Abstract: During the two refueling outages of the Tianwan Nuclear Power Station, the investigation of weakly penetrating radiation of Units 1 and 2 was carried out, mainly including radiation dose rate monitoring at sites that may have a higher probability of weakly penetrating radiation, the weakly penetrating radiation dose monitoring received by some representative workers and the protective effect test of protective equipment. From the measurement results of weak penetrating radiation, the radionuclides deposited on the surface of the maintenance equipment of Tianwan nuclear power plant are basically the same, including ⁵⁸Co, ⁶⁰Co, ⁹⁵Nb, ⁹⁵Zr, ⁵¹Cr, ¹²⁴Sb, ⁵⁴Mn, ^110mAg, ⁵⁹Fe, etc. The β-ray energy is mainly concentrated below 600 keV.It is measured that the maximum value of H·′(3)/H·^*(10) is 2.08 and H·′(0.07)/H·^*(10) has a maximum value of 34.9 for reactor coolant pump item; H·′(3)/H·^*(10) has a maximum value of 2.58 and H·′(0.07)/H·^*(10) has a maximum value of 10.7 for the steam generator item; H·′(3)/H·^*(10) has a maximum value of 1.25, H·′(0.07)/H·^*(10) has a maximum value of 26.4 for the reactor item; The maximum value of H·′(3)/H·^*(10) is 3.80 and H·′(0.07)/H·^*(10) has a maximum value of 55.6 for the other pumps item; H·′(3)/H·^*(10) has a maximum value of 1.15 and the monitoring value of H·′(0.07)/H·^*(10) is 4.18 for the valves item. The maximum value of H·′(3)/H·^*(10) is 1.53 and H·′(0.07)/H·^*(10) has the maximum value of 2.16 for the other items. The results of weakly penetration dose monitoring showed that the maximum values of H_p(0.07)/H_p(10) and H_p(3)/H_p(10) are 7.66 and 3.73 respectively, and the personal dose equivalent H_p(10) during the overhaul monitoring period are all below 0.35 mSv. In addition, the personal dose equivalent H_p(10) of the entire staff in these overhauls is less than 2 mSv. It indicates that H_p(0.07)and H_p(3) are less likely to exceed the national standard personal dose limit of 500 mSv/a and the new IAEA limit of 20 mSv/a, respectively. It is suggested to carry out eye crystal dose and skin dose monitoring for special maintenance personnel such as reactor coolant pump maintenance, reactor pool cleaning, KBA system pumps and valves maintenance, radioactive waste sorting, etc.

Key words: Tianwan Nuclear Power Station, weakly penetrating radiation, skin dose monitoring, eye lens dose monitoring