Decommissioning of nuclear facilities such as research reactors and commercial reactors is an important issue that needs to be dealt with globally in the medium and long term in order to protect and purify the environment (IAEA, 1999; IAEA, 2023; Laraia, 2022). Due to the complex neutron and photon radiation fields generated by the long-term fission reaction and other secondary nuclear reactions, the main components of reactor block will be activated to produce radionuclides except for the fission product nuclides in the core active zone. Therefore, the radiation source terms of the reactor block components should be accurately evaluated in the decommission of nuclear reactor to make reasonable decommissioning plan.
The Heavy Water Research Reactor (HWRR) is the first nuclear reactor and the first large-scale research reactor to be decommissioned in China (Ding et al., 2012; Wu et al., 2020), which was built in 1956 and located in the China Institute of Atomic Energy (CIAE). HWRR has been operating for nearly 50 years from June 1958 to December 2007. The HWRR reactor has made historic contributions to the development of nuclear science and technology of China. The transition period is from 2008 to 2013, so that the preparations were made with the decommissioning of HWRR reactor. During the transition period, the investigation of initial radioactive source items of the HWRR reactor (Ding et al., 2012; Zhang et al., 2016a) was implemented by CIAE. Through this investigation and research, a preliminary understanding of the types, levels, and distribution of existing radioactive nuclides in the decommissioning area of the HWRR reactor were initially obtained. In addition, the types and quantities of existing radioactive waste and liquid waste in the HWRR reactor were also determined (Ding et al., 2012).
At present, the first phase of decommissioning of the HWRR reactor has been approved and the engineering tasks of this phase is nearing completion. The first stage of the decommissioning of HWRR mainly involves the dismantling of reactor peripheral pipelines, equipment systems, but the reactor block is not involved, so the investigation results of initial source term can provide enough data support. Recently, the development of the decommissioning plan for the second phase and the engineering research of the reactor block are gradually starting (Sun et al., 2018; Wu et al., 2020; Ren et al., 2022). Therefore, it is necessary to master the detailed source item data of the components in the HWRR reactor block, in order to provide source item data support for the preparation of the retirement report and engineering research implementation in the second phase. Based on the above engineering background and task requirements, this article conducted the radiation source term calculation for the HWRR reactor block and a detailed analysis of the source term data is also provided.
The contents of this paper are organized as follows. The reactor block model and main components of HWRR is introduced in Section 2. Section 3 is about the investigation method for the radiation source term of HWRR. Further, Sections 4 provides the source term analysis results of HWRR reactor block, and the final conclusion are presented in Section 5.