Calculation and Analysis of Water Activation Products Source Term In

Progress in Nuclear Energy 109 (2018) 66–73

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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 obvious impact on the radioactivity of long-lived nuclides 3H and 14C, while has almost no impact on the radioactivity 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 operating 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. In this model, the average fl influence of 7Li abundance on 3H production is analyzed. neutron ux of the loop is adopted. The concentration for any nuclide considered obeys the following equation, which is set up based on the law of mass conservation.

67 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73 dN 6Li in coolant, i = 7 refers to natural deuterium in coolant; =−Pt() Rt () −1 −1 dt (1) C, average fission rate per unit of thermal power, s ·MWt ; Where, P, core thermal power, MWt; F, fraction of fuel rods with defective cladding, %; − ff fi N, is the number of nuclide, m 3; Y, e ective ssion yield; − − 3 1 Fbp, fraction of burnable poison rods with defective cladding, %; P(t), is the production rate, m s ; − − − bp 10 3 R(t), is the reduction rate, m 3s 1. NB10 (t), inventory of B in combustible poisonous rods, m ; bp 7 −3 NLi7 ()t , inventory of Li in combustible poisonous rods, m ; 10 −3 Different nuclide have different production rate and reduction rate. NB10 (0), initial inventory of B in coolant, m ; 2 The concentration of 3H produced by various ways in primary water- σmn→ , cross section of converting nuclide m to nuclide n, cm ; −1 cooled loop can be calculated respectively as follows. λn, decay constant of nuclide n, s ; n 2 σa ()E , absorption cross section of nuclide n, cm ; 1 fl 2 dNH3 () t ⎛ H3 ηQ 1 ⎞ ϕE( ), neutron ux, n/(cm ·s); =−CPYF λH3 ++∑ σa ()() E ϕ E NtH3 () dt ⎜ V ⎟ η, collection efficiency of filter and resin in chemical and volume ⎝ E ⎠ (2) control system (CVCS), %; bp Q, volume flow rate of coolant into CVCS, m3/s; dNB10 () t ⎛ ⎞ bp =− ∑∑(σBH10→→ 3 ()()) EϕE+ ( σBLi 10 7 ()()) EϕE NB10 () t 3 dt ⎜ ⎟ V , coolant volume, m ; ⎝ E E ⎠ −1 ktB10 ( ), boron migration rate, s . (3a) 2 14C in the primary water-cooled loop of PWR contains two main dNH3 () t bp = ∑ (()())()σEϕENtFBH10→ 3 bp 17 α 14 14 14 dt B10 sources, which are O(n, ) C and N(n, p) C. The concentration of E 14C produced by 17O and 14N is as follows. ⎛ H3 ηQ ⎞ 1 − λσEϕEH3 ++∑ a ()()NtH3 () 1 ⎜ V ⎟ dNC14 () t ⎛ ⎞ ⎝ E ⎠ (3b) ∑ σEϕENtOC17→ 14 ()() O17 () dt ⎜ ⎟ ⎝ E ⎠ bp dNLi7 () t ⎛ ⎞ bp ηQ =− ∑ (()())(σEϕENtBLi10→ 7 B10 ) ⎛ C14 ⎞ 1 ⎜ ⎟ − λσEϕEC14 ++∑ a ()()NtC14 () dt E ⎜ V ⎟ ⎝ ⎠ ⎝ E ⎠ (9) bp − ∑ (()())()σEϕENtLi73→ H Li7 2 E (4a) dNC14 () t ⎛ ⎞ ⎛ C14 ηQ ⎞ 2 ∑∑σEϕENtλσEϕENC14→ 14 ()()OC14 ()− 14 ++a ()()NtC14 () dt ⎜ ⎟ ⎜ V ⎟ 3 ⎝ E ⎠ ⎝ E ⎠ dNH3 bp = ∑ (()())()σEϕENtFLi73→ H Li7 bp (10) dt E Where, ⎛ H3 ηQ ⎞ 3 − λσEϕEH3 ++∑ a ()() NtH3 () ⎜ EϕE)()⎟ i 14 −3 ⎝ E ⎠ (4b) NC14 (t), C inventory produced by nuclide i, m , the subscript i = 1 refers to 17O, i = 2 refers to 14N. NBB10()tN=− 10 (0)(1 kt B 10 ()) (5a) dN4 () t The water in the primary water-cooled loop of PWR is activated by H3 16 17 = ∑ (()())()σEϕENtBH10→ 3 B10 fast neutron to produce N and N. Only the reactions with energy dt E threshold 16O(n, p)16N (energy threshold ∼ 10 MeV) and 17O(n, p)17N ∼ ⎛ H3 ηQ ⎞ 4 (energy threshold 8.36 MeV) are considered. The following equa- − λσEϕEH3 ++∑ ()()Nt () ⎜ a V ⎟ H3 tions are used to calculate the concentration of 16N and 17N. ⎝ E ⎠ (5b) 1 5 dNN16 () t ⎛ ⎞ ⎛ N16 ηQ ⎞ 1 dNH3 () t = ∑∑σEϕENtλσEϕEON16→ 16 ()() O16 ()− N 16 ++a ()()NtN16 () = (()())()σEϕENt dt ⎜ ⎟ ⎜ V ⎟ ∑ Li73→ H Li7 ⎝ E ⎠ ⎝ E ⎠ dt E (11) ⎛ H3 ηQ ⎞ 5 − λσEϕEH3 ++∑ a ()()NtH3 () 1 ⎜ V ⎟ dNN17 () t ⎛ ⎞ ⎛ N17 ηQ ⎞ 1 E (6) = ∑∑σEϕENtλσEϕEON17→ 17 ()() O17 ()− N 17 ++a ()()NtN17 () ⎝ ⎠ dt ⎜ ⎟ ⎜ V ⎟ ⎝ E ⎠ ⎝ E ⎠ 6 dNH3 () t (12) = ∑ (()())()σEϕENtLi63→ H Li6 dt E Where, ηQ ⎛ H3 ⎞ 6 − − λσEϕEH3 ++∑ a ()()NtH3 () 1 16 16 3 ⎜ V ⎟ NN16 (t), N inventory produced by nuclide O, m ; ⎝ E ⎠ (7) 1 17 17 −3 NN17 (t), N inventory produced by nuclide O, m . 7 dNH3 () t = ∑ (()())()σEϕENtHH23→ H2 2.3. Two-node method of activation products dt E

⎛ H3 ηQ ⎞ 7 In two-node model, coolant ﬂow in the loop is considered. Some − λσEϕEH3 ++∑ ()()Nt () ⎜ a V ⎟ H3 ⎝ E ⎠ (8) hypotheses are adopted as follows.

Where, (1) The loop is divided into two parts according to the neutron flux. The places with high neutron flux are named “In-Flux” region, i 3 −3 NH3 (t), H inventory produced by nuclide i, m , the subscript i = 1 while the other places without neutron flux are named “Out-Flux” refers to fission of uranium, i = 2 refers to 10B in combustible poi- 7 region. sonous rods, i = 3 refers to Li in combustible poisonous rods, i = 4 (2) The concentration of the inherent nuclides and impurities added refers to 10B in coolant, i = 5 refers to 7Li in coolant, i = 6 refers to

68 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73

reabsorption in circulation of the coolant. After a complete cycle, the inventory of the radionuclide is as follows.

⎛ ⎛ ⎛ n ⎞ ti ηQ ⎞ ⎞ − λσEϕEn+ ∑ ()() + T ⎜ ⎜ a ⎟ T V ⎟ Nni()tNte= ni ()⎜ ⎝ ⎝ E ⎠ ⎠ ⎟ ⎜ ⎟ ⎝ ⎠ (18)

Tt=+io t (19) Where,

to, time of coolant passing through the “Out-Flux” region, s; Fig. 2. Diagram of coolant circulation based on two-node model. T, time of coolant passing through a complete cycle, s.

(except soluble boron) in coolant are assumed to be constant. Fig. 2 After a complete cycle, the inventory of 10B is as follows. presents coolant circulation based on two-node model. NBi10(t )=−− N B 10 (0)(1 kt Bi 10 )(1 kT B 10 ) (20) When the coolant ﬂows through “In-Flux” region, the equilibrium The inventory of radionuclide in the exit of “In-Flux” region after equation of activation products in the coolant is as follows. the water passing through the irradiation region secondly is as follows. For nuclide n with the precursor of nuclide m (except 10B): For nuclide n with the precursor of nuclide m (except 10B): N (2tNtθNt )=+ ( ) ( ) (21) dNn () t ⎛ ⎞ ⎛ n ⎞ n i ni ni = ∑∑σEϕENtλmn→ ()()m ()− n+ σEϕENta ()()n () dt ⎜ ⎟ ⎜ ⎟ ⎝ E ⎠ ⎝ E ⎠ ⎛ ⎛ n ⎞ ti ηQ ⎞ − λσEϕEn+ ∑ ()() + T (13) ⎜ ⎜ a ⎟ T V ⎟ θe= ⎝ ⎝ E ⎠ ⎠ (22) Where, For nuclide n with the precursor nuclide of 10B:

Nn ()t , the inventory of nuclide n, m-3; Nn(2tNtθNtkT i )=+ ni ( ) ni ( )(1 − B10 ) (23) N (t), the inventory of nuclide m, m-3. m The inventory of radionuclide in the exit of “In-Flux” region after the water passing through the irradiation region for n times is as fol- For nuclide n with the precursor nuclide of 10B: lows. For nuclide n with the precursor of nuclide m (except 10B): dNn () t ⎛ ⎞ = ∑ σEϕENBn10→ ()() B 10 (0)(1− kt B 10 ) dt ⎜ ⎟ n−−−123n n ⎝ E ⎠ Nni(nt )=++++ Ntθ ni () Ntθni () Ntθni () ... Ntni () (24) 10 ⎛ n ⎞ For nuclide n with the precursor nuclide of B: − ⎜λσEϕENtn + ∑ a ()()⎟ n () E (14) n−−1 n 2 2 n −2 ⎝ ⎠ Nni(nt )=+−+− Ntθ ni () Ntni ()(1 k B10 Tθ ) Ntni ()(1 k B10 Tθ ) ﬂ “ ” n−1 When the coolant ows through Out-Flux region, the equilibrium ++...Ntni ( )(1 − k B10 T ) (25) equation of activation products in the coolant is as follows. That is to say, after the operation time t, the inventory of radio- dNn () t ηQ nuclide in the exit of “In-Flux” region is as follows. =−⎛λnn+ ⎞Nt( ) dt ⎝ V ⎠ (15) For nuclide n with the precursor of nuclide m (except 10B): When the water ﬁrst passes through the irradiation region, the ⎛ ⎛ n ⎞ ⎛ −⎜λσEϕEtn+ ∑ a ()()⎟ i⎞ concentration of radionuclide in the exit is as follows. ∑E σEϕEmn→ ()() ⎜ ⎜ ⎟ N ()t = Nt() 1− e⎝ ⎝ E ⎠ · For nuclide n with the precursor of nuclide m (except 10B): n n m λσEϕEn + ∑E a ()() ⎜ ⎟ ⎝ ⎠ ⎛ ⎛ ⎞ n t ηQ ⎛ −⎜λσEϕEtn+⎜∑ a ()()⎟ i⎞ n i ∑E σEϕEmn→ ()() ⎜ ⎟ −+λσEϕEtn (()())∑E a + ⎝ E 1 − e ()T V Nni()t = n Ntm () 1− e⎝ ⎠ λσEϕEn + ∑ a ()() ⎜ ⎟ n ti ηQ E −+λσEϕETn (()())∑ + ⎝ ⎠ (16) 1 − e ()E a T V (26) 10 Where, For nuclide n with the precursor nuclide of B:

⎛ ⎛ n ⎞ “ ” − λσEϕEtn+∑ a ()() i ti, time of coolant passing through the In-Flux region, s. (()())(0)∑E σEϕENBn10→ B 10 ⎛ ⎜ ⎟ ⎞ Nn ()t = ⎜ 1 − e ⎝ E ⎠ λn ⎜ ⎟ 10 ⎜ For nuclide n with the precursor nuclide of B: ⎝ ⎝ ⎠

⎛ ⎞ ⎛ n ⎞ − λσEϕEt+ n ()() − λσEϕEtn+∑ a ()() i (()())(0)∑ σEϕENBn10→ B 10 ⎛ ⎜ n ∑ a ⎟ i⎞ (()())(0)∑E σEϕENBn10→ B 10 ⎛ ⎜ ⎟ ⎞ E ⎝ E ⎠ Nni()t = 1 − e ⎝ E ⎠ + 2 keB10 1 − λn ⎜ ⎟ λn ⎜ ⎟ ⎝ ⎠ ⎝ ⎠

⎛ n ⎞ ⎞ − λσEϕEtn+∑ a ()() i (()())(0)∑ σEϕEN (()())(0)∑E σEϕENBn10→ B 10 ⎛ ⎜ ⎟ ⎞ E Bn10→ B 10 ⎝ E ⎠ − kt⎟· + 2 keB10 1 − Bi10 λn ⎜ ⎟ λn ⎟ ⎝ ⎠ ⎠ t ηQ (()())(0)∑ σEϕENBn10→ B 10 tTi/ n i E (1−−+kTB10 ) λn ∑ σEϕEa ( ) ( ) + t − ktBi10 ()E T V λn (17) (1−−+kT ) λ∑ σEϕEn ( ) ( ) ti + ηQ T Bn10 ()E a T V (27) Radionuclide decreases under the eﬀects of decay, puriﬁcation and

69 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73

The inventory of radionuclide in “Out-Flux” region is as follows. the primary loop of AP1000 is calculated. Then, the dose rate of activation products is calculated using the point kernel code ARShield. ηQ x −⎛λ + ⎞· 3 n V v Nnn(,tx )= N ()· t e⎝ ⎠ (28) Finally, H production under mechanical shim operating mode and the impact of water chemistry parameters (7Li abundance) on 3H produc- Where, tion is analyzed.

N (,tx), the inventory of radionuclide at x meters from the exit of n 3.1. Description of the example for calculation “In-Flux” region, m-3; v, the average flow rate of coolant, m/s. The design parameters of AP1000 primary loop (Winters et al., 2004) is presented in Table 1. 3 2.4. Calculation model of H under mechanical shim operating mode In the calculation, the nuclear data, including half-life, decay branching ratio, and cross section are derived from EAF-2007 (Forrest According to the change characteristics of boron concentration et al., 2007), in which the cross sections are stored in several kinds of under mechanical shim operating mode, the concentration of soluble energy group structure and for different reactor types. In the following boron in coolant is simulated using a ladder curve and the equilibrium calculation, the cross sections of 172-group XMAS structure for fission 3 equations of H under mechanical shim operating mode are as follows. reactor will be used. T(1) < t ≤ T(2):

4 dNH3 () t 3.2. Radioactivity of activation products = ∑ (()())(0)σEϕENBH10→ 3 B10 dt E The primary loop of AP1000 is simulated for one year's operation ⎛ H3 ηQ ⎞ 4 using homogeneous model and two-node model respectively. For im- − λσEϕEH3 ++∑ ()()Nt () ⎜ a V ⎟ H3 ⎝ E ⎠ (29) proving the corrosion resistance of structural materials to reduce the production of activated corrosion products, it needs a certain amount of ≤ T(2) < t T(2)+Td: LiOH to adjust pH of coolant. In general, 7Li abundance of LiOH 4 adopted in PWR is more than 99.9%. dNH3 () t =−∑ (σEϕENβtTBH10→ 3 ( ) ( )) B 10 (0)(1 (1))(− (2)) Tables 2–7 show radioactivity and contributions from different dt E generation paths of 3H, 14C, 16N, 17N using two different calculation ⎛ H3 ηQ ⎞⎛ 4 models at the conditions with purification and without purification. − λσEϕEH3 ++∑ ()() Nt() ⎜ a V ⎟⎜ H3 Tables 8 and 9 compares the 3H, 14C and 16N activity with the results ⎝ E ⎠⎝ (30) calculated by other international methods. ≤ T(2)+Td

T(1), starting time point of operation, s; Coolant pressure (MPa) 15.51 T(n) (n ≥ 2), time when M-banks reach the maximum end of the Coolant temperature (°C) 303.4 optimal range, s; Core thermal power (MWth) 3400 Volume of coolant (m3) 218.5 Td, boron dilution time, s; ff Initial concentration of boron under chemical shim mode (ppm) 1155 β (n), boron migration rate corresponding to di erent boron con- Initial concentration of boron under mechanical shim mode (ppm) 838.71 centration regulation phases, s-1. Initial concentration of lithium (ppm) 3 Dissolved nitrogen content (ppm) 5 3. Calculation analysis and discussion Cycle time (d) 450 Mass flow rate in filter (kg/s) 4.09 Collection efficiency of filter (%) 50 Based on above models, the concentration of 16N, 17N, 3H and 14Cin

70 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73

Table 2 The results of 3H calculated using homogeneous model.

3H generation paths Homogeneous model

Without puriﬁcation Contribution share (%) With puriﬁcation Contribution share (%)

Fission in fuel rods (Bq) 3.7123512E+12 22.46 2.0231201E+09 10.38 10B(n,2α)T in burnable poison rods (Bq) 2.1131784E+11 1.28 2.8510364E+08 1.46 10B(n,α)7Li(n, nα)T in burnable poison rods (Bq) 1.5638644E+11 0.95 3.3412541E+08 1.71 10B in coolant (Bq) 8.7848126E+12 53.16 7.5797870E+09 38.90 7Li in coolant (Bq) 4.0725126E+11 2.46 1.0303221E+09 5.29 6Li in coolant (Bq) 3.1938158E+12 19.32 8.0801695E+09 41.47 2H in coolant (Bq) 6.0756448E+10 0.37 1.5371031E+08 0.79 Total (Bq) 1.6526692E+13 1.9486338E+10

Table 3 The results of 3H calculated using two-node model.

3H generation paths Two-node model

Without puriﬁcation Contribution share (%) With puriﬁcation Contribution share (%)

Fission in fuel rods (Bq) 3.7123512E+12 16.53 2.0231201E+09 4.12 10B(n,2α)T in burnable poison rods (Bq) 2.1131784E+11 0.94 2.8510364E+08 0.58 10B(n,α)7Li(n, nα)T in burnable poison rods (Bq) 1.5638644E+11 0.70 3.3412541E+08 0.68 10B in coolant (Bq) 1.4712045E+13 65.52 3.7223724E+10 75.76 7Li in coolant (Bq) 4.0725126E+11 1.81 1.0304080E+09 2.10 6Li in coolant (Bq) 3.1938158E+12 14.23 8.0808425E+09 16.45 2H in coolant (Bq) 6.0756449E+10 0.27 1.5372311E+08 0.31 Total (Bq) 2.2453924E+13 4.9131047E+10

Table 4 The results of14C calculated using homogeneous model.

14C generation paths Homogeneous model

Without puriﬁcation Contribution share (%) With puriﬁcation Contribution share (%)

14N in coolant (Bq) 2.4146982E+10 10.89 5.9426085E+07 10.89 17O in coolant (Bq) 1.9746118E+11 89.11 4.8595493E+08 89.11 Total (Bq) 2.2160862E+11 5.4538102E+08

Table 5 The results of14C calculated using two-node model.

14C generation paths Two-node model

Without puriﬁcation Contribution share (%) With puriﬁcation Contribution share (%)

14N in coolant (Bq) 2.4146976E+10 10.89 5.9431041E+07 10.89 17O in coolant (Bq) 1.9746114E+11 89.11 4.8599546E+08 89.11 Total (Bq) 2.2160812E+11 5.4542650E+08

Table 6 Table 7 The results of16N and17N calculated using homogeneous model. The results of16N and17N calculated using two-node model.

Nuclide name Homogeneous model Nuclide name Two-node model

Without purification With purification Without purification With purification

16N in coolant (Bq) 1.0027454E+15 1.0026117E+15 16N in coolant (Bq) 1.3110578E+15 1.3109701E+15 17N in coolant (Bq) 2.0301246E+11 2.0299692E+11 17N in coolant (Bq) 3.0547267E+11 3.0546615E+11

From Tables 8 and 9, it can be seen that the results from different intensity of gamma rays from nuclide decay. And dose rate can be used methods are generally consistent, which shows that the calculation to calculate the annual permissible work time, the annual ORE and so results from homogeneous model and two-node model are theoretically on. In this paper, the dose rate caused by activation products of coolant reliable to some extent. is calculated using ARShield code. The ARShield code is an advanced version of point kernel code, 3.3. Dose rate of activation products developed by North China Electric Power University. It provides the pre-job for visualization of large-scale radiation field and virtual Dose rate is an important parameter in radiation protection. roaming in nuclear plant, by breaking the restrictions of the traditional Compared with radioactivity, dose rate also reflects the quantity and point kernel integration codes. The detailed characteristics of ARShield

71 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73

Table 8 r, point at which gamma dose rate is to be calculated; 3H activity produced in AP1000 with different methods (Balonov et al., 2004; r’, location of source; Fei et al., 2016; Chandrasekaran et al., 1985). S(r’), source strength; method 3H Activity (Bq/a) V, volume of source; μ, total attenuation coefficient at energy E; Design value in AP1000 4.86E+13 rr→′, distance between source point and point at which gamma Statistical average amount from IAEA 3.70E+13 intensity is to be calculated; Calculation results by PWR-GALE 5.03E+13 fl Calculation results by homogeneous model 1.6526692E+13 K, ux-to-dose conversion factor; Calculation results by two-node model 2.2453924E+13 B, dose buildup factor.

The geometry of hot leg pipe, linking the core and the heat ex- Table 9 changer, is adopted for dose rate calculation here. The position for dose 14C and16N activity produced in AP1000 with different methods (Winters et al., rate calculation is chosen to be in the middle of the pipe in axial di- 2004). rection, and at the outer surface of the pipe, so the contact dose rate can 3 14 method 14C Activity (Bq/a) 16N Activity (Bq/a) be derived. Since H and C decay to stable nuclides without releasing gamma rays, the major contributors of dose rate are 16N and 17N. The Design value in AP1000 2.701E+11 1.817E+15 results calculated by ARShield code are shown as follows. Calculation results by homogeneous 2.2160862E+11 1.0027454E+15 From Table 10, it is found that the total dose rate of the primary model Calculation results by two-node 2.2160812E+11 1.3110578E+15 loop is 3.103E-01 mSv/h after one year's operation of AP1000 using model homogeneous model, while the total dose rate is 4.056E-01 mSv/h using two-node model, which are almost from the contribution of 16N. The results calculated using two-node model are more conservative Table 10 than that using homogeneous model. Dose rate of activation products. Nuclide name Contact dose rate using Contact dose rate using two- 3.4. 3H production under mechanical shim operating mode homogeneous model (μSv/h) node model (μSv/h) ff 3 16N 3.103E+02 4.056E+02 Owing to that change in soluble boron concentration only a ects H 3 10 17N 2.048E-03 3.082E-03 production, so only H produced by soluble B is calculated, which is shown in Fig. 3. 3H radioactivity in coolant tends to saturation with operation time. can be seen in Ref. (He et al., 2017; Zhang et al., 2016). At the beginning of reactor operation, amount of 3H produced by so- The density of each radionuclide at chosen region is introduced into luble 10B under chemical shim operating mode calculated in linear si- ARShield and then converted to dose rate using point kernel integration mulation method is higher than that of mechanical shim operating method, which is as follows. mode calculated in ladder simulation method. Alone with fuel con- ff Ks()( r′→′−→′ B μ r r , E ) exp ( μ r r ) dV sumption, this numerical gap between two di erent modes gradually Dr()= ∫ 4πr→′ r 2 (34) decreases, and then increases in the opposite direction. After one year's operation, amount of 3H under chemical shim operating mode is Where, 8.785E12 Bq, while reaching 1.064E13 Bq under mechanical shim operating mode. 3H production under mechanical shim operating mode D(r), dose rate; is 21.12% higher than that under chemical shim operating mode.

Fig. 3. 3H amount produced by soluble 10B under two diﬀerent operating modes.

72 Q. Guo et al. Progress in Nuclear Energy 109 (2018) 66–73

Fig. 4. Inﬂuence of 7Li abundance in coolant on contribution to 3H production.

3.5. Inﬂuence of 7Li abundance in coolant on 3H production References

3 In AP1000, H produced by lithium in coolant accounts for more Aghoyeh, R.G.*, Khalafi, H., 2012. Evaluation of tritium and Carbon-14 radioactivity in than 15% at the condition that 7Li abundance is 99.9%. At a specificpH primary loop of tehran research reactor (TRR). Prog. Nucl. Energy 60, 135–139. 3 7 Balonov, M., Dubourg, M., Efremenkov, V., et al., 2004. Management of Waste Containing or LiOH concentration in coolant, H production may change with Li Tritium and Carbon-14, TRS 421–2004. IAEA, Vienna. 3 7 abundance. Fig. 4 presents H production varying with Li abundance. Chandrasekaran, T., Lee, J.Y., Willis, C.A., et al., 1985. Calculation of Releases of The contribution of lithium to 3H production decreases linearly with the Radioactive Materials in Gaseous and Liquid Effluents from Pressurized Water 7 Reactors (PWR-gale Code). NUREG-0017, Rev.1.USA: NRC. increase of Li abundance in LiOH of coolant. Drudy, K.J., Morita, T., Connelley, B.T., 2009. Robustness of the MSHIM operation and control strategy in the AP1000 design. In: Proceedings of the 17th International Conference on Nuclear Engineering ICONE17. 4. Conclusions Fei, Gao, Linjun, Yang, yuelong, Pan, 2016. Production and release of tritium in PWR nuclear power plant. J. Nucl. Radiochem. 38 (1), 52–56. Forrest, R.A., Kopecky, J., Sublet, J-Ch, 2007. The European Activation File: EAF-2007 16 17 3 14 In this study, activation analysis of N, N, H and C in AP1000 Neutron-induced Cross Section Library. UKAEA FUS 535. has been performed. By comparing homogeneous model with two-node He, S., Zang, Q., Zhang, J., et al., 2017. Development and validation of an interactive efficient dose rates distribution calculation program ARShield for visualization. model, it is found that when calculating long-lived nuclide, the – fi Radiat. Protect. Dosim. 174 (2), 159 166. homogeneous model can be selected rstly. When calculating short- Lin, C., 2008. Passive Safety Advanced Nuclear Power Plant AP1000. Atomic Energy lived nuclide, it is more suitable to use two-node model. After one year's Publishing House, Beijing. operation with purification, the radioactivity of 16N, 17N, 3H and 14C Liu, Y.Z., 1986. A method and computer code for calculating radionuclide concentration in primary coolant circuit of LWRs. Radiat. Protect. 6, 409–424 (in Chinese). are respectively 1.311E+18 Bq, 3.055E+14 Bq, 4.913E+10 Bq, Morita, et al., 1974. Power Distribution Control and Load Following Procedures, WCAP- 5.454E8 Bq and the resulted dose rate is 4.056E-01 mSv/h. Under 8403. Westinghouse Electric Corporation. chemical shim operating mode, 3H production calculated with linear Morita, et al., 1988. Load Follow Operation with MSHIM Control System, vol 56 ANS Topical Meeting Transaction No. 2. simulation method is 8.785E12 Bq, while reaching to 1.064E13 Bq Neeb, K.H., 1997. The Radiochemistry of Nuclear Power Plants with Light Water under mechanical shim operating mode. At a specific LiOH concentra- Reactors. Walter de Gruyter, New York, pp. 227–229. tion, the contribution of lithium to 3H production decreases linearly Onoue, M., Kawanishi, T., Carlson, W.R., et al., 2003. Application of MSHIM Core Control 7 Strategy for Westinghouse AP1000 Nuclear Power Plant. GENES4/ANP203 Paper with increasing Li abundance in LiOH in the water. And according to No. 1030. 3 7 this, H radioactivity can be reduced by increasing Li abundance in Pan, Z.Q., Cheng, J.P., 2007. Ionizing Radiation Protection and Safety of Radiation LiOH. Sources. Atomic Energy Press, Beijing (in Chinese). Shan, C.Y., Lu, H.L., Shi, X.A., et al., 2012. Analysis of 16N source term in PWR nuclear island system. China Nucl. Power 5 (4), 329–334 (in Chinese). Winters, J.W., Vijuk, R.P., Cummins, W.E., 2004. AP1000 Design Control Document [J].APP- Acknowledgments gwgl-700, Revision 15. Westinghouse Electric Company, LLC, Pittsbrugh, PA, US. Yang, Q., Dang, T.Q., Ying, D.C., et al., 2012. Activation analysis of coolant water in ITER – The authors would like to express their gratitude for the support: blanket and divertor. Fusion Eng. Des. 87, 1310 1314 (in Chinese). Yim, M.S., Caron, F., 2006. Life cycle and management of carbon-14 from nuclear power Project 11605058 supported by National Natural Science Foundation of generation. Prog. Nucl. Energy 48, 2–36. China, Project 2014GB119000 supported by National Special Project Zhang, C.X., 2003. Source terms calculation analysis for the reactor and primary coolant for Magnetic Confined Nuclear Fusion Energy of China, Project system of qinshan phase II NPP Project. Nucl. Power Eng. 24 (2), 73–77 (in Chinese). Zhang, J., Li, L., He, S., et al., 2016. Calculation of radioactivity and dose rate of activated 2017MS041 supported by the Fundamental Research Funds for the corrosion products in water-cooled fusion reactor. Sci. Technol. Nucl. Install., Central Universities. 6051834.