Page 24 - RP90
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2. residuos norm
2.1. corrientes de residuos norm
Los radionucleidos de origen natural que se encuentran en los yacimientos de petróleo y gas incluyen, entre otros,- 232Th,238U y sus correspondientes descendientes consecuen- cia de su decaimiento radiactivo. Los isótopos de Th y U per- manecen inmovilizados en las rocas de los yacimientos, pero sus descendientes radiactivos de Ra (226Ra, 228Ra, etc.) son solubles en agua y pueden fluir con las corrientes acuosas.
El Ra es químicamente similar al Ba, Sr, Ca y Mg, por tan- to, puede permanecer en solución (corrientes de residuos lí- quidos) o sedimentar en depósitos de sulfato o carbonato, en forma de lodos (sludge) o incrustaciones (scales) (corrientes de residuos sólidos). Los lodos se suelen acumular en tanques
y pozos, y las incrustaciones se forman normalmente en las tuberías de producción, bocas de los pozos, válvulas, bom- bas y equipos de perforación.
Además, el decaimiento del 226Ra produce 222Rn, que es un gas noble radiactivo que se transporta junto con el gas natural (corriente de residuos gaseosos). El 222Rn decae en elementos radiactivos sólidos, llamados descendientes del radón (p. ej. 218Po, 214Po, 214Pb, 210Po y 210Pb), que se pueden acumular en las superficies interiores de las líneas de trans- misión de gas y en otros equipamientos, formando capas finas de NORM (principalmente de 210Pb).
En la Tabla I se muestran los rangos típicos de concentra- ciones de actividad para los isótopos más relevantes y los distintos tipos de corrientes de residuos NORM típicos de la industria del petróleo y el gas.
Gases
Líquidos
Gas Natural (Bq/m3)
Gas Natural Licuado (Bq/L)
Crudo (Bq/L)
Agua de producción (Bq/L)
Serie
del 232Th
232Th
n.r.a
n.r.
0,03 – 2
0,0003 – 0,001
228Ra
n.r.
n.r.
n.r.
0,3 – 180
228Th
n.r.
n.r.
0,5 – 40
238U
n.r.
n.r.
n.r.
0,0001 – 10
Serie
del 238U
226Ra
n.r.
n.r.
0,1 – 40
0,0003 – 0,1
0,002 – 1.200
222Rn
5 – 200.000
0,01 – 1.500
n.r.
n.r.
210Pb
0,005 – 0,02
0,3 – 230
n.r.
0,05 – 190
210Po
0,002 – 0,08
0,3 – 100
0 – 10
n.r.
Sólidos
Incrustaciones (Bq/g)
Depósitos (Bq/g)
Lodos (Bq/g)
Raspaduras (Bq/g)
Serie
del 232Th
232Th
0,001 – 0,002
0,001 – 0,07
0,002 – 0,01
n.r.
228Ra
0,05 – 2.800
0,05 – 300
0,5 – 50
0,01 – 10
Serie
del 238U
238U
0,001 – 0,5
0,001 – 0,05
0,005 – 0,01
n.r.
226Ra
0,1 – 15.000
0,8 – 400
0,05 – 800
0,01 – 75
210Pb
0,02 – 75
0,05 – 2.000
0,1 – 1300
0,05 – 50
210Po
0,02 – 1,5
n.r.
0,004 – 160
0,1 – 4
an.r. = no reportado
Tabla I. RRangos típicos de concentraciones de actividad para los isótopos más relevantes y los distin- tos tipos de corrientes de residuos NORM típicos de la industria del petróleo y el gas.
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Figura 1. Diseño conceptual de la planta NORM.
PROTECCIóN RADIOLóGICA Y GESTIóN DE RESIDUOS NORM EN LA INDUSTRIA DEL PETRóLEO Y EL GAS
2.2. Plantas de residuos norm
Las plantas de tratamiento de residuos NORM de la industria del petróleo y el gas están diseñadas para recibir, proce- sar y desechar los residuos NORM origi- nados como resultado de las actividades relacionadas con esta industria. Los princi- pales objetivos de una planta NORM son eliminar los residuos NORM de los equi- pamientos y materiales, haciendo posible su reutilización o reciclado, y acondicio- nar el resto del material y residuos para su eliminación. Algunos de los procesos llevados a cabo en estas plantas pueden, a su vez, ocasionar residuos NORM nue- vos, que también son gestionados en las propias instalaciones.
La planta NORM en la que Tecnatom ha participado consta de tres áreas dife- renciadas: (i) área de servicios e instala- ciones comunes, (ii) área de tratamiento y procesado, y (iii) Landfill (celdas almace- naje de residuos). En la Figura 1 se puede observar un esquema del diseño concep-
tual de la planta NORM que incluye las distintas zonas e instalaciones.
Estas plantas pueden usar diferentes mé- todos de descontaminación, que incluyen limpieza y eliminación manual, eliminación mecánica mediante perforación o escaria- do, limpieza con agua a presión, aspira- ción, baños químicos, fundido, etc. Para la minimización de residuos, se pueden utili- zar otras estrategias, como compactación,
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