EJ/T 1192-2005 in English

Standard Overview and Technical Background

EJ/T 1192-2005, "Technical Guidelines for Source Term Investigation and Sampling in the Decommissioning of Production Reactors," is a professional technical standard developed by China's nuclear industry for the investigation of radioactive source terms during the decommissioning process of production reactors. This standard was issued in 2005 by the Commission of Science, Technology and Industry for National Defense and is under the jurisdiction of the Nuclear Industry Standardization Institute.

As special reactors used to produce fissile materials and other nuclear materials, the decommissioning process of production reactors involves complex investigations and sampling of radioactive materials. This standard was developed against the backdrop of the rapid development of China's nuclear industry and the gradual decommissioning of early-built production reactors, aiming to standardize decommissioning source term investigation and sampling activities and ensure the scientific, economic, and safe nature of decommissioning projects.

In-depth Analysis of Core Content

Sampling Principles and Basic Requirements

The standard establishes four basic principles for sampling: **goal-oriented principle**, **historical investigation principle**, **protection optimization principle**, and **representative principle**. Before sampling, a thorough investigation of the historical status of the production process, system, and equipment must be conducted to optimize the legitimacy of the sampling work, ensuring that while meeting the investigation requirements, the level of personnel exposure is minimized.

Sampling Point Design System

The standard establishes a complete sampling point design system, mainly divided into two categories: reactor body sampling and process system sampling.

Process System Sampling Technical Requirements

The standard specifies the detailed sampling requirements for various process systems:

Process Measurement System: 2-3 samples should be collected from the inner wall of the pulse tube in each of the four main parts: humidity signal, flow signal, tightness check, and temperature signal systems. 3-5 samples should be collected from detachable components such as pumps and relay protection devices. Remote unloading system: Collect 2-3 samples from the inner wall of each pulse tube in the system, and 3-5 samples from detachable components such as the pressure device system and the electromagnetic distribution valve. Process exhaust system: Collect 2 samples from the inner wall of each exhaust duct, the inner wall of the instrument tube in the 108 error correction room, the inner wall of the main exhaust duct, the inner wall of the chimney, and from sediment. Collect 2-3 samples from detachable components such as the fan, the iodine remover, and the filter.

Sampling Method Technical Specifications

Principles for Determining Sampling Methods

The standard specifies eight principles for determining sampling methods, covering sampling requirements in different scenarios:

Specific Sampling Technical Details

Sampling of Contaminated Building Surfaces: Before sampling, a pollution level survey is conducted to divide the area into sampling units. Sampling points are determined using diagonal sampling, plum blossom sampling, star sampling, or serpentine sampling methods. The sampling area is generally selected as 300cm², and the sampling depth on concrete surfaces is generally 5-10mm.

Sampling of Metal Contaminated Surfaces: Scraping or cutting/removal methods can be used. The sampling area is also selected as 300cm², and the sampling depth is 1-5μm. When sampling the paint layer on the equipment surface, the entire paint layer must be scraped off. When collecting rust samples from carbon steel surfaces, all surface rust should be scraped off until the metal substrate is exposed.

Sampling of sediment at the bottom of the pool: Using a specialized sampler, sampling points are determined using cloverleaf, star, or serpentine sampling methods. Samples of sediment at the bottom of the pool are collected vertically, approximately 100 mL at each point, for a total of 500-1000 mL.

Sample Pretreatment Technical Requirements

Pretreatment Objectives and Classification

The standard classifies samples into two categories: surface samples and solid samples, and sets pretreatment objectives for each:

Surface Samples: After physical treatment, the particle size is approximately 40-100 mesh.

Metallic Solid Samples: After physical treatment, they become fragments that can be effectively dissolved in radiochemical sample preparation.

Non-metallic Solid Samples: They require ashing treatment to facilitate storage and further radiochemical analysis.

Pretreatment Methods

Physical Methods: Metallic solid samples can be treated by turning, milling, planing, drilling, etc.; surface samples can be treated by isothermal baking, grinding, sieving, etc.

Chemical Methods: Non-metallic solid samples can be treated by dry ashing, calculating the ash-to-freshness ratio to reduce their mass or volume to 1%-10%.

Radiation Protection and Quality Assurance

Radiation Protection Requirements

The standard emphasizes that sampling of the decommissioned reactor body and various process systems must be carried out in a specific radiation field, and the provisions of GB 18871-2002 must be strictly followed. Sampling operations are limited by conditions such as radiation field and working space, and effective protective measures should be taken, and special sampling tools should be developed and used.

Quality Assurance System

The standard establishes a complete quality assurance system, including:

Standard Implementation Recommendations

Key Technical Implementation Points

When applying this standard, it is recommended to focus on the following key technical points:

Sampling Plan Development: A detailed sampling plan should be developed based on the specific decommissioning phase objectives and the current status of the items, including on-site investigation of the sampling objects and determination of operational, safety, and quality requirements.

Specialized Tool Development: For special environments such as reactor bodies with strong radiation fields and limited working space, specialized sampling tools should be developed in advance to ensure the feasibility and safety of sampling work.

Sample Identification and Management: After sample collection, identification tags should be filled out promptly, indicating the sampling time, sampling component, sampling personnel, etc., and a complete sample record and computer database system should be established.

Personnel Training Requirements

Sampling personnel should undergo rigorous safety culture and professional knowledge training and assessment, and can only be employed after passing the examination.

Continuous Improvement Mechanism

It is recommended to establish a continuous improvement mechanism for sampling work, continuously improving sampling methods and technical requirements through experience accumulation in actual sampling processes, thereby enhancing the efficiency and accuracy of sampling work.