ML18144A957

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Redacted Hs Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A Safkeg Type B Transport Package
ML18144A957
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Issue date: 03/12/2018
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GOMMERGIAL IN ommoD~CE HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type 8 Transport Package Croft Associates 12 March 2018

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Notice*

This document and its contents have been prepared and are intended solely for Croft Associates' information and use in relation to the licence application for the 3977 A HS Transport Container.

Atkins Limited assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents.

This document has 24 pages including the cover.

Document history Job number: 5163778 Document ref: 5163778-HS-REP-001 Revision Purpose description Originated Checked Reviewed Authorised Draft OOA Issued for Client comment BW / AH AC AC BW 001 Formal Issue BW /AH AC AC BW Client signoff Client Croft Associates Project 3977 A SAFKEG Type B Transport Package Shielding Assessment Document title HS Container Shielding Assessment with Thorium Target Job no.

5163778 Copy no.

1 Document 5163778-HS-REP-001-001 reference Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 I 12 March 2018 15163778 COM~1ERCIAL "4 C0Pffl9EP4CE Date 09/03/18 12/03/18

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Table of contents Chapter Pages

1.

Introduction 4

2.

Shielding Assessment Specification 4

3.

Model Derivation 4

3.1.

MCNP 4

3.2.

MCNP Geometry Definition 4

3.3.

Materials Definition 6

3.4.

Tally Definitions 6

3.5.

Source Derivation 7

3.6.

Nuclear Data Library 8

3.7.

Fluence to Dose Rate Conversion 8

4.

Dose Rate Assessment 9

4.1.

Scoping Results 9

4.2.

Detailed Results 9

4.3.

Cross-Check Calculations and Results 10

5.

Conclusions 11

6.

References 11

7.

Tables 12

8.

Figures 18 Tables Table 7-1 Table 7-2 Table 7-3 Table 7-4 Table 7-5 Table 7-6 Table 7-7 Table 7-8 Table 7-9 Table 7-10 Table 7-11 List of Radionuclides Assessed............................................................................................... 12 Figures Figure 8-1 Figure 8-2 Figure 8-3 Figure 8-4 Figure 8-5 Figure 8-6 Figure 8-7 Figure 8-8 Figure 8-9 Figure 8-10 Figure 8-11 Approximate Bulk Thicknesses for the SAFKEG-HS Outer Keg Materials............................. 12 Approximate Bulk Thicknesses for the SAFKEG-HS CV Materials......................................... 13 Materials Definitions................................................................................................................ 13 List of Radionuclides Progressed for Bremsstrahlung Assessment........................................ 14 Fluence to Dose Conversions Factors Derived from ANS 6.1.1 Coefficients......................... 14 Results from Initial Scoping Calculations................................................................................ 15 Results from Detailed Calculations.......................................................................................... 16 Contributions to Dose Rate...................................................................................................... 17 Cross-Check Against External Assessment [17]..................................................................... 17 Comparison between ICRP-107 Line Energies and ORIGEN 47-Group Energies................. 17 SAFKEG-HS Outer Keg CAD drawing [3]

MCNP Visualisation of the SAFKEG-HS Outer Keg SAFKEG-HS CV CAD drawing [5]

MCNP Visualisation of the SAFKEG-HS CV MCNP Visualisation of the SAFKEG-HS Complete Geometry MCNP Visualisation of the SAFKEG-HS Cut Down Model Tally Visualisation - above and below the package Tally Visualisation - package side Tally Visualisation - below packge (detailed calculations)

ANS 6.1.1-1977 Flux-to-Dose Coefficients Calculations Extract Scoping Results Visualisation - Kr-88 18 19 19 20 20 21 21 21 22 22 23 Atkins Shielding Assessment of the 3977A SAFKEG Type B Transport Package I Version 1.0 I 12 March 201815163778 COMMERCIAL 1~4 COPfflDDJCE

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package

1.

Introduction The SAFKEG-HS transport package (Design No. 3977A) is designed as a reusable Type B package for the shipment of solid and liquid radioactive materials.

There is a requirement to use this package to transport an activated thorium target which is contained within a thin lnconel housing.

This report outlines the assessment undertaken to determine the maximum allowed activities (which meet the surface dose rate criteria of < 2 mSv/h) for a series of individual radionuclides.

This report details the specification for the assessment, input parameters, model assumptions and results of the calculations performed, followed by a discussion.

2.

Shielding Assessment Specification The 3977A Type B SAFKEG-HS package is required to contain a thorium target consisting of a radioactive thorium disc surrounded by a thin lnconel housing. The source contains a host of radionuclides present in both the thorium disc and the lnconel housing. These radionuclides are listed in Table 7-1 and were provided by Reference [1 ].

The scope of the investigation is to assess the peak package surface dose rate for 1 Ci of each individual radionuclide and then to determine the maximum activity of each radionuclide that could be present, with the peak surface dose rate remaining below 2 mSv/h.

In this assessment all package items will be centrally located and no assessment of normal or accident conditions of transport will be undertaken.

All radionuclides are to be modelled separately (each with an activity of 1 Ci) and no combined sources will be considered.

A scoping assessment was undertaken to determine the peak dose rate location (either top, side or bottom) with subsequent detailed calculations focussing on the peak dose rate region.

Some of the radionuclides being assessed emit both gamma and beta radiation. A high-level scoping assessment was undertaken to determine the significance of beta emissions (producing bremsstrahlung photons) on the surface dose rates, with only potentially significant contributors progressed to formal calculation.

3.

Model Derivation 3.1.

MCNP All calculations were undertaken using the Monte-Carlo radiation transport software MCNP - Version 6.1 (Ref. [2]).

3.2.

MCNP Geometry Definition A series of CAD drawings of the SAFKEG-HS package (Design no. 3977A) have been provided by Croft Associates (Refs. [3], [4], (5], [6]). Using these drawings, a 30 model of the 3977 A SAFKEG-HS container was reproduced in MCNP. The main model constituents are described in the following sections:

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package 3.2.1.

SAFKEG-HS Outer Keg The outer keg is made up of a steel structure, within which is the outer cork packing. The definitions of these materials are given in Section 3.3. There is an air gap between the outer cork packing and the inner cork packing, which houses the Containment Vessel (CV). The following assumptions and simplifications were made in modelling the outer keg:

Nuts and bolts were omitted; The 2x2 cm square cross-section tubing at either end of the container has not been modelled; The lid handles were omitted; The low melting point alloy bar at the bottom of the container was modelled as 0.2 cm thick and horizontal for the length of the bar, opposed to a 0.4 cm thick central section 0.2 cm thick outer sections, as a conservative assumption; The lid was modelled as a 0.2 cm thick horizontal bar, opposed to the 0.6 cm thick central section with 0.2 cm thick outer sections, as a conservative assumption.

The CAD drawing provided by Croft Associates for the SAFKEG-HS Outer Keg geometry is shown in Figure 8-1, with the dimensions illustrated on the drawing (Ref. [3]). A visualisation of the SAFKEG-HS Outer Keg geometry model produced in MCNP is shown in Figure 8-2.

The bulk thicknesses of each material used in the Outer Keg are shown in Table 7-2.

3.2.2.

SAFKEG-HS Containment Vessel (CV)

The CV is made up of a steel structure with depleted uranium (OU) internal shielding. The definitions of these materials are given in Section 3.3. The following assumptions and simplifications were made when modelling the CV:

The air gap between the steel structure and the DU shielding was modelled as 0.75 cm for the length of the air gap, opposed to thinning to 0.25 cm, as a conservative assumption; The left and right screw holes at the top of the CV were omitted as they would be filled with screws In the completed structure; The central screw hole below the central DU in the stainless steel was modelled as square, with the triangular section of the screw hole omitted.

The CAD file of the CV (Ref. [6]) illustrates tungsten inserts and a stainless-steel flask within the cavity inside the steel structure and DU internal shielding; however, these will not be present in the SAFKEG-HS CV considered in this assessment. There will be aluminium spacers present within the CV to restrict the movement of the target source disc; however, the design of these has not been confirmed and these have been omitted as they are likely to have limited impact with respect to shielding. Therefore, for the purpose of this assessment, the CV is modelled as empty with the exception of the target source.

The CAD drawing provided by Croft Associates for the SAFKEG-HS CV geometry is shown in Figure 8-3 (Ref. [5]). A visualisation of the SAFKEG-HS CV geometry model produced in MCNP is shown in Figure 8-4.

The bulk thicknesses of each material used in the CV are shown in Table 7-3.

3.2.3.

Thorium Target Source The thorium target source (housed within lnconel) is located 6 cm from the bottom of CV cavity. This source is a cylindrical disc of thorium with radius 3 cm and height 0.5 cm, surrounded by a 0.1 cm thick lnconel housing, as illustrated in the drawing provided by Croft Associates (Ref. [7)).

3.2.4.

SAFKEG-HS Complete Model The CV was modelled to fit inside the Outer Keg to produce a complete model of the SAFKEG-HS geometry, as illustrated in Figure 8-5.

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package 3.2.5.

SAFKEG-HS Cut Down Model Following initial scoping calculations, the peak dose rates were found to be at the bottom of the container. In order make the calculations more efficient, the MCNP model was subsequently cut down to focus on this bottom region. This is illustrated in Figure 8-6.

3.3.

Materials Definition The materials utilised in the SAFKEG-HS MCNP model are outlined in Table 7-4. The material properties for dry air, stainless steel, thorium and lnconel were extracted directly from the references given in Table 7-4.

The mass fractions for each of cork's elemental substituents were obtained by first extracting the atomic density from Reference [8), converting the atomic density to units of atoms/cm 2 and then to an atomic fraction. The mass fraction for each element was then calculated using the known mass of each element. The density of cork in Reference [9) is given as 280 +/- 50 kg/m3, therefore; to be conservative, the lower bound of 230 kg/m 3 was used in this model.

Depleted uranium is alloyed with 2% molybdenum, which is reflected in the mass fraction. The density was extracted directly from the reference given in Table 7-4.

3.4.

Tally Definitions Tally locations were defined within the MCNP models to calculate the fluence (and subsequent dose rates) at areas of interest. Different tallies were employed for initial scoping calculations than were used for the final detailed calculations. These are described in the following sections:

3.4.1.

Scoping Calculations For the initial scoping calculations, tallies were setup to cover two aspects. One aspect was to calculate the overall location of the peak surface dose rate (i.e. top, side or bottom). The second was to take the opportunity to identify any areas where specific design details had significant impact on localised dose rates.

3.4.1.1.

Above & Below the Package The tallies above and below the package are modelled to be square grids covering the circular package's entire surface area. The grid is 21 cm x 21 cm wide and has a height of 1 cm. This grid is subdivided via 42 equal intervals in both the X and Y-directions.

The 'Above Package' tallies are located just above the package lid (at a height of 53.2 cm from the bottom of the model}.

The 'Below Package' tallies are located just below the horizontal steel base of the package (at a height of 6 cm from the bottom of the model).

These tallies are illustrated in Figures 8-7.

3.4.1.2.

Package Side Two sets of tallies are used to calculate dose rates to the side of the package, which extend up opposite sides of the package. Each contain forty-six 1 x 1 x 1 cm deep tallies running from the steel bottom of the package up to the top of the lid. These tallies are illustrated in Figure 8-8.

3.4.2.

Detailed Calculations The scoping calculations identified that the peak surface dose rate was located at the bottom of the package (directly underneath the disc source).

The scoping calculations also gave confidence that there were no areas of concern with respect to local effects of lesser shielding dramatically impacting the dose rates.

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package New tallies were arranged for the detailed calculations, focussing on the bottom of the package whilst also accounting for the size of the package and the size of any potential dose rate detector used to take measurements.

This led to the definition of 5 tallies: 1 central disc of radius 2.5 cm and 4 annuli with outer radii 5, 10, 15 and 18.92 cm respectively.

These tallies are appropriately sized to allow for efficient calculations to be undertaken whilst also providing a dose rate output that displays the fall off outwards from the centre and that is appropriate if used, at a later date, in comparison with measurements.

These tallies are illustrated in Figure 8-9.

3.5.

Source Derivation A list of the radionuclide sources has been provided by Croft Associates and has been previously discussed in Table 7-1. All sources were modelled at an activity of 1 Ci (37 GBq).

The dose rates associated with these sources will most often be dominated by the emission of primary photons.

However, the decay of many of the radionuclides also involves the emission of beta particles. As the radionuclides are based in a high Z material (thorium), the emission of these beta particles means that there is also the potential for a contribution to dose rates from bremsstrahlung radiation.

3.5.1.

Primary Gamma Sources All of the radionuclides being investigated emit primary/direct gamma radiation with the exception of Pb-209 and Sn-121 (dose rates for these two radionuclides will be only generated by bremsstrahlung photons).

Gamma line emission data for the 55 radionuclides that produce primary gamma radiation has been used from ICRP-107 (Ref. [101), which was extracted via Radiological Toolbox (Ref [11]).

3.5.2.

Bremsstrahlung Sources Some of the radionuclides being assessed decay via the emission of a beta (electron) particle (along with an associated antineutrino). The total energy released via this process (Q-value) is shared across both particles.

The overall output is a continuous energy spectrum of electrons energies being released (up to the Q-value) which is dependent on the specific radionuclide involved. The mean beta particle energy is typically of the order of 1/3 of the maximum Q-energy.

Following emission, the beta particle loses kinetic energy via interactions with local charged particles and hence slows down. This loss of energy is conserved via photon emission - called bremsstrahlung radiation.

The energy of the gamma photon emitted is proportional to the energy of the electron and the Z value of the surrounding material (as beta energy spectrum is continuous, so is the bremsstrahlung radiation spectrum). In most shielding scenarios, only a small fraction (a few%) of the beta energy is converted to a bremsstrahlung photon.

The significance of the bremsstrahlung radiation is very much dependent upon the beta spectrum (considering the mean and maximum beta particles energies) when compared with the primary gamma emission energies for each radionuclide decay. In most cases, the primary gamma radiation is more numerous and penetrating than bremsstrahlung and hence dominates, except for those radionuclides that are pure beta-emitters.

There are 4 radionuclides that do not emit beta particles and hence no bremsstrahlung investigation is required.

There are 2 radionuclides that are pure beta emitters (Pb-209 and Sn-121) and hence bremsstrahlung radiation will need to be modelled as this is the only contribution to dose rate.

The remaining 51 radionuclides have undergone high-level screening to determine those whose beta spectrum are likely to have a significant dose rate contribution and were therefore worth pursuing.

Atkins Shielding Assessment of the 3977A SAFKEG Type 8 Transport Package I Version 1.0 112 March 2018 15163778 COJ'tJ1J'tJ1EROIAL !Pd CotfflDENCE 7 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package This screening involved comparing the mean and peak beta energies with the corresponding gamma energy emissions (and yields).

The beta spectrum information was obtained from ICRP-107 data (and supported by ICRP-38 data (Ref (12]),

where other data was not readily accessible}.

Where the gamma energies (taking into consideration decay yields} were above the peak and mean beta energies then these radionuclides were immediately screened out -

as the dose rates would be totally dominated by the primary gamma emissions.

Where the gamma energies (and associated yields} were of order of / lower than the beta energies then these radionuclides were continued for further bremsstrahlung investigation.

Whilst it was likely ( considering that only a small fraction of the beta energies are actually converted to photons) that many of the nuclides that had passed the screening would still not have significant contribution from bremsstrahlung radiation, these were still progressed for completeness to ensure that this contribution was covered via this assessment.

As a further check and in support of the screening process, the software code ORIGEN-ARP (Ref. (13]) was also used to assess the significance of bremsstrahlung photons (from interactions with U02) compared to the primary gamma decay emissions.

As a result of this screening there are 13 radionuclides (including the 2 sole beta emitters) that have been progressed for bremsstrahlung contributions. These radionuclides are presented in Table 7-5.

ICRP-107 data was used to generate beta spectra (uniform 20-group structure) for each of the radionuclides being assessed. Each beta spectra was input into MCNP models from which the tra11sport code subsequently generated bremsstrahlung photons (via modelling the beta interactions) and transported the photons thorough the remaining model geometry to the dose rate tallies.

The only exception to this was Kr-85m (where the beta spectra data was not available), which had its bremsstrahlung contribution calculated using an ORIGEN-ARP photon source derived in a standard SCALE-47 energy group structure. This was considered appropriate considering that it is expected that the dose rate will be dominated by the primary gamma emissions.

3.6.

Nuclear Data Library Nuclear data was taken from the ENDF/B-VII Photoatomic Data Library (Ref. [141).

3.7.

Fluence to Dose Rate Conversion All calculations have used fluence to dose conversion factors for gamma radiation derived from ANS 6.1.1 1977 (Ref. (15)). Figure 8-10 shows the method used for the coefficient calculation.

The photon energies used to derive the coefficients are the same as ICRP116 (Ref. (16)) and are shown, along with the corresponding calculated fluence to dose conversion factor, in Table 7-6.

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package

4.

Dose Rate Assessment 4.1.

Scoping Results As discussed previously, a scoping assessment was undertaken to determine the overarching location of the peak surface dose rate.

A selection of the radionuclides (modelled at an activity of 1 Ci) were used to calculate the dose rates above, to the side of and below the transport package. The radionuclides chosen were those emitting a higher proportion of higher energy photons; allowing for the calculation of dose rates in a more time efficient manner.

The results of the scoping calculations are found below in Table 7-7:

4.1.1.

Discussion of Scoping Results Table 7-7 clearly shows that the peak surface dose rate is located below the package. The calculations for all radionuclides (both for gamma and beta contributions) were therefore focussed on the bottom region of the package.

The dose rate results for the top, side and bottom meshes for Kr-88 have been visualised and presented in Figure 8-11. This figure clearly shows the peak dose rates being present at the bottom of the package and shows how the dose rates vary along the height of the package and across the top.

The other radionuclides assessed in this scoping section show similar results to the Kr-88.

4.2.

Detailed Results Table 7-8 provides the peak surface dose rate (based on 1 Ci activity) for each of the radionuclides investigated along with the associated maximum activity that would allow the peak surface dose rate to remain within 2 mSv/h.

4.2.1.

Discussion of Detailed Results A number of radionuclides investigated had low gamma and beta emission energies that it was not efficient to transport these particles through a complete package model (i.e. with full amounts of shielding). These radionuclides are highlighted in Table 7-8.

Because of these low energies the 3977 A transport package would be able to host large activities of these radionuclides before nearing the 2 mSv/h surface dose rate limit. In order to provide a maximum activity that would effectively bound proposed contents, dose rates inside of the package were determined (these were calculated much more efficiently) and used to determine activity limits.

The dose rate locations used for determining maximum activity for each of the relevant radionuclide was as follows:

Fe-55 & Kr-83m-at the bottom of the CV, i.e. no additional shielding beyond the targeUhousing self-shielding Pa-229 & Sn-121 - directly underneath the complete steel CV thickness (0.31 cm)

Pd-112 - directly underneath 0.01 cm of the steel CV thickness Pb-209, Tc-99m, Te-132 & Th-231 - directly underneath 0.5 cm of the depleted uranium thickness Because surface dose rates will always be significantly less than the dose rate calculated for these particular isotopes, the associated maximum activities reported via this assessment are very conservative. This assessment strategy has been agreed with Croft Associates as being appropriate as the maximum activities quoted are orders of magnitudes higher than those being planned to be transported.

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package 4.2.1.1.

Importance of Bremsstrahlung Radiation Table 7-9 presents the dose rate contribution from bremsstrahlung radiation of those radionuclldes investigated. It shows that for the majority of the radionuclides the primary gamma emission dominates the dose rate. The exception to this is Te-127, where bremsstrahlung photons contributed 60% of the peak surface dose rate. It is worth noting that there were significant bremsstrahlung contributions to dose rate for Br-83, Ag-111 and Pd-109.

Pb-209 and Sn-121 are sole beta emitters and hence 100% of the dose contribution is from bremsstrahlung photons.

4.3.

Cross-Check Calculations and Results A number of cross checks have been undertaken to give confidence in the main assessment's output results.

4.3.1.

Model & Materials Geometry A previous assessment of the 3977 A Package has been undertaken that considered the transport of a Cs-137 source (Ref. [17]) using the Monte Carlo radiation transport code MCBEND. As a cross check, the model generated as part of this assessment was aligned (where appropriate) to match this previous assessment.

This included:

3000 Ci Cs-137 source (modelled as a point source), located at the bottom of the CV cavity; Cork packaging modelled as void; 5 cm disc and 10, 15 & 18.925 cm annuli dose rate tally regions; ICRP-74 dose rate conversion factor utilised.

The result of this cross-check calculation and comparison to Reference [17] is presented in Table 7-10.

Considering that there will still be differences between the two comparison models (the exact model detail of the previous assessment is not available in the main report - Ref [17]) and that there are statistical errors of up to -5% on each of the sets of calculations, the cross-check results give confidence in the accuracy of the geometry and materials of this assessment.

4.3.2.

ICRP-107 Gamma Line Energy Data To cross check the source terms used in the model, the dose rates produced by the model using the ICRP-107 line energies for a selection of radionuclides were compared to the dose rates using the source produced by ORIGEN in the SCALE6 47-Group structure. The results of this cross-check can be found in Table 7-11.

Good agreement between to the two source model methods is found across most radionuclides. There were three exceptions. Br-83, Te-127 and Th-231-further investigation showed that the ORIGEN 47-Group photon energy structure did not accurately represent the peak line energies from these isotopes. The energy structure was suitably refined to more appropriate model these line energies and the results matched the original ICRP-107 results well.

These results give confidence in the source generations methods used in this assessment.

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HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package

5.

Conclusions An assessment of the 3977A SAFKEG-HS transport package containing a thorium target source has been undertaken. 57 specified radionuclides present in the thorium disc and lnconel housing have been independently investigated with peak surface dose rates for 1 Ci and associated maximum activities (to remain within a 2 mSv/h limit) reported.

The assessment includes calculations to determine dose rate contributions from both primary and secondary (bremsstrahlung) photons.

A number of cross-checks have been undertaken and reported which give confidence in the main report results.

6.
1.
2.
3.
4.
5.
6.
7.
8.
9.

References Email, "RE: non-disclosure agreement", Croft Associates, 09 January 2018 LA-CP-13-00634, "MCNP6, Version 1 ", Los Alamos National Laboratory, May 2013 OC-5949, "SAFKEG HS Construction", Issue A, Croft Associates, October 2009 1 C-5997, "Containment Vessel HS Lid Construction", Issue A, Croft Associates, October 2009 1 C-5999, "Containment Vessel HS Body Construction", Issue A. Croft Associates, October 2009 Electronic CAD File, "i2031 d.dwg", Croft Associates, provided January 2018 Sketch, 3799A-Thorium Target and Spacers 001.jpg", Croft Associates, provided January 2018 CTR95/18, "Summary of Physical Properties and Composition of Resin Bonded Cork", Issue A, Croft Associates, March 1997 CM063-D, "Material Specification for Resin Bonded Composition Cork", Issue E, Croft Associates, March 2013

10. ICRP Publication 107, "Nuclear Decay Data for Dosimetric Calculations",lnternational Commission on Radiological Protection, 2008
11. Radiological Toolbox - Version 3.0.0, ORNL, April 2013
12. ICRP Publication 38, "Radionuclide Transformations Energy and Intensity of Emissions",International Commission on Radiological Protection, 1983
13. ORIGEN-ARP (SCALE Version 6.1 ): Automatic Rapid Process for Spent Fuel Depletion, Decay and Source Term Analysis, ORNL, 2011
14. ENDF/B-Vll.1, National Nuclear Data Center Released December 22, 2011
15. ANSI/ANS 6.1.1-1977, "Neutron and Gamma-Ray Fluence-to-Dose Factors", American Nuclear Society, 1977
16. ICRP Publication 116, "Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposures",lnternational Commission on Radiological Protection, 2010
17. AMEC/SF6652/001, "Monte Carlo Modelling of Safkeg HS", Issue 2. Amee, August 2013
18. PIET-43741-TM-963, PNNL-15870, "Compendium of Material Composition Data for Radiation Transport Modelling", Rev. 1, PNNL, March 2011
19. Email. "RE: 3977A-Materials Spec", Croft Associates, 15 January 2018 Atkins Shielding Assessment of the 3977A SAFKEG Type B Transport Package I Version 1.0 112 March 2018 15163778 COMMERCIAL IPd COPdflDErdCE 11 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package

7.

Tables Table 7-1 List of Radionuclides Assessed Present in Present in the Thorium Target lnconel Housing Ac-225 Kr-83m Ru-105 Co-55 Ac-226 Kr-85m Sb-127 Co-56 Ac-228 Kr-87 Sb-128 Cr-51 Ag-111 Kr-88 Sb-129 Fe-55 Ag-112 La-141 Sn-121 Mn-52 Ag-113 La-142 Sr-91 Mn-54 Br-83 Mo-99 Sr-92 Mn-56 Cd-115 Nb-96 Tc-99m Ni-56 Cd-117 Pa-228 Te-127 Ni-57 Ce-143 Pa-229 Te-132 V-48 1-130 Pa-232 Th-231 1-132 Pb-209 Xe-135 1-133 Pd-109 Y-92 1-135 Pd-112 Y-93 ln-115m Pr-145 Zr-97 ln-117m Rh-105 Table 7-2 Approximate Bulk Thicknesses for the SAFKEG-HS Outer Keg Materials Material Bulk Thickness (cm)

Stainless Steel (Sides) 0.20 Stainless Steel (Bottom) 0.60 Cork (Sides) 5.90 Cork (Bottom) 6.75 Cork {Lid) 8.45 Air Gap 0.25 Atkins Shielding Assessment of the 3977A SAFKEG Type B Transport Package I Version 1.0 I 12 March 2018 I 5163778 COMMERCIAL IP~ cormorncc 12 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Table 7-3 Approximate Bulk Thicknesses for the SAFKEG-HS CV Materials Material Bulk Thickness (cm)

Stainless Steel (Sides) 0.30 Stainless Steel (Bottom) 0.60 Stainless Steel (Top) 4.69 Depleted Uranium (Sides) 4.76 Depleted Uranium (Bottom) 4.60 Depleted Uranium (Top) 4.58 Air Gap 0.07 Table 7-4 Materials Definitions Material Mass Fraction Density (g/cm3)

Reference Dry Air (near sea level) 0.000124 C 0.001205 Reference [18]

0.755268 N 0.231781 0 0.012827 Ar Stainless Steel (304L) 0.000150 C 8.000000 Reference [18]

0.005000 Si 0.000230 P 0.000150 S 0.190000 Cr 0.010000 Mn 0.694480 Fe 0.100000 Ni Thorium Metal 1.000000 Th 11.72000 Reference [18]

lnconel (Type 625) 0.007500 H 2.320000 Reference [18]

0.055200 C 0.000200 N 0.484900 0 0.006300 Na 0.012500 Mg 0.021700 Al 0.155000 Si 0.001900 S 0.013700 K 0.230000 Ca 0.001000 Ti 0.1 0100 Fe Cork 0.06174 H 0.230000 References [8] &

0.44452 C

[9]

0.49374 0 Depleted Uranium 0.98000 U 18.00000 Reference 19 (alloyed with 2%

0.02000 Mo Molybdenum)

Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 j 12 March 2018 J 5163778 COMMERCIAL It~ COtfflDDJCE 13 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Table 7-5 List of Radionuclides Progressed for Bremsstrahlung Assessment Radionuclides Ag-111 Kr-85m I La-141 I Pd-109 I Sn-121 I Th-231 Y-93 Br-83 Kr-87 I Pb-209 I Pr-145 I Te-127 I Y-92 Table 7-6 Fluence to Dose Conversions Factors Derived from ANS 6.1.1 Coefficients Conversion Factor Conversion Factor Energy

( mrem/hr)/( photons/cm2-s)

(µSv/hr)/( photons/cm2-s}

0.010 3.96E-03 3.96E-02 0.0150 1.95E-03 1.95E-02 0.020 1.18E-03 1.18E-02 0.030 5.82E-04 5.82E-03 0.040 3.61E-04 3.61 E-03 0.050 2.90E-04 2.90E-03 0.060 2.65E-04 2.65E-03 0.070 2.58E-04 2.58E-03 0.080 2.61 E-04 2.61E-03 0.100 2.83E-04 2.83E-03 0.150 3.79E-04 3.79E-03 0.200 5.01 E-04 5.01 E-03 0.300 7.59E-04 7.59E-03 0.400 9.85E-04 9.85E-03 0.500 1.18E-03 1.18E-02 0.511 1.20E-03 1.20E-02 0.600 1.36E-03 1.36E-02 0.662 1.46E-03 1.46E-02 0.800 1.68E-03 1.68E-02 1.000 1.98E-03 1.98E-02 1.1 17 2.14E-03 2.14E-02 1.330 2.42E-03 2.42E-02 1.500 2.64E-03 2.64E-02 2.000 3.21 E-03 3.21 E-02 3.000 4.19E-03 4.19E-02 4.000 5.03E-03 5.03E-02 5.000 5.82E-03 5.82E-02 6.000 6.56E-03 6.56E-02 6.129 6.65E-03 6.65E-02 8.000 8.03E-03 8.03E-02 10.000 9.51 E-03 9.51 E-02 15.000 1.33E-02 1.33E-01 Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package J Version 1.0 J 12 March 2018 J 5163778 COMMERCIAL It~ cmmDENGE 14 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Table 7-7 Results from Initial Scoping Calculations Peak Dose Rate (mSv/h)@ 1 er Activity Radionuclide Peak Location Above Side of Below Package Package Package Thorium Target Ac-228 0.09 0.23 0.42 Below Package 1-135 0.39 1.14 1.96 Below Package Kr-88 1.19 3.24 5.32 Below Package La-142 1.31 3.51 5.80 Below Package Sb-129 0.19 0.53 0.94 Below Package Y-93 0.03 0.08 0.13 Below Package lnconel Housing Co-56 1.27 4.45 5.82 Below Package Mn-56 0.50 1.84 2.43 Below Package Ni-56 0.09 0.33 0.46 Below Package Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 I 12 March 2018 I 5163778 COMMERCIAL II~ cmmorncE 15 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Table 7-8 Results from Detailed Calculations Radionuclide Peak Dose Rate Max Activity (Ci}

Radionuclide Peak Dose Rate Max Activity (Ci)

(mSv/hr per Ci)

< 2 mSv/hr hmit (mSv/hr per Ci)

< 2 mSv/hr lfmit Thorium Target Ac-225 1.38E-06 1.45E+06 Pa-228 6.29E-01 3.18E+OO Ac-226 5.41E-07 3.70E+06 Pa-229*

3.92E-02 5.10E+01 Ac-228 3.62E-01 5.53E+OO Pa-232 1.09E-01 1,83E+01 Ag-111 5.87E-06 3.40E+05 Pb-209*

5.39E-03 3.71 E+02 Ag-112 7.18E-01 2.78E+OO Pd-109 6.27E-06 3.19E+05 Ag-113 6.73E-03 2.97E+02 Pd-112*

6.40E-03 3.13E+02 Br-83 1.30E-06 1.54E+06 Pr-145 3.82E-03 5.23E+02 Cd-115 1.04E-05 1.93E+05 Rh-105 7.88E-11 2.54E+10 Cd-117 9.70E-01 2.06E+OO Ru-105 2.31 E-02 8.67E+01 Ce-143 4.18E-03 4.79E+02 Sb-127 1.51 E-02 1.33E+02 1-130 1.16E-01 1.72E+01 Sb-128 2.47E-01 8.09E+OO 1-132 5.63E-01 3.55E+OO Sb-129 8.46E-01 2.36E+OO 1-133 5.36E-02 3.73E+01 Sn-121 6.85E-02 2.92E+01 1-135 1.79E+OO 1.12E+OO Sr-91 1.61 E-01 1.24E+01 ln-115m 3.36E-09 5.96E+08 Sr-92 1.55E+OO 1.29E+OO ln-117m 4.84E-05 4.13E+04 Tc-99m*

2.21 E-06 9.05E+05 Kr-83m*

7.86E-04 2.54E+03 Te-127 3.0?E-09 7.23E+08 Kr-85m 9.02E-07 2.22E+06 Te-132*

8.52E-03 2.35E+02 Kr-87 1.49E+OO 1.35E+OO Th-231*

7.18E-05 2.79E+04 Kr-88 4.72E+OO 4.23E-01 Xe-135 6.72E-05 2.98E+04 La-141 4.0?E-02 4.92E+01 Y-92 1.68E-01 1.19E+01 La-142 5.25E+OO 3.81 E-01 Y-93 1.32E-01 1.52E+01 Mo-99 2.78E-03 7.19E+02 Zr-97 1.26E-01 1.59E+01 Nb-96 5.22E-01 3.83E+OO lnconel Housing Co-55 6.08E-01 3.29E+OO Mn-54 4.89E-02 4.09E+01 Co-56 5.31E+OO 3.77E-01 Mn-56 2.13E+OO 9.38E-01 Cr-51 8.19E-1 6 2.44E+15 Ni-56 4.06E-01 4.93E+OO Fe-55*

2.32E-07 8.62E+06 Ni-57 2.17E+OO 9.20E-01 Mn-52 2.29E+OO 8.73E-01 V-48 1.68E+OO 1.19E+OO

  • These radionuclides have such low energy primary gamma / bremsstrahlung gamma emissions that modelling the transport of these photons through the high density shielding was determined to be too inefficient (with respect to time and effort). Conservative dose rates were calculated and maximum activity limits derived for these radionuclides via modelling reduced shielding {allowing for more efficient transport modelling).

Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 I 12 March 2018 I 5163778 COMMERCIAL IPd CONFIDEPWE 16 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Table 7-9 Contributions to Dose Rate Peak Dose Rate Primary Gamma Bremsstrahlung Radionuclide (mSv/hr per Ci)

Contribution(%)

Contribution (%)

Ag-111 5.87E-06 72%

28%

Br-83 1.30E-06 68%

32%

Kr-85m 9.02E-07 86%

14%

Kr-87 1.49E+OO 98%

2%

La-141 4.0?E-02 88%

12%

Pd-109 6.27E-06 75%

25%

Pr-145 3.82E-03 87%

13%

Te-127 3.07E-09 40%

60%

Th-231 7.18E-05 100%

0% (0.2%)

Y-92 1.68E-01 78%

22%

Y-93 1.32E-01 89%

11%

Table 7-10 Cross-Check Against External Assessment [17]

Peak Dose Rate - mSv/hr

% Difference Source (ti. I Ref [17])

Cross Check Ref [17) 3 kCi Cs-137 11.44 14.50 21 Table 7-11 Comparison between ICRP-107 Line Energies and ORIGEN 47-Group Energies Radionuclide Peak Dose Rate (µSv/hr per Ci)

% Difference ICRP-107 ORIGEN 47 Group (A/ ICRP-107)

Thorium Target Ag-111 4.25E-03 4.05E-03 5

Br-83 8.83E-04 2.37E-03 168*

Kr-85m 7.77E-04 1.09E-03 41 Kr-87 1.46E+03 1.49E+03 2

La-141 3.57E+01 3.79E+01 6

Pd-109 4.?0E-03 4.55E-03 3

Pr-145 3.32E+OO 3.30E+OO 1

Te-127 1.23E-06 3.68E-06 200*

Th-231 7.17E-02 2.30E-01 220*

Y-92 1.31 E+02 1.30E+02 1

Y-93 1.17E+02 1.16E+02 1

  • Poor agreement was due to the 47-Group energy structure not accurately representing peak energy lines for Br-83, Te-127 and Th-231.

Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 J 12 March 2018 15163778 COMMERCIAL 1~4 CONFID04GE 17of24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package

8.

Figures Figure 8-1 SAFKEG-HS Outer Keg CAD drawing [3]

SECURITY-RELATED INFORMATION FIGURE WITHHELD UNDER 10 CFR 2.390 Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 I 12 March 2018 15163778 COMMERCIAL 11~-CONFIDENCE 18 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Figure 8-2 MCNP Visualisation of the SAFKEG-HS Outer Keg Components in green are stainless steel, components in red are cork and blue areas are air.

Figure 8-3 SAFKEG-HS CV CAD drawing [5)

SECURITY-RELATED INFORMATION FIGURE WITHHELD UNDER 10 CFR 2.390 Atkins Shielding Assessment of the 3977A SAFKEG Type B Transport Package I Version 1.0 112 March 2018 I 5163778 COMMERCIAL I~~ CONFIDENCE 19 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Figure 8-4 MCNP Visualisation of the SAFKEG-HS CV Components in light blue are stainless steel, components in red are depleted uranium, the surrounding orange components are the cork of the Outer Keg, components in green are thorium, components in yellow are lnconel and blue areas are air.

Figure 8-5 MCNP Visualisation of the SAFKEG-HS Complete Geometry Components in light blue are stainless steel, components in red are depleted uranium, components in orange are cork, components in light green are thorium, components in yellow are lnconel and blue areas are air.

Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 112 March 2018 j 5163778 CO~IMERCIAL It~ C0tff1DD4CE 20 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Figure 8-6 MCNP Visualisation of the SAFKEG-HS Cut Down Model Components in light blue are stainless steel, components in red are depleted uranium, components in orange are cork, components in light green are thorium, components in yellow are lnconel and blue areas are air.

Figure 8-7 Tally Visualisation - above and below the package The figure on the left shows the tallies in the x-z plane and the figure on the right shows a cut through the model above the package in the x-y plane.

/

I l J ' r--s II II II If 1;

r, I~ J l's.

/

/

Figure 8-8 Tally Visualisation - package side Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package I Version 1.0 112 March 201 8 I 5163778 COMMERCIAL IN cormorncG=

21 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977A SAFKEG Type B Transport Package Figure 8-9 Tally Visualisation - below packge (detailed calculations) 1"

/1

/

sos I 504 I sM J,;O?J 501 lso2I sM I 504 I,;ns Figure 8-10 ANS 6.1.1-1977 Flux-to-Dose Coefficients Calculations Extract Gamma-Ray-Flux-to-Dose-Rate Convenion Facto1*s. Polynomial Coefficients in Analytic fit -

  • ht OF 11 (Ii!) = A +.H X + C xz + D.x,3.

DF11 (E) -

(re1n/ha-)/(JJhoLous/cw 2-lj), E = Photon energy in MeV, uml X = lu E Photon Energy (MeV)

A B

C D

0.01 to 0.03

-2.0477 +01

-1.7464 0.03 to 0.6

-1.3626 +01

- 6.7117-01

-1.0954

- 2.4897 - 01 0.fi to 6.0

-1.3133 +01 7.2008-.01

-3.3603-0i 6.0 to 16.0

-1.2791 +01 2.8309-01 1.0873 - 01 Atkins Shielding Assessment of the 3977A SAFKEG Type B Transport Package I Version 1.0 112 March 2018 15163778 66,MMERGIAL IN 60Pff1DE~JGE 22 of 24

HS Container Shielding Assessment with Thorium Target Shielding Assessment of the 3977 A SAFKEG Type B Transport Package Figure 8-11 Scoping Results Visualisation - Kr-88 Atkins Shielding Assessment of the 3977 A SAFKEG Type B Transport Package J Version 1.0 J 12 March 2018 J 5163778 COMMERCIAL Ir~ C0tff1DD4GE 23 of 24

Ben Williamson Atkins Chadwick House Birchwood Park Warrington WA3 6AE

' C011,111,1ERCIAL IN COPdFIDEPJCE '

Benjamin. Will iamson@atkin sglobal.com

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