WS/T 668-2019Requirements for radiological protection for radon in public underground structure and using geothermal water (English PDF)

4.1 Control Principles

4.1.1 In the design and construction related to radiation protection, the principle of radiation protection optimization should be observed.

4.1.2 Appropriate measures to attach personnel to radon in the air in underground buildings

Exposure is controlled to the lowest acceptable level.

4.2 Reference level

The reference level for average radon concentration in underground buildings is 400 Bq/m3.

The reference level of average radon concentration in geothermal water development and utilization sites is 800 Bq/m3.

4.3 Control measures

4.3.1 When selecting the location of a new underground building, avoid areas with high radium content in soil or rocks, and choose construction materials that comply with GB 6566 during construction.

4.3.2 When the radon concentration in the existing underground building is between 400 Bq/m3 and 1000 Bq/m3, it is advisable to adopt strengthening machinery within 6 months after the measurement.

Ventilation, shielding radon sources, purifying and removing radon; for radon concentrations > 1000 Bq/m3, it is advisable to adopt mechanical ventilation and shielding within 3 months.

Radon sources, purification radon removal and other radon reduction measures; when the average radon concentration still exceeds the reference level after taking the measures, block or remove radon sources Land improvement and other permanent measures to reduce radon.

4.3.3 When the radon concentration in the local hot water development and utilization place is 800 Bq/m3 ~ 1000 Bq/m3, it should be taken within 6 months after the measurement.

Strengthening mechanical ventilation, shielding radon sources, purifying and removing radon; for radon concentrations > 1000 Bq/m3, it is advisable to take mechanical Measures to reduce radon, such as wind, shielding radon sources, purifying and removing radon; take measures to block or remove radon sources, Carry out permanent reduction measures such as base reconstruction.

5 Measurement of radon concentration in underground buildings and geothermal water applications

5.1 Measurement scheme

It adopts two-level measurement method of screening measurement and tracking measurement. First, a quick screening measurement was performed to determine whether the radon concentration in the place was consistent.

Meet the requirements of the reference level in this standard; for places where radon concentrations are greater than or equal to the reference level, follow-up measurements are used to confirm recognize.

5.2 Preparation before measurement

5.2.1 Understand the basic situation of the measured place in detail before measurement, including the type, partition, use, building (production) year, building Materials, surrounding geological background, whether relevant tests have been performed.

5.2.2 Collect the weather forecast data during the planned measurement period, and avoid measuring in high winds (wind speed > 13.4 m/s) or heavy rain.

5.3 Detection methods

Measure according to the standard measurement method in GBZ/T 182-2006.

5.4 Selection of detection points

5.4.1 Distribution principle

Choose places where the public often stays. Underground buildings, such as subway station platforms, work rooms, and corresponding work areas; underground hospitals the first floor selects medical staff offices, patient waiting places, etc .; the underground shopping malls select counters and other corresponding work areas, etc .; other places according to actual conditions it depends. Geothermal water development and utilization place, choose office, work room or duty room, guest room, bathing place, etc.

5.4.2 Number of points

The number of points is determined according to the area of the site and the site conditions. When the use area of the place is less than 100 m2, set 2 to 3 detection points;

When the area of the area is 100 m2 to 500 m2, 3 to 5 detection points are set. When the area of the area is > 500 m2, at least 5 detection points are set.

For places where the screening measurement result is greater than or equal to the reference level, the density of detection points can be appropriately increased. Using the alpha track detector method in line sampling, parallel samples and blank samples are also required, and their numbers are not less than 10% and 5% of the total, respectively.

5.4.3 Detection point height

In principle, it corresponds to the height of the human breathing zone (1.5 m).

5.4.4 Distribution method

Multi-point sampling should be arranged in a diagonal or plum blossom uniformly, avoiding the vents, humidifiers and heating devices in the place, and the distance from the wall > 0.5 m.

5.5 Measuring time and frequency

5.5.1 Screening measurements

When measuring radon concentration in the development and utilization sites of underground buildings and geothermal water, it is carried out under daily conditions. Screening measurement See Table A.1 in Appendix A for time and frequency.

5.5.2 Tracking measurement

Perform a second measurement on the place where the screening measurement result is greater than or equal to the reference level of this standard to determine whether the radon concentration in the measured place is Whether it meets this standard. For the tracking measurement method and sampling time, see Table A.2 in Appendix A, and for the schedule of tracking measurement, see Table A.3 in Appendix A.

5.6 Evaluation of results

5.6.1 Evaluation of screening measurement results

5.6.1.1 Underground buildings. the radon concentration at each detection point is < 400 Bq/m3, and the arithmetic mean of the detection results at each point is taken as the the detection value can determine that the radon concentration in the place meets this standard. If there is more than one point of radon concentration >=400 Bq/m3, Line tracking measurement.

5.6.1.2 Geothermal water development and utilization sites. The radon concentration at each detection point is less than 800 Bq/m3, and the arithmetic mean of the detection results at each point is taken as the detection value of the place, it can be determined that the radon concentration in the place meets this standard. If there is more than one point of radon concentration >=800 Bq/m3, Tracking measurements are required on the site.

5.6.2 Evaluation of tracking measurement results

5.6.2.1 Underground buildings. The radon concentration is less than 400 Bq/m3 (all values). The radon concentration in this place complies with this standard. Thorium concentration >=400 Bq/m3 (Arbitrary value), you need to find the cause and consider taking intervention or reduction measures.

5.6.2.2 The location of geothermal water development and utilization. The radon concentration is less than 800 Bq/m3 (all values), and the radon concentration in this location complies with this standard. Kano Degree >=800 Bq/m3 (arbitrary value), you need to find the cause and consider taking intervention or reduction measures.

Appendix A

(Informative appendix) Screening measurement and tracking measurement sampling time and frequency recommendations A.1 Sampling time and frequency recommendations for screening measurements the sampling time and frequency of the screening measurement are shown in Table A.1.

Table A.1 Sampling time and frequency for screening measurements

Measurement type Minimum sampling (measurement) time and frequency method Instant measurement from 8.00 to 11.00 in the morning; >=1 time/d for 2 consecutive days Scintillation flask method, double filter method Balloon method, ionization chamber method Continuous measurement >=2 d ~ 7 d Continuous radon monitor Continuous working level monitor Cumulative measurement >=2 d ~ 7 d Alpha track detector method (active) Activated carbon method 30 d ~ 90 d alpha track detector method (passive) A.2 Tracking measurement methods and sampling time recommendations the tracking measurement method and sampling time are shown in Table A.2.

Table A.2 Method and sampling time for tracking measurement

Method sampling time Alpha track detector method (passive) Under the condition of keeping the daily condition, sample 90 d ~ 1 a and then measure Electret method A.3 Timing of tracking measurements See Table A.3. For the schedule of follow-up measurements.

Table A.3 Timing of tracking measurements

Radon concentration

Bq/m

Timeline for tracking measurements Underground building Geothermal water development and utilization place > 1000 Implement follow-up measurement within one month after screening measurement, and consider reducing radon concentration within months 400 ~ 1000 800 ~ 1000 Follow-up measurement within three months after screening measurement references [1] GB/T 14582 Standard measurement method for radon in ambient air [2] IAEA, 2014. Radiation Protection and Safety of Radiation Sources. International Basic Safety Standards [3] ICRP Publication 126, 2014. Radiological Protection against Radon Exposure