Radiation Safety Analysis of Neutron Colimator Based on Nickel Material for Piercing Radial Beamport Utilization of Kartini Research Reactor

Radiation safety analysis of nickel material neutron colimator (as requirement) for pearcing radial beamport utilization of Kartini research reactor has been done before the neutron colimator instaled. The neutron collimator made of nickel material with cyllindrical geometry which is 156 cm length. The Inside and outside diameter are 16 cm and 19 cm respectively with mean cyllindrical thickness is 1.5 cm. Irradiation process to the neutron collimator begin when the reactor beeing operated for 6 (six) hours per day and assumed optimum at 100 kW power level. Results of the analysis showed that gamma dose rate which was generated by collimator at a distance of 50 cm from the end of the collimator is 1.5328e-03 mr/hours. The dose rate is still below the dose limit value which was required by Nuclear Energy Regulatory Agency (BAPETEN) is 1 mr/hours. It can be concluded that utilization neutron colimator of nickel material which installed at the radial pierching beamport of Kartini Reactor is safelly.Telah dilakukan kajian analisis keselamatan paparan radiasi terhadap kolimator neutron (sebagai persyaratan) sebelum dipasang pada beamport tembus radial reaktor kartini. Kolimator neutron terbuat dari bahan nikel berbentuk silinder panjang 156 cm dengan diameter dalam 16 cm dan diameter luar 19 cm sehingga tebal silinder 1.5 cm. Proses iradiasi terhadap kolimator neutron terjadi pada saat reaktor dioperasikan pada suatu daya dan diasumsikan optimal pada daya 100 kw selama 6 jam dalam satu hari. Hasil analisis menunjukan laju dosis gamma yang dihasilkan kolimator pada jarak 50 cm dari ujung kolimator sebesar 1.5328e-03 mr/jam. Laju dosis tersebut masih dibawah nilai batas dosis yang ditetapkan oleh bapeten sebesar 1 mr/jam, sehingga penggunaan kolimator tersebut dalam batas aman


INTRODUCTION
The development of nuclear technology utilization is increasing in various field such as industry, medicine, agriculture and research. Besides the benefit of nuclear technology utilization contained potential risk to human live and environment. So that it need to maintain and analyze radiation safety for workers, society, and environment. There are two methods facility shield design. Neutron and capture gamma dose rates at the accessible areas are estimated (Sunny & Subbaiah, 2014). To make neutrons available outside the reactor core, beam ports are designed around the core. These beam ports can be characterized by neutron flux level which is useful for neutron beam application in a reactor. The neutron and gamma flux variation was studied as a function of different orientations of beam tubes and optimally minimum information is produced to understand neutron beam design and use (Yasmeen & Mahmood, 2016). The advantage of using a TRIGA reactor for BNCT is its stability and reliability in addition to the high neutron intensity and low background radiation of the treatment beam (Savolainen et al., 2013) For radiation safety purpose, requires radiation personal dose limit value assigned by Nuclear Energy Regulatory Agency (BA-PETEN). According to regulation by The Head of BAPETEN State No. 4 2013, the personal radiation dose limit value is average effective dose of 20 mSv of five-year period, so the dose accumulated in 5 years should not exceed 100 mSv. While effective radiation dose limit value for community is 1 mSv per year (BAPETEN, 2013).
To improve the utilization of the Kartini research reactor, one of irradiation facility that is radial pearcing beamport will be used for in vivo/in vitro neutron irradiation test facility as a basic research for developing Boron Neutron Capture Therapy (BNCT) method. By instaling neutron collimator of nickel material in the radial piercing beamport to optimizing the neutron flux (Wahyono et al., 2012). Boron Neutron Capture Therapy (BNCT) has been advocated for many decades as an innovative form of radiotherapy that, in principle, has the potential to be the ideal form of treatment for many types of cancers (Moss 2014). The BNCT has been performed using research reactors which are usually located at place far from hospitals. At Kyoto University Research Reactor Institute (KURRI), more than 450 clinical studies of boron neutron capture therapy (BNCT) have been performed using a research reactor as of December 2013 (Tanaka et al., 2014). In BNCT method, it is needed a neutron source which is produced neutron flux that is suitable for BNCT system. BNCT neutron flux may be produced from a neutron Beam Shaping Assembly (BSA) design. BSA is a system tool that is used to produce the neutron flux corresponding to the flux of neutrons for BNCT therapy (Rasouli, Masoudi, & Kasezas, 2012;Faghihi & Khalili, 2013).
Before the neutron collimator inserted in the radial piercing beamport, it should be carried out to analysis especially radiation safety aspect, because assume when the collimator in the beamport will be radioactive material because of neutron interaction when the reactor operated at power level . By the analysis of radiation safety aspect it can be used for basic requirement developing utilzation of the Kartini research reactor (Karmanto, 2016 ).
A major release of radioactivity to the environment is always of concern, owing to potential acute and long-term health effects. Evidence from historic events confirms that any major uncontrolled release of radiation should be cause for immediate response and scientific assessment of potential health effects (WHO, 2013).

Radiation Efect to Human Live
The main biological effects of radiation is damaging the cells and tissues of the human body. Type the biological effects of radiation can be classified into two types, namely (Umbara, 2011): 1. Stochastic radiation effects severity is not dependent on the size of the dose and the probability of no specific threshold dose.

2.
Deterministic radiation effects severity is dependent on large doses.

Collimator
Determination of mass the collimator of nickel is useful for determining of radiation exposure when the collimator activated by neutron since inserting in the beamport and being activation process when the reactor is operated at power level. Figure 1. Indicate dimension of cylindrical collimator form with with size of length is 156 cm, outside diameter (r 0 ) is 19 cm and inside diameter (r i ) is 16 cm, mean the thickness of colimator is 1,5 cm (Arrozaqi, Widiharto, & Sardjono, 2013).

Neutron Activation.
Neutron activation is reaction betwen material atomic nuclei with neutron when the material put on the neutron field. By neutron activation the nuclei will nucleus in an excited state condistion and radioactive emit particles weather α, β, γ or α and γ, β and γ simultaneously. Activities of material that has been activated can be determined using equation (1) (Suparman, 2011).
= activity (Bq) ∑ act = macrosscopic crosscection (cm -1 ) ϕ = neutron flux (n cm -2 s -1 ) V = volume of materials (cm 3 ) λ = decay time (s -1 ) After irradiation process the nuclei material will emmite radiation activity with spesific decay time and value of activity as formula (2) follow (Awaludin, 2009). Figure 1. is indicate the neutron collimator which will be inserted to radial pierching beamport with cyllindrical form. When the neutron collimator inserted to beamport while reactor operated, it can be assumed that the collimator will be radioactive material. Radiation activity of the collimator should be determine for safety analysis report related with radiation workers, public and environment. Determination dose rate assume that closed position at the distance of point P where area worker done can be calculated by formula (3) follow (Stabin, 2007):  Segmen length (p) = 13 cm Total segmen (n) = 12 segmen Mass each segmen (m) = 8 kg Total mass (m t ) = 96 kg The nickel purity data of collimator material is arround 95 % which used to manufactured the neutron collimator obtained from studies conducted by KKhoirunisa & Widarto (2015) with the title "Analysis of Type And Elements Content In Neutron Collimator Materials Before And After Manufacturing Using Neutron Activation Analysis Method (NAA)" (Khoirunisa & Widarto, 2015).

Neutron Flux
Neutron flux data along the radial pearcing beamport of Kartini Research Reactor which is operates at 100 kW was studied by Sardjono et al, (2014) titled "Current Status of Boron Neutron Capture Therapy Technology Development and Application With Compact Neutron Generator" (Widarto, 2014).

Data Analysis Technique
Equation (1) was used to determined the activity of each collimator elements when irradiation process take place. In determining the activity of each collimator elements after irradiation process was stopped we used equation ( 2 ). In determining the dose rate generated by collimator used equation ( 3 ).

Elements of Neutron Collimator
Research conducted by Khairunnisa, (2015) with the title " Analysis of Type And Elements Content In Neutron Collimator Materials Before And After Manufacturing Using Neutron Activation Analysis Method (NAA)" were obtained the collimator elements before and after manufacturing. Table 1 shows the concentration of constituent elements of neutron collimator after manufacturing.

Tabel 1.Collimator Elements Concentration Elements
Concentration ( Based on neutron collimator homogeneousity, the mass of each neutron collimator elements in each segment is same. By using equation (1), it will obtain the mass of each neutron collimator elements in each segment. Table 2 shows the mass of each neutron collimator elements in each collimator segment.

Neutron Flux of The Piercing Radial Beamport
Research conducted by Widarto et al, (2014) titled "Current Status of Technology Development and Application of Boron Neutron Capture Cancer Therapy With Compact Neutron Generator" calculated that the quantity of the thermal and fast neutron flux along the piercing radial beamport when the reactor Kartini operated at a power of 100 kW shown in Table 3. Figure 3 shows the dimensions of the neutron collimator (Novitasari, 2015).    Table 3 data, it can be made a relationship between the beamport length and neutron flux. Figure 4 shows the relationship between the beamport length and thermal neutron flux, while Figure 5 shows the relationship between beamport length with fast neutron flux.
Equation (4) shows the distribution of thermal neutron flux, where the thermal neutron flux expressed in y-axis and x-axis specifies the beamport length.

Thermal Neutron Flux Maping
Collimator will be placed on the piercing radial beamport at a 118 cm distance from the reactor core. Figure 6 shows the placement of the neutron collimator in piercing radial beamport of Kartini Research Reactor.
Neutron flux wich is interacting with the neutron collimator are thermal neutron flux (Ger-  Table 4 shows the magnitude of the thermal neutron flux which interacts with each collimator segments (where length of each collimator segment separated with X 1 and X 2 ). So, each collimator segment length is X 2 -X 1 = 13 cm, and number of collimator segment is 12 segment. It mean that the total of collimator length is 12 x 13 cm = 156 cm.

Collimator Dose Rate While Irradiation
The activity of each collimator elements is an activity accumulation of each collimator segments. Table 5 shows the amount activity of every collimator elements in the irradiation time.
The results are shown in Table 5 shows that the longer irradiation time, so that the activity of each collimator elements will be greater.
When the collimator is irradiated, each collimator elements will be activated. It will become radioactive and emit radiation. Table  6 shows the magnitude of the dose rate produced by the collimator at a 50 cm distance from the end of the collimator. The total dose rate which is produced from neutron collimator is accumulated dose rate from each neutron collimator elements.  The results are shown in Table 6 shows that the longer irradiation time, dose rate generated by neutron collimator will be greater.
Based on Table 6 data, it can be made the relationship between the irradiation time and the dose rate. Figure 7 until Figure 13 shows the relationship between the irradiation time and the dose rate for each collimator elements.
Based on Figure 7, it was obtained the equation (6) where irradiation time expressed to x-axis and y-axis expressed the dose rate.
Based on Figure 8, it was obtained the equation (7) where irradiation time expressed to x-axis and y-axis expressed the dose rate. Based on Figure 9, it was obtained the equation (8) where irradiation time expressed to x-axis and y-axis expressed dose rate.
Based on Figure 10, it was obtained the equation (9) where irradiation time expressed to x-axis and y-axis expressed dose rate.
Based on Figure 11, it was obtained the equation (10) where irradiation time expressed to x-axis and y-axis expressed the dose rate.
Based on Figure 12, it was obtained the equation (11) where irradiation time expressed to x-axis and y-axis expressed the dose rate

Collimator Dose Rate after 6 Hours Irradiation
After irradiated for 6 hours was stopped, the activity of each collimator elements were decay. The total activity of each collimator elements are accumulation of each collimator elements activities. Table 7 shows the amount of every collimator elements activity after 6 hours irradiation time, whereas Table 8 shows the dose rate generated by a collimator at a distance of 50 cm from the end of the collimator after irradiated for 6 hours. The total dose rate which is generated by neutron collimator is accumulated dose rate of each collimators elements in each segments. The results are shown in Table 7 states that the longer delay time, the lower activity of each collimator elements. The results are shown in Table 8 shows that the longer the delay time, the smaller the dose rate generated collimator elements.
Based on Table 8 data, it can be made the relationship between the delay time and the dose rate of each collimator elements. Figure  14 until Figure 20 shows the relationship between the delay time and the dose rate of each collimator elements.
Based on Figure 14, it was obtained the equation (13) where delay time expressed to xaxis and y-axis expressed the dose rate Based on Figure 15, it was obtained the equation (14) where delay time expressed to xaxis and y-axis expressed the dose rate. Based on Figure 16, it was obtained the equation (15) where delay time expressed to xaxis and y-axis expressed the dose rate.
total dose rate calculated at deley time (td ) for 0 hours (suddenly irradiated), 3 hour, 6 hour and 9 hour. Further more for safety aspect such as requirement by regulatory, should be calculated by assumed that dose rate for distance 50 cm from the collimator . The result of Dose Rate of Collimator After Irradiated for 6 hour could be shaw as Table 9.
Total dose rate generated by the neutron collimator has ben calcullated when irradiated by neutron for 6 (six) hour, assumed at 50 cm distance and with various delay time (td) for 0 hour (sudenly irradiated) is 1.5328E-03 mR/ hour, for 3 hour is 6.7680E-04, for 6 hour is 3.0001E-04 and for 9 is 1.3408E-04 (Akbar, 2015). According to safety aspect requiremet autorized by regulatory body (Badan Pengawas Tenaga Nuklir) is 1 mR / h). Its could be concluded that utilization of the neutron colimator made of Nickel when inserted in the radial piercing beamport is safely, because the dose rate which generated by neutron collimator is much lower than dose rate requirements regulatory.

CONCLUSION
The total dose rate generated by neutron collimator at a distance of 50 cm from the end of the collimator after 6 (six) hours irradiation for delay time (td) 0 hour (sudenly irradiated) is 1.5328E-03 mR/hour, for 3 hour is 6.7680E-04, for 6 hour is 3.0001E-04 and for 9 is 1.3408E-04 mR / h. The dose rate are much lower than the dose limit which authorized by Nuclear Energy Regulatory Agency (BAPETEN) i.e. 1 mR / hour. 1.5328E-03 its means that utilization of the neutron collimator is safely.

Remarks
It is required α and β spectroscopy to study both α and β radiation which is may occur from collimator elements activity.