Study on LOFA and LOHS Accidents with Passive Safety System for Integrated Marine Reactor

Abstract

To simulate the complex accident phenomena of a marine reactor, the thermal-hydraulic system code RELAP5 is modified to perform the analysis under ocean conditions. An integrated reactor with a passive residual heat removal system (PRHRS) is modeled by the improved code, and the effects of different ocean motions under a total loss-of-flow accident (LOFA) and a loss-of-heat-sink (LOHS) accident are analyzed with respect to safety characteristics. The results indicate that for LOFA, the primary loop can form an effective natural circulation to cool the core, and for LOHS, the PRHRS can effectively remove the residual heat from the core to ensure the core safety. The results also show that heaving motion accelerates the drop of the first-loop temperature and enhances the heat transfer capacity of the PRHRS. Inclining motion reduces the natural circulation flow in the core. A rolling condition causes fluctuations in the mass flow rate, the variations of which are not strictly sinusoidal, and increasing the rolling period also improves the heat exchange capacity of the PRHRS.

Keywords:

• Modified system code
• ocean motion
• passive safety system
• LOFA, LOHS

Acronyms

LOFA:	=	loss-of-flow accident
LOHS:	=	loss of heat sink
PRHRS:	=	passive residual heat removal system
SG:	=	steam generator
SMART:	=	System-integrated Modular Advanced ReacTor
SMR:	=	small modular reactor

Nomenclature

$A$ =	=	flow area (${\mathrm{m}}^2$)
$\mathit{a}$ =	=	additional acceleration ($\mathrm{m}\cdot {\mathrm{s}}^{-2}$)
${\mathit{a}}_c$ =	=	centripetal acceleration
${\mathit{a}}_t$ =	=	tangential acceleration
${\mathit{a}}_u$ =	=	Coriolis acceleration
$\mathit{e}$ =	=	rolling axis
$\mathit{F}$ =	=	additional forces ($\mathrm{N}$)
$F_b$ =	=	body force ($\mathrm{N}$)
$F_i$ =	=	interface frictional drag ($\mathrm{N}$)
$F_v$ =	=	interface friction ($\mathrm{N}$)
$F_w$ =	=	wall friction ($\mathrm{N}$)
${\mathit{f}}_c$ =	=	unit vector in direction of rolling axis in noninertial system
${\mathit{f}}_t$ =	=	tangential acceleration in noninertial system
$\mathit{g}$ =	=	gravitational acceleration (9.8 $\mathrm{m}\cdot {\mathrm{s}}^{-2}$)
$\mathit{i}$ =	=	unit vector in x-direction
$\mathit{j}$ =	=	unit vector in y-direction
$\mathit{k}$ =	=	unit vector in z-direction
$P$ =	=	pressure ($\mathrm{M}\mathrm{P}\mathrm{a}$)
$\mathit{r}$ =	=	position vector of each control volume
$T_h$ =	=	heaving period ($\mathrm{s}$)
$T_r$ =	=	rolling period ($\mathrm{s}$)
$t$ =	=	time ($\mathrm{s}$)
$\mathit{u}$ =	=	velocity of the medium with respect to the moving coordinate
$v$ =	=	velocity ($\mathrm{m}\cdot {\mathrm{s}}^{-1}$)
$x_h$ =	=	heaving amplitude ($\mathrm{m}$)
x y z =	=	axial position

Greek

$\alpha$ =	=	void fraction
$\mathit{\beta }$ =	=	angular acceleration ($\mathrm{r}\mathrm{a}\mathrm{d}\cdot {\mathrm{s}}^{-2}$)
$\theta$ =	=	inclination angle (deg)
${\theta }_a$ =	=	rolling amplitude ($\mathrm{m}$)
${\theta }_{roll}$ =	=	rolling angle (deg)
$\rho$ =	=	density ($\mathrm{k}\mathrm{g}\cdot {\mathrm{m}}^{-3}$)
$\mathit{\omega }$ =	=	angular velocity ($\mathrm{r}\mathrm{a}\mathrm{d}\cdot {\mathrm{s}}^{-1}$)
Subscript	=
heav =	=	heaving condition
k =	=	phase (l = liquid, g = vapor)
roll =	=	rolling condition

Acknowledgments

This work was supported by the Shanghai Sailing Program under grant number 19YF1416800 and by the Science and Technology Commission of Shanghai Municipality [19YF1416800].