5.2.4.7 Conocimiento de los padres sobre los intereses de la elección de la especialidad de sus hijos/ representantes.
5.2.5 LA FAMILIA FRENTE A LOS ESTUDIOS COMPLEMENTARIOS
RADIONUCLIDE SCREENING
A total of 31 radionuclides have been identified for consideration in the GSA (see Section 3.1.1). The maximum inventory found across all the countries considered is given in Table 30, which also provides the half-life for each radionuclide. It is assumed for the purposes of the screening calculations that the total inventory is distributed evenly over the 50 capsules disposed in the borehole.
For reasons of practicality, it is desirable to screen out any radionuclides that, due to their half-life, maximum activity, or radiotoxicity, will not result in significant post-closure impacts. For the purposes of radionuclide screening, the dose constraint of 0.3 mSv/yis considered (Section 2.4).
Institutional control periods are often taken into consideration such that there is a period within which exposures are assumed not to occur. For the GSA an institutional control period of 30 years has been assumed (Section 2.7), within which exposures are considered not to occur.
Radionuclide screening has been undertaken in two simple steps:
• Preliminary screening – doses associated with direct exposure via ingestion, inhalation and external irradiation to a single disused source following a 30 year institutional control period are calculated; and
• Main screening – for those radionuclides remaining after Step 1, a simple assessment of doses associated with the groundwater and gas pathways is undertaken.
I.1. PRELIMINARY SCREENING
The preliminary screening calculation assumes that a human is directly exposed to a single disused sealed radioactive source following the end of the institutional control period. Exposure through ingestion, inhalation and external irradiation is considered. For the inhalation pathway, Kr-85 exposure is via inhalation of the gas, for all other radionuclides exposure is due to inhalation of particulate material. The resulting doses are given in Table 31.
84
TABLE 30. RADIONUCLIDES CONSIDERED IN THE SCREENING CALCULATIONS
Note: a Data taken from Ref. [47].
Radionuclide Maximum inventory (Bq)
Half life (y)a
H-3 2.8E+14 1.24E+01
Na-22 3.4E+06 2.60E+00
Mn-54 1.0E+05 8.56E-01
Fe-55 9.9E+09 2.70E+00
Co-57 1.7E+10 7.42E-01
Co-60 2.9E+15 5.27E+00
Ni-63 2.1E+10 9.60E+01
Zn-65 3.7E+05 6.68E-01
Se-75 3.0E+11 3.28E-01
Kr-85 6.3E+11 1.07E+01
Y-88 1.0E+05 2.92E-01
Sr-90 5.3E+11 2.91E+01
Cd-109 3.1E+09 1.27E+00
Ba-133 3.3E+08 1.07E+01
Cs-137 7.5E+14 3.00E+01
Pm-147 2.7E+11 2.62E+00
Sm-151 7.8E+09 9.00E+01
Eu-152 4.0E+08 1.33E+01
Gd-153 1.5E+11 6.63E-01
Yb-169 2.2E+11 8.76E-02
Ir-192 9.3E+14 2.03E-01
Au-195 4.0E+07 5.01E-01
Hg-203 1.5E+06 1.28E-01
Tl-204 5.0E+08 3.78E+00
Pb-210 1.0E+07 2.23E+01
Po-210 1.0E+10 3.79E-01
Ra-226 2.6E+13 1.60E+03
Pu-238 2.0E+10 8.77E+01
Pu-239 6.7E+11 2.41E+04
Am-241 1.2E+13 4.32E+02
Cf-252 4.1E+09 2.64E+00
TABLE 31. PRELIMINARY SCREENING - DOSES ASSOCIATED WITH DIRECT EXPOSURE TO A DISUSED SEALED RADIOACTIVE SOURCE
Radionuclide
Maximum inventory at 30 y (Bq)
Dose coefficientsa
Ingestion dose (Sv)
Inhalation dose (Sv)
External dose (Sv)g Ingestion
(Sv/Bq)b
Inhalation (Sv/Bq)b, c
External (Sv/h per Bq)d
H-3 1.0E+12 1.8E-11 4.5E-11 0.0E+00 1.9E+01 4.7E+01 0.0E+00
Na-22 2.3E+01 3.2E-09 1.3E-09 3.1E-13 7.3E-08 3.0E-08 7.0E-11
Mn-54 5.6E-08 7.1E-10 1.5E-09 1.2E-13 4.0E-17 8.5E-17 6.6E-20
Fe-55 9.0E+04 3.3E-10 7.7E-10 3.4E-19 3.0E-05 6.9E-05 3.0E-13
Co-57 2.3E-04 2.1E-10 5.5E-10 1.7E-14 4.8E-14 1.3E-13 3.9E-17
Co-60 1.1E+12 3.4E-09 1.0E-08 3.5E-13 3.8E+03 1.1E+04 3.9E+00
Ni-63 3.4E+08 1.5E-10 4.8E-10 0.0E+00 5.1E-02 1.6E-01 0.0E+00
Zn-65 2.2E-10 3.9E-09 1.6E-09 8.1E-1414 8.7E-19 3.6E-19 1.8E-22
Se-75 1.8E-18 2.6E-09 1.0E-09 5.4E-1444 4.6E-27 1.8E-27 9.5E-31
Kr-85 1.8E+09 0.0E+00 9.2E-13e 0.0E+00 0.0E+00 1.7E-03f 0.0E+00
Y-88 2.4E-28 1.3E-09 4.4E-09 3.8E-13 3.1E-37 1.0E-36 8.9E-40
Sr-90 5.2E+09 3.1E-08 3.8E-08 2.8E-16 1.6E+02 2.0E+02 1.5E-05
Cd-109 4.8E+00 2.0E-09 8.1E-09 4.5E-16 9.6E-09 3.9E-08 2.1E-14
Ba-133 9.5E+05 1.5E-09 3.1E-09 5.1E-14 1.4E-03 2.9E-03 4.8E-07
Cs-137 7.5E+12 1.3E-08 3.7E-08 7.8E-14 9.8E+04 2.8E+05 5.9E+00
Pm-147 1.9E+06 2.6E-10 5.0E-09 4.8E-19 5.0E-04 9.6E-03 9.3E-12
Sm-151 1.2E+08 9.8E-11 4.0E-09 4.5E-18 1.2E-02 5.0E-01 5.6E-09
Eu-152 1.7E+06 1.4E-09 4.2E-08 1.6E-13 2.3E-03 7.0E-02 2.7E-06
Gd-153 7.2E-05 2.7E-10 2.1E-09 7.3E-15 1.9E-14 1.5E-13 5.3E-18
Yb-169 3.6E-94 7.1E-10 3.0E-09 3.9E-14 2.5E-103 1.1E-102 1.4E-106
Ir-192 6.1E-32 1.4E-09 6.6E-09 1.1E-13 8.5E-41 4.0E-40 6.9E-44
Au-195 7.5E-13 2.5E-10 1.7E-09 1.1E-14 1.9E-22 1.3E-21 8.3E-26
Hg-203 8.4E-67 1.9E-09 2.4E-09 3.3E-14 1.6E-75 2.0E-75 2.8E-79
Tl-204 4.1E+04 1.2E-09 3.9E-10 1.5E-16 4.9E-05 1.6E-05 6.0E-11
Pb-210 7.9E+04 6.9E-07 1.2E-06 5.4E-17 5.4E-02 9.4E-02 4.3E-11
Po-210 3.0E-16 1.2E-06 3.3E-06 1.2E-18 3.6E-22 9.8E-22 3.6E-33
Ra-226 5.1E+11 2.8E-07 3.5E-06 2.4E-13 1.4E+05 1.8E+06 1.2E+00
Pu-238 3.2E+08 2.3E-07 4.6E-05 1.0E-18 7.3E+01 1.5E+04 3.2E-09
Pu-239 1.3E+10 2.5E-07 5.0E-05 7.0E-18 3.3E+03 6.7E+05 9.4E-07
Am-241 2.3E+11 2.0E-07 4.2E-05 3.0E-15 4.6E+04 9.6E+06 6.9E-03
Cf-252 3.1E+04 9.0E-08 2.0E-05 8.6E-13 2.8E-03 6.2E-01 2.7E-07
86
Notes: a Short lived daughters with a half life of less than 25 days are assumed to be in secular equilibrium with their parent and included in the parent’s dose coefficient. A list of short lived daughters is given in Table 33.
b Data taken from Ref. [141] for adults.
c Data taken from Ref. [141] for adults, adopting the recommended default absorption class, where no recommendation is made, then the most conservative (highest) dose coefficient is adopted from the range of absorption classes reported.
d Dose factor for point source at a distance of 1 m calculated by multiplying mean gamma energy in MeV by 1.4E-13 Sv/h per Bq/MeV [142]. Emissions data are taken from Refs [143], [144]. Photons with individual energies below 50 keV have not been included because the equation used to calculate the dose coefficient from a point source substantially over-estimates the dose rate below this value, and the contribution to effective dose equivalent, given the existence of other exposure pathways, would in any event be very small.
e Units are Sv/h per Bq/m3.
f Dose calculated assuming inventory to be in 1 m3 of air and exposure duration of 1 hour.
g Dose calculated assuming an exposure duration of 10 hours.
The following radionuclides give a dose of less than 0.3 mSv/y following direct exposure to the disused sealed radioactive source for all three potential exposure pathways: Na-22, Mn-54, Fe-55, Co-57, Zn-65, Se-75, Y-88, Cd-109, Gd-153, Yb-169, Ir-192, Au-195, Hg-203, Tl-204 and Po-210. These radionuclides are therefore screened out.
I.2. MAIN SCREENING
A simple exposure model has been developed for the groundwater and gas pathways using the AMBER code (as applied within the main GSA calculations – see Section 5.4). The model uses the reduced decay chains described in Tables 32 and 33, and the dose coefficients and half lives given in Table 34. The model was run for a simulation time of 1E+06 years to investigate the effects of in-growth, and in particular the generation of Rn-222 gas.
TABLE 32. RADIONUCLIDES AND ASSOCIATED DAUGHTERS CONSIDERED IN THE MAIN SCREENING CALCULATIONS
Disposed radionuclide Short lived daughter(s)a
Daughter(s)a H-3
Co-60 Ni-63 Kr-85
Sr-90 *
Ba-133
Cs-137 *
Pm-147 Sm-151 Eu-152
Pb-210 * →Po-210
Ra-226 * →Pb-210*→ Po-210
Pu-238 →U-234→ Th-230→ Ra-226*→ Pb-210*→ Po-210
Pu-239 →U-235*→Pa-231→Ac-227*
Am-241 →Np-237→ Pa-233→ U-233→ Th-229*
Cf-252
→ (branching ratio 0.9691)Cm-248 → (branching ratio 0.9161)Pu-244*→ Pu-240→U236→Th-232→Ra-228*→ Th-228**
Note: a * indicates a daughter with a half-life of less than 25 days (see Table 33).
TABLE 33. SHORT LIVED DAUGHTERS WITH HALF-LIVES OF LESS THAN 25 DAYS ASSUMED TO BE IN SECULAR EQUILIBRIUM WITH THEIR PARENTS
Parent Short lived daughters
Sr-90 → Y-90
Cs-137 → (branching ratio 0.946) Ba-137m Pb-210 → Bi-210
Ra-226 → Rn-222→ Po-218→ (branching ratio 0.999 8) Pb-214 → Bi-214 → (branching ratio 0.999 8) Po-214 → (branching ratio 0.000 2) At-218 → Bi-214 → (branching ratio 0.999 8) Po-214 Ac-227 → (branching ratio 0.013 8) Fr-223→(branching ratio 0.9862) Th-227 →Ra-223→Rn-219→Po-215→Pb-211
→ Bi-211
→ (branching ratio 0.997 2) →Tl-207→(branching ratio 0.0028) Po-211
Th-229 → Ra-225→ Ac-225→ Fr-221→ At-217→ Bi-213→ (branching ratio 0.978 4) Po-213→ Pb-209 → (branching ratio 0.021 6) Tl-209→ Pb-209 Ra-228 → Ac-228
Th-228 Ra-224 Rn-220 Po-216 Pb-212 Bi-212 (branching ratio 0.641)Po-212 →→ (branching ratio 0.359)Tl-208 U-235 → Th-231
Pu-244 (branching ratio 0.9988)U-240 Np-240m (branching ratio 0.0011)Np-240
88
TABLE 34. MAIN SCREENING – DOSE COEFFICIENTS AND HALF LIVES
Radionuclide
Dose coefficientsa Half life (y)c Ingestion
(Sv/Bq)
Inhalation (Sv/Bq)
H-3 1.8E-11 4.5E-11
1.8E-11 (HTO gas) 1.24E+01
Co-60 3.4E-09 1.0E-08 5.27E+00
Ni-63 1.5E-10 4.8E-10 9.60E+01
Kr-85 0.0E+00 9.2E-13b 1.07E+01
Sr-90 3.1E-08 3.8E-08 2.91E+01
Ba-133 1.5E-09 3.1E-09 1.07E+01
Cs-137 1.3E-08 3.7E-08 3.00E+01
Pm-147 2.6E-10 5.0E-09 2.62E+00
Sm-151 9.8E-11 4.0E-09 9.00E+01
Eu-152 1.4E-09 4.2E-08 1.33E+01
Pb-210 6.9E-07 1.2E-06 2.23E+01
Po-210 1.2E-06 3.3E-06 3.79E-01
Ra-226 2.8E-07 3.5E-06
9.0E-09 Rn-222b 1.60E+03
Ra-228 6.9E-07 1.6E-05 5.75E+00
Ac-227 1.2E-06 5.7E-04 2.18E+01
Th-228 1.4E-07 4.4E-05 1.91E+00
Th-229 6.1E-07 8.6E-05 7.34E+03
Th-230 2.1E-07 1.4E-05 7.70E+04
Th-232 2.3E-07 1.1E-04 1.40E+10
Pa-231 7.1E-07 1.4E-04 3.28E+04
Pa-233 8.7E-10 3.9E-09 7.39E-02
U-233 5.1E-08 3.6E-06 1.59E+05
U-234 4.9E-08 3.5E-06 2.45E+05
U-235 4.7E-08 3.1E-06 7.04E+08
U-236 4.7E-08 8.7E-06 2.34E+07
Np-237 1.1E-07 2.3E-05 2.14E+06
Pu-238 2.3E-07 4.6E-05 8.77E+01
Pu-239 2.5E-07 5.0E-05 2.41E+04
Pu-240 2.5E-07 5.0E-05 6.54E+03
Am-241 2.0E-07 4.2E-05 4.32E+02
Pu-244 2.4E-07 4.7E-05 8.26E+07
Cm-248 7.7E-07 1.5E-04 3.39E+05
Cf-252 9.0E-08 2.0E-05 2.64E+00
Notes: a Data taken from Ref. [141] for adult, except for Rn-222 gas which is taken from Ref. [144]. Short lived daughters with a half life of less than 25 days are assumed to be in secular equilibrium with their parent and included in the parent’s dose coefficient. For inhalation, the recommended default absorption class given in Ref. [141] is adopted. Where no recommendation is made, then the most conservative (highest) dose coefficient is adopted from the range of absorption classes reported.
b Units are Sv/h per Bq/m3.
c Data taken from Ref. [143].
For the groundwater pathway it is assumed that, following an institutional control period of 30 years, a groundwater well is sunk immediately adjacent to a disposal borehole. The well is of the same depth as the disposal borehole and is open throughout its length. It is assumed to immediately capture all the contamination released from the disposal borehole. It is assumed that water is drawn into the well from a column of radius 5 m and length 50 m, with a rock porosity of 0.3. For the purposes of calculating ingestion doses, it is assumed that the well is used to supply drinking water (assumed to be 0.6 m3/y per person). For the purposes of calculating inhalation doses, it is assumed that the well is used to irrigate a small garden (4 m2) and humans are exposed from inhalation of contaminated soil.
External irradiation is not considered in the main scoping calculations since the preliminary scoping
calculations have shown that external irradiation calculations are lower than ingestion and inhalation doses (see Table 31).
For the gas scenario, it is assumed that, following the 30 year institutional control period, a house is built directly above a disposal borehole and a resident is exposed to all the gas released from the disposed packages in the borehole. No account is taken of dilution, dispersion, or attenuation. All gas released from the borehole is assumed to enter the house, which is assumed to be continuously occupied. The house dimensions were assumed to be conservatively small (4 × 4 × 2.5 m) and a ventilation rate of 0.25 h-1 which is typical for a well insulated building [54].
For the main screening assessment, for both the groundwater and gas pathways, it is also considered appropriate to take the engineering performance into consideration. It is assumed that 5 of the 50 packages disposed in a single disposal borehole fail after 30 years, releasing their entire inventory.
The remaining 45 disposal packages are assumed to fail after 100 years releasing their entire inventories into the groundwater (for the groundwater pathway calculations) or the house (for the gas pathway calculations).
The results for the groundwater and gas pathways are presented in Tables 35 and 36, respectively. For the groundwater pathway, calculated doses for Ba-133, Pm-147, Sm-151, Eu-152 and Cf-252 are below the screening dose of 0.3 mSv/y and are therefore screening out of the GSA. The gas pathway results for all four radionuclides exceed the screening dose of 0.3 mSv/y and are therefore included in the assessment.
Following the preliminary and main screening calculations, the following 11 radionuclides are identified for inclusion in the GSA: H-3, Co-60, Ni-63, Kr-85, Sr-90, Cs-137, Pb-210, Ra-226, Pu-238, Pu-239 and Am-241.
TABLE 35. MAIN SCREENING – RESULTS FOR THE GROUNDWATER PATHWAY
Radionuclide Peak ingestion dose (Sv/y) Peak inhalation dose (Sv/y)a
H-3 4.8E-02 3.5E-05
Co-60 9.7E+00 8.3E-03
Ni-63 7.8E-04 7.2E-07
Sr-90 7.7E-01 2.8E-04
Ba-133 3.5E-06 2.1E-09
Cs-137 4.9E+02 4.1E-01
Pm-147 1.3E-06 7.2E-09
Sm-151 1.8E-04 2.1E-06
Eu-152 6.0E-06 5.2E-08
Pb-210 4.3E-04 3.0E-07
Ra-226 2.7E+04 2.9E+01
Pu-238 1.1E+00 6.2E-02
Pu-239 8.5E+01 4.9E+00
Am-241 1.0E+03 6.3E+01
Cf-252 1.2E-05 6.8E-07
Note: a Calculated assuming soil depth of 0.3 m, soil porosity of 0.3, grain density of 2650 kg/m3, dust loading of 1E-6 kg/m3 and inhalation rate of 1.8 m3/h.
90
TABLE 36. MAIN SCREENING – RESULTS FOR THE GAS PATHWAY
Radionuclide (parent) Peak inhalation dose (Sv/y)
H-3 9.4E+00
Kr-85 8.3E-04
Rn-222 (Ra-226) 2.2E+04
Rn-222 (Pu-238) 3.7E-03