Design of "MASTER-JM" reactor

Design of nuclear power facility MASTER-JM

The facility consists of the following main parts (see fig.): reactor, outside case, pressurizer, heat exchangers and circulation pipes. The outside case, pressurizer, heat exchangers and the pipes connecting all them form the third circulation circuit filled with water. There is nature circulation in this circuit. The reactor is a source of heat in this circuit; heat from reactor is transferred in the heat exchangers to the Consumer’s water. Water circulation for the Consumer is suggested to be forced.

Design of reactor MASTER-JM is presented in Fig. 3. The core is formed by the fuel rod elements with outside diameter of 2 см located in the triangle lattice (cage) with spacing of 20.1 mm. Dimensions of the core are: diameter – 25.52 cm, height – 51.04 cm. Central part of the fuel element consists from the nuclear fuel itself and the end parts that are the front steel reflectors. The side reflector of the core is made from beryllium with thickness of 10 cm. 3 drams that put reactor at the power level are located at the beryllium reflector.
The core with the beryllium reflector is placed into the copper collector with outside ribs that enlarge the heat exchange surface. The core, draft tube and a gap between the Beryllium reflector and copper collector form the first circulation circuit filled with Na-K (22% - 78%) alloy. There is nature circulation in the circuit. The circuit is provided with protective cover made from the stainless steel with thickness of 1 mm.
The core with the beryllium reflector and copper collector are placed into the reactor case provided with the heat insulating partition. The space between the mentioned case and copper collector is filled with water and forms the second circulation circuit.

Design of reactor MASTER-JM

The top part of the case is used as the pressurizer of the second circuit. Heat from the copper collector is transferred to the second circuit water that is cooled through the outside wall of the reactor case by water of the third circuit mentioned in the facility description. There is natural circulation in the second circuit. The reactor is fast by the spectrum type. The fuel enrichment at the start charge is 20%.

Comparison of MASTER-IATE and MASTER-JM constructions

Neutronics characteristics of MASTER-IATE and MASTER-JM reactors (see Table 1) meet, to a lesser or larger degree, the requirements to the extra-small power reactors.

Table 1. Neutron-physical characteristics of MASTER-IATE and MASTER-JM reactors

Parameter	MASTER-IATE	MASTER-JM
Power, kW	300	300
Lifetime, years	60	60
Height of EP, cm	160	51.0
Radius of EP, cm	50	12.8
Flattening H/D	1.6	2
Fuel	UBe13+Mg	U+Mo
Coolant	---	22% Na – 78% K
Average temperature of EP, 0C	350	235
235U in the start charge, kg	240.2	72.2
Average neutron flux, n/cm2/sec	3.4·1012	2.2·1013
Temperature effect of reactivity, pcm/K	-3.5	-1
Maximum change of reactivity in the lifetime, pcm	113	161
Loss of reactivity due to reactor heating up and going at the power level, pcm	1600	200

Reactor MASTER-JM has the significant advantage over MASTER-IATE reactor in fuelling of the fissible nuclides (in the first case the needed charge is almost 4 times less), but it also has the significant disadvantage in the rate of reactivity loss connecting with the fuel burning up. To decrease the rate of reactivity loss of MASTER-JM reactor probably it should increase the charge of the fissible nuclides and/or increase the core temperature.
Common thermal-hydraulic characteristics of these two reactors are summarized in Table 2. Hydraulic problems form two divisions:

Heat generation in the nuclear reactor (NR) and heat transfer to the coolant;
Organization of the coolant and Consumer’s water natural circulation.

These problems are solved in different ways depending on the reactor construction, see table 2.
It follows from the presented data that at the reactors given power of 300 kW there is no any advantages in considered reactors one above another. However, with power increasing MASTER-JM reactor demonstrates its advantages.

Table 2. Hydraulic principles of NR MASTER-IATE and MASTER-JM

№	Thermohydraulics methodology (principles of thermohydraulics organization)	Reactor type
№		«Single fuel pin» thermal reactor with high heat-conducting core and heat conduction from outside surface	“Multi-fuel pin” fast reactor with liquid metal coolant and natural circulation (NC) circuit
1	Prototype	“Romashka” INPE	«BUK» IPPE
2	Fuel	UBe₁₃	U with addition of Mo
3	Moderator	Be	No
4	Coolant inside reactor	No	NaK
5	Reflector	Be	Be
6	Control and scrum system rods	Central rod for start up and shut down	Absorbing rotary drums in reflector
7	Limitative temperature drop fuel Т=Тmax-Tmin is a function of thermal power of nuclear reactor- Q.	Tmax is fixed due to reason of fuel serviceability Tmin is specified by the conditions of heat conduction	Tmax is fixed due to reason of fuel serviceability Tmin is specified by the conditions of heat conduction
8	Limitative temperature drop fuel Т=Тmax-Tmin is a function of thermal power of nuclear reactor- Q	Saturated boiling water in thermosyphon surrounding reactor at low pressure	NaK circuit of NC with riser flow and heat transfer outside through copper ribbing of the vessel
9	Interim coolant with developed outside heat conduction surface	Hot water at atmosphere pressure (80°С)	Hot water at atmosphere pressure (80°С)
10	Coolant of consumer	NC circuit with heat exchanger. Extraction of heat in the upper part of plant	NC circuit with heat exchanger. Extraction of heat in the upper part of plant
11	Consumption of NC depends on height of riser flow and nuclear reactor power	Moving head is equal to hydraulic losses	for water of heat exchanger circuit and NaK circuit Moving head is equal to hydraulic losses
12	Coolant heating in NC curcuit	for water of heat exchanger circuit:	for water of heat exchanger circuit and Na-K circuit:
13	Limitative factors	Temperature of UBe₁₃and Be	Temperature of U
		High heat-conducting contact layers in moderator	High heat-conducting contact layer between fuel and cladding
		Pressure and temperature in boiling water of thermosiphon	Consumption and heating of NaK in NC circuit
		Pressure and temperature in boiling water of thermosiphon	High heat conductivity of ribbing of vessel
		Critical heat flow in water	Critical heat flow in water
		Reactor vessel and thermosiphon casing integrity	Integrity of NaK circuit
		Consumption of NC and heating of water of heat exchanger circuit	Consumption of NC and heating of water of heat exchanger circuit
		Dimension and mass of the plant	Dimension and mass of the plant

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