IRRADIATION-INDUCED SWELLING OF BOR-60 SMALL ROTATION PLUG STUDS State Scientific Center – Research Institute of Atomic Reactors IRRADIATION-INDUCED SWELLING OF BOR-60 SMALL ROTATION PLUG STUDS V.S. Neustroev, D.A. Sokolovsky, S.V. Belozerov, I.Yu. Zhemkov, E.I. Makarov, Yu.V. Naboishchikov, A.I. Plotnikov, N.S. Poglyad, N.I. Shirokova JSC «SSC RIAR», Dimitrovgrad, Russia neustroev@niiar.ru ХI Conference of the reactor material science (Dimitrovgrad, 27-31 May 2019)

Introduction • To know the basic laws of radiation swelling from the practical point of view is necessary to extend life-time of reactors internals, made of Fe-18Cr-10Ni-Ti steel. • For calculations when extending the life-time of non-replaceable long-irradiated elements, it is necessary to take into account the change in irradiations conditions for many years. Purpose of the work is to specify the basic swelling formula of Fe-18Cr-10Ni-Ti steel, and on its basis to calculate the swelling of the faces of the blanket assembly E-169 wrapper and the pins of the BOR-60 small rotation plug (SRP).

S = C · Dn exp[–β(T – Tmax)2] An empirical dose-temperature formula mainly used to calculate swelling S = C · Dn exp[–β(T – Tmax)2] 0,2-0,4 dpa/year 5-20 dpa/year S/exp[–1.83 ·10–4(T – 470)2] Damage dose D, dpa where S – swelling, %, T – irradiation temperature, °С; D – damage dose, dpa; C, n, β, Tmax – constants. The constants were calculated based on the many experimental data of irradiating Fe-18Cr-10Ni-Ti steel: S = 1.04·10–2 · D1,88 exp[–1.83 ·10–4(T – 470)2], %

Models for calculating the irradiation temperature and dose in BOR-60 core using in swelling formula D = Dmax cos π 2 ∙ Z – 200 450 T = T0(1+BZ) E-169 assembly Distance from the bottom of the reactor core Z, mm Damage dose D, dpa IR-1 and IR-2 Dmax = 81 dpa Dmax = 50 dpa Dmax = 48 dpa ТIR-1 = 484 °С ТE-169 Temperature Т, °C Т0 = 320 °С Distance from the bottom of the reactor core Z, mm

Parameters of the irradiation rigs IR-1 and IR-2 Studied elements were central tubes of the rigs (initial diameter – 14 mm and length – 325 mm). Central tube 489 467 444 578 556 533 Tav = 484°С Tav = 570°С а) б) Irradiation temperature distribution of the central tubes in IR-1 (top) and in IR-2 (bottom) 5

Swelling of the IR-1 and IR-2 central tubes and specifying of the formula Constant С In original formula For IR-1 For IR-2 For irradiating temperature 0.0104 0.0054 (Т = 484°С) 0.0010 (Т = 570°С) For temperature using in formula Т = 470°С 0.0056 0.0063 S = 5.6·10–3 · D1.88 exp[–1.83·10–4 (T – 470)2], % 6

Temperature operation history of E-169 assembly blanket assembly 1575 1 3 2 5 4 BOR-60 reactor cartogram: 1 – CPS rod, 2 – fuel assembly, 3 – blanket assembly, 4 – research assembly, 5 – Е-04 cell (E-169) During the 27-year operation each face of the E-169 assembly wrapper had a different maximum temperature due to the change of adjacent assemblies.

Temperature operation history of assembly E-169 Temperature operation history of assembly E-169. Temperature corrections The temperature of some faces may be too high due to calculation errors of energy release and linear approximation of the temperature distribution along the core height. In this regard a correction factor 0.9 was introduced for some temperatures. Initial temperature Tmax Corrected temperature 0.9Tmax Temperature, °C Operating time, years Temperature dependence of D-38 face of the assembly on operating time without corrections and with corrections

Swelling calculation results of the E-169 assembly faces C = 0,01035; initial Тmax C = 0,0056; corrected Тmax Face Face Method of calculating swelling by the formula Swelling level of the faces in the top of the reactor core, % K-1 K-2 Е-03 D-38 D-40 Е-08 C = 0.01035; initial Тmax 5.4 5.6 10.5 24.8 25.8 8.9 C = 0.0056; 0.9Тmax for D-38 and D-40 faces in a period of 17.5-25.6 years 2.9 3.0 5.7 6.0 5.2 4.8 Density changes measurements 4.6-6.5 %

Sh1 pin irradiation conditions According to the calculation of “GIROPRESS” (2009), swelling ≈ 2% and the corresponding total damage Dε = 1 were achieved by the end of 2009. Sh1 pin irradiation conditions Damage dose (predict) Tempera-ture, °С Calculation of 2009 25 dpa at the end of 2015 500-520 Current calculation 30 dpa 520-625 Sh1 Pins and nuts of SRP Small rotation plug (SRP) of BOR-60 reactor

Calculation of the Sh1 pin swelling Swelling formula Тirr, °С Exposure dose D, dpa 2015 2020 2025 D = 24.7 D = 27.3 D = 30.0 S0 = С ·D1.88 × × exp[–1.83·10– 4·(Tirr – 470)2], C = 5.6·10–3 520 1.4 1.8 2.1 530 1.2 1.7 570 0.4 0.5 Critical swelling value 2,1 % on the Sh1 pin will be obtain at the end of 2025.

Conclusion Constant С was specified in the swelling formula of Fe-18Cr-10Ni-Ti steel at temperatures above 480 °С; recommended to use the specified formula is at follows: S0 = 0.56·10–2 · D1.88 exp[–1.83 · 10–4 (T – 470)2], %. The correctness of specified formula was confirmed by a good fit of calculated and experimental results that makes the formula applicable.

Conclusion The calculation by the specified formula showed that the pins swelling is 2.1 % at temperatures above 520 °С. From the viewpoint of this component, it allowed the extension of the BOR-60 lifetime till 2025. Additional data will be obtained in future on swelling of Fe-18Cr-10Ni-Ti steel used for manufacturing IR-1 and IR-2 components to increase the statistical relevancy of swelling dose-temperature dependence at high temperatures.