Nuclear Science and Engineering Research

4-5 Quicker Calculation of Atmospheric Dispersion of Radioactive Materials under Various Conditions－Development of the Atmospheric Dispersion Database System WSPEEDI-DB－Previousmethod

Start ofDispersion analysis

Setting of release condition
Release point, release duration, Results ofradionuclides, release rate
dispersion calculation (e.g.)
Case 1 Case 2

Dispersion calculation

Meteorological calculation

Concentration,
deposition,
doses

Dispersion calculation
Dispersion calculation

Newmethod

Meteorological calculation

Setting of release condition

Dispersion calculation

Release duration, radionuclides,release rate

• Preset release point• Split release period• Five representative
nuclides for deposition
property• Unit release rate
• No radioactive decay

Concentration
anddeposition
database

Execution in advance

Case 1 Case 2

Time required for
100 cases ofdispersion analysis

Case 3 䞉䞉䞉Case 3 䞉䞉䞉

About 12 hTime

Less than
1/100thResults ofdispersion calculation

Analysis ofdispersion distribution
Application of releasecondition to the database

About 5 minConcentration,deposition,
doses

Fig.4-11 Comparison of the previous method (upper) and new method (lower)
The new method makes it unnecessary to perform dispersion calculations for each release condition required by the previous method.
The results of a 1-day test calculation with the previous method, which required about 7 minutes per case, was obtained in 3-4 seconds
with the new method, i.e., the results can be provided in less than 1/100th of the time needed for the previous method.
Meteorologicalforecast data
by JapanMeteorological
AgencyWSPEEDI-DB

Periodical online data acquisition

Calculation function

UserWeb GUI

Auto‐execution

Analysis function

Meteorological model
Local‐scale meteorological calculation

Setting of releasecondition!Setting and execution

Time series ofrelease rates

Distribution map Time‐series graphAuto‐execution
Dispersion modelCalculations with unit release condition

Analysis of dispersion
distribution

Outputs
Database of outputs of calculation under unit
release condition for all cases of release period
segment (1 h)×release height (stack, building)!Output (visualization)

Spatiotemporal distributions of
air concentration,
surface deposition, fallout,
and air dose rate

Operation via
web browser

e.g., air concentratione.g., deposition

Fig.4-12 Structure and calculation flow of WSPEEDI-DB
The calculation function creates an output database; the analysis function applies release conditions to this database tocreate dispersion analysis results. The results can be visualized by creating various figures. These functions can be easily
operated using a web browser.

According to the basic disaster management plan issued by
the National isaster anagement Council, the overnmentof apan provides professional and technical support to local
governments when they use atmospheric dispersion calculations
to improve their regional disaster prevention and evacuation
plan. o contribute to this, it is necessary to e ciently
provide the detailed dispersion calculation results using theWorldwide version of System for Environmental Emergency
Dose Information, WSPEEDI, which has been used for source
term estimation and atmospheric dispersion analysis in nuclear
emergencies. However, this sophisticated numerical model
re uires computation time, ma ing it di cult to uic lycompare calculation results under various conditions, including
meteorological conditions.
Therefore, we developed a new calculation method assummari ed in ig.
. sing this method, if a release point(e.g., a nuclear facility) is known, the prediction results could
be rapidly obtained by applying a source term (radionuclides,release rate, and release period) to the database of dispersion
calculation results that is prepared in advance without specifying
the source term. Each dispersion calculation is conducted under aunit release condition ( B h) for each release segment divided
by a fixed time interval, and all calculated release segment
results are saved. ive radionuclides, which represent fivegroups classified by diffusion behavior, are calculated without

radioactive decay the decay rate for each specific radionuclide
is applied later. These calculations are conducted regularlyalong with daily meteorological data updates to construct a
continuous database that includes past data and predictions
for the next few days. By applying a release condition of eachrelease segment to the database and aggregating the results of
all release periods, calculation results can be quickly created forarbitrary release conditions. We then developed the atmosphericdispersion database system WSPEEDI-DB using a user-friendlyinterface for easy function operation, as summarized in Fig.4-12.
Dispersion calculation results under various release and weather
conditions can be used for optimization of monitoring plans anddrills by creating simulated monitoring data. As an example, thedeployment of monitoring posts around the Shimane Nuclear
Power Station was assessed by analyzing the past 1-year
dispersion calculation results. We could demonstrate that thepresent monitoring post deployment can capture the distributionof air dose rates during periods without rainfall. For periods with
precipitation, however, high-dose-rate areas are assumed notto be grasped. mobile measurement is effective in such areas.
his study includes the results of the20 –20
joint research with the Shimane Prefectural Nuclear Power
Environmental Center.
(Hiroaki Terada)

Reference
Terada, H. et al., Atmospheric-Dispersion Database System that Can Immediately Provide Calculation Results for Various Source Term and MeteorologicalConditions, ournal of Nuclear Science and echnology, vol. , issue , 2020, p.
.
JAEA R&D Review 2021-2253