1. CN−２４２ 03b–12/ID52 Exposure Scenario and Pathway
A Plan and Its Safety Assessment of VLLW Disposal Site in order to Dispose of Waste Materials Generated from Decommissioning of Tokai Nuclear Power Plant
K.Tanaka1,2, H.Noguchi2, S.Nomura2, H.Tanabe2, K.Morii2, K.Fujimura2
The Institute of Applied Energy, The Japan Atomic Power Company 1 2
Outline of Tokai NPP and Tokai VLLW disposal site (TK-L3)
Bird eye view of TK-1 and
Classification map of Radioactive waste
Tokai Nuclear Power plant (TK1) is about 100km to the north of Tokyo.
TK1 is the first commercial nuclear rector in Japan.
Tk1 is a graphite moderate and CO2 gas-cooling reactor (GCR)
TK1 is now under decommissioning
Tokai　Dai-ni
NPP
Tokai　NPP
Location of TK-L3
: Location of monitoring post
L3 wastes will be generated from areas colored in green.
Theses are :
Steam Rising Units
Hot & Cold Gas Ducts
Materials in Operation floor
Concrete of primary and secondly Biological Shielding Wall
TK1
Location of TK1
Bird eye view of TK1
Major specifications of Tokai NPP site
Location of TK-L3 in Tokai NPP site
Reactor type : Gas Cooling Reactor (GCR)
Start up : July,1966
Shutdown permanently :march, 1998
Electric Output : 166 MWe
An area of the site : 600,000 m2
Total amounts of waste : 16,000 tons.
A specification of Tokai VLLW (L3)disposal site (TK-L3)
Cover soil：2.5m
0.5m
Retaining wall
Divider
0.25m 1m
Retaining pile
Paving the cover soil surface
Upper limit of groundwater
5.6～6.7m
7.5m 4m
Side ditch
Waste materials
A well for radiological observation
:Location of a well for observation of the flow of the groundwater
Location of TK-L3
Tokai　Dai-ni
NPP
Tokai　NPP
：The boundary of the Tokai site
Distance of 400m from the shoreline
B-Trench
A-Trench
Cross section view of TK-L3
Design view of TK-L3
There will be three layers of waste materials in the trenches of TK-L3 of which the depth is 4m.
Since 4m of the depth will prevent that waste materials soak in the groundwater, radionuclides will migrate to the groundwater by only rain infiltrating into the waste material.
Cover soil of thickness 2.5 m with pavement will reduce public exposure by Gamma-ray from waste materials to safe enough.
Retaining walls and dividers will be installed to ensure the safety of emplacement activities of waste materials.
Two trenches named A-trench and B-trench will be constructed.
Metal wastes will be mainly disposed of in A-trench → Metal wastes will be mainly generated from dismantling of Steam Rising Units (SRU) and from piping which connects a reactor and SRU
Concrete wastes will be mainly disposed of in B-trench. → Concrete wastes will be generated from dismantling of the primary Biological Shielding Wall (BSW) and some parts of the secondary BSW.
LOCATIONS OF A WELL FOR OBSERVATION
35 observation-wells for boring investigations have been dug to perform observations about a structure of groundwater-flow and the stratum in TK1 site.
The observation showed that the groundwater always flows toward the sea and that the upper limit of the groundwater is around 5.6m in depth.
Processes of waste materials of L3
Exposure Scenario and Pathway
Intake of feed contaminated with radioactivity by livestock
Layer of the waste　materials and the filling soil
Layer of the cover soil
Migration of radioactivity to farm products through its roots
Intake of farm products
Intake of livestock product
Cover soil
Waste materials
Migration of radioactivity to an ocean caused by groundwater
Intake of marine products
Intake by drinking
An use of a well water*
(Drinking, 　Irrigation,　Breeding)
Migration of radioactivity to groundwater caused by rain
Exposure by the activities at the sea shore
<Possible matters> Depth of the digging:3m
<matters of the low possibility> Digging of a gross quantity of waste materials
Exposure by construction activities after the controlled period
Layer of the waste　materials and the filling soil
The mixed soil which is comprised of waste and the filling soil and cover soil
Migration of radioactivity to gardening plants through its roots
Exposure by a residence after the controlled period
Exposure by the migration of radioactivity to the groundwater
Exposure by land-reuse as farmland
Exposure by land-reuse to dig the site
Public Exposures by Each Pathway of Each Scenario
Public exposures of each pathway of each scenario have been assessed by applying appropriate procedure with appropriate parameters . - Pathways of each scenario are shown in text- boxes colored in blue
We also evaluated exposure by Gamma-ray from waste materials directly and by sky-shine of Gamma-ray in the operation period of the emplacement by using calculation codes