The investigations performed at VNIIEF on different types of NOCs and the neodymium lasers excited by them permit consideration of a series of schemes for pulsed reactor lasers (RLs) using neodymium active elements with laser radi­ation energy <10 MJ and intended for studies of some problems of inertial confinement fusion [41, 42].

One of the variants is a modular design. The modules are placed in the reactor matrix, which contains nuclear fuel, reactor control units, a neutron moderator and reflector, etc. Inside the module, which has an 80-cm diameter, are about 100 neo­dymium rods 45 mm in diameter and 1,200-cm long (Fig. 11.13a). The space between the rods, which are arranged as a hexagonal grate with 80 mm steps, is filled with a UF6-Xe (4:1) mixture at 2 atm.

The laser rods are pumped with the optical radiation of the plasma (temperature <104 K), which forms under the impact of neutron pulses ~3 ms duration with a fluence of ~3 x 1014 cm~2. The total energy of the laser radiation of a single module is about 400 kJ at ~2.5 % efficiency for conversion of the released nuclear energy into laser radiation.

Fig. 11.13 A schematic of a laser module with uranium hexafluoride (a) and uranium layers (b) [42]:

(1) laser elements; (2) filters that absorb UV-emission; (3) NOC; (4) NOC body with a uranium layer; (5) the module body

Fig. 11.14 Schematic of a pulsed RL [42]: (1) laser module; (2) “start-up” reactor; (3) peripheral reactor module — multiplicator; (4) neutron moderator; (5) reactor body

Another possible variant in the module design uses uranium fission fragments that escape from the uranium layers to excite the xenon plasma (Fig. 11.13b). The uranium layers are deposited to the internal surface of the NOC body (hexagonal in cross-section), which is filled with xenon at ~1 atm. There are 60-70 laser elements at the same module dimensions, and the energy of the laser radiation is no more than 250 kJ. If this variant of the module design is used, the efficiency will be approximately ten times lower due to the lower transmission efficiency of the fission fragment energy to the gas medium. This requires an increase in the total energy release in the module.

It should be noted that the modules considered have a significant neutron multiplication factor, and, as follows, contribute to the total reactivity of the reactor system. This allows loading of additional nuclear fuel into the reactor to decrease.

A RL based on these modules with an output laser energy of ~10 MJ can be proposed, for example, in an 18 module design with the modules placed in six channels and three tiers (Fig. 11.14) [42]. In the central part, there is a “start-up” reactor with control units. All of the device elements are placed in a matrix-neutron moderator and comprise a single nuclear-physical system. The pulse duration of the nuclear fission and laser radiation in the free-running mode may be 1-10 ms. The typical liner dimensions of such a facility are 3 m; the total mass is no more than 100 t.