*9.2.4. Rankin cycle characteristics*

Calculations of cycle variants, which are different by maximal steam pressure, number of interim stages of re-heating and steam expansion characteristics on it, are conducted. The most economic variant of possible by complexity manufacturing is shown at table 5 and figure 14.

This cycle use two interim overheating and minimal total steam expansion. Zero water content in steam at turbine exit is obtained. This means small turbine HWD, usage possibility in turbine design cheaper materials for the blades and correspondingly smaller cost.

Cooler of this variant also has small HWD and comparatively high temperature of fluidized steam supplies possibility of its use as heat source for home and business needs.

The second variant has steam quality on the exit of turbine 0.93, which differs much from steam quality in VVER – 0.75. Total steam expansion is 3.7 times bigger than in VVER, and 42.4% efficiency is obtained.

Problem of material for turbine last stage blades here is not so strong, as in nuclear power plants with VVER or ABWR reactors [31].

For electro stations, which work in autonomic regime, for example in distant areas from common electrical supply network, the first variant is preferable by two reasons:



Tmax at fuel rod shell, 0С 805 758 813 Tmax fuel rod, 0С 1125 979 1035 Tmax of gas gap of fuel assembly, 0С 337 336 388 203 Tmax of fuel assembly screen, 0С 364 420 223 Tmax of fuel assembly casing, 0С 182 181 202 168


All this features obtained with simple fuel assembly design and its base elements – fuel rods. Used fuel rods are well fine-tuned at practice of large number of reactors. Small hydraulic losses lead to small required power of coolant pumps. It characterizes costs level

Calculations of cycle variants, which are different by maximal steam pressure, number of interim stages of re-heating and steam expansion characteristics on it, are conducted. The most economic variant of possible by complexity manufacturing is shown at table 5 and

This cycle use two interim overheating and minimal total steam expansion. Zero water content in steam at turbine exit is obtained. This means small turbine HWD, usage possibility in turbine design cheaper materials for the blades and correspondingly smaller

Cooler of this variant also has small HWD and comparatively high temperature of fluidized

The second variant has steam quality on the exit of turbine 0.93, which differs much from steam quality in VVER – 0.75. Total steam expansion is 3.7 times bigger than in VVER, and

Problem of material for turbine last stage blades here is not so strong, as in nuclear power

For electro stations, which work in autonomic regime, for example in distant areas from

2. Electro station cost is significantly cheaper with less HWD of turbine and less cost of

steam supplies possibility of its use as heat source for home and business needs.

common electrical supply network, the first variant is preferable by two reasons:

1. In this case obvious, that there is need in heat of low potential;

blades. Turbine cost is significant part of NPP cost [31].

**Table 4.** Thermal characteristics of fuel assemblies with gaseous coolant.

Basic features of these assemblies are listed below.

for reactor creation and losses level during exploitation.


*9.2.4. Rankin cycle characteristics* 

42.4% efficiency is obtained.

plants with VVER or ABWR reactors [31].

figure 14.

cost.

**Table 5.** Steam and water parameters in cycle with 3 re-heating at Pmax=200 gauge atmospheres and Tmax= 500 оС. Theoretical efficiency is 41.7 %, with account of losses on turbine 38.8 %

**Figure 14.** Pressure and temperature dependencies from entropy at final steam quality 1.0.

At variant with common electrical supply network and absence of heat need (for example in the tropics) it is required to take into account turbine cost difference of first and second variants, works financing at NPP building.

Thermal Reactors with High Reproduction of Fission Materials 213

Coolant temperature, which supplies possibility of effective usage of neutron moderation energy, plays here positive role. Moderator temperature increase requires pressure rise in reactor vessel that allows making channel walls thinner and decrease neutron loss in it. Let us take that moderator inlet temperature is 210 °C, outlet temperature 225 °C, flow - 80 kg/s,

Moderator boiling at unplanned power increase with work pressure and temperature leads to 12 time volume increase of evaporated mass and pressure increase at moderator volume. Core bottom water moves out through nozzle of accident drainage of moderator. Liquid moderator of core upper part is replaced with steam. Preliminary calculations have shown that heavy water deletion from core upper quarter decreases reactivity margin by 2.5 β, that

Damping effect of reactivity accident in this reactor may be not less than in graphite HTGR. Positive feature of this scheme is possibility of work parameters adaptation of safety system by way of specifying work temperature and pressure of moderator, when it

Described actions sufficient using for fission materials reproduction in thermal reactor supplies besides high portion of raw uranium usage (up to 25% in contrast to ~1 % for thermal reactors with enriched fuel) small fuel requirement for core loading. Sum of these

Requirement in raw uranium and thorium of these reactors can be determined by

Figure 16 shows development variant of power production with even power grow to the

level of 8000 GW during 80 years with subsequent power level stabilization.

mU n \* t \* m \* Yu \* m \* K \* Ku / 2 ; <sup>s</sup> g i (12)

mTh n \* t \* m \* 1 Yu \* m \* 1 Ku / 2 ; s g (13)

**10. About possible scale of nuclear power engineering development** 

effects allows creation of world big nuclear power production industry.

moderator pressure - 25 atmospheres.

supplies damping of earlier added reactivity.

n – number of this type built reactor per annum;

mg – fuel mass needed for year feeding of reactor; Ki – portion of raw uranium usage in fuel cycle; Ku – portion of raw uranium in feeding fuel.

Yu – raw uranium portion in fuel;

t – time of nuclear power engineering development, years; ms – mass of raw materials, needed for core loading;

starts boiling.

formulae:

where:

In all case it should be noted, that NPP with 39% efficiency is more attractive than other small power NPP variants with efficiency up to 33%. Especially if we take into account many times lower raw uranium requirement and absence of uranium enrichment works for fuel preparation.

On the base of described solutions heavy water gas cooled high power nuclear reactor can be built. Increase of core HWD leads to neutron leakage decrease, which is base neutron loss for nuclear reactor with 80 MW thermal power.

### *9.2.5. About nuclear safety*

Figure 15 shows coolant and moderator ducts scheme in heavy water gas cooled reactor, which prevents power increase at reactivity accident [32].

**Figure 15.** Coolant and moderator ducts scheme in heavy water gas cooled reactor. 1 – reactor vessel, 2 – moderator, 3 – channel casing, 4 – fuel assembly, 5 – channel thermal isolation, 6 – integral coolant collector, 7, 8 – inlet and outlet of moderator, 9 – opening, which connects channel with collector, 10, 12 inlet and outlet of coolant, 11 – nozzle of accident drainage of moderator.

Coolant temperature, which supplies possibility of effective usage of neutron moderation energy, plays here positive role. Moderator temperature increase requires pressure rise in reactor vessel that allows making channel walls thinner and decrease neutron loss in it. Let us take that moderator inlet temperature is 210 °C, outlet temperature 225 °C, flow - 80 kg/s, moderator pressure - 25 atmospheres.

Moderator boiling at unplanned power increase with work pressure and temperature leads to 12 time volume increase of evaporated mass and pressure increase at moderator volume. Core bottom water moves out through nozzle of accident drainage of moderator. Liquid moderator of core upper part is replaced with steam. Preliminary calculations have shown that heavy water deletion from core upper quarter decreases reactivity margin by 2.5 β, that supplies damping of earlier added reactivity.

Damping effect of reactivity accident in this reactor may be not less than in graphite HTGR. Positive feature of this scheme is possibility of work parameters adaptation of safety system by way of specifying work temperature and pressure of moderator, when it starts boiling.
