# Heat Storage as a Way to Increase Energy Efficiency and Flexibility of NPP in Isolated Power System
## 3 Results
### Results of Calculation of NPP Thermal Scheme  
The results of the calculation of the thermal scheme of a low-power NPP in a standard version and a version with a heat accumulator in the discharge mode are presented in Table 7.  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Designation, Unit of Change**} & \multicolumn{3}{c}{**Number**} & \\ \cline{3-5}  & & **Scheme with Accumulator** & **Standard Scheme** & **Note** \\ \hline Thermal power of the reactor & Q\({}_{\text{react}}\), MW & 164.1 & 164.1 & - \\ \hline Power of the turbine unit & N\({}_{\text{turbine}}\), MW & 54.7 & 51.7 & - \\ \hline Thermodynamic efficiency of the cycle & \(\eta_{\text{s}}\) \% & 33.4 & 31.5 & - \\ \hline  & \(\alpha_{1}\), relative units & 0.00 & 0.06 & To HPH1 \\ \cline{2-5}  & \(\alpha_{2}\), relative units & 0.05 & 0.05 & To HPH2 \\ \cline{2-5}  & \(\alpha_{\text{s}}\), relative units & 0.01 & 0.02 & To deaerator \\ \cline{2-5} Regenerative bleed-off & \(\alpha_{\text{s}}\), relative units & 0.03 & 0.03 & To LPH1 \\ \cline{2-5}  & \(\alpha_{\text{s}}\), relative units & 0.02 & 0.02 & To LPH2 \\ \cline{2-5}  & \(\alpha_{\text{s}}\), relative units & 0.10 & 0.10 & To SH \\ \hline Condensate flow rate from the separator & \(\alpha_{\text{s}}\), relative units & 0.06 & 0.05 & - \\ \hline Steam flow from the LPC to the condenser & \(\alpha_{\text{c}}\), relative units & 0.72 & 0.66 & - \\ \hline  & G\({}_{\text{G}}\)\(\circ\), kg/s & 72.5 & 72.5 & From SG \\ \cline{2-5}  & G\({}_{\text{G}}\)\(\circ\)1, kg/s & 65.1 & 65.6 & HPC 0-1 \\ \cline{2-5}  & G\({}_{\text{G}}\)\(\circ\)2, kg/s & 65.1 & 61.0 & HPC 1-2 \\ \cline{2-5} Steam flow by sections & G\({}_{\text{G}}\)\(\circ\)4, kg/s & 61.2 & 57.1 & HPC 2-S \\ \cline{2-5}  & G\({}_{\text{G}}\)\(\circ\)8, kg/s & 60.1 & 55.9 & D-S \\ \cline{2-5}  & G\({}_{\text{G}}\)\(\circ\)8, kg/s & 55.9 & 52.0 & S-SH \\ \cline{2-5}  & G\({}_{\text{SHLPC}}\)\(\circ\)3, kg/s & 55.9 & 52.0 & SH-LPC 3 \\ \cline{2-5}  & G\({}_{\text{2 LPC}}\)\(\circ\)3,4, kg/s & 53.9 & 49.9 & LPC 3-4 \\ \cline{2-5}  & G\({}_{\text{2 LPC}}\)\(\circ\)4,5-C, kg/s & 52.1 & 48.1 & LPC 4-5-C \\ \hline \end{tabular}
\end{table}
Table 7: Results of calculation of the NPP thermal scheme.  
Figure 13: Results of heat exchange simulation (PCM—solar salt) along the entire length of the heat exchange element. Inlet and outlet water temperatures for different straight sections of the heat exchange surface at different periods. Dotted line: along the vertical axis—the required outlet water temperature, along the horizontal axis—the required working time of accumulator.  
By shutting down regenerative bleed-off 1 from the HPC (high-pressure cylinder) to HPH1, the steam flow through the subsequent stages of the HPC and LPC (low-pressure cylinder) increases, thereby increasing the power of the turbine plant. Heating of feed water to the nominal value instead of HPH1 was carried out in a parallel-connected heat accumulator with the PCM. The increase in the power of the turbine plant was 3 MW or 5.8% of the nominal power.