valuable in flexibly studying and developing a decommissioning plan. We therefore studied and evaluated uncertainties in model parameters by analyzing the JPDR decommissioning experience data. This report describes an evaluation method of the model parameter uncertainties and their evaluated results.

Study on residual radioactivity measurement method for site release of nuclear facilities; In-situ radioactivity measurement test with the use of portable Ge semiconductor detector (Contract research)

Sukegawa, Takenori; Shimada, Taro; Ito, Takeshi*; Tanaka, Tadao

JAEA-Technology 2011-025, 41 Pages, 2011/09

JAEA-Technology-2011-025.pdf:5.83MB

Nuclear facility sites after decommissioning are allowed to be released from nuclear safety regulations after confirming that sites have been decontaminated to acceptable levels. In-situ measurement with the use of a portable Ge detector is a suitable technology for confirmatory survey. A conservative method to evaluate residual radioactivity was proposed in this study. In the evaluation method concept, all of the radionuclide, which are in reality distributed across the area of interest, is assumed to be the single point source located at the furthest position of the area from a Ge detector. Based on this assumption, the detectable minimum time of the interest radionuclide were predicted by the calculation. If radiation from the point source is not detected for longer than the predicted detectable time, it can be proven that the radioactivity remaining in the interest area is lower than the radioactivity corresponding to the assumed point source. Results of the field test in JAEA site indicate that the proposed method was reasonable for the conservative evaluation of residual radioactivity.

Determination of environmental uranium concentration by utilizing -ray emission from the progeny radionuclides

Tanaka, Tadao; Shimada, Taro; Ito, Takeshi*; Sukegawa, Takenori

Proceedings of 13th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2010) (CD-ROM), p.551 - 557, 2010/10

https://doi.org/10.1115/ICEM2010-40096

-ray from the progeny radionuclides of U-238, such as Th-234, Pa-234m and Ra-226, has been utilized for the evaluation of uranium concentration. In the present study, we proposed an evaluation method for U-238 concentration of background level in environment and for probate of vast land areas, in which the -ray radiations from Th-234, Pa-234m, Ra-226 is measured with the portable Ge detector. The U-238 concentration estimated by the in-situ metrology with portable Ge detector was in the order of 0.01 Bq/g in radioactive concentration, and was in comparable level with the concentrations decided by the ICP-MS established as high sensitive uranium analytical method. The method may be available for the U-238 concentration determination in vast land areas for the site release after decommissioning nuclear fuel handling facilities.

Development of safety assessment code for decommissioning of nuclear facilities (DecDose)

Shimada, Taro; Oshima, Soichiro*; Sukegawa, Takenori

Journal of Power and Energy Systems (Internet), 4(1), p.40 - 53, 2010/02

https://doi.org/10.1299/jpes.4.40

A safety assessment code, DecDose, for decommissioning of nuclear facilities has been developed, based on the experiences of the decommissioning project of Japan Power Demonstration Reactor (JPDR) at Japan Atomic Energy Research Institute DecDose evaluates the annual exposure dose of the public and workers according to the progress of decommissioning, and also evaluates the public dose at accidental situations including fire and explosion. As for the public, both the internal and the external doses are calculated by considering inhalation, ingestion, direct radiation from radioactive aerosols and radioactive depositions, and skyshine radiation from waste containers. For external dose for workers, the dose rate from contaminated components and structures to be dismantled is calculated. Internal dose for workers is calculated by considering dismantling conditions, e.g. cutting speed, cutting length of the components and exhaust velocity. DecDose was partially verified by comparison with the actual external dose of workers which were acquired during JPDR Decommissioning Project.

Computer code system "RADO" for evaluating residual radioactive inventory in decommissioning of nuclear reactor

Sukegawa, Takenori; Shimada, Taro; Shiraishi, Kunio; Tachibana, Mitsuo; Ishigami, Tsutomu

JAEA-Data/Code 2008-009, 57 Pages, 2008/03

JAEA-Data-Code-2008-009.pdf:3.62MB

We developed the RADO code system for evaluating residual radioactive inventory in decommissioning of nuclear reactor. The code system consists of computer programs which calculate macroscopic effective cross section, neutron flux, and radioactive inventory. This report describes an evaluation method of radioactive inventory, structure and functions of RADO, input and output of RADO, and sample run with RADO.

Decommissioning database; Public presentation by intranet

Shiraishi, Kunio; Sukegawa, Takenori; Ishigami, Tsutomu

JAEA-Data/Code 2005-002, 162 Pages, 2006/01

JAEA-Data-Code-2005-002.pdf:27.87MB

In order to efficiently develop a decommissioning plan of a nuclear facility, it is useful to develop a database containing information on decommissioning technology, cost and risk analysis results, and decommissioning projects such as the JPDR decommissioning project by collecting the information systematically. A decommissioning database has been developed by collecting decommissioning related information and analyzing it. The database provides information on not only data of decommissioning technology and decommissioning projects but also laws and safety standards for decommissioning in each country and international organizations. The database is released in a Homepage on Web and is available for use via intranet with functions of retrieval, display and printing.

Evaluation of radioactive inventory in JRR-1

Akutsu, Atsushi; Kishimoto, Katsumi; Sukegawa, Takenori; Shimada, Taro

JAERI-Tech 2003-090, 75 Pages, 2004/01

JAERI-Tech-2003-090.pdf:6.83MB

The Japan Research Reactor No.1 (JRR-1) that was constructed first in Japan was permanently shut down after operation from 1957 to 1968. At present, the reactor part is in safe store conditions. The JRR-1 facility is being used as an exhibition room for the time being, and will be dismantled in the future. In consideration of future dismantling of the facility, the radioactive inventory in reactor part was calculated using computer codes that are Two-Dimensional Discrete Ordinates Transport Code (DORT) and Oak Ridge Isotope Generation and Depletion Code (ORIGEN-MD). The average concentration of radioactivity is estimated to be 6.40 Bq/g in the core tank as of April, 2002. It is also expected that the low level waste (LLW) weights approximately 400kg and very low level waste (VLLW) weights approximately 14,000kg, and the waste which doesn't need to deal as a radioactive material weights approximately 250,000kg.

Development of computer systems for planning and management of reactor decommissioning; A Study on influence of work difficulty factors on project management data and simplification of work breakdown structures (Contract research)

Oshima, Soichiro; Sukegawa, Takenori; Shiraishi, Kunio; Yanagihara, Satoshi

JAERI-Tech 2001-086, 83 Pages, 2001/12

JAERI-Tech-2001-086.pdf:5.23MB

Project management data on dismantling the Japan Power Demonstration Reactor (JPDR) was calculated using the Code System for Planning and Management of Reactor Decommissioning (COSMARD), and then its validity was studied by comparing the calculation results with actual data. In addition, work breakdown structure models and database were modified to meet an evaluation with changing work difficulty of preparation and cleanup activities, and calculations were further conducted to analyze feasibility by changing various conditions on cutting and conditioning activities. As the results, COSMARD was verified to be useful by confirming calculation capability on reflection of actual work conditions and relatively good agreement between actual data and calculations. Moreover, it was cleared that main parameters such as work difficulty of preparation and cleanup activities and the cutting speed in demolition work could affect to manpower within 30% in each calculations.

Study on residual radioactive inventory estimation in reactor decommissioning program (Contract research)

Sukegawa, Takenori; Hatakeyama, Mutsuo; Yanagihara, Satoshi

JAERI-Tech 2001-058, 81 Pages, 2001/09

JAERI-Tech-2001-058.pdf:5.98MB

In general, neutron transport and activation calculation codes are used for residual radioactive inventory estimation; however, it is essential to verify calculations by measurement results because of geometrical complexity of the reactor and so on. The comparison between measured and calculated radioactivity in the JPDR core components showed a relatively good agreement (factor of 2), and it was cleared that water content and weight ratio of steel bars to concrete materials significantly influenced the neutron flux distribution in the biological shield (factor of 2-10 error). The measured radioactivity inside of the reactor pressure vessel wall and at the inner part of the biological shield was compared in detail with the calculations to verify the methodology applied to calculations of radioisotope production. Then it was found that the radioactive inventory could be estimated accurately with combination of calculations and measurement of radioactivity in samples and dose rate distribution for planning of dismantling activities.