NRA presentation
C2 Revised REIA
KONISHI Koji
Nuclear Regulation Authority JAPAN
2nd IAEA Regulatory Review Mission on ALPS Treated Water Handling
17 January 2023
1. Results of revised REIA with selected nuclides
2. Review results as of July 2022 approval
3. Independent modeling of dispersion
Contents1Mr. NIISOE presentation
In TEPCO’s Application submitted in Nov. 2022, only the source
term is revised. The assumption and methodology of the REIA is
not changed.
Therefore, the NRA only reviewed 1 the revised source term
and 2 assessment result revised with this source term. The
other parts of the NRA’s Review Results published in July 2022
are still valid.
Considering above, the NRA’s Review Results document for this
Application will cover 1 & 2.21. Results of revised REIA with selected nuclides
confirmed that the assessment results are below the criteria that
the NRA commission decided
1. Results of revised REIA with selected nuclides3selected nuclides (30 nuclides) @ Dec. 2022
Assessment Result
(April 2022)
Assessment Result
(This time)
The Criteria
Exposure to humans 0.4 μSv/year 0.03 μSv/year 50 μSv/year
Potential Exposure 0.3 mSv/case 0.01 mSv/case 5 mSv/case
Exposure
to animals
and plants
in the sea
flat fish ×ばつ10-5 mGy/day ×ばつ10-7 mGy/day 1-10 mGy/day
crab ×ばつ10-5 mGy/day ×ばつ10-7 mGy/day 10-10 mGy/day
seaweed ×ばつ10-5 mGy/day ×ばつ10-7 mGy/day 1-10 mGy/day
Results with the source term above
H-3 C-14 Mn-54 Fe-55 Co-60 Ni-63 Se-79 Sr-90 Y-90 Tc-99
Ru-106 Sb-125 Te-125m I-129 Cs-134 Cs-137 Ce-144 Pm-147 Sm-151 Eu-154
Eu-155 Pu-238 Pu-239 Pu-240 Pu-241 Am-241 Cm-244 U-234 U-238 Np-237
TEPCONRA4
Six items as being relevant to the design and operation of the Discharge Facility
as well as the radiological impact of discharge within the Government Policy:
(Measures relevant to the design and operation of the Discharge Facility)
1. Necessary procedures and the construction of the facility for starting the
discharge in around spring 2023
2. Involvement of a third party with expertise in analysis of radioactive materials
3. Extensive dilution of ALPS treated water
4. Total amount of tritium discharged per year
5. Starting with a small amount of discharge, and discharge suspension when
unusual values are observed by marine monitoring
(Measures to assess impact on the marine environment)
6. Radiological impact assessment of discharge
Chapter 22-1reviewed along
with the
examination based
on the Reactor
Regulation Act.
2. Review results as of July 2022 approval
the NRA confirmed and concluded that the Radiological Impact Assessment is
conducted with reference to the relevant IAEA Safety Standards’
Requirements and Guides (GSR-Part3, GSG-9, GSG-10), and that the
assessment results are below the criteria and thus the impact both on
humans and the environment is sufficiently small. 5
2-1. Radiological impact assessment of discharge
1. Assessment of radiation dose to humans
>Criterion: dose constraint 50 μSv/year
2. Assessment of radiation dose to humans in potential exposures
>Criterion: 5 mSv per event which is shown in GSG-10 as a typical criterion for
radioactive material and sources with a low capacity for a radioactive release in
an accident
3. Assessment of radiation dose to marine animals and plants in normal operation
>Criterion: the lowest values of the Derived Consideration Reference Levels
4. Consideration of uncertainty
2. Review results as of July 2022 approval61. Assessment of radiation dose to humans
(1) Selection of the source term
The NRA confirmed mainly whether the selected source term
is the composition and amount of relevant radionuclides
typical to the activity subject to the assessment.
【NRA confirmation result】
• Using the data of ALPS treated water in the three tank groups
for which 64 radionuclides have been measured and evaluated.
• There is no substantial difference in radionuclide composition
between ALPS treated water in the three tank groups and the
water in the other tank groups of which the sum of the ratios of
radionuclides other than tritium to each concentration limit is
less than 1.
• Even if there exists any other radionuclide than ALPS removal
target 62 radionuclides and carbon14, the impact to humans is
considered small because of low-energy radiation, and thus the
impact of the revisit of the source term to the assessment would
be small.
2. Review results as of July 2022 approval7Source: TEPCO’s Radiological Impact Assessment Report
Regarding the Discharge of ALPS Treated Water into the
Sea(Design stage /Revised version), April 2022
Application Documents for Approval to Amend the
Implementation Plan for Fukushima Daiichi Nuclear Power
Station Specified Nuclear Facility [Partially revised]
(tepco.co.jp)
2. Review results as of July 2022 approval81. Assessment of radiation dose to humans
(2) Modelling of dispersion and transfer in the environment
The NRA mainly confirmed whether the selected dispersion and
transfer model is suitable for simulating dispersion, dilution, transfer,
accumulation of radionuclides and their decay as necessary, taking
into account the characteristics of discharge expected during normal
operation.
【NRA confirmation result】
• For radionuclides other than tritium, the dynamics does not
necessarily coincide with tritium, which is a tracer in simulation, in
the environment due to adsorption such as into seabed soil.
However it is assumed in the estimation that the other radionuclides
are advected and diffused in a state dissolved in seawater like
tritium, and this assumption is conservative without account taken of
decrease in concentration in seawater.
2. Review results as of July 2022 approval
• On the other hand, the accumulation of radionuclides associated with transfer such as
to beach sand, is assumed in equilibrium with the radioactive concentration in seawater
from the start of discharge, which means the assessment is conducted in a state where
the radioactive concentrations in the environment are considered to become the
highest during the long-term discharge.91. Assessment of radiation dose to humans
(6) Comparison of estimated doses with dose constraint
【NRA confirmation result】
• As a result of the above assessment, the estimated dose to
the representative person is approximately 10-2 to 10-1
μSv/year, which is considerably small compared to 50
μSv/year, the criterion approved by the NRA Commission.
• With the above result in mind, recognizing that, in the process
of deciding the Government Policy, consideration was given to
factors for optimization of protection and safety associated
with ALPS treated water discharge such as the planning of the
entire decommissioning, the effect of decay, the risk of
accidental discharge during storage, occupational exposure,
and societal impacts, TEPCO has decided that the annual
amount of tritium to be discharged is controlled at a level
lower than 22 tera Bq.
• TEPCO plans to periodically revisit the annual amount of
tritium to be discharged within the range of the dose constraint
taking into account factors to be considered in the optimization
process.
2. Review results as of July 2022 approval102.Assessment of radiation dose to humans in potential exposures
The NRA mainly confirmed:
Whether scenarios for potential exposures are identified on
the basis of the safety assessment for the facility and
activities;
Whether radiation dose to the representative person is
estimated after identifying source term, dispersion and
transfer model, exposure pathways and the representative
person appropriate to the identified scenarios; and
Whether the estimated dose is below the criteria for potential
exposure.
2. Review results as of July 2022 approval
【NRA confirmation result】
Conservative scenarios are assumed for two cases identified as damages
which could lead to an unintended discharge, beyond equipment malfunctions
postulated for the assessment of the design of the Discharge Facility:
(1)rupture of ALPS treated water transfer pipe, and (2)breakage to the tank
groups for measurement and confirmation.
3. Assessment of radiation dose to marine animals and plants in normal operation
【NRA confirmation result】
• The transfer models are selected from the ones identified in 1. with account
taken of the habitat environment of marine animals and plants.
• According to the marine ecosystem in the sea area near the FDNPS, reference
flatfish, reference crab and reference brown seaweed are selected.
• Dose coefficients based on GSG-10 are used for external and internal
exposures.112. Review results as of July 2022 approval
The NRA mainly confirmed:
Whether dose rates are estimated for the reference animals
and plants selected according to the marine ecosystem in the
sea area near the FDNPS, with the same source term and
modelling of dispersion and transfer as used in 1. as well as
the exposure pathways to be considered for marine animals
and plants; and
Whether the estimated dose rates are below the lowest values
of the Derived Consideration Reference Levels.124. Consideration of uncertainty
The NRA mainly confirmed:
Whether the level of uncertainty is understood with the nature of uncertainty
included in the assessment being comprehended; and
Whether consideration is given to identify sources of uncertainty contributing
most to the assessment result.
【NRA confirmation result】
• Understanding the nature of uncertainty, such as random uncertainty with
statistical distribution and uncertainty arising from incomplete knowledge,
sources of uncertainty contributing largely to the assessment result are
identified as the radionuclide composition of the source term and concentration
factors in sea animals.
• As the estimated dose to the representative person in 1.(6) is considerably
small compared to the criterion, there is no need to give detailed consideration
to uncertainty. Even if the main source of uncertainty identified as above is
considered in the assessment, the variance would be one order of magnitude
and therefore the conclusion that the estimated dose is below the criterion
remains the same.
2. Review results as of July 2022 approval