Role of molecular nitrogen in the radiolysis of the primary coolant of a water-water energy reactor

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Abstract

The results of modeling of radiation-chemical transformations in the coolant of the VVER primary circuit are presented. It is shown that under conditions of intensive irradiation molecular nitrogen dissolved in the coolant exhibits chemical activity. The reaction of N2 molecule with excited hydroxyl initiates the formation of ammonia and nitrous acid. Further decomposition of ammonia yields only oxidized forms of nitrogen, with N2 acting as an intermediate product. Maintenance of hydrogen and oxygen concentrations within the norms at ammonia water-chemical regime (WCR) appears to be possible only at constant dosing of NH3 and degassing of the coolant. On the contrary, in the case of WCR with dosing (at the initial moment) of H2 in the absence of perturbations the steady-state regime is quickly established, satisfying the requirements of the WCR norms for VVER. The difference between the two WCRs is due to the presence of nitrogen in the NH3 molecule and its transformations as an element, regardless of the initial chemical form.

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About the authors

V. A. Grachev

Kurchatov Institute

Author for correspondence.
Email: Grachev_VA@nrcki.ru
Russian Federation, Moscow

O. S. Bystrova

Kurchatov Institute

Email: Grachev_VA@nrcki.ru
Russian Federation, Moscow

A. B. Sazonov

Kurchatov Institute

Email: Grachev_VA@nrcki.ru
Russian Federation, Moscow

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2. Fig. 1. Decomposition of ammonia in the coolant of a research reactor. Points – experiment [24], lines – calculation. 1, □ – 5.5 mmol/l NH3 + 70 mmol/l H3BO3 (30°C); 2, ▲ – 5.25 mmol/l NH3 (30°C); 3, × – 5.3 mmol/l NH3 + 168 mmol/l H3BO3 (180°C).

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3. Fig. 2. The yield of nitrogen binding during irradiation of a solution of H2 (mg/kg) / N2 (mg/kg): 1 – 3/20; 2 – 4/35; 3 – 5/50; 4 – 6/65; 5 – 8/95.

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4. Fig. 3. Yields of bound nitrogen and ammonia formation (N atom/100 eV) at 25°C depending on the nitrogen pressure P above the solution. Dots – experiment [2], solid lines – calculation. ♦, 1 – N2; ◊, 2 – NH3.

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5. Fig. 4. Concentration of water and ammonia radiolysis products in the coolant of WWER, WCR “N”: 1 – N2; 2 – H2; 3 – NH3; 4 – HNO2; 5 – oxidation products; 6 – O2.

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6. Fig. 5. Concentration of water and ammonia radiolysis products in the coolant of WWER, WCR “A”: 1 – N2; 2 – H2; 3 – NH3; 4 – HNO2; 5 – oxidation products; 6 – O2.

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7. Fig. 6. Concentration of water and ammonia radiolysis products in the coolant of WWER, WCR “AN”: 1 – N2; 2 – H2; 3 – NH3; 4 – HNO2; 5 – oxidation products; 6 – O2.

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8. Fig. 7. Concentration of water and ammonia radiolysis products in the coolant of WWER, WCR “C”: 1 – N2; 2 – H2; 3 – NH3; 4 – HNO2; 5 – oxidation products; 6 – O2.

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9. Fig. 8. Concentration of water and ammonia radiolysis products in the coolant of WWER, WCR “N”: 1 – N2; 2 – H2; 3 – NH3; 4 – HNO2; 5 – NO.

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