Progress in Nuclear Energy 109 (2018) 66–73 Contents lists available at ScienceDirect Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene Calculation and analysis of water activation products source term in AP1000 T ∗ Qingyang Guoa, Jingyu Zhanga, , Sheng Fangb,c, Yixue Chena a School of Nuclear Science and Engineering, North China Electric Power University, Beijing, 102206, China b Key Laboratory of Advanced Reactor Engineering and Safety, Ministry of Education, Beijing, 100084, China c Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing, 100084, China ARTICLE INFO ABSTRACT Keywords: During AP1000 operation, the water itself in the primary loop and the impurities in the water will be activated Water activation products by neutrons. The activation products 16N, 17N, 3H and 14C are considerable radiation hazard in AP1000. In this Source term analysis paper, two analysis models (homogeneous model and two-node model) are developed to calculate the radio- AP1000 activity of activation products in the primary coolant of AP1000. The calculated density of each radionuclide at Mechanical shim chosen region is introduced into ARShield code and then converted to dose rate using point kernel integration Dose rate method. In addition, for 3H, inventory produced under mechanical shim operating mode is calculated by the 7Li abundance ladder model proposed in this article and the influence of 7Li abundance is analyzed. The results lead to the following conclusions: (1) coolant flow has obvious impact on the radioactivity of nuclides 16N, 17N and 3H and the results from the two-node model considering coolant flow are more conservative; (2) purification has ob- vious impact on the radioactivity of long-lived nuclides 3H and 14C, while has almost no impact on the radio- activity of short-lived nuclides 16N and 17N; (3) the major contributors of dose rate are 16N and 17N and the total dose rate of the primary loop is 4.056E-01 mSv/h after one year's operation; (4) under mechanical shim oper- ating mode of AP1000, the quantity of 3H produced by soluble boron is approximately 21.12% higher than that under chemical shim operating mode; (5) the contribution of lithium to 3H production decreases linearly with increasing 7Li abundance in LiOH in the water. 1. Introduction water and they can induce internal radiation damage (Yim and 16 17 Caron, 2006). Although N(T1/2 =7.14s)and N(T1/2 =4.13s) Advanced passive technology of AP1000 has been introduced in have short half-lives, they may bring more dangers for workers under China and some parameters are still in the phase of engineering design. operation condition. These two nitrogen isotopes are important for The water itself in the primary loop and the impurities in the water will the short-term activation. be activated by neutrons when passing through some irradiation re- In recent years, theoretical work has been performed, and some gions in reactor. Numerous nuclear reactions will be caused in the computational models have been developed, to describe and predict primary loop of AP1000, resulting in a variety of radioactive nuclides activation product behavior. For example, Aghoyeh R G evaluated tri- (Pan and Cheng, 2007). Among these nuclides, 16N, 17N, 3H and 14C are tium and carbon-14 radioactivity and concentration in Tehran Research the dominant activation products and directly determine the occupa- Reactor (Aghoyeh and Khalafi, 2012). Yang Qi calculated 16N and 17N tional radiation exposure during operation and maintenance. concentration distribution in the heat transfer systems of blanket and 3 14 − H(T1/2 = 12.3 a) and C(T1/2 = 5730 a) are β emitters divertor in ITER (Yang et al., 2012). Liu Yuanzhong proposed homo- without associated γ transition. They almost leak into environment geneous model and two-node model for calculating radionuclide con- in forms of gas or liquid. Considering their relatively long half-lives, centration in the primary coolant circuit of LWRs (Liu, 1986). Zhang high residence time in the environment, high isotopic exchange rate Chuanxu studied 16N and 17N source term by homogeneous model in and ease of assimilation into living matter, they are drawing more the primary coolant system of Qinshan II Nuclear Power Plant using and more attention (Aghoyeh and Khalafi, 2012). If they are not SLODO code (Zhang, 2003). Shan Chenyu adopted more fine neutron separated effectively from biosphere, they will become a part of the flux distribution to calculate 16N source term (Shan et al., 2012)inPWR global cycle. Simultaneously, 3Hand14C will steadily exist in hu- by homogeneous model. But no one compares homogeneous model mans for long time once they are absorbed through air, food and with two-node model. And for AP1000, source term analysis of 16N, ∗ Corresponding author. E-mail address: [email protected] (J. Zhang). https://doi.org/10.1016/j.pnucene.2018.07.007 Received 5 February 2018; Received in revised form 24 May 2018; Accepted 21 July 2018 Available online 03 August 2018 0149-1970/ © 2018 Elsevier Ltd. All rights reserved. Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73 Fig. 1. Concentration of soluble boron in coolant under two different operating modes. 17N, 3H and 14C in the primary loop has not been seen in the open 2. Production mechanism and calculation method literature by now. In traditional pressurized water reactors, core reactivity depends 2.1. Production mechanism of activation products largely on change of chemical shim concentration in reactor coolant. However, AP1000 adopts mechanical shim operating mode, namely 3H decays to 3He by emitting low energy beta rays with an average MSHIM, to control reactivity, instead of chemical compensation with energy of 5.7 keV and a maximum energy of 18.6 keV. 14C decays to 14N boric acid (Lin, 2008). The control of slow reactivity changes in AP1000 by emitting low energy beta rays with an average energy of 49.5 keV is primarily via the control rod banks, which is different from tradi- and a maximum energy of 156 keV (Neeb, 1997). 16N decays to 16Oby tional PWRs. During reactor operation, the M-banks move from emitting beta rays and 7 MeV gamma rays and induces heat enhance- minimum position to maximum position to provide reactivity. When ment in some equipment. 17N decays with the emission of 0.9 MeV the M-banks reach the maximum end of the optimal range, the operator (Yang et al., 2012) secondary neutrons, which may cause the activation would take action to initiate a linear change to the boron concentration of pipe wall. in the primary loop until the M-banks withdraw to the minimum po- In PWR, 3H in primary coolant mainly comes from the following sition. In mechanical shim operating mode, the range of M-Banks de- (,nα ) ways: (1) fission of uranium, 235Un+⎯⎯⎯⎯⎯⎯⎯⎯ →XY + + 3H; (2) neutron termines the time interval between boron concentration changes. 10 103(,2)nα 4 Generally speaking, the boron concentration in the coolant is changed activation of B in burnable poison rods, Bn+⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ →HH + 2 e. 10 once per 7 days–14 days (Drudy et al., 2009; Morita et al., 1974; Morita Besides that, B can be activated indirectly in burnable poison rods, (,nα ) et al., 1988). Simulation results show that mechanical shim operation in the mechanism of reaction: 107Bn+⎯⎯⎯⎯⎯⎯⎯⎯ →Li + 4 He, 7L AP1000 is achievable for up to 95% of cycle life (Onoue et al., 2003), (.nnα ) i +⎯n ⎯⎯⎯⎯⎯⎯⎯⎯⎯ →34HHe + + n; (3) neutron activation of 10B in boric acid without the need to change boron concentration. Fig. 1 shows con- (,2)nα centration change of soluble boron in coolant under chemical shim added to coolant, 103Bn+⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ →HH + 24e; (4) neutron activation operating mode and mechanical shim operating mode. of 7Li and 6Li in lithium hydroxide added to coolant, 3 Under chemical shim operating mode, the quantity of H produced 73(.nnα ) 46 (,nα )34 Li+⎯ n ⎯⎯⎯⎯⎯⎯⎯⎯⎯ →HHen + + , Li+⎯ n ⎯⎯⎯⎯⎯⎯⎯ →HH + e; (5) neutron by soluble boron can be calculated using the linear simulation method. 23(,nγ ) However, under mechanical shim operating mode, the linear simulation activation of deuterium in water, Hn+⎯⎯⎯⎯⎯⎯⎯⎯ →H + γ. 14 14 17 method to calculate 3H inventory produced by boron may bring some The long-lived nuclide C mainly arises from N and O in water (,np ) (,nα ) deviation. Owing to special operating modes of AP1000, other re- via the reactions 141Nn+⎯⎯⎯⎯⎯⎯⎯⎯ →4CH + 1and 171On+⎯⎯⎯⎯⎯⎯⎯⎯ →4CHe + 4. searchers' models can not been directly applied to AP1000. It is ne- 14N and 17O exist as major impurities in fuel, coolant and structural cessary to investigate the formation and consumption mechanism of material. The short-lived nuclide 16N arises from 16O via the reaction activation products in the primary loop of AP1000 and to predict the (,np ) 161On+⎯⎯⎯⎯⎯⎯⎯⎯ →6N + 1H. And the short-lived nuclide 17N is produced related variation and distribution of radioactivity. (,np ) Therefore, the following research work are performed: (1) two through the reaction 171On+⎯⎯⎯⎯⎯⎯⎯⎯ →7N + 1H. analysis models (homogeneous model and two-node model) are estab- lished to calculate the concentration of 16N, 17N, 3H and 14C along the primary loop of AP1000; (2) the dose rate of the activation products is 2.2. Homogeneous method of activation products calculated using the point kernel code ARShield. (3) the quantity of 3H ff fl produced by soluble boron is calculated respectively under mechanical In the homogeneous model, the e ect of coolant ow in the loop is shim operating mode and chemical shim operating mode, and the re- not taken into account, which means the concentration of nuclides in sults of two different modes are compared with each other; (4) the the coolant is homogeneous along the loop.