The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October2001

Concept of Clearance Level and Its Application
Toshiso KOSAKO
Research Center for Nuclear Science and Technology
The University ofTokyo
2-11-16 Yayoi Bunkyo-ku, Tokyo 113-0032, Japan

Abstract
In radioactive waste management, the discussion
on clearance level for solid radioactive waste is very
important because of getting a reasonable "cut-off''. level on the deep consideration of radiation safety. The
clearance level will be used in the radioactive waste
management of reactor and large accelerator
decommissioning. In this paper the recent Japanesediscussion of clearance level decision is presented andthe key issue in it are reviewed.

1. INTRODUCTIONRadioactive wastes are classified into three
categories in Japan: High-Level Radioactive Waste(HLW), Low-Level Radioactive Waste (LLW) andWastes below Clearance Level. HLW is now underdiscussion for a deep geological disposal withincorporating public opinions. LLWs are undertaking
in Rokkasyo Village Repository.
The relating
regulations for LLW disposal have already prepared
except those on Relatively High Concentration LLWand TRU waste.
After the experience of more than 40 years reactor
operations Japan entered into the period of reactor
decommissioning. For the successful accomplishmentof the decommissioning of reactor and large accelerator
facilities, the well · organized radioactive waste
management is inevitable. For the reasonable disposalof very low level radioactive waste or reuse of thesematerials, the setting of clearance level is quite
important.
Several countries like Germany have alreadystarted the application of the clearance level for the"cut-off'' of radioactivity of very low level wastes. As ageneric clearance level, IAEA-TECDOC-855 isfrequently referred. For the real application to Japanesesituation the government committee is continuing thecalculations and estimations to make up the Japaneselevel of clearance. This committee was assigned from1997 imder the Nuclear Safety Commission to examine
the clearance level of low level radioactive waste.
In the field of large accelerator, the discussion on
the clearance level is not yet started in Japan. So theanther would like to express the situation in the reactor
field as a reference.

2. METHOD AND RESULTThe target individual dose for radiation safety togeneral public is 10 /.l Sv/ y . This value was used toeach considering scenario to keep radiation safety. The
selection of 20 major nuclides were also done for theperformance of the migration and dose calculations.
The first route of cleared materials is disposal.
The cleared radioactive waste will be transported to theland disposal site. The first estimation is land fill at
seashore or inland. Repository site reuse, flow ofground water and river water were assumed for thecalculation. The 41 pass ways were considered and the9 important pass ways were selected.
The second route is Recycle/Reuse. The clearedradioactive wastes are directly reused like pumps etc.,
or transported to the scrap treatment plant for therecycle. In this case the 32 pass ways were selected forthe industrial and home applications of the recycling
materials. Finally the 12 pass ways were listed as animportant pass ways.
In these calculations the selections of the various
parameters are very important and sometimes the mostconservative values are selected. But this kind ofimaginary value may give too much "safe" value far
beyond the reality. To avoid this kind of special
situation the parameters are investigated to get typicalvalues and the extreme case was estimated by sampling
calculation from the probability density function ofeach parameter (stochastic analysis). The 95 percentile
was used for the candidate of clearance level including
safety margin.
Another extreme values are obtained in case of
low probability or unlikely scenarios. This will behandled by classifying the scenarios probability. The
results will give us several acceptable dose levels forclearance. This issue is discussed in the committee.
The procedures of comparison with the otherregulations of radiation dose levels like discharge limits
and methodology development of confirmation
technique of final waste form to guarantee the,---417-The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Thb1e 1CJearance level examp1es fur so1id materials arising from nuclear reactxJrs:(Bq/g)
Derived value

Range in

1000·10000

Mn-54

200
1Co-60

0.4

0.1-1

Sr90
Cs-134

11·10

0.5

0.1-1

Cs-1371

0.1·1

Eu-1520.4
Eu-1540.4
1btal a emitters 0.2

0.1-1

Radionuclide
H-3

Thb1e 2

IAEA-TECDOC-855

0.1-1

0.1-1 (Pu-239,Am·241)

Result of c1earanre level

Range ofRadioactivity
levels (Bq!g)>=0.1

Reoommended Rangein
IAEA-TECDOC-855
Mn-54
Co-60

Zn-65

< 1.0>=1.0

Nb-94
Cs-134
Cs-137
Eu-152
Pu-239Am-241
Sr90<100>=100<1000>=1000

Disposal

Recycle/Reuse

Overall

Co-60
Nb-94
I-129
Cs-134Eu-152
Eu-154

Co-60
Nb-94
Cs-134
Cs-137
Eu-152
Eu-154
Pu-239
Am.-241

Co-60
Nb-94
I-129
Cs-134
Cs-137
Eu-152

Cl-36
Mn-54

Mn-54

Zn-65

Zn-65

I-129

Zn-65

I-129

H-3
C-14C-14
Cl-36
Fe·55

Ca-41

Tc-99
H-3
Ni-63

Eu~154

Pu-239Am-241
Cl-36
Mn-54

Sr90
Tc-99
Cs-137
Pu-239Am-241<10>=10Results

Ni-59
Ni-63

<10000

Sr90
Tc-99

Cl-36
Sr90
Tc-99
H-3
C-14
Ca-41
Fe·55
Ni-59

H-3
C-14
Ca-41

Fe-55
Ni-59
Ni-63

* Used soonarios, models and data are based on the Japanese experience(e.g. :fixxl oonsum.ption rates)* *The underlined nuclides are smaller intwo orders of magnitude than the value ofIAEA·TECDOC-855.

-418-The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

clearance level will be discussed.
The severest case will give us the radioactivity
level of clearance. The result of clearance level ofradioactivity from power reactor is shown in Table 1.
The radioactivity is classified following theIAEA-TECDOC-855. I-129, Cl-36, Tc-99and H-3 aresmaller in two orders of magnitude than the values ofIAEA-TECDOC-855.
This was caused by thedifference of the scenarios, models, and data derived
from Japanese experience, e.g. food consumption rates.

3. DISCUSSION POINTSThe first point is the uncertainty of parametervalues. The first step of calculation of clearance level isa deterministic model calculation by using typicalparameters. In this stage the fluctuations of the levelare estimate by introducing stochastic analysis based on
the selection of parameters from the probability density
function.
Second point is a collective dose. In the newPublication of ICRP77 (Radiological Protection Policyfor the Disposal of Radioactive Waste) the use ofcollective dose concept to the radioactive waste isindicated. The guided value of collective dose appears
in BSS (IAEA-SS-115) and ICRP Pub1.46. The value is
1 man· Sv. But is this value really applicable to a very
low level dose rate situations like 10 /.1 Sv/y? Thisissue will be also discussed.
The third point is an unlikely or very low·probability scenario. In ICRP Pub1.46 the concept of.risk derived from the multiplication between annual
dose and the probability is shown as an effective
method to grasp this kind situation. Or the concept ofpotential exposure (e.g. ICRP Pub1.76) may beeffective to understand this kind of low probablescenario. The risk concept scarcely appeared inJapanese regulatory system under Nuclear Safety
Commission. How to handle this kind of problem, will
be needed to discuss.

nearly same procedure will be requested to establish theclearance level for accelerator facilities. This is eagerly
desired for the reasonable management of accelerator
radiation protection.

S. REFERENCES[1] (IAEA-TECDOC-855): "Clearance Levels forRadionuclides in Solid Materials," IAEA, Vienna(1996).
[2] (IAEA-TECDOC-1000): "Clearance of Materials
Resulting from the Use of Radionuclides inMedicine, Industry and Research," IAEA, Vienna(1998).
[3] (IAEA-SS-115): "International Basic Safety
Standards for Protection against Ionizing
Radiation and for the Safety of Radiation
Sources," IAEA Safety Series No.115, IAEA,Vienna (1996).
[4] (ICRP 46): "Radiation Protection Principle for the
Disposal of Solid Radioactive Waste," ICRP
Publication 46, ICRP (1985).
[5] (ICRP 76): "Protection from Potential Exposure:
Application to Selected Radiation Sources," ICRP
Publication 76, ICRP (1997).
[6] (ICRP 77): "Radiological Protection Policy for the
Disposal of Radioactive Waste," ICRP Publication
77,ICRP (1997).
[7] "Clearance Levels for Solid Materials arising from
Nuclear Reactors in Japan," Nuclear Safety
Commission, Special Committee on Standards ofRadioactive Waste (1999) (in Japanese) .

4. CONCLUSION
The present status of discussion on the clearance
level in Japan is presented. As a result of the clearance
level for each radioactive material fro power reactor
was sown. The distribution of calculated radiation
doses are estimated by the stochastic analysis byselecting parameters from the probability density
functions. These values of clearance level will begreatly useful for the real scene of reactor
decommissioning. For large accelerator facilities,-419-