Conceptual Study on Disposal Facility for Waste from Decommissioning of NPPs
Norie KAWAHATA, Ryoichi HOJO, Takayuki HAMANAKA, Takashi KOZAWARadioactive waste disposal business division, Japan Nuclear Fuel Limited
504-22, Nozuki, Obuchi, Rokkasho-mura, Kamikita-gun, Aomori-ken, Japan

Key words; disposal facility, low-level waste, nuclear power plant, reprocessing plant, decommissioning waste,high surface dose rate, lower radiation exposure, skyshine, external exposure, horizontal emplacement

Abstract
In Japan, low-level waste (LLW) from the operation of nuclear power plants (NPPs) has been contained in the200-liter drums with solidification materials and converted into the waste packages. The waste packages havebeen disposed in the near-surface disposal facilities of Rokkasho LLW Disposal Center.
In the near future, the large-size radioactive waste with higher radiation level will arise from thedecommissioning of NPPs and the operation of reprocessing plant. Therefore, we studied a concept of thedisposal facility which can reduce radiation exposure to the public, compared to the above-mentioned
near-surface disposal facilities.
For the purpose of more efficiently processing and containing of the waste from the decommissioning of NPPs
and the operation of reprocessing plant, waste producers have considered the use of a cubic container (1.6 m on aside) for the packaging of the waste, instead of the 200-liter drum. Additionally, the waste packages are expected
to have higher surface dose rate. Thus, we concern about the increase in radiation exposure to the public causedby direct or skyshine gamma-rays. From the viewpoint of reducing the radiation exposure to the public, it iseffective to adopt not a pit-type facility but a box-culvert-type facility with higher shield effect.
In consideration of the adaptation of the box-culvert-type facility, the waste packages will be emplaced
horizontally by forklift truck, not vertically by crane as used in Rokkasho LLW Disposal Center.
There are the following advantages of the box-culvert-type facilities over the pit-type ones:- Lower radiation exposure to the public;- All weather operation;- Expectation of use a candidate area effectively, in the case of multi-layered structure.
1. Introduction

In Japan, radioactive waste is classified roughly
into high-level waste (HLW) and low-level waste(LLW). HLW consists of fission products
remaining in the spent fuel which uranium andplutonium are separated from in the reprocessing
plant. LLW arises from the operation and thedecommissioning of nuclear power plants (NPPs).
Furthermore, LLW is divided into three according toits radiation level.
LLW from the operation of NPPs has been
contained in 200-liter drums with solidificationmaterials and converted into waste packages. Thewaste packages have been disposed in thenear-surface disposal facilities of Rokkasho LLW
Disposal Center.
In the near future, large-size radioactive waste withrelatively higher radiation level will arise from thedecommissioning of NPPs and the operation ofreprocessing plant. Therefore, we studied a conceptof the disposal facility which can reduce the radiation
exposure to the public, compared to the current
near-surface disposal facilities.
2. Rokkasho LLW disposal center [1] [2]
In Rokkasho-mura of Aomori Prefecture, we havedeveloped uranium enrichment, reprocessing, MOX
fuel fabrication, HLW storage, and LLW disposal.
Regarding the LLW disposal, The No.1 and theNo.2 disposal facility are approved in 1990 and 1998
respectively, and have been operating. Each facility
has disposed about 150,000 drums, and the total
number of disposed drums is about 300,000 as ofSeptember 30, 2017.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanEach facility was certified to dispose
40,000m3(equivalent to 200,000 of the 200-literdrums) of LLW.
At present, only LLW from the operation of NPPs
is disposed in Rokkasho LLW Disposal Center.
Radioactive waste arising from the decommissioningof NPPs and the operation/decommissioning of thenuclear fuel cycle facilities is planned to dispose.
In the future, some 600,000m3 (equivalent to3,000,000 of the 200-liter drums) of LLW are
expected to be disposed at this site.

operation/decommissioning of nuclear fuel cycle
facilities is excepted in Tab.2.
Tab.2 Outline of waste packages

3. Low-level radioactive waste [3]The classification of radioactive waste in Japan isshown in Table.1. Liquid LLW and solid LLW are
produced by the operation of NPPs. Radioactivewaste with relatively low radiation level of these isdisposed in a pit-type facility.
In Rokkasho LLW Disposal Center, liquid LLW
and solid LLW are disposed in the No.1 and No.2
disposal facility respectively.

Tab.1 Classification of radioactive waste in Japan
These excepted wastes are planned to dispose in
the future. Particularly, the decommissioning waste
will be preferentially disposed because some NPPs
are on decommissioning stage.
The specifications of the decommissioning waste
packages currently expected differ from theoperational waste package currently disposed in thetype of package, weight and surface dose. The cubic
container is considered as the decommissioning waste
package to contain the large size waste (e.g.:dismantled equipment, building) and its size is 1.6m
×1.6m×1.6m with a maximum weight of 20 tons.
In
addition,maximum
surfacedoseofdecommissioning waste package is designed to be 20mSv/h.
In order to dispose the decommissioning waste, weneed to take account of these two points: size andsurface dose.

Liquid LLW includes condensed liquid waste andspent resin, which are mixed with cement, asphalt orplastic. They are then poured into the drums forsolidification. Solid LLW includes metals, plastics,insulation and filters. They are classified, andcut/condensed, after which they are stored in thedrums and solidified with mortar. The procedures andthe cross-section images of each solidification are
shown in Tab.2.
The waste shown in Tab.2 arises from theoperation of NPPs. The waste from thedecommissioningofNPPs
and
the4. Concept of new facility for decommissioning
wastesRegarding the surface dose of the decommissioning
waste stated in section 3, there would be a concern
about the increase in radiation exposure to the publiccaused by direct or skyshine gamma-rays from the
top of disposal facilities during the emplacement
work in the current pit-type facility as the No.1 andNo.2 disposal facilities. (Fig.1)
Thus, it is necessary to consider about the reductionof exposure from the disposal facility.
Direct or skyshine gamma-rays affect the highest
radiation exposure to the public during the operating
period of No.1 and No.2 disposal facilities because
the radiation exposure increases during theemplacement work of waste packages without a

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanshield-lid. Therefore, new facility design must be
considered to reduce the radiation exposure during
the emplacement work.
As shown in Fig.2, for the reduction of the radiation
exposure, we considered to make a pit opening on theopposite side from the evaluation point. Radiationfrom the top of the disposal facility scatters inhemispherical space above the disposal facility, but
the scattering of radiation from the side of thedisposal facility is predicted to decrease due to thelimitation of the scattering space and angle. This willlead to reduction of a skyshine exposure.
Consequently, we decided to study on thebox-culvert-type facility as a new concept over thecurrent pit-type facility.

Emplacement

cubic container for the decommissioning waste. (Fig.
3)
Waste package(cubic container)
Temporal shield

Forklift(remote control)

Fig.3 Image of emplacement process
The box-culvert-type facility is regarded as one ofthe promising design. There are the following
advantages of the box-culvert-type facilities.
First, the radiation exposure to the public can bereduced as described above.
Second, it is effective to prevent the entry ofrainwater. The waterproof of the disposal facility isrequired to reduce nuclide migration from thedisposal facility. In the current facility, we set thetemporary shield-lid of the steel or concrete, andcover the facility by the waterproof sheet. On theother hand, install of roof in the proposed facility isexpected that rainwater more hardly enter the facility
during the operation.
Third, it is enable to establish the multi-layered
facility, because the box-culvert facility has an
opening on the side, and waste packages areemplaced by forklift from the side of the facility.
When the waste packages are emplaced from the topof the multi-layered facility by crane, it is necessary
to consider the influence of the damage of the falling
waste packages. However, when the waste packages
are emplaced from the side of the facility, theinfluence of the damage of the falling the waste
packages is less. Therefore, it is unnecessary tostrengthen the measure to prevent falling the waste
packages. In addition, a multi-layered facility willlead to the effective use of site area, because of theincrease of the amount of disposal waste per unit area.
(Fig.4)

Fig.1 Emplacement process of waste packages

Scattering area
Evaluation point

OpeningFig.2 Image of Box-culvert-type facility
The operation process of the box-culvert-type
facility is considered to use a forklift to emplacewaste packages, because the emplacement machine isneeded to enter from the side. The forklift is widelyused for the container movement in the generalindustry, so it is also considered to be suitable for theFig.4 Image of disposal facilities of current design
and multi-layered
While there are the above-mentioned merits, there
are also the challenges about the box-culvert-typefacility.
First challenge is the method of the backfill bymortar after the emplacement of waste packages.
Since there is no partition wall, temporary mobile
formwork is necessary to gradually fill with mortar in
the box-culvert-type facility. Several methods areproposed, but we should study and realize the mostrational way considering both of the merits anddemerits.

6th East Asia Forum on Radwaste Management ConferenceNovember 27-29, 2017, Osaka, Japan

Second challenge is realization of remote-controlledlarge forklift. There are the real examples ofhuman-operated large forklift and remote-controlled
small forklift, but there are no the real examples ofremote-controlledlarge
forklift.
The
remote-controlled large forklift is required the same
performance as current equipment from theviewpoints of the efficiency and accuracy.
5. Summary
We studied about the box-culvert-type facility as
one of the promising design for the emplacement of
the decommissioning waste.
In consideration of the adaptation of thebox-culvert-type facility, the waste packages will beemplaced horizontally by forklift truck, not verticallyby crane as used in Rokkasho LLW Disposal Center.
There are the following advantages of thebox-culvert-type facilities over the pit-type ones;- Lower radiation exposure to the public;- All weather operation;- Expectation of use a candidate area effectively, incase of the multi-layered structure.
6. References[1] Japan
Nuclear
Fuel
Limited.
(2016),CORPORATE PROFILE, Japan Nuclear FuelLimited.
[2] Japan Nuclear Fuel Limited. (2017), Low-levelRadioactiveWasteDisposal,
http://www.jnfl.co.jp/en/business/llw/ (accessed2017-10-31)[3] Japan Nuclear Fuel Limited. (2015), Rokkasho
Low-level Radioactive Waste (LLW) Disposal
Center, Japan Nuclear Fuel Limited.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan